Abstracts

Supbage of SAV
This page shows citations and abstracts for all papers found relevant or cited in papers on
Super-Abundant Vacancies
Table of Links to Abstract Anchors

        1. 1965 Ferguson:  Neutron diffraction study of temperature-dependent properties of Palladium containing absorbed hydrogen
        2. 1980 Semiletov:  Electron-Diffraction Studies of a Tetragonal Hydride PdH1 (No abstract)
        3. 1984 Blaschko: Structural features occurring in PdDx within the 50 K anomaly region
        4. 1985 ASM: Metallography and Microstructures
        5. 1988 Baba: The Transition of the hydrogen-induced LI2 ordered structure of Pd3Mn to the Ag3Mg structure
        6. 1989 Shirai: Positron Annihilation (No abstract)
        7. 1991 Flanagan: The Palladium-Hydrogen System
        8. 1991 Storms: The effect of hydriding on the physical structure of palladium and on the release of contained tritium
        9. 1991 Noh: Hydrogen-induced metal atom mobility in palladium-rhodium alloys
        10. 1991 Okamoto: Thermodynamically Improbable Phase Diagrams
        11. 1992 Noh: An Illustration of phase diagram determination using H-induced lattice mobility
        12. 1993 FukaiEvidence of copious vacancy formation in Ni and Pd under a high hydrogen pressure
        13. 1993 Fukai: in Computer Aided Innovation of New Materials (Probable citation error) (No abstract)
        14. 1993 Fukai: Some High-Pressure Experiments on the Fe — H System
        15. 1994 Fukai: Formation of superabundant vacancies in Pd hydride under high hydrogen pressures
        16. 1994 Balasubramaniam: Mechanism of hydrogen induced ordering in Pd3Mn
        17. 1994 Oates: On the Copious Formation of Vacancies in Metals
        18. 1994 Manchester: The H-Pd (hydrogen-palladium) System
        19. 1995 Fukai: Formation of superabundant vacancies in metal hydrides at high temperatures
        20. 1995 Felici: In situ measurement of the deuterium (hydrogen) charging of a palladium 380 electrode during electrolysis by energy dispersive x-ray diffraction
        21. 1995 Osono: Agglomeration of hydrogen-induced vacancies in nickel
        22. 1995 Nakamura: High-pressure studies of high-concentration phases of the TiH system
        23. 1995 Oates: On the formation and ordering of superabundant vacancies in palladium due to hydrogen absorption
        24. 1996 Watanabe, Superabundant vacancies and enhanced diffusion in Pd-Rh alloys under high hydrogen pressures
        25. 1996 Gavriljuk: Hydrogen-induced equilibrium vacancies in FCC iron-base alloys
        26. 1997 Birnbaum: Hydrogen in aluminum
        27. 1997 Fukai: Superabundant Vacancy Formation and Its Consequences in Metal–Hydrogen Alloys
        28. 1998 Skelton: In situ monitoring of crystallographic changes in Pd induced by diffusion of D
        29. 1998 Hayashi: Hydrogen-Induced Enhancement of Interdiffusion in Cu–Ni Diffusion Couples
        30. 1999 dos Santos:  A high pressure investigation of Pd and the Pd–H  system
        31. 1999 Buckley: Calculation of the radial distribution function of bubbles in the aluminum hydrogen system
        32. 2006 Sakaki: The effect of hydrogenated phase transformation on hydrogen-related vacancy formation in Pd1−xAgx alloy
        33. 2000 Fukai:  Formation of superabundant vacancies in Pd–H alloys
        34. 2000 Eliaz: Hydrogen-assisted processing of materials
        35. 2001 Fukai: Superabundant vacancy formation in Ni–H alloys
        36. 2001 Miraglia: Investigation of the vacancy ordered phases in the Pd–H system
        37. 2001 Fukai: Hydrogen-Induced Superabundant Vacancies and Diffusion Enhancement in Some FCC Metals
        38. 2001 Klechkovskaya: Electron diffraction structure analysis—from Vainshtein to our days
        39. 2001 Nagumo: Hydrogen thermal desorption relevant to delayed-fracture susceptibility of high-strength steels
        40. 2001 Miraglia: Investigation of the vacancy-ordered phases in the Pd–H system
        41. 2002 Fukai: Phase Diagram and Superabundant Vacancy Formation in Cr-H Alloys
        42. 2002 Shirai: Positron annihilation study of lattice defects induced by hydrogen absorption in some hydrogen storage materials
        43. 2002 Chalermkarnnon: Excess Vacancies Induced by Disorder-Order Phase Transformation in Ni3Fe
        44. 2003 Santos: Analysis of the nanopores produced in nickel and palladium by high hydrogen pressure
        45. 2003 Tateyama: Stability and clusterization of hydrogen–vacancy complexes in α-Fe: An ab initio study
        46. 2003 Fukai: Formation of superabundant vacancies in M–H alloys and some of its consequences: a review
        47. 2003 Fukai, Superabundant vacancy–hydrogen clusters in electrodeposited Ni and Cu
        48. 2003 Fukai: The phase diagram and superabundant vacancy formation in Fe–H alloys under high hydrogen pressures
        49. 2003 Fukai: Superabundant Vacancies Formed in Metal–Hydrogen Alloys
        50. 2003 Pitt: Tetrahedral occupancy in the Pd-D system observed by in situ neutron powder diffraction
        51. 2004 Cizek: Hydrogen-induced defects in bulk niobium
        52. 2004 Koike: Superabundant vacancy formation in Nb–H alloys; resistometric studies
        53. 2004 Kyoi: A novel  magnesium–vanadium hydride synthesized by a gigapascal-high-pressure technique
        54. 2004 Tavares: Evidence for a superstructure in hydrogen-implanted palladium
        55. 2004 Araki: Phase Diagram of Hydrogen in Palladium
        56. 2004 Nagumo: Hydrogen related failure of steels – a new aspect
        57. 2005 FukaiThe Metal–Hydrogen System: Basic Bulk Properties
        58. 2005 Harada: A relation between the vacancy concentration and hydrogen concentration in the Ni–H, Co–H and Pd–H systems
        59. 2005 Fukai: The structure and phase diagram of M–H systems at high chemical potentials—High pressure and electrochemical synthesis
        60. 2005 Iida: Enhanced diffusion of Nb in Nb–H alloys by hydrogen-induced vacancies
        61. 2005 Tanguy: Superabundant vacancies in a metal-hydrogen system:  Monte Carlo simulations
        62. 2006 Sakaki: The effect of hydrogen on vacancy generation in iron by plastic deformation
        63. 2007 Fukai: Formation mechanism of defect metal hydrides containing superabundant vacancies
        64. 2007 Fukai: (Citation error, see Harada2007)
        65. 2007 Harada: The defect structure with superabundant vacancies to be formed from fcc binary metal hydrides: Experiments and simulations
        66. 2007 Fukai: Formation of Hydrogen-Induced Superabundant Vacancies in Electroplated Nickel-Iron Alloy Films
        67. 2007 Eriksson: Resistivity changes in Cr/V(0 0 1) superlattices during hydrogen absorption
        68. 2008 Kala: Hydrogen-induced electrical and optical switching in Pd capped Pr nanoparticle layers
        69. 2009 Vekilova: First-principles study of vacancy–hydrogen interaction in Pd
        70. 2009 Wen: Hydrogen-enhanced dislocation activity and vacancy formation during nanoindentation of nickel
        71. 2009 Sugimoto: Migration mechanism in defect metal hydrides containing
          superabundant vacancies
        72. 2009 Shackelford: Introduction to Materials Science for Engineers
        73. 2010 Yagodzinskyy: Effect of hydrogen on plastic strain localization in single crystals of austenitic stainless steel
        74. 2010 Richmond: Evidence for hydrogen induced vacancies in Plutonium metal. (No Abstract.)
        75. 2011 Isaeva: Dynamic stability of palladium hydride: An ab initio study
        76. 2011 Chen: On the formation of vacancies in α-ferrite of a heavily cold-drawn pearlitic steel wire
        77. 2011 Fukumuro: Influence of hydrogen on room temperature recrystallisation of electrodeposited Cu films: thermal desorption spectroscopy
        78. 2011 Zaginaichenko: The structural vacancies in palladium hydride. Phase diagram
        79. 2011 Khalid: Hydrogen-induced ferromagnetism in ZnO single crystals investigated by magnetotransport
        80. 2011 Fukai: Hydrogen-Induced Superabundant Vacancies in Metals: Implication for Electrodeposition
        81. 2012 Knies: In-situ synchrotron energy-dispersive x-ray diffraction study of thin Pd foils with Pd:D and Pd:H concentrations up to 1:1
        82. 2012 Azofeifa:Temperature- and hydrogen-induced changes in the optical properties of Pd capped V thin films
        83. 2013 Hisanaga: Hydrogen in Platinum Films Electrodeposited from Dinitrosulfatoplatinate(II) Solution
        84. 2013 Fukumuro: Hydrogen-induced enhancement of atomic diffusion in electrodeposited Pd films
        85. 2013 Yabuuchi: Effect of Hydrogen on Vacancy Formation in Sputtered Cu Films Studied by Positron Annihilation Spectroscopy
        86. 2014 Supryadkina, Ab Initio Study of the Formation of Vacancy and Hydrogen–Vacancy Complexes in Palladium and Its Hydride
        87. 2014 Tsirlin: Comment on the article ‘Simulation of Crater Formation on LENR Cathodes Surfaces’
        88. 2014 Nazarov: Ab initio study of H-vacancy interactions in fcc metals: Implications for the formation of superabundant vacancies
        89. 2014 Houari:  Electronic structure and crystal phase stability of palladium hydrides
        90. 2015 Wulff: Formation of palladium hydrides in low temperature Ar/H2-plasma
        91. 2015 Fukada: In situ x-ray diffraction study of crystal structure of Pd during hydrogen isotope loading by solid-state electrolysis at moderate temperatures 250−300 °C
        92. 2015 Robertson: Hydrogen Embrittlement Understood
        93. 2016 Fukada: Multiple phase separation of super-abundant-vacancies in Pd hydrides by all solid-state electrolysis in moderate temperatures around 300 °C
        94. 2017 Bukonte: Thermodynamics of impurity-enhanced vacancy formation in metals
        95. 2018 Staker: Coupled Calorimetry and Resistivity Measurements, in Conjunction with an Emended and More Complete Phase Diagram of the Palladium – Isotopic Hydrogen System

REFERENCES AND ABSTRACTS

1965 —

G. A. Ferguson, Jr., A. I. Schindler, T. Tanaka, and T. Morita, “”, Phys. Rev, 137 (2A) (1965) 483.

Neutron diffraction study of temperature-dependent properties of Palladium containing absorbed hydrogen

Neutron diffraction techniques have been employed to study the hydrogen-atom configuration in a single-phase sample of beta-PdH at several selected temperatures. The suggested low-temperature (T55°K) structure of this compound is one which conforms to the space group R¯3m, which differs from the high temperature (T55°K) structure [Fm 3m]. The low-temperature structure is formed by a partial migration of hydrogen atoms from octahedral to nearby tetrahedral crystallographic sites in the face-centered cubic palladium lattice. Approximate values of the root-mean-square vibrational amplitude of the hydrogen atoms have been determined to be 0.25 Å (T=293°K) and 0.17 Å (T=4.2°K). The anomalous behavior observed in measurements of the temperature dependence of the electrical resistivity and heat capacity of this compound is explained by the transfer of the hydrogen atoms between the lattice sites.

1980 —

Semiletov, S. A., R. V. Baranova, Yu P. Khodyrev, and R. M. Imamov. “, 33.” Kristallografiya 25, no. 6 (1980): 1162-1168.

ELECTRON-DIFFRACTION STUDIES OF A TETRAGONAL HYDRIDE PDH1

No abstract found. Many papers on crystallography. The field of electron diffraction is reviewed in the following article (which cites the above paper):

1984 —

O. Blaschko, J. Less-Comm. Met., 100 (1984) 307–320

Structural features occurring in PdDx within the 50 K anomaly region

The concentration-dependent ordered states of deuterium occurring in PdDx at low temperatures are discussed in the light of recent experimental and theoretical work. The ordering processes occur within the temperature region of the known 50 K anomaly in the specific heat.

1985 —

Metals Handbook, Vol. 9, 9th ed., 1985, American Society for Metals, Metals Parks, OH (1985) p.245. Googlebooks. There are more recent editions.

Metallography and Microstructures

1988 —

K. Baba, Y. Niki, Y. Sakamoto, A. P. Craft. Ted B. Flanagan, J. Mats. Sci. Letters, November 1988, Vol. 7 Issue 11, pp 1160-1162

The transition of the hydrogen-induced LI2 ordered structure of Pd3Mn to the Ag3Mg structure

In previous papers [1, 2], we have shown that when an  initially disordered and an initially ordered alloy  (Ag3Mg-type structure) of Pd3Mn were exposed to  hydrogen gas at elevated temperatures at pH2 > 1 MPa,  they transform to an ordered LI2 structure with an  accompanying introduction of large dislocation densities. This hydrogen-induced LI2 ordered alloy, when annealed in vacuo at 778 K for 24 h, transforms to a one-dimensional long-period structure of the Ag3Mg type. The temperature range where the Ll2-type structure is stable in the absence of hydrogen was not determined.

The goal of this work is to obtain detailed information about the reverse transformation from the hydrogen-induced LI2 structure to the Ag3Mg structure, using electrical resistance measurements and transmission electron microscopic (TEM) observations.

The Pd3Mn alloy was prepared from palladium (purity 99.98 wt %) and managnese  [sic, manganese] (99.99 wt %) using high-frequency induction heating under an argon atmosphere. The button was then rolled to a thickness of 100 to 140 μm. The samples used for electron microscopy were in the form of discs of 3 mm diameter which were trepanned from the foil, and for electrical resistance measurements samples were cut from the foil so that the dimensions were 2 mm x 25 mm.

The samples of the hydrogen-induced LI2-type ordered strucure used in this study were prepared  from the following two kinds of the alloy starting material: one was “initially disordered” and the other was “initially ordered” (Ag3Mg structure). The former samples were prepared by a rapid quenching from about 1190 K into ice-water, while simultaneously breaking the closed silica tubes which contained the samples wrapped in titanium foil and then sealed in vacuo. The samples of the Ag3 Mg-type structure were prepared by slow cooling in vacuo from about 1175 K to room temperature at a cooling rate of 2 K h-1. All of the samples were lightly abraded with fine emery paper and then chemically etched with a solution of 2 : 2 : 1 H2SO4 : HNO3 : H2O mixture.

1989 —

Y. Shirai, F. Nakamura, M. Takeuchi, K. Watanabe, and M. Yamaguchi, in Eighth International Conference on Positron Annihilation, edited by V. Dorikens, M. Drikens, and D. Seegers (World Scientific, Singapore, 1989), p. 488. Paper not found. Book available used. Not listed on World Scientific site, bu the title was found on Google Scholar.

Positron Annihilation

1991 —

Flanagan, T.B. and W.A. Oates,  Annu. Rev. Mater. Sci., 1991. 21: p. 269. Britz, P.Flan1991

The Palladium-Hydrogen System

In this review an attempt is made to highlight some of the important properties of the palladium-hydrogen system. (The term hydrogen will be used as a collective term when referring to all three isotopes, but otherwise the names of the specific isotopes, protium, deuterium, and tritium, will be used.) Most of the data in the literature are for the palladium-protium  system; generally the three isotopes behave similarly, however, the thermodynamic and kinetic (diffusion) behavior of the isotopes differ quantitatively and these differences are discussed below.

1991 —

E. K. Storms, C. Talcott-Storms,  Fusion Technol. 20, 246 (1991). Britz Stor1991a

The effect of hydriding on the physical structure of palladium and on the release of contained tritium

The behavior of tritium released from a contaminated palladium cathode is determined and compared with the pattern found in cells claimed to produce tritium by a cold fusion reaction. Void space is produced in palladium when it is subjected to hydrogen absorption and desorption cycles. This void space can produce channels through which hydrogen can be lost from the cathode, thereby reducing the hydrogen concentration. This effect is influenced, in part, by impurities, the shape of the electrode, the charging rate, the concentration of hydrogen achieved, and the length of time the maximum concentration is present.

1991 —

H. Noh, Ted B. Flanagan, B. Cerundolo, and A. Craft, Scripta Met. et Mat., Vol. 25 (1991) 225-230

H-Induced atom mobility in Palladium-Rhodium alloys

[Introduction] The phase diagram for the Pd-Rh system shows a miscibility gap which has been characterized down to temperatures of ~800K [1,2]. The limiting solid solution concentrations at 800 K are Pd0.90Rh0.10 and Pd0.10Rh0.90+. Normally, when Pd-Rh alloys are prepared and cooled from temperatures above the miscibility gap to temperatures well below, the fcc solid solution alloys are metastable and show no tendency to segregate according to the phase diagram. For this reason the phase diagram has not been extended to temperatures below about 800 K. In the most recent study [2] the phase boundaries were established by electrical resistivity changes. Those authors found no evidence for two phase formation from electron microprobe analysis. From this they concluded that the scale of the spinodal decomposition which occurs upon phase segregation was too fine, <10 nm, to detect any spatial compositional variations.

There have been several investigations of the absorption of hydrogen by palladium-rhodium alloys[3,4,5]. These alloys have been found to form hydride phases and, in contrast to most other substitutional elements in palladium, rhodium does not decrease the H/M ratio of the hydride phase. The hydrogen pressure for hydride formation increases with XRh.

It is known that hydrogen can induce metal atom mobility under conditions where such mobility does not occur in the absence of hydrogen. One recent example of such H-induced lattice mobility is the ordering of disordered Pd3Mn in the presence of hydrogen at temperatures where ordering is too slow to observe in the absence of hydrogen. Using Pd-Rh alloys, whose compositions lie well within the miscibility gap, two methods will be used in an attempt to observe hydrogen-induced segregation: (i) the alloys will be exposed to 5.0 MPa of H2 at 523 K; under these conditions the alloy’s hydride phase does not form, and (ii) the alloys will be cycled through the  α →  α’ phase change where α’ is the hydride phase. The rationale for the first approach is that dissolved hydrogen might induce segregation of the homogeneous alloy into Pd- and Rh- rich regions because under these conditions the resulting alloy having Pd-enriched regions should dissolve more hydrogen than the homogeneous alloy; the rationale for the second approach is that the lattice mobility which occurs as the hydride/dilute phase interface moves through the solid might assist segregation. [“Experimental” follows]

1991 —

H. Okamoto and T. Massalski, “”, J. Phase Equilibria, 12, No.2 (1991) p148-168. Open copy available.

Thermodynamically Improbable Phase Diagrams

Phase diagrams showing very unlikely boundaries, while not explicitly violating thermodynamic principles or phase rules, are discussed. Phase rule violations in proposed phase diagrams often become apparent when phase boundaries are extrapolated into metastable regions. In addition to phase rule violations, this article considers difficulties regarding an abrupt change of slope of a phase boundary, asymmetric or unusually pointed liquidus boundaries, location of miscibility gaps, and gas/liquid equilibria. Another frequent source of phase diagram errors concerns the initial slopes of liquidus and solidus boundaries in the very dilute regions near the pure elements. Useful and consistent prediction can be made from the application of the van’t Hoff equation for the dilute regions.

1992 —

H. Noh, Ted B. Flanagan, M.H. Ransick, Scripta Met. et Ma., Vol. 26 (1992) 353-358.

An Illustration of phase diagram determination using H-induced lattice mobility

[Introduction] It has been recently shown that hydrogen-induced lattice mobility (HILM) can lead to ordering of a disordered alloy at temperatures where the ordering is immeasurably slow in the absence of the dissolved hydrogen [1]. In this research we report an example of HILM where hydrogen catalyzes a longer range metal atom diffusion than that needed for the disorder → order transition. In the present case a nearly homogeneous alloy will be shown to undergo segregation under the influence of HILM. This can be of importance as an aid in the establishment of equilibrium for the determination of phase diagrams at relatively low temperatures where, because of sluggish equilibrium, they cannot be determined in the absence of H. It should be emphasized that hydrogen is not a component of the phase equilibrium, but acts as a catalyst promoting equilibrium under conditions where it is not established after long times in its absence.

Pd-Rh has a miscibility gap shown in figure 1 [2, 3]; segregation according to this phase diagram does not, however, normally occur when the alloys are cooled from elevated temperatures and consequently a continuous series of metastable fcc solid solutions can be prepared. Raub et al [2] found that annealing the Rh0.26Pd0.74 alloy at 873 K for 1 year did not result in segregation into Pd- and Rh-rich phases. A Rh0.51Pd0.49 alloy segregated into Pd- and Rh-rich phases after annealing at 873 K for 6 months. Evidence for segregation was obtained from the presence of two sets of fcc lattice parameters. Shield and Williams [3] did not find any evidence for phase separation in slowly cooled samples using analytical techniques but confirmed the earlier phase diagram from resistivity changes as the phase envelope was entered.

Alloy-H systems are usually thermodynamically characterized from their isotherms where pH2 is measured as a function of H/M. The equilibrium hydrogen pressure is a measure of the relative chemical potential of hydrogen, i.e.,

ΔμH =  μH – 1/2μH2  = 1/2RT ln pH2 [1] 

In single phase regions of the solid the H2 pressure (and ΔμH) changes continuously with HIM. When two solid phases co-exist with the gaseous phase, however, a pressure invariant region (the plateau pressure) occurs.

Hydrogen dissolves readily in Pd-Rh alloys forming hydride phases when the hydrogen concentrations exceed the terminal hydrogen solubilities. The plateau pressures increase with XRh [4, 5, 6]. This Pd-alloy system is unique because the extent of the two phase co-existence region does not decrease with increase of atom fraction of substituted metal as it does for other Pd-alloys. Typical hydrogen isotherms for homogeneous Pd-Rh alloys consist of a small dilute phase region where the pressure increases markedly with H content; this is followed by a two phase, invariant (plateau) pressure region and finally a single phase region at high hydrogen contents obtains where the pressure increases markedly with H content. If this alloy were to segregate into Pd-rich and Rh-rich phases according to the phase diagram (Fig. 1 ), then the isotherm should alter in a predictable way. […]

1993 —

Y. Fukai, N. Okuma,  Jpn. J. Appl. Phys. 32, L1256-1259 (1993). Britz Fukai1993

Evidence of copious vacancy formation in Ni and Pd under a high hydrogen pressure

From in situ observation of X-ray diffraction of Ni and Pd under a high hydrogen pressure (sime5 GPa) and temperatures (≤800°C), anomalous lattice contraction of the hydride was found to occur in 2~3 h. This contraction, amounting to ~0.5 Å3 per a metal atom, remained in the recovered specimen even after the hydrogen was removed by heating to 400°C, but was annealed out at 800°C. The concentration of vacancies responsible for this effect is estimated at ~20% of metal-atom sites. Anomalous concentration dependence of the hydrogen-induced volume and enhanced diffusion of metal atoms are explained in terms of this effect.

1993 —

Y. Fukai, Computer Aided Innovation of New Materials (Elsevier, Amsterdam, 1993), Vol. II, pp. 451–456. [the Fukai paper appears to be in Vol I? Vol 1 is missing.] [paper needed, not found]

1993 —

Y. Fukai, M. Yamakata, and T. Yagi, Z. Phys. Chem. 179, 119 (1993).

Some High-Pressure Experiments on the Fe — H System

In situ X-ray diffraction measurements have been performed of the hydriding process of iron under high hydrogen pressure and temperatures using a synchrotron radiation source. After hydrogenation, a sample of FeHx, in equilibrium with ~6 GPa of fluid Hundergoes a sequence of phase transitions dhcp → fcc → new phase → melt, at 650~700°C. 800~900°C and 1200°C. respectively. The structure of the new high-temperature phase is tentatively identified as a defect-bcc structure in which many vacancies exist in one of the simple cubic sublattices of bcc-Fe.

1994 —

Y. Fukai, N. Okuma, Phys. Rev. Lett. 73, 1640-1643 (1994). Britz Fukai1994

Formation of superabundant vacancies in Pd hydride under high hydrogen pressures

In situ x-ray diffraction on Pd hydride under 5 GPa of hydrogen pressure show that lattice contraction due to vacancy formation occurs in 2-3 h at 700-800 °C, and two-phase separation into PdH and a vacancy-ordered phase of Cu3Au structure (Pd3VacH4) on subsequent cooling. After recovery to ambient conditions and removal of hydrogen, the vacancy concentration in Pd metal was determined by measuring density and lattice parameter changes to be 18 ± 3 at.%. This procedure provides a new method of introducing superabundant vacancies in metals.

1994 —

R. Balasubramaniam, Scripta Met. et Mat., Vol. 30, No. 7 (1994) 875-880.

Mechanism of hydrogen induced ordering in Pd3Mn

[Introduction] In the Pd-Mn system (Fig 1), the Pd3Mn composition undergoes an order-disorder transformation [1-4]. Pd3Mn, above its critical temperature (Tc), has a disordered fcc structure an~ attains an ordered structure when it is slowly cooled below its Tc. On the other hand, if it is quenched rapidly to a temperature below Tc, it retains its disordered fcc stucture. This ‘quenched’ structure is truly not disordered because electron diffraction studies [2,5,6,7] have indicated that faint superlattice reflections of the ordered structure exist in the rapidly quenched material. Therefore, the fully disordered structure is difficult to [obtain] even by rapid quenching. This aspect of the transformation has to be noted as this will have relevance in the proposed mechanism described below. The ordered Pd3Mn structure can be precisely indexed as being of the A3Zr type [8] and not of the Ag3Mg type [2,9] by recognizing a center of symmetry [8]. It is denoted as the long period structure (LPS) of the L12-s type. The phase diagram of the Pd-Mn system (Fig 1) [10, 11] also shows composition dependence of the critical ordering temperature (obtained during heating and cooling) for hypostoichiometric Pd3Mn compositions. It is important to note that in these hypostochiometric compositions, a two phase region separating the ordered and disordered phase fields does not exist, thus indicating that this transformation is of the second order. The disordered phase is denoted as α (Fig i) and the ordered phase obtained by slow cooling as α-L12-s . The phase transitions in the Pd-Mn system have • . 2-6 • , • been investigated by a variety of techniques and the reader is [referred] to reference [11] for details of the transformations and phase domains.

It was first shown by Flanagan et al. [6] that the introduction of hydrogen at relatively low pressures and high temperatures (below Tc ) induced ordering of both the L12-s type and the ‘quenched’ structure to the ordered L12 structure. For example, at 523K and a partial pressure of hydrogen 5MPa, Pd3Mn transforms to the L12 structure (Cu3Au type) [6]. Incidentally, this was the first time that the L12 form of Pd3Mn had been prepared [6] and this implied that hydrogen could be employed to prepare ordered structures that are not possible to produce by conventional methods like annealing of the alloy. It is important to note that the L12 is the stable form of Pd3Mn below the critical temperature and the transformation to the L12 form does not occur even for long periods of exposure at high temperatures in the absence of hydrogen [6]. […]

1994 —

W. A. Oates and H. Wenzl, Scripta Met. et Mat., Vol. 30, No. 7 (1994) 851-854.

On the Copious Formation of Vacancies in Metals

Fukai and Ōkuma (1) have recently given convincing evidence for the formation of extremely high vacancy concentrations (≈ 20% of the metal atom sites) when Ni and Pd are annealed for a few hours at high temperatures (≤ 800°C) when under high H2 pressures (≈ 5GPa), i.e., at very high H concentrations. As indicated by Fukai and Ōkuma (1), the implications of this effect, especially through its possible influence on enhanced metal diffusion, could be profound.

Fukai and Ōkuma (1) discuss some other results which also seem to indicate large vacancy concentrations at very high H concentrations. These include the maximum observed H concentration exceeding that expected from structural considerations (2) and an anomalous change in the apparent partial molar volume of H in Pd alloys at high H concentrations (3).

Fukai and Ōkuma (1) gave a tentative explanation for the formation of large vacancy concentrations in terms of vacancy-hydrogen complexes. In the following we develop a simple model which may explain the origin of such large vacancy concentrations in a more plausible way.

1994-

Manchester, F.D., San-Martin, A. & Pitre, J.M. JPE (1994) 15: 62. DOI there is a preview of the first two pages, used in lieu of an abstract below. There is a list of references on the journal page. Anchors have been added and used as links from citations here, see the subpage Manchester 1994 references

The H-Pd (hydrogen-palladium) System

The Pd-H system is the paradigm of metal hydrogen systems: the longest studied (since 1866 [1866Gra]), the easiest to activate for hydrogen absorption, and probably the richest in the number of physically interesting phenomena that have been observed in this type of system. In matters of the thermodynamics of hydrogen absorption, the details of phase diagram delineation, description and analysis of electronic properties and a number of other features, work on the Pd-H system has tended to provide leading developments that have subsequently been used in other metal-hydrogen systems.

The T-X phase diagram (Fig. 1) assessed here for pressures* above 102 Pa, consists of the α and α’ phases, in both of which the H occupies, randomly, the interstitial octahedral sites of the fcc Pd lattice. Table 1 gives the crystal structure and the lattice parameters of the system.

Fig. 1 Assessed Pd-H phase diagram. T-X projection from a P-X-T surface onto a plane at P = 102 Pa.

Table 1 (a) In the literature this has often been referred to as the βmin value for the Pd-H lattice parameter [75Sch]. (b) This structure is an ordered arrangement of vacancies in the fcc H(D) lattice on interstitial octahedral sites in the Pd lattice. The Pearson symbol has been chosen to count both the vacancies and the interstitial H(D) corresponding to a structure that is stoichiometric at X = 0.5 to maintain consistency with the usual listings of this symbol for tetragonal structures. (c) Values for lattice parameters of tetragonal cell estimated from [75Sch] with the help of [84Hem] for the X value and temperature given by [83Bon]. (d) As in (b), except that counting interstitials together with vacancies corresponds to a structure that is stoichiometric at X = 1. (e) Values for lattice parameters of tetragonal cell estimated from [75Sch] with the help of [84Hem] for the X value and temperature given by [79Ell]. The sets of tetragonal lattice parameters referred to in (c) and (e) are for PdD x.

Refs in table: [78Kin], [64Mae],  [64Axe], [78And2], [79Ell], [81Bla]

The α phase is the low-concentration phase of the system, separated from the high-concentration α’ phase by a mixed (α + αt’) phase region. The boundary of this mixed phase region was delineated by taking an average of the limiting T-X values for the isotherm plateaus (see Fig. 2) determined by [64Wic], [73Fri], [83Las], [85Las], and [87Wic] from experimental P-X isotherms shown in Fig. 3. Because hysteresis** is observed in absorption and desorption isotherms for T < Tc [36Gil, 60Eve,
89Fla], it is possible to draw two different sets of boundaries for the mixed-phase region at each temperature. For clarity, only P-X desorption isotherms reproduced from the available literature are displayed in Fig. 3. (See further discussion on locating coexistence boundaries below.)
———
*For H-in-metal systems, the equilibrium pressure of the H gas surrounding the metal is always a significant thermodynamic variable, in conlrast to most situations involving metallic alloys. Thus, sections of the P-X-T surface in a T-X plane and a P-X plane are always necessary. In the presentation given here, P is the pressure in pascals, T is the temperature plotted in both K and ~ and Xis the H concentration expressed either as atomic percent H or as X = H/Pd, the atomic ratio.
**Hysteresis in metal-hydrogen systems with mixed phase regions, as in the α/α’ regions of the Pd-H system, arises from plastic deformation due to a large volume change as one phase, e.g.  α, changes to the other, e.g.  α’, or vice versa (see [89Fla]).
———

At -25 ~ the maximum H solubility in the α phase is X = 0.017 (1.68 at.% H), whereas the single α’ phase exists for X > 0.60 (37.6 at. % H). The two-phase region in Fig. I bounded by the coexistence curve closes at the critical point located at T = 293°C, X = 0.29 (22.5 at.% H), and P = 20.15 × 105 Pa (see Table 2). There is no distinction between the α and α’ phases above this critical temperature consistent with the applicability of the lattice gas model for the Pd-H system [60Hill, 69Ale,76Man]. Table 2 compares critical point parameters reported for the Pd-H system. Values obtained by [78Pic] are not included because they lack the overall consistency of those quoted in Table 2, and there is no compelling reason to try to justify this. With the exception of the values from [74Riba], the critical point parameters have all been observed from analysis of absorption/desorption isotherms only.

[37Lac1] used what amounted to a lattice gas calculation in the Bragg-Williams (i.e. mean field approximation [37Lac2]) to calculate the form of the Pd-H absorption isotherms and, using the Maxwell equal area rule, to determine the location of the α/α’ coexistence curve. [37Lac1] used the experimentally determined location of the critical point (i.e. Tc and Xc [36Gil]) to fix the value of the attractive H-H interaction and the value he assumed for the maximum permitted H concentration. The [37Lac1] calculation, apart from giving the first statistical thermodynamic model for H absorption in Pd-H, provided a parametric relation for analyzing the absorption of H in Pd, which is useful today (see “Solubility”). However, the [37Lac1] model was not founded on an assessment of the basic mechanisms responsible for the attractive H-H interaction or on other basic physical features of the Pd-H system. Also using a lattice gas calculation [79Die] estimated values for Tc and Xc and the form of the coexistence curve, which were roughly comparable to those obtained from experiment. [79Die] used a description of the elastic contribution to the H-H interaction, which was based on the earlier work of [74Wag] and [74Hor], and added to this an estimate of the electronic contribution to this interaction. […]

1995 —

H. Osono, T. Kino, Y. Kurokawa, Y. Fukai,J. Alloys and Compd. 231, 41-45 (1995). Britz Oson1995

Agglomeration of hydrogen-induced vacancies in nickel.

Scanning electron microscope observations of Ni samples annealed after recovery from high temperature heat treatment in the hydride phase showed the presence of numerous holes 20–200 nm in size. From various features of the holes they are identified as voids formed by agglomeration of supersaturated vacancies (about 5 at.% in concentration) which have diffused from the surface to the interior of the sample during heat treatment.

1995 —

K. Nakamura and Y. Fukai, J. Alloys Compd. 231, 46 (1995)

High-pressure studies of high-concentration phases of the TiH system

In situ X-ray diffraction at high pressure (5 GPa) and high temperatures (less than or approximately 1100 °C) of the TiH system revealed that two different kinds of phase transition take place at high hydrogen concentrations. [H]/[Ti] ≳ 2, a reversible transition due to absorption-desorption of hydrogen and an irreversible transition due to the formation of metal-atom vacancies. The general implication of the formation of defect-hydride phases in the phase diagrams of MH systems is discussed.

1995 —

Y. Fukai, J. Alloys Compd. 231, 35 (1995)

Formation of superabundant vacancies in metal hydrides at high temperatures

It has been found from X-ray diffraction on several MH systems under high p, T conditions that a large number of M-atom vacancies amounting to ca. 20 at.% are formed at high temperatures, leading to a vacancy-ordered L12 structure in some f.c.c. hydrides. The energetics of vacancy formation in hydrides suggests that defect-hydrides containing many vacancies are generally more stable thermodynamically than ordinary defect-free hydrides and therefore most phase diagrams of MH systems reported heretofore are metastable.

1995 —

R. Felici, L. Bertalot, A. DeNinno, A. LaBarbera and V. Violante, Rev. Sci. Instrum., 66(5) (1995) 3344. Britz P.Feli1995.

In situ measurement of the deuterium (hydrogen) charging of a palladium 380 electrode during electrolysis by energy dispersive x-ray diffraction

A method to determine the concentration of deuterium inside a palladium cathode during the electrolysis of LiOD–heavy water solution is described. This method is based on the measurement of the host metal lattice parameter which is linearly related to the concentration in a wide range. A hard‐x‐ray beam which is able to cross two glass walls and few centimeters of water solutions without suffering a strong attenuation has been used. The measurement of the lattice parameter is performed in situ, during the electrolysis, by using energy dispersive x‐ray diffraction. The sample volume illuminated by the x‐ray beam is limited to a small region close to the surface and depends on the incident photon energy.In principle, this allows one to study the dynamics of the charging process and to determine the concentration profile in the range from few up to tens of micrometers. The deuterium concentration, determined by this method, was then checked by degassing the cathode in a known volume and was always found in a very good agreement, showing that the charging was uniform for the whole sample.

1995 —

W. A. Oates and H. Wenzl, Scripta Met. et Mat., Vol. 33, No. 2 (1995) 185-193.

On the formation and ordering of superabundant vacancies in palladium due to hydrogen absorption

Fukai and Ōkuma (1,2) have recently presented some extremely interesting results concerning the formation of high concentrations of vacancies (¤) in Pd and other metals which result from the absorption of hydrogen. In their first paper (l), they showed that when Pd is annealed for long times (hours) at high temperatures (≈ 800°C) in high pressures of H2(g) (≈ 5 GPa), vacancy concentrations as high as N¤/NPd  ≈ 0.2 can be obtained (1). In their second paper (2), they demonstrated that these vacancies can order when the alloys containing high vacancy concentrations are slowly cooled to lower temperatures (below ≈ 6OO°C).

The hydrogen chemical potential, μH is very high under the conditions used in these experiments. This can be seen in Fig. (l), which shows ½(μH2μ0H2)/RT as a function of H2(g) pressure at 1000K (3). μ0H2 is the ideal gas reference state value at 1 bar and the temperature of interest. It should be appreciated that, in this temperature and pressure range, the curve represents a substantial extrapolation from the available experimental results. Such extrapolations are sensitive to the analytical form chosen for the fluid’s equation of state (a modified van der Waals equation in this case) and although the rapid increase in PH with H2(g) pressure in the GPa range shown in Fig. (1) is undoubtedly correct, the quantitative aspects of the relation may be questionable.

A brief explanation for the formation of the high vacancy concentrations in terms of a simple statistical model has been given previously (4). In the present note we wish to present a more quantitative confirmation of this model and also demonstrate how it can also explain the ordering of the ‘superabundant’ vacancies in Pd observed by Fukai and Ōkuma (2).

1996 —

K. Watanabe, N. Okuma, Y. Fukai, Y. Sakamoto, and Y. Hayashi, Scr. Mater. 34, 551 (1996).

Superabundant vacancies and enhanced diffusion in Pd-Rh alloys under high hydrogen pressures

In our recent experiments on a number of metal-hydrogen systems, we discovered that the equilibrium concentration of metal-atom vacancies is greatly enhanced under high hydrogen pressures [l-5]. The vacancy concentration as high as x, – 0.2 was attained when Ni and Pd specimens were held at 700 – 800°C in fluid hydrogen of 5 GPa [1,2]. In Pd hydride, formation of a Cu,Au-type vacancy-ordered structure was also observed [2].
We suggested that this phenomenon of superabundant vacancy formation should be the cause of the hydrogen-induced migration of metal atoms reported for some Pd alloys. In quenched specimens of Pd, &I,,~ alloy, where no phase separation was observed in vacuum after annealing at 600°C for 1 year [6], Noh et al. obtained indications of phase separation after annealing for only 4 h in 5.5 MPa of H2 gas [7,8]. Similar indication of hydrogen-induced phase separation was reported subsequently for Pd-Pt alloys[9]. These experiments were, however, not sufficiently convincing because their inference of phase separation was based on the form of “diagnostic” p-x-T curves without any direct structural information.
The purpose of this paper is to provide detailed structural information on the formation of superabundant vacancies and its effects on the phase separation process in P&&h0 2 alloys by performing in situ Xraydiffraction at high temperatures and high hydrogen pressures.

1996 —

 V. Gavriljuk, V. Bugaev, Y. Petrov, A. Tarasenko, and B. Yanchitski, Scr. Mater. 34, 903 (1996).

Hydrogen-induced equilibrium vacancies in FCC iron-base alloys

Dissolution of interstitials leads to an increase of equilibrium concentration of the site vacancies as a result of two main contributions: increase of entropy of solid solution and expenditure of energy for injection of the interstitial atoms. After hydrogen outgassing vacancies become thermodynairfically unstable and form dislocation loops which can be detected by means of TEM. In our opinion, the concept of hydrogen-induced vacancies can be useful for interpretation of hydrogen-induced phase transformations and mechanism of plastic deformation of hydrogenated materials.

1997 —

H. Birnbaum, C. Buckley, F. Zaides, E. Sirois, P. Rosenak, S. Spooner, and J. Lin, J. Alloys Compd. 253, 260 (1997).  

Hydrogen in aluminum

The introduction of solute hydrogen in high purity aluminum has been studied using a variety of experimental techniques. Very large hydrogen concentrations were introduced by electrochemical charging and by chemical charging. Length change and lattice parameter measurements showed that the hydrogen was trapped at vacancies which entered in a ratio close to Cv/CH=1. Small angle X-ray scattering showed that the hydrogen-vacancy complexes clustered into platelets lying on the {111}.

1997 —

Y. Fukai, Y. Kurokawa, H. Hiraoka, J. Japan Inst. Metals, 61 (1997) 663–670 (in Japanese).

Superabundant Vacancy Formation and Its Consequences in Metal–Hydrogen Alloys

A theory is proposed for the formation of super-abundant vacancies, in metal-hydrogen alloys, amounting to 10~20 at%, considering hydrogen effects to decrease the formation energy of a vacancy by cluster formation and the configurational entropy of the system at high hydrogen concentrations. A formula derived for the vacancy concentration is found to give excellent descriptions of experimental results on nickel-hydrogen and molybedenum-hydrogen alloys obtained under high hydrogen pressures. Some of the consequences of the superabundant vacancy formation are discussed, including solubility enhancement, formation of defect structures and voids, and enhancement of metal-atom diffusion.

1998 —

E. Hayashi Y. Kurokawa and Y. Fukai, Phys.Rev.Lett., 80(25) (1998) 5588.

Hydrogen-Induced Enhancement of Interdiffusion in Cu–Ni Diffusion Couples

Drastic enhancements of the interdiffusion were observed in Cu-Ni diffusion couples when samples were heated under high hydrogen pressures (5GPa). Interdiffusion coefficients measured between 600800°C were increased by 104 times on the Ni-rich end and by 10 times on the Cu-rich end. The observation is explained in terms of superabundant vacancy formation in the presence of interstitial hydrogen atoms.

1998 —

E.F. Skelton, P.L. Hagans, S.B. Qadri, D.D. Dominguez, A.C. Ehrlich and J.Z. Hu,Phys. Rev., B58 (1998) 14775.

In situ monitoring of crystallographic changes in Pd induced by diffusion of D

Crystallographic changes in a palladium wire cathode were monitored in situ, as deuterium was electrochemically deposited on the surface and diffused radially into the wire. Initially, the wire was pure Pd. A constant electrolysis current density of 1 mA/cm2 was maintained and D slowly diffused into the wire. As the D concentration increased, the wire transformed from pure Pd, to the α phase, and finally into the β phase. This reversible phase transformation begins on the surface and progresses radially inward. During the experiment, x-ray-diffraction data were collected from a volume element of about 180 pl. This volume element was systematically moved in 50-μm steps from the edge to the center of a 1.0 mm diameter Pd wire. Throughout the course of the experiment, the bulk value of x in PdDx, as determined from simultaneous measurements of the electrical resistivity, increased from 0 to ∼0.72. For each setting of the volume element, a monotonic increase in the volume of the α phase was observed, until the material entered the two-phase region. Once the β phase appeared, the volumes of both phases decreased slightly with continued loading. The integrated intensities of diffraction peaks from each phase were used in conjunction with the known phase diagram to estimate the rate of compositional change within the volume element. The diffusion rate for the solute atoms was estimated to be 57±nm/s, based on the temporal and spatial dependence of the integrated intensities of the diffraction peaks from each phase. These data also were used to evaluate the time dependence of the concentration of the solute atoms c/t and their diffusivity D. The value of c/t increased linearly from 6.2×105s1 at the surface, to  1999 —

D. S. dos Santos, S. Miraglia, D. Fruchart, J. Alloys and Compd. 291, L1-L5 (1999). Britz dSan1999

A high pressure investigation of Pd and the Pd–H  system

The effect of high pressure (3.5 GPa) on the Pd and Pd–H systems has been investigated. We have been able to induce a cubic–monoclinic structural transformation in the case of pure Pd treated at 450°C for 5 h. Hydrogen has been introduced at high pressures using an alternative hydrogen source (C14H10). It is shown that such a route can be operated to produce vacancy-ordered phases that are stable at ambient pressure and temperature.

1999 —

C.E. Buckley, H.K. Birnbaum, D. Bellmann, P. Staron, J. Alloys Compd., 293–295 (1999) 231–236.

Calculation of the radial distribution function of bubbles in the aluminum hydrogen system

Aluminum foils of 99.99% purity were charged with hydrogen using a gas plasma method with a voltage in the range of 1.0–1.2 keV and current densities ranging from 0.66 to 0.81 mA cm−2, resulting in the introduction of a large amount of hydrogen. X-ray diffraction measurements indicated that within experimental error there was a zero change in lattice parameter after plasma charging. This result is contradictory to almost all other FCC materials, which exhibit a lattice expansion when the hydrogen enters the lattice interstitially. It is hypothesised that the hydrogen does not enter the lattice interstitially, but instead forms a H-vacancy complex at the surface which diffuses into the volume and then clusters to form H2 bubbles. The nature and agglomeration of the bubbles were studied with a variety of techniques, such as small angle, ultra small angle and inelastic neutron scattering (SANS, USANS and INS), transmission and scanning electron microscopy (TEM and SEM), precision density measurements (PDM) and X-ray diffraction. The USANS and SANS results indicated scattering from a wide range of bubble sizes from <10 Å up to micron size bubbles. Subsequent SEM and TEM measurements revealed the existence of bubbles on the surface, as well as in the bulk and INS experiments show that hydrogen is in the bulk in the form of H2 molecules. In this paper we calculate the radial distribution function of the bubbles from the SANS and USANS results using methods based on the models derived by Brill et al., Fedorova et al. and Mulato et al. The scattering is assumed to be from independent spherical bubbles. Mulato et al. model is modified by incorporating smearing effects, which consider the instrumental resolution of the 30 m SANS spectrometer at NIST. The distribution functions calculated from the two methods are compared, and these distributions are then compared with the range of particle sizes found from TEM and SEM techniques.

2000 —

Y. Fukai, Y. Ishii, T. Goto, and K. Watanabe, J. Alloys Compd. 313, 121 (2000).

Formation of superabundant vacancies in Pd–H alloys

Temporal variation of the lattice parameter of Pd was measured under high hydrogen pressures (2–5 GPa) and temperatures (672–896°C) by X-ray diffraction using a synchrotron radiation, and observed lattice contraction was interpreted as being due to the formation of a large number of vacancy–hydrogen (Vac–H) clusters, i.e. superabundant vacancies. Analysis of the result led to the conclusion that a major part of Vac–H clusters (amounting to ∼10 at.%) were introduced by diffusion from the surface, after a small number of them had been formed at some internal sources. The thermal-equilibrium concentration of Vac–H clusters at high temperatures shows a saturation behavior, which indicates the presence of a maximum possible concentration (ca.16 at.%) of the clusters. The formation energy, entropy and volume of a Vac–H cluster are found to be 0.72 eV, 7.2k and 0.60Ω, respectively, and the migration energy and volume are 1.20 eV and 0.49Ω, respectively. Various other implications of the results are also discussed.

2000 —

N. Eliaz, D. Eliezer, D. L. Olson, “s”, Mat. Sc. and Engr. A289 (2000) 41-53.

Hydrogen-assisted processing of materials

Under certain conditions, hydrogen can degrade the mechanical properties and fracture behavior of most structural alloys; however, it also has some positive effects in metals. Several current and potential applications of hydrogen for enhancing the production and processing of materials are reviewed. These include thermohydrogen processing (THP) and forming of refractory alloys, processing of rare earth-transition metal magnets by hydrogen decrepitation (HD) and hydrogenation–decomposition–desorption–recombination (HDDR), hydrogen-induced amorphization (HIA) and microstructural refinement, extraction of elements from ores and alloys, and the use of hydrogen as a reducing gas for welding and brazing. Hydrogen is found to enhance the formability, microstructure and properties of a large variety of materials, including steels, Ti-based alloys and metal matrix composites(MMCs), refractory metals and alloys, rare earth-transition metal alloys, metalloid-containing metallic glasses, etc.

2001 —

Y. Fukai, Y. Shizuku, Y. Kurokawa, J. Alloys Compds. 329, 195-201 (2001). Britz Fukai2001

Superabundant vacancy formation in Ni–H alloys

X-ray diffraction measurements on the Ni–H system were made using synchrotron radiation at high hydrogen pressures p(H2)=3∼5 GPa and high temperatures T≲1000°C. Gradual lattice contraction occurring over several hours at high temperatures revealed the formation of superabundant vacancies (vacancy-hydrogen clusters). Superlattice reflections due to ordered arrangements of Vac-H clusters were also observed. The concentration of Vac-H clusters (xcl≅0.30), deduced from the magnitude of the lattice contraction, was very nearly independent of pressure and temperature, and indicates the maximum possible cluster concentration to be accommodated by the metal lattice. A simple enlightening description of the physics of superabundant vacancy formation is given in Appendix A.

2001 —

S. Miraglia, D. Fruchart, E. K. Hill, S. S. M. Tavares, D. Dos Santos, J. Alloys and Compounds 317, 77-82 (2001). Britz Mira2001

Investigation of the vacancy ordered phases in the Pd–H system

It has been shown that hydrogen–metal reactions operated at high pressures (3–5 GPa) may lead to hydrogen-induced lattice migration. The occurrence of fast diffusion processes that take place within the metal lattice has been established. Under these conditions, modifications of the diffusion kinetics and of the phases equilibria allow to produce vacancy-ordered phases with high vacancy concentrations (20%). An alternative route which leads to such phases that are stable at ambient pressure and temperature is presented. The structural properties of the Pd-(vacancy, H) system which have been studied by means of X-ray diffraction, scanning electron microscopy and transmission electron microscopy will be discussed. In the case of palladium, the vacancy-ordered state is characterized by the loss of superconductivity with respect to the Pd hydride. This spectacular modification of the physical properties will be presented and discussed in the light of band structure calculations that have been performed modeling different types of decorated vacancies with octahedral coordination.

2001 —

Y. Fukai, T. Haraguchi, E. Hayashi, Y. Ishii, Y. Kurokawa, and J. Yanagawa, Defect Diffus. Forum 194, 1063 (2001).

Hydrogen-Induced Superabundant Vacancies and Diffusion Enhancement in Some FCC Metals

Lattice contractions caused by the formation of extremely high concentrations of vacancies (superabundant vacancies of ~ 10 at.% ) were observed in the fcc phases Mn-H, Fe-H, Co-Hi, Ni-H and Pd-H samples at high temperatures(≤900°C ) and high H2 pressures ( ≤5 GPa). Comprehensive measurements in the Pd-H system, analysed in terms of our theory of vacancy- hydrogen ( Vac-H) cluster formation, have allowed to determine the formation and migration properties of the Vac-H clusters. From the observed lattice contraction process and concomitant diffusion enhancement, it is concluded that most Vac-H clusters are introduced by diffusion from the surface over a long time but some of them are created instantly at internal sources.

2001 —

Klechkovskaya, V.V. & Imamov, R.M. Crystallogr. Rep. (2001) 46: 534.

Electron diffraction structure analysis—from Vainshtein to our days

The physical grounds of the modern electron diffraction structure analysis have been analyzed. Various methods and approaches developed in electron diffraction studies of various structures are considered. The results of the structure determinations of various inorganic and organic materials are discussed.

2001 —

S. Miraglia, D. Fruchart, E. Hlil, S. Tavares, and D. D. Santos, J. Alloys Compd. 317-318, 77 (2001).

Investigation of the vacancy-ordered phases in the Pd–H system

It has been shown that hydrogen–metal reactions operated at high pressures (3–5 GPa) may lead to hydrogen-induced lattice migration. The occurrence of fast diffusion processes that take place within the metal lattice has been established. Under these conditions, modifications of the diffusion kinetics and of the phases equilibria allow to produce vacancy-ordered phases with high vacancy concentrations (20%). An alternative route which leads to such phases that are stable at ambient pressure and temperature is presented. The structural properties of the Pd-(vacancy, H) system which have been studied by means of X-ray diffraction, scanning electron microscopy and transmission electron microscopy will be discussed. In the case of palladium, the vacancy-ordered state is characterized by the loss of superconductivity with respect to the Pd hydride. This spectacular modification of the physical properties will be presented and discussed in the light of band structure calculations that have been performed modeling different types of decorated vacancies with octahedral coordination.

2001 —

M. Nagumo, M. Takamura, and K. Takai, Metall. Mater. Trans. A 32, 339 (2001).

Hydrogen thermal desorption relevant to delayed-fracture susceptibility of high-strength steels

The susceptibility to hydrogen embrittlement (HE) of martensitic steels has been examined by means of a delayed-fracture test and hydrogen thermal desorption analysis. The intensity of a desorption rate peak around 50 °C to 200 °C increased when the specimen was preloaded and more remarkably so when it was loaded under the presence of hydrogen. The increment appeared initially at the low-temperature region in the original peak. As hydrogen entry proceeded, the increment then appeared at the high-temperature region, while that in the low-temperature region was reduced. The alteration occurred earlier in steels tempered at lower temperatures, with a higher embrittlement susceptibility. A defect acting as the trap of the desorption in the high-temperature region was assigned to large vacancy clusters that have higher binding energies with hydrogen. Deformation-induced generation of vacancies and their clustering have been considered to be promoted by hydrogen and to play a primary role on the HE susceptibility of high-strength steel.

2002 —

Y. Shirai, H. Araki, T. Mori, W. Nakamura, and K. Sakaki, J. Alloys Compd. 330, 125 (2002).

Positron annihilation study of lattice defects induced by hydrogen absorption in some hydrogen storage materials

Some AB5 and AB2 hydrogen storage compounds have been characterized by using positron-annihilation lifetime spectroscopy. It has been shown that they contain no constitutional vacancies and that deviations from the stoichiometric compositions are all compensated by antistructure atoms. Positron lifetimes in fully-annealed LaNi5−xAlx and MmNi5−xAlx alloys show good correlation with their hydrogen desorption pressures. On the other hand, surprising amounts of vacancies together with dislocations have been found to be generated during the first hydrogen absorption process of LaNi5 and ZrMn2. These lattice defects may play a key role in initial activation processes of hydrogen storage materials.

2002 —

P. Chalermkarnnon, H. Araki, and Y. Shirai, Mater. Trans. JIM 43, 1486 (2002). [copy

Excess Vacancies Induced by Disorder-Order Phase Transformation in Ni3Fe

The order-disorder transformation and lattice defects in Ni3Fe have been studied by positron lifetime measurements. Anomalous vacancy-generation during ordering transformation, which was originally found on the ordering process of super-cooled disordered Cu3Au, has been confirmed on the ordering transformation of Ni3Fe. Disordered fcc solid solution of Ni3Fe was brought to room temperature by quenching the specimen from temperatures above the order-disorder transformation point TC. The ordering process into L12 structure was promoted by heating the sample isochronally or isothermally. It has been found that vacancies are generated in both heating processes, i.e., during the ordering process of super-cooled disordered Ni3Fe. Generated vacancies are not stable up to TC and annealed out at temperatures below TC.

2003 —

Y. Fukai,  J. Alloys and Compounds 356-357, 263-269 (2003).  Britz Fukai2003a

Formation of superabundant vacancies in M–H alloys and some of its consequences: a review

Superabundant vacancies (SAVs) are the vacancies of M atoms formed in M-H alloys, of concentrations as large as 30 at.%. After presenting some results of SAV formation as revealed by X-ray diffraction (XRD) at high temperatures and high hydrogen pressures, its mechanism in terms of vacancy-hydrogen (Vac-H) cluster formation is described, including the underlying information of Vac-H interactions. One of the most important conclusions of the theory is that defect structures containing SAVs are in fact the most stable structure of M-H alloys, and therefore SAVs should be formed whenever the kinetics allow. It is shown subsequently that SAVs can be formed in the process of electrodeposition. Some of the consequences of SAV formation including the enhancement of M-atom diffusion and creep are described, and its possible implication for hydrogen embrittlement of steels is mentioned.

2003 —

Y. Fukai, M. Mizutani, S. Yokota, M. Kanazawa, Y. Miura, T. Watanabe, J. Alloys and Compd. 356-357, 270-273 (2003). Britz Fukai2003b

Superabundant vacancy–hydrogen clusters in electrodeposited Ni and Cu

Superabundant vacancies (SAVs) are the vacancies of M atoms formed in M–H alloys, of concentrations as large as ≲30 at.%. After presenting some results of SAV formation as revealed by X-ray diffraction (XRD) at high temperatures and high hydrogen pressures, its mechanism in terms of vacancy-hydrogen (Vac-H) cluster formation is described, including the underlying information of Vac-H interactions. One of the most important conclusions of the theory is that defect structures containing SAVs are in fact the most stable structure of M–H alloys, and therefore SAVs should be formed whenever the kinetics allow. It is shown subsequently that SAVs can be formed in the process of electrodeposition. Some of the consequences of SAV formation including the enhancement of M-atom diffusion and creep are described, and its possible implication for hydrogen embrittlement of steels is mentioned.

2003 —

Y. Fukai, K. Mori, and H. Shinomiya, J. Alloys Compd. 348, 105 (2003).

The phase diagram and superabundant vacancy formation in Fe–H alloys under high hydrogen pressures

In situ XRD measurements at high temperatures and high hydrogen pressures were performed on Fe–H alloys, and in combination with all available data a p(H2)–T diagram was constructed up to p(H2)=10 GPa and T=1500 °C. A drastic reduction of the melting point with dissolution of hydrogen, down to 800 °C at 3 GPa, was observed. In the f.c.c. phase, a gradual lattice contraction due to superabundant vacancy formation was found to take place over several hours. The lattice parameter at 784 °C, 4.7 GPa decreased by 6%, which implies that a vacancy concentration as high as 19 at.% was attained.

Y. Fukai, Y. Kurokawa, and H. Hiraoka, J. Jpn. Inst. Met. 61, 663 (1997). [reference obscure, no vol 61, paper not at page in 1997. About Mo, see this 2003 paper[working reference to find abstract, or paper needed] 

2003 —

Y. Fukai and M. Mizutani, Mater. Trans. 43, 1079 (2002). (copy)  

Phase Diagram and Superabundant Vacancy Formation in Cr-H Alloys

X-ray diffraction measurements on the Cr–H system were made using synchrotron radiation at high hydrogen pressures and high temperatures, and the phase diagram was determined up to p(H2)=5.5 GPa and T\\lesssim1400 K. Three solid phases were found to exist; a bcc phase (α) of low hydrogen concentrations, x=[H]⁄[Cr]\\lesssim0.03 existing at low hydrogen pressures (\\lesssim4.4 GPa), and two high-pressure phases, an hcp (ε) phase at lower temperatures and an fcc (γ) phase at higher temperatures, both having high hydrogen concentrations x∼1. A drastic reduction of the melting point is caused by dissolution of hydrogen. A gradual lattice contraction observed in the fcc phase indicates the formation of superabundant Cr-atom vacancies (vacancy-hydrogen clusters). Thermal desorption measurements after recovery from high p(H2), T treatments revealed several desorption stages including those due to the release from vacancy-hydrogen clusters and from hydrogen-gas bubbles, and allowed determination of relevant trapping energies.

2003 —

Y. Fukai, Phys. Scr. T103, 11 (2003)

Superabundant Vacancies Formed in Metal–Hydrogen Alloys

Superabundant vacancies of metal atoms, of concentrations as high as 10 ~ 30 at %, can be formed in the presence of interstitial hydrogen as a consequence of reduction of the formation energy by trapping H atoms. The equilibrium concentration and mobility of Vac-H clusters were determined by in situ XRD and resistivity measurements, and their sources were identified. The binding energies of trapped H atoms were determined by thermal desorption spectroscopy. Some of these experimental results are described, with particular reference to Pd, Ni and Cr.

2003 —

Y. Tateyama and T. Ohno, Phys. Rev., B67 (2003) 174105.

Stability and clusterization of hydrogen–vacancy complexes in α-Fe: An ab initio study

By means of ab initio supercell calculations based on the density-functional theory, we have investigated stability of hydrogen-monovacancy complexes (VHn) and their binding preferences in αFe. We have found that VH2 is the major complex at ambient condition of hydrogen pressure, which corrects the conventional model implying the VH6 predominance. It is also demonstrated that monovacancies are not hindered from binding by the hydrogen trapping in the case of VHpredominance. Besides, the presence of hydrogen is found to facilitate formations of line-shaped and tabular vacancy clusters without the improbable accumulation. These anisotropic clusters can be closely associated with the fracture planes observed in experiments on hydrogen embrittlement in Fe-rich structural materials such as steel. The present results should suggest implications of hydrogen-enhanced vacancy activities to microscopic mechanism of hydrogen embrittlement in those materials.

2003 —

D. S. dos Santos, S. S. M. Tavares, S. Miraglia, D. Fruchart, D. R. dos Santos, J. Alloys Compd., 356–357 (2003) 258–262.

Analysis of the nanopores produced in nickel and palladium by high hydrogen pressure

Samples of pure nickel and palladium were submitted to a high hydrogen pressure (HHP) of 3.5 GPa at 800 °C for 5 h. Analysis of the resulting structural modification was performed using X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM) and small-angle X-ray scattering (SAXS), the latter specifically for Ni. The formation of superabundant vacancies (SAVs) was observed in the structure in both cases. For Pd, the pores, which formed by the coalescence of vacancies, had dimensions of 20–30 nm when present in the interior of the metal and 1–3 μm when condensed at the surface. The pores were seen to be dispersed homogeneously across the surface of Pd. For Ni, however, pores were created preferentially at the grain boundaries, which promoted significant decohesion in the metal. The distribution of pores induced by heat treatment of Ni subjected to HHP was determined by SAXS analysis and two populations of pores, with population mean diameters of 50 and 250 Å, were observed.

2004 —

H. Koike, Y. Shizuku, A. Yazaki, and Y. Fukai, J. Phys.: Condens. Matter 16, 1335 (2004).

Superabundant vacancy formation in Nb–H alloys; resistometric studies

The formation of superabundant vacancies (SAVs; vacancy–hydrogen clusters) was studied in Nb–H alloys by means of resistivity measurements as a function of temperature, pressure and H concentration. The formation energy of a vac–H cluster (0.3 ± 0.1 eV), which is 1/10 of the formation energy of a vacancy in Nb, is explained tentatively as being the consequence of six H atoms trapped by a vacancy with the average binding energy of 0.46 eV/H atom. The SAVs were introduced from the external surface, and transported into the interior by direct bulk diffusion and/or by fast diffusion along dislocations. The activation volumes for the formation and migration of vac–H clusters were determined to be 3.7 and 5.3 Å3, respectively.

2003 —

M. P. Pitt and E. MacA. Gray, Europhys. Lett., 64 (3), pp. 344–350 (2003). Copy on ResearchGate

Tetrahedral occupancy in the Pd-D system observed by in situ neutron powder diffraction

The crystallography of the Pd-Dx system has been studied by in situ neutron powder diffraction at 309 °C, in the supercritical region, and, after quenching in the pure β phase to 50 °C, in the two-phase region at 50 °C. Rietveld profile analysis of the supercritical diffraction patterns showed that 14% of D interstitials were occupying tetrahedral interstices, in sharp contrast to previous studies at lower temperatures. Tetrahedral occupancy was maintained through the two-phase region at 50 °C. These results are discussed in the light of first-principles total-energy calculations of hydrogen states in palladium.

2004 —

J. Cizek, I. Prochazka, F. Becvar, R. Kuzel, M. Cieslar, G. Brauer, W. Anwand, R. Kirchheim, and A. Pundt, Phys. Rev. B 69, 224106 (2004)

Hydrogen-induced defects in bulk niobium

Our aim in the present work was to investigate changes of the defect structure of bulk niobium induced by hydrogen loading. The evolution of the microstructure with increasing hydrogen concentration was studied by x-ray diffraction and two complementary techniques of positron annihilation spectroscopy (PAS), namely positron lifetime spectroscopy and slow positron implantation spectroscopy with the measurement of Doppler broadening, in defect-free Nb (99.9%) and Nb containing a remarkable number of dislocations. These samples were electrochemically loaded with hydrogen up to XH=0.06[H/Nb], i.e., in the α-phase region, and it was found that the defect density increases with hydrogen concentration in both Nb samples. This means that hydrogen-induced defects are created in the Nb samples. A comparison of PAS results with theoretical calculations revealed that vacancy-hydrogen complexes are introduced into the samples due to hydrogen loading. Most probably these are vacancies surrounded by 4 hydrogen atoms.

2004 —

M. Nagumo, Mater.Sci.Tech., 20 (2004) 940–950.

Hydrogen related failure of steels – a new aspect

Recent studies of the characteristics and mechanism of hydrogen related failure in steels are overviewed. Based on an analysis of the states of hydrogen in steels, the role of hydrogen in reducing ductile crack growth resistance is attributed to the increased creation of vacancies on straining. Cases showing the involvement of strain induced vacancies in susceptibility to fracture are presented. The function of hydrogen is ascribed to an increase in the density of vacancies and their agglomeration, rather than hydrogen itself, through interactions between vacancies and hydrogen. The newly proposed mechanism of hydrogen related failure is supported by a recent finding of amorphisation associated with crack growth.

2004 —

Daisuke Kyoi, Toyoto Sato, Ewa R¨onnebro, Yasufumi Tsuji, Naoyuki Kitamura, Atsushi Ueda, Mikio Ito, Shigeru Katsuyama, Shigeta Hara, Dag Nor´eus, Tetsuo Sakai, J. Alloys  Compd., 375 (2004) 253–258.

A novel  magnesium–vanadium hydride synthesized by a gigapascal-high-pressure technique

A magnesium-based vanadium-doped hydride was prepared in a high-pressure anvil cell by reacting a MgH2–25%V molar mixture at 8 GPa and 873 K. The new magnesium–vanadium hydride has a cubic F-centred substructure (a=4.721(1) Å), with an additional superstructure, which could be described by a doubling of the cubic cell axis and a magnesium atom framework, including an ordered arrangement of both vanadium atoms and vacancies (a=9.437(3) Å, space group (no. 225), Z=4, V=840.55 Å3). The metal atom structure is related to the Ca7Ge type structure but the refined metal atom composition with vacancies on one of the magnesium sites corresponding to Mg6V nearly in line with EDX analysis. The thermal properties of the new compound were also studied by TPD analysis and TG-DTA. The onset of the hydrogen desorption for the new Mg6V hydride occurred at a 160 K lower temperature when compared to magnesium hydride at a heating rate of 10 K/min.

2004 —

S. Tavares, S. Miraglia, D. Frucharta, D.Dos Santos, L. Ortega and A. Lacoste, J. Alloys Compd., 372 (2004) L6–L8.

Evidence for a superstructure in hydrogen-implanted palladium

An alternative route for hydrogenation has been investigated: plasma-based ion implantation. This treatment applied to the Pd–H system induces a re-ordering of the metal lattice and superstructure lines have been observed by grazing incidence X-ray diffraction. These results are similar to those obtained by very high-pressure hydrogenation of palladium and prompt us to suggest that plasma-based hydrogen implantation is likely to induce superabundant vacancy phase generation.

2004 —

H. Araki, M. Nakamura, S. Harada, T. Obata, N. Mikhin, V. Syvokon, M. Kubota, J. Low Temp. Phys., 134 (2004) 1145–1151.

Phase Diagram of Hydrogen in Palladium

Hydrogen in palladium, Pd-H(D), is an interesting system because of the highly mobile hydrogen and the presence of a phase boundary below 100 K. Experimentally, however, the nature of this transition has not been established. Historically this transition around 55 to 100 K has been thought to be an order-disorder transition. Such a transition would produce a phase boundary with anomalies at specific hydrogen concentrations corresponding to the specific ordered structures. In order to check this phase boundary we have performed a detailed study of the hydrogen concentration dependence of the specific heat of PdH x over the temperature range from below 0.5 K to above 100 K using PdH x specimens with x up to 0.8753. The measured heat capacity has been analyzed as the sum of contributions due to the lattice specific heat of Pd, the electronic specific heat of PdH x , and the excess contribution caused by hydrogenation of the specimen. The excess specific heat result shows a sharp peak which indicates a phase boundary with transition temperature T1=55 K to 85 K depending linearly on the hydrogen concentration from x=0.6572 to 0.8753. We do not observe anomalies at specific x values as would be expected for the specific ordered structures.

2005 — 

Y. Fukai, Second, Revised and Updated Edition, Springer, 2005, Britz Fukai2005

The Metal–Hydrogen System: Basic Bulk Properties

Metal hydrides are of inestimable importance for the future of hydrogen energy. This unique monograph presents a clear and comprehensive description of the bulk properties of the metal-hydrogen system. The statistical thermodynamics is treated over a very wide range of pressure, temperature and composition. Another prominent feature of the book is its elucidation of the quantum mechanical behavior of interstitial hydrogen atoms, including their states and motion. The important topic of hydrogen interaction with lattice defects and its materials-science implications are also discussed thoroughly. This second edition has been substantially revised and updated.

2005 —

T. Iida, Y. Yamazaki, T. Kobayashi, Y. Iijima, and Y. Fukai, Acta Mater. 53, 3083 (2005).

Enhanced diffusion of Nb in Nb–H alloys by hydrogen-induced vacancies

The diffusion coefficient of 95Nb in pure Nb and Nb–H alloys whose hydrogen concentration ranges between H/Nb = 0.05 and 0.34 in atomic ratio has been determined in the temperature range 823–1598 K using a serial sputter-microsectioning technique. The diffusion coefficient of Nb in the Nb–H alloys was found to increase significantly with increasing hydrogen concentration. The dependence of the diffusion enhancement on temperature and hydrogen concentration was examined in some detail, and explained tentatively in terms of average occupation number of hydrogen atoms per vacancy, r. The diffusion enhancement comes primarily from the decrease of the activation energy Q, resulting from the increase of r with increase of hydrogen concentration. Some remaining problems with this interpretation are pointed out for future investigations.

2005 —

S. Harada, S. Yokota, Y. Ishii, Y. Shizuku, M. Kanazawa, Y. Fukai, J. Alloys Compd., 404–406 (2005) 247–251.

A relation between the vacancy concentration and hydrogen concentration in the Ni–H, Co–H and Pd–H systems

The formation of superabundant vacancies (Vac-H clusters) has been observed in many M–H alloys, but the factors that determine the equilibrium concentration of vacancies have not been identified yet. To identify these factors, the equilibrium concentration of vacancies was estimated from lattice contraction measurements on Ni, Co and Pd having a fcc structure, at high temperatures (930–1350 K) and high hydrogen pressures (2.4–7.4 GPa). The results show that the vacancy concentration is not so much dependent on temperature and hydrogen pressure as the hydrogen concentration. In Ni and Co, the vacancy concentration (xcl) increases linearly with the hydrogen concentration (xH) for the whole concentration range, reaching xcl∼0.3 at xH∼1.0. In Pd, the vacancy concentration is very small up to xH∼0.6 and increases linearly thereafter with nearly the same slope as in Ni and Co. The maximum vacancy concentration reached in Pd is xcl∼0.12. It is noted that the observed difference in the  2005 —

C. Zhang, Ali Alavi, J. Am. Chem. Soc., 127(27) (2005) 9808–9817.

First-Principles Study of Superabundant Vacancy Formation in Metal Hydrides

Recent experiments have established the generality of superabundant vacancies (SAV) formation in metal hydrides. Aiming to elucidate this intriguing phenomenon and to clarify previous interpretations, we employ density-functional theory to investigate atomic mechanisms of SAV formation in fcc hydrides of Ni, Cu, Rh, Pd, Ag, Ir, Pt, and Au. We have found that upon H insertion, vacancy formation energies reduce substantially. This is consistent with experimental suggestions. We demonstrate that the entropy effect, which has been proposed to explain SAV formation, is not the main cause. Instead, it is the drastic change of electronic structure induced by the H in the SAV hydrides, which is to a large extent responsible. Interesting trends in systems investigated are also found:  ideal hydrides of 5metals and noble metals are unstable compared to the corresponding pure metals, but the SAV hydrides are more stable than the corresponding ideal hydrides, whereas opposite results exist in the cases of Ni, Rh, and Pd. These trends of stabilities of the SAV hydrides are discussed in detail and a general understanding for SAV formation is provided. Finally, we propose an alternative reaction pathway to generate a SAV hydride from a metal alloy.

2005 —

Y. Fukai, J. Alloys Compd., 404–406 (2005) 7–15.

The structure and phase diagram of M–H systems at high chemical potentials—High pressure and electrochemical synthesis

Efforts to provide a unified picture of metal–hydrogen alloys over a wide range of chemical potentials are described. High chemical potentials are produced either by high-pressure molecular hydrogen or high excess potentials in electrolytic charging or electrodeposition. General systematics of the phase diagram of 3d-metal–hydrogen systems are noted; a drastic reduction of the melting point and the stabilization of close-packed structures with dissolution of hydrogen. Supercritical anomalies are observed in the fcc phase of Fe–H, Co–H and Ni–H systems. In the electrodeposition of metals, it is shown that structural changes are caused by dissolution of hydrogen, and superabundant vacancies of concentrations 10−4 are present.

2005 —

D. Tanguy and M. Mareschal, Physical Review B 72, Issue 17 (2005) 174116.

Superabundant vacancies in a metal-hydrogen system:  Monte Carlo simulations

An equilibrium Monte Carlo simulation capable of treating superabundant vacancy formation and ordering in metal-hydrogen systems (MH) is developed. It combines lattice site occupations and continuous degrees of freedom which enables one to perform insertion/removal moves and hydrogen-vacancy cluster moves while the position of the particles are sampled. The bulk phase diagram in (μM,NH,V,T) ensemble is estimated for concentrations lower than 1  at. %. Within the framework of an EAM Al-H potential, ordering of superabundant vacancies in the shape of chains and platelets is reported at room temperature.

2006 —

K. Sakaki, R. Date, M. Mizuno, H. Araki, and Y. Shirai, Acta Mater. 54, 4641 (2006).

The effect of hydrogenated phase transformation on hydrogen-related vacancy formation in Pd1−xAgx alloy

To clarify the hydrogen-related vacancy formation mechanism, positron lifetime measurements were performed for Pd1−xAgx alloys that were hydrogenated at 296 or 373 K. Positron lifetime increased only when the alloys were hydrogenated below the critical temperature for phase transformation of the hydrogenation reaction, while it remained constant when they were hydrogenated above the critical temperature. This strongly suggests that vacancies formed only when phase transformation occurs. Therefore, hydrogen-related vacancy formation must be caused by the strain generated as the result of the phase transformation.

2006 —

K. Sakaki, T. Kawase, M. Hirato, M. Mizuno, H. Araki, Y. Shirai, and M. Nagumo, Scr. Mater. 55, 1031 (2006).

The effect of hydrogen on vacancy generation in iron by plastic deformation

Positron lifetime spectroscopy was applied to examine the synergistic effect of hydrogen and plastic straining on the vacancy generation in iron. Hydrogen enhanced the increase in mean positron lifetime, τm, by plastic straining and elevated the recovery temperature of τmon isochronal annealing. Multi-component analyses of positron lifetime spectra showed that the presence of hydrogen enhances the generation of vacancies, rather than of dislocations. These results are consistent with previous interpretations on thermal desorption analysis of hydrogen in deformed steels.

2007 —

 Y. Fukai, T. Hiroi, N. Mukaibo, and Y. Shimizu, J. Jpn. Inst. Met. 71, 388 (2007). (In Japanese. Figure captions are in English.)

Formation of Hydrogen-Induced Superabundant Vacancies in Electroplated Nickel-Iron Alloy Films

The structure and formation of superabundant vacancies in electroplated Ni64Fe36 alloy films have been studied by XRD and thermal desorption spectroscopy. The films, as deposited, consist of fine grains of ca. 10 nm in size, which, upon heating, start to undergo a gradual grain growth at ~600 K, and a rapid growth above ~670 K. The desorption of hydrogen occurred in seven stages; P0(385 K), P1(440 K), P2(560 K), P3(670 K), P4(960 K), P5(1170 K), and P6(>1270 K). P0 is attributed to desorption of H atoms on regular interstitial sites, P1~P2 and P4~P5 to H atoms trapped by vacancies, and P6 to hydrogen bubbles precipitated in the matrix. P3 and a desorption peak of CO+ (1100 K) are attributed to the decomposition of occluded C, H compounds. Binding energies of H in these trapped states are estimated, and possible configurations of these vacancy-H clusters are discussed.

2007 —

Y. Fukai, H. Sugimoto, J. Phys.: Condens. Matter, 19 365 (2007) 436201.

Formation mechanism of defect metal hydrides containing superabundant vacancies

The formation of defect hydrides containing a large number of M-atom vacancies (superabundant vacancies; SAVs) was studied in bcc NbHx and in the fcc phase of FeHx, CoHx, NiHx and PdHx, by resistivity and XRD measurements under different conditions of hydrogen pressure and temperature, with/without allowing for exchange of hydrogen with environment (open-/closed-system methods). Two distinctly different behaviors were observed: in metals with small formation energy of Vac–H clusters, both H and vacancies enter abundantly into the M-lattice to form the ultimate defect-ordered structure, whereas in metals with relatively large formation energies, vacancy concentrations remain relatively small. This general trend was examined by Monte Carlo simulations based on a lattice–gas model. The result showed the occurrence of two distinct phases in the vacancy distribution caused by the combined action of the long-range elastic interaction and local Vac–H interactions, in accordance with the observation. Conditions for the occurrence of these ‘vacancy-rich’ and ‘vacancy-poor’ states are examined.

2007 —

Y. Fukai, H. Sugimoto,  J. Alloys Compd., 446–447 (2007) 474–478.

[See the paper below. The list of authors is incomplete, leaving out the first two authors.]

2007 —

S. Harada, D. Ono, H. Sugimoto, Y. Fukai, J. Alloys Compd.
Journal of Alloys and Compounds, 446–447 (2007) 474–478

The defect structure with superabundant vacancies to be formed from fcc binary metal hydrides: Experiments and simulations

The process of formation of defect hydrides containing a large number of metal-atom vacancies was studied experimentally in the fcc phase of Fe, Co, Ni and Pd, under different conditions of hydrogen pressure and temperature. Two distinctly different behaviors were observed: In metals with small formation energies of Vac–H clusters, both H and vacancies readily enter the metal lattice to attain the ultimate composition M3VacH4, whereas in metals with relatively large formation energies, the formation of this ultimate structure may become appreciable only at H concentrations exceeding some critical value. This general trend was confirmed by a model calculation including a long-range elastic interaction and short-range interatomic interactions between H atoms and vacancies.

2007 —

A.K. Eriksson, A. Liebig, S. Olafsson, B. Hjörvarsson, “”, J. Alloys Compd. 446–447 (2007) 526-529ResearchGate

Resistivity changes in Cr/V(0 0 1) superlattices during hydrogen absorption

The hydrogen induced resistivity changes in Cr/VHx(0 0 1) superlattices where investigated in the concentration range 0<x<0.7. Initially, the resistivity increases with H content, reaching a maximum at H/V≈0.5 atomic ratio. At concentration above 0.5, the resistivity decreases with increasing H concentration. These results are in stark contrast to the H induced resistivity changes in Fe/V(0 0 1) superlattices, in which the resistivity increases monotonically up to H/V≈1. The results unambiguously prove the importance of the interface scattering, which calls for better theoretical description of the H induces changes in the electronic structure in this type of materials.

2008 —

S. Kala and B. R. Mehta, Bull. Mater. Sci., Indian Academy of Sciences, Vol. 31, No. 3, June 2008, pp. 225–231.

Hydrogen-induced electrical and optical switching in Pd capped Pr nanoparticle layers

In this study, modification in the properties of hydrogen-induced switchable mirror based on Pr nanoparticle layers is reported. The reversible changes in hydrogen-induced electrical and optical properties of Pd capped Pr nanoparticle layers have been studied as a function of hydrogenation time and compared with the conventional device based on Pd capped Pr thin films. Faster electrical and optical response, higher optical contrast and presence of single absorption edge corresponding to Pr trihydride state in hydrogen loaded state have been observed in the case of nanoparticle layers. The improvement in the electrical and optical properties have been explained in terms of blue shift in the absorption edge due to quantum confinement effect, larger number of interparticle boundaries, presence of defects, loose adhesion to the substrate and enhanced surface to volume atom ratio at nanodimension.

2009 —

O.Yu. Vekilova, D.I. Bazhanov, S.I. Simak, I.A. Abrikosov, Phys.Rev. B, 80 (2009) 024101.

First-principles study of vacancy–hydrogen interaction in Pd

Hydrogen absorption in face-centered-cubic palladium is studied from first principles, with particular focus on interaction between hydrogen atoms and vacancies, formation of hydrogen-vacancy complexes, and multiple hydrogen occupancy of a Pd vacancy. Vacancy formation energy in the presence of hydrogen, hydrogen trapping energy, and vacancy formation volume have been calculated and compared to existing experimental data. We show that a vacancy and hydrogen atoms form stable complexes. Further we have studied the process of hydrogen diffusion into the Pd vacancy. We find the energetically preferable position for hydrogen to reside in the palladium unit cell in the presence of a vacancy. The possibility of the multiple hydrogen occupancy (up to six hydrogen atoms) of a monovacancy is elucidated. This theoretical finding supports experimental indication of the appearance of superabundant vacancy complexes in palladium in the presence of hydrogen.


2009 —

M. Wen, L. Zhang, B. An, S. Fukuyama, and K. Yokogawa, Phys. Rev. B 80, 094113

Hydrogen-enhanced dislocation activity and vacancy formation during nanoindentation of nickel

The effect of hydrogen on dislocation activities during the nanoindentation of Ni(110) is studied by molecular-dynamics simulation at 300 K. The results reveal that the critical event for the first dislocation nucleation during nanoindentation is due to the thermally activated formation of a small cluster with an atom’s relative displacement larger than half the magnitude of the Burgers vector of partial dislocations. Hydrogen only enhances homogenous dislocation nucleation slightly; however it promotes dislocation emission, induces slip planarity, and localizes dislocation activity significantly, leading to locally enhanced vacancy formation from dislocations. The present results, thus, prove hydrogen-enhanced localized dislocation activity and vacancy formation to be the main reason of hydrogen embrittlement in metals and alloys.

2009 —

H. Sugimoto, Y. Fukai, “”, Diffusion-fundamentals.org 11 (2009) 102, pp 1-2. (full copy)

Migration mechanism in defect metal hydrides containing superabundant vacancies

[Introduction] In the presence of interstitial H atoms, the concentration of M-atom vacancies is
enhanced dramatically, forming a defect structure containing superabundant vacancies
(SAVs). The diffusivity of M atoms is enhanced accordingly. Physically, these
phenomena are the result of the lowering of the formation energy of a vacancy by
trapping H atoms [1, 2].

A Monte Carlo calculation on the SAV formation process revealed that, in hydrides of fcc
metals, two distinct defect phases are formed; a vacancy-ordered phase of high
concentrations of vacancies on the L12 structure, and a vacancy-disordered phase of
relatively low concentrations where vacancies are randomly distributed over the M lattice.
Transitions between these two phases take place, as shown in Fig.1 [2].

Figure 1. Temperature dependence of the vacancy concentration for several different
H concentrations, x=[H]/[M], calculated for eb=0.4 eV.

Note that, in both phases, the vacancy concentration is many orders of magnitude
higher than in pure metals. The present paper addresses, specifically, the migration of H
atoms and M-atom vacancies in the vacancy-disordered phase.
Experimental data available for Pd, Ni and Nb indicate that the migration energy of a
vacancy is increased by amounts comparable to the migration energy of an H atom, and
the pre-exponential factor is reduced by 1 ~ 2 orders of magnitude [3 ~ 5].

2009 —

J. F. Shackelford, 7th ed.,  Prentice Hall, Upper Saddle River, NJ, 2009, pp. 272-3. Googlebooks There is an 8th edition, the 7th is much less expensive. Publisher description:

Introduction to Materials Science for Engineers

[Publisher description} This book provides balanced, current treatment of the full spectrum of engineering materials, covering all the physical properties, applications and relevant properties associated with engineering materials. The book explores all of major categories of materials while offering detailed examinations of a wide range of new materials with high-tech applications. The reader is treated to state-of-the-art computer generated crystal structure illustrations, offering the most technically precise and visually realistic illustrations available. The book includes over 350 exercises with sample problems to provide guidance. Materials for Engineering, Atomic Bonding, Crystal Structure and Defects, Diffusion, Mechanical Behavior, Thermal Behavior, Failure Analysis & Prevention. Phase Diagrams, Heat Treatment, Metals, Ceramics and Glasses, Polymers, Composites, Electrical Behavior, Optical Behavior, Semiconductor Materials, Magnetic Materials, Environmental Degradation, Materials Science. For mechanical and civil engineers and machine designers.

2010 —

Y. Yagodzinskyy, T. Saukkonen, S. Kilpelinen, F. Tuomisto, and H. Hnninen, Scr. Mater. 62, 155 (2010)

Effect of hydrogen on plastic strain localization in single crystals of austenitic stainless steel

Tensile tests accompanied with on-line in situ field emission gun-scanning electron microscopy observations were performed to study hydrogen effects on plastic strain localization in the form of slip lines in single crystals of austenitic stainless steel. It was found that the slip lines on the hydrogen-charged specimens were markedly shorter and more grouped together than the straight slip lines on the hydrogen-free specimens. Hydrogen thermal desorption and positron annihilation spectroscopy were applied to study the combined effect of hydrogen and plastic deformation on excessive generation of vacancies.

2010 —

No abstract. Scott Richmond, Joseph Anderson, and Jeff Abes, “Evidence for hydrogen induced vacancies in Plutonium metal”, Plutonium Futures — The Science Keystone, CO, September 19-23, (2010) 206. This refers to  a CD-ROM, apparently the proceedings. Program schedule. The authors’ affiliation shows as LANL.  See also The solubility of hydrogen and deuterium in alloyed, unalloyed and impure plutonium metal, contemporaneous. Copy available.

 

2011 —

L.E. Isaeva, D.I. Bazhanov, E.I. Isaev, S.V. Eremeev, S.E. Kulkova, I.A. Abrikosov, International Journal of Hydrogen Energy 36, 1254 (2011). (copy)

Dynamic stability of palladium hydride: An ab initio study

We present results of our ab initio studies of electronic and dynamic properties of ideal palladium hydride PdH and its vacancy ordered defect phase Pd3VacH4 (“Vac” – vacancy on palladium site) with L12 crystal structure found experimentally and studied theoretically. Quantum and thermodynamic properties of these hydrides, such as phonon dispersion relations and the vacancy formation enthalpies have been studied. Dynamic stability of the defect phase Pd3VacH4 with respect to different site occupation of hydrogen atoms at the equilibrium state and under pressure was analyzed. It was shown that positions of hydrogen atoms in the defect phase strongly affect its stability and may be a reason for further phase transitions in the defect phase.

2011 —

Y. Z. Chen, G. Csiszar, J. Cizek, C. Borchers, T. Ung ´ ar, S. Goto, and R. Kirchheim, Scr. Mater. 64, 390 (2011).

On the formation of vacancies in α-ferrite of a heavily cold-drawn pearlitic steel wire

Cold-drawn pearlitic steel wires are widely used in numerous engineering fields. Combining X-ray line profile analysis and positron annihilation spectroscopy methods, up to 10−5–10−4vacancies were found in α-ferrite of a cold-drawn pearlitic steel wire with a true strain of ε = 3. The formation of deformation-induced vacancies in α-ferrite of cold-drawn pearlitic steel wire was quantitatively testified.

2011 —

N. Fukumuro, T. Adachi, S. Yae, H. Matsuda, Y. Fukai, Trans. Inst. Met. Finish., 89 (2011) 198–201.

Influence of hydrogen on room temperature recrystallisation of electrodeposited Cu films: thermal desorption spectroscopy

The mechanism of recrystallisation observed at room temperature in electrodeposited Cu films has been examined in light of the enhancement of metal atom diffusion by hydrogen induced superabundant vacancies. Thermal desorption spectroscopy revealed that Cu films electrodeposited from acid sulphate bath containing some specific additives showed a pronounced peak, which was ascribed to the break-up of vacancy–hydrogen clusters. The amount of desorbed hydrogen was comparable to that of vacancy type clusters estimated in previous positron annihilation experiments. The grain size of Cu films increased as hydrogen desorption proceeded. Such grain growths were not observed in the films deposited from the baths without additives. These results indicate that the room temperature recrystallisation of electrodeposited Cu films is caused by hydrogen induced superabundant vacancies.

2011 —

S.Yu. Zaginaichenko, Z.A. Matysina, D.V. Schur, L.O. Teslenko, A. Veziroglu, , Int. J. Hydrogen Energy, 36 (2011) 1152–1158.

The structural vacancies in palladium hydride. Phase diagram

The theory development of structural vacancies formation in palladium hydride on the molecular-kinetic presentations is the subject of this paper. The production of vacant-ordered superstructure of Cu3Au type has been considered at the high temperatures. The calculation of free energies of the PdH and Pd3VH phases has been carried out. The constitution diagram defined the temperature and concentration regions of phases formation with the A1 and L12 structures and regions of two A1 + L12 phases realization has been constructed. The results of theoretical calculations are in agreement with experimental data.

2011 —

M. Khalid and P. Esquinazi, Phys. Rev. B 85, 134424 – Published 13 April 2012.

Hydrogen-induced ferromagnetism in ZnO single crystals investigated by magnetotransport

We investigate the electrical and magnetic properties of low-energy H+-implanted ZnO single crystals with hydrogen concentrations up to 3 at% in the first 20-nm surface layer between 10 K and 300 K. All samples show clear ferromagnetic hysteresis loops at 300 K with a saturation magnetization up to 4 emu/g. The measured anomalous Hall effect agrees with the hysteresis loops measured by superconducting quantum interferometer device magnetometry. All the H-treated ZnO crystals exhibit a negative and anisotropic magnetoresistance at room temperature. The relative magnitude of the anisotropic magnetoresistance reaches 0.4% at 250 K and 2% at 10 K, exhibiting an anomalous, nonmonotonous behavior and a change of sign below 100 K. All the experimental data indicate that hydrogen atoms alone in the few percent range trigger a magnetic order in the ZnO crystalline state. Hydrogen implantation turns out to be a simpler and effective method to generate a magnetic order in ZnO, which provides interesting possibilities for future applications due to the strong reduction of the electrical resistance.

2011 —

Y. Fukai, Defect and Diffusion Forum, Vol. 312-315 (2011) pp. 1106-1115.

Hydrogen-Induced Superabundant Vacancies in Metals: Implication for Electrodeposition

The equilibrium concentration of vacancies in metals is invariably enhanced in the presence of interstitial hydrogen atoms – a phenomenon called superabundant vacancy (SAV) formation. It has been recognized that the SAV formation occurs in electrodeposition, as M-, H-atoms and M-atom vacancies are deposited by atom-by-atom process. Effects of SAV formation are described for electrodeposited Ni, Ni-Fe alloys, Fe-C alloys and Cu. Possible implication of SAV formation for corrosion in Al and steels is also briefly described.

(See also preview of the first page.)

2012 —

D.L. Knies, V.Violante, K.S. Grabowski, J.Z. Hu, D.D. Dominguez, J.H. He, S.B. Qadri and G.K. Hubler, J. Appl. Phys., 112 (2012) 083510. Copy on Research Gate.

In-situ synchrotron energy-dispersive x-ray diffraction study of thin Pd foils with Pd:D and Pd:H concentrations up to 1:1

Time resolved, in-situ, energy dispersive x-ray diffraction was performed in an electrolysis cell during electrochemical loading of palladium foil cathodes with hydrogen and deuterium. Concentrations of H:Pd (D:Pd) up to 1:1 in 0.1 M LiOH (LiOD) in H2O (D2O) electrolyte were obtained, as determined by both the Pd lattice parameter and cathode resistivity. In addition, some indications on the kinetics of loading and deloading of hydrogen from the Pd surface were obtained. The alpha-beta phase transformations were clearly delineated but no new phases at high concentration were determined.

2012 —

D. E. Azofeifa, N. Clark, W. E. Vargas, H. Solís, G. K. Pálsson, and B. Hjörvarsson, Physica Scripta, Volume 86, Number 6, Published 15 November (2012).

Temperature- and hydrogen-induced changes in the optical properties of Pd capped V thin films

Optical properties of V thin films deposited on MgO substrates have been obtained from spectrophotometric measurements. The V films were coated with a thin Pd layer to protect them from oxidation and to favor absorption of atomic hydrogen. Electrical resistance was recorded while hydrogen pressure was increased slowly up to 750 mbar keeping the temperature constant. Simultaneously, visible and near-infrared transmittance spectra of this Pd/V/MgO system were measured. The spectra were numerically inverted to obtain the spectral behavior of the Pd and V dielectric functions at 22 and 140 °C. Hydrogen concentrations were first determined from the combined effect of hydrogen content on the electrical resistance and on the optical direct transmission of the system. Then, determination of these concentrations was improved using retrieved values of the absorption coefficients of the hydrides and taking into account the structural change of V and the volumetric expansion of Pd. Good agreement is established when considering qualitative correlations between spectral features of the optimized PdHy and VHx dielectric functions and band structure calculations and densities of states for these two transition metal hydrides.

2013 —

N. Hisanaga, N. Fukumuro, S. Yae, H. Matsuda, ECS Trans., 50(48) (2013) 77–82.

Hydrogen in Platinum Films Electrodeposited from Dinitrosulfatoplatinate(II) Solution

The influence of hydrogen on the microstructure of Pt films electrodeposited from a dinitrosulfatoplatinate(II) solution was investigated with thermal desorption spectroscopy, X-ray diffraction, transmission electron microscopy, and scanning electron microscopy. Two pronounced desorption peaks were observed in the thermal desorption spectrum of hydrogen from the Pt films. The total amount of desorbed hydrogen in the range from 300 to 1100 K in the atomic ratio (H/Pt) was 0.1. The deposited Pt film consisted of fine grains (~10 nm) and many nano-voids. The lattice parameter of the Pt grains was lower than that of bulk Pt. Drastic grain growth and reduction in the lattice contraction occurred from heat treatment at a temperature corresponding to the first hydrogen desorption peak of 500 K.

2013 —

N. Fukumuro, M. Yokota, S. Yae, H. Matsuda, Y.Fukai, J. Alloys Compd., 580 (2013) s55–s57.

Hydrogen-induced enhancement of atomic diffusion in electrodeposited Pd films

The hydrogen-induced enhancement of atomic diffusion in electrodeposited Pd films on Cu substrate has been investigated with thermal desorption spectroscopy, X-ray diffraction, and transmission electron microscopy. The hydrogen content in Pd films (= H/Pd) was 2.2–7.7 × 10−2 and decreased with time at room temperature. For Pd films with lower hydrogen contents (x ≦ 4.0 × 10−2), lattice contraction and grain growth proceeded as hydrogen desorption proceeded. For Pd films with higher hydrogen contents (x ≧ 5.8 × 10−2), fine grains became large columnar grains, and a large-grained Cu–Pd interlayer was formed by interdiffusion between the Cu substrate and the Pd film.

2013 —

Atsushi Yabuuchi, Teruo Kihara, Daichi Kubo, Masataka Mizuno, Hideki Araki, Takashi Onishi and Yasuharu Shirai, Jpn.J.Appl.Phys., 52 (2013) 046501.

Effect of Hydrogen on Vacancy Formation in Sputtered Cu Films Studied by Positron Annihilation Spectroscopy

As a part of the LSI interconnect fabrication process, a post-deposition high-pressure annealing process is proposed for embedding copper into trench structures. The embedding property of sputtered Cu films has been recognized to be improved by adding hydrogen to the sputtering argon gas. In this study, to elucidate the effect of hydrogen on vacancy formation in sputtered Cu films, normal argon-sputtered and argon–hydrogen-sputtered Cu films were evaluated by positron annihilation spectroscopy. As a result, monovacancies with a concentration of more than 10-4 were observed in the argon–hydrogen-sputtered Cu films, whereas only one positron lifetime component corresponding to the grain boundary was detected in the normal argon-sputtered Cu films. This result means monovacancies are stabilized by adding hydrogen to sputtering gas. In the annealing process, the stabilized monovacancies began clustering at around 300 °C, which indicates the dissociation of monovacancy-hydrogen bonds. The introduced monovacancies may promote creep deformation during high-pressure annealing.

2014 —

M. Tsirlin, J. Cond. Matter Nucl. Sci. 14, 1-4 (2014).

Comment on the article ‘Simulation of Crater Formation on LENR Cathodes Surfaces’

Formation of small craters on the surface of Pd cathode during electrolysis in electrolytes based on heavy water is sometimes interpreted as a consequence of low-temperature nuclear reactions. In this note we discuss the validity of these statements.

2014 —

Nazarov, R. and Hickel, T. and Neugebauer, J., Phys. Rev. B 89, 144108 (2014). Britz Naza2014

Ab initio study of H-vacancy interactions in fcc metals: Implications for the formation of superabundant vacancies

Hydrogen solubility and interaction with vacancies and divacancies are investigated in 12 fcc metals by density functional theory. We show that in all studied fcc metals, vacancies trap H very efficiently and multiple H trapping is possible. H is stronger trapped by divacancies and even stronger by surfaces. We derive a condition for the maximum number of trapped H atoms as a function of the H chemical potential. Based on this criterion, the possibility of a dramatic increase of vacancy concentration (superabundant vacancy formation) in the studied metals is discussed.

2014 —

A. Houari, A., S. Matar, V. Eyert,  arXiv (2014).

Electronic structure and crystal phase stability of palladium hydrides

The results of electronic structure calculations for a variety of palladium hydrides are presented.
The calculations are based on density functional theory and used different local and semilocal
approximations. The thermodynamic stability of all structures as well as the electronic and chemical
bonding properties are addressed. For the monohydride, taking into account the zero-point energy
is important to identify the octahedral Pd-H arrangement with its larger voids and, hence, softer
hydrogen vibrational modes as favorable over the tetrahedral arrangement as found in the zincblende
and wurtzite structures. Stabilization of the rocksalt structure is due to strong bonding of the 4d
and 1s orbitals, which form a characteristic split-off band separated from the main d-band group.
Increased filling of the formerly pure d states of the metal causes strong reduction of the density
of states at the Fermi energy, which undermines possible long-range ferromagnetic order otherwise
favored by strong magnetovolume effects. For the dihydride, octahedral Pd-H arrangement as
realized e.g. in the pyrite structure turns out to be unstable against tetrahedral arrangement as found
in the fluorite structure. Yet, from both heat of formation and chemical bonding considerations
the dihydride turns out to be less favorable than the monohydride. Finally, the vacancy ordered
defect phase Pd3H4 follows the general trend of favoring the octahedral arrangement of the rocksalt
structure for Pd:H ratios less or equal to one.

2014 —

I.A. Supryadkina, D.I. Bazhanov, and A.S. Ilyushin, Journal of Experimental and Theoretical Physics, 118 (2014) 80–86.

Ab Initio Study of the Formation of Vacancy and Hydrogen–Vacancy Complexes in Palladium and Its Hydride

We report on the results of ab initio calculations of vacancy and hydrogen-vacancy complexes in palladium and palladium hydride. Comparative analysis of the energies of the formation of defect complexes in palladium and its hydride has revealed that the formation of vacancy clusters is easier in the palladium hydride structure. Investigation of hydrogen-vacancy complexes in bulk crystalline palladium has shown that a hydrogen atom and a vacancy interact to form a stable hydrogen-vacancy (H-Vac) defect complex with a binding energy of E b = −0.21 eV. To investigate the initial stage in the formation of hydrogen-vacancy complexes (H n -Vac m), we consider the clusterization of defects into clusters containing H-Vac and H2-Vac complexes as a structural unit. It is found that hydrogen-vacancy complexes form 2D defect structures in palladium in the (100)-type planes.

2015 —

H. Wulff, M. Quaas, H. Deutsch, H. Ahrens, M. Frohlich, C.A. Helm, Thin Solid Films, 596 (2015) 185–189.

Formation of palladium hydrides in low temperature Ar/H2-plasma

20 nm thick Pd coatings deposited on Si substrates with 800 nm SiO2 and 1 nm Cr buffer layers were treated in a 2.45 GHz microwave plasma source at 700 W plasma power and 40 Pa working pressure without substrate heating. For obtaining information on the effect of energy influx due to ion energy on the palladium films the substrate potential was varied from Usub = 0 V to − 150 V at constant gas flow corresponding to mean ion energies Ei from 0.22 eV ∙ cm− 2 ∙ s− 1 to 1.28 eV ∙ cm− 2 ∙ s− 1.

In contrast to high pressure reactions with metallic Pd, under plasma exposure we do not observe solid solutions over a wide range of hydrogen concentration. The hydrogen incorporation in Pd films takes place discontinuously. At 0 V substrate voltage palladium hydride is formed in two steps to PdH0.14 and PdH0.57. At − 50 V substrate voltage PdH0.57 is formed directly. However, substrate voltages of − 100 V and − 150 V cause shrinking of the unit cell. We postulate the formation of two fcc vacancy palladium hydride clusters PdHVac(I) and PdHVac(II). Under longtime plasma exposure the fcc PdHVac(II) phase forms cubic PdH1.33.

The fcc PdH0.57 phase decomposes at temperatures > 300 °C to form metallic fcc Pd. The hydrogen removal causes a decrease of lattice defects. In situ high temperature diffractometry measurements also confirm the existence of PdHVac(II) as a palladium hydride phase. Stoichiometric relationship between cubic PdH1.33 and fcc PdHVac(II) becomes evident from XR measurements and structure considerations. We assume both phases have the chemical composition Pd3H4. Up to 700 °C we observe phase transformation between both the fcc PdHVac(II) and cubic PdH1.33 phases. These phase transformations could be explained analog to a Bain distortion by displacive solid state structural changes.

2015 —

Y. Fukada, T. Hioki, T. Motohiro, S. Ohshima, J. Alloys Compd., 647 (2015) 221–230.

In situ x-ray diffraction study of crystal structure of Pd during hydrogen isotope loading by solid-state electrolysis at moderate temperatures 250−300 °C

Hydrogen isotopes and metal interaction with respect to Pd under high hydrogen isotope potential at moderate temperature region around 300 °C was studied. A dry electrolysis technique using BaZr1−x YxO3 solid state electrolyte was developed to generate high hydrogen isotope potential. Hydrogen or deuterium was loaded into a 200 nm thick Pd cathode. The cathode is deposited on SiO2 substrate and covered with the solid state electrolyte and a Pd anode layer. Time resolved in situ monochromatic x-ray diffraction measurement was performed during the electrolysis. Two phase states of the Pd cathodes with large and small lattice parameters were observed during the electrolysis. Numerous sub-micron scale voids in the Pd cathode and dendrite-like Pd precipitates in the solid state electrolyte were found from the recovered samples. Hydrogen induced super-abundant-vacancy may take role in those phenomena. The observed two phase states may be attributed to phase separation into vacancy-rich and vacancy-poor states. The voids formed in the Pd cathodes seem to be products of vacancy coalescence. Isotope effects were also observed. The deuterium loaded samples showed more rapid phase changes and more formation of voids than the hydrogen doped samples.

2015 —

Ian M. Robertson, P. Sofronis, A. Nagao, M.L. Martin, S. Wang, D.W. Gross, and K.E. Nygren, Edward DeMille Campbell Memorial Lecture”, ASM International, Metallurgical and Materials Transactions B, (28 March 2015) DOI: 10.1007/s11663-015-0325-y  (copy available.)

Hydrogen Embrittlement Understood

The connection between hydrogen-enhanced plasticity and the hydrogen-induced fracture mechanism and pathway is established through examination of the evolved microstructural state immediately beneath fracture surfaces including voids, “quasi-cleavage,” and intergranular surfaces. This leads to a new understanding of hydrogen embrittlement in which hydrogen-enhanced plasticity processes accelerate the evolution of the microstructure, which establishes not only local high concentrations of hydrogen but also a local stress state. Together, these factors establish the fracture mechanism and pathway.

2016 —

Yoshiki FukadaTatsumi HiokiTomoyoshi Motohirob,  Journal of Alloys and Compounds, Volume 688, Part B, 15 December 2016, Pages 404-412. DOI * ResearchGate

Multiple phase separation of super-abundant-vacancies in Pd hydrides by all solid-state electrolysis in moderate temperatures around 300 °C

The dynamics of hydrogen-induced vacancies are the key for understanding various phenomena in metal–hydrogen systems under a high hydrogen chemical potential. In this study, a novel dry-electrolysis experiment was performed in which a hydrogen isotope was injected into a Pd cathode and time-resolved in situ monochromatic X-ray diffraction measurement was carried out at the Pd cathode. It was found that palladium-hydride containing vacancies forms multiple phases depending on the hydrogen chemical potential. Phase separation into vacancy-rich, vacancy-poor, and moderate-vacancy-concentration phases was observed when the input voltage was relatively low, i.e., ∼0.5 V. The moderate-vacancy-concentration phase may be attributed to Ca7Ge or another type of super-lattice Pd7VacH(D)8. Transition from the vacancy-rich to the moderate-vacancy-concentration phase explains the sub-micron void formations without high temperature treatment that were observed at the Pd cathode but have never been reported in previous anvil experiments.

Graphical Abstract|

2017 —

L. Bukonte, T. Ahlgren, and K. Heinola, “”, J. Appl. Phys. 121, (2017) pp. 045102-1 to -11. https://doi.org/10.1063/1.4974530. (full copy available) (extensive references with links)

Thermodynamics of impurity-enhanced vacancy formation in metals

Hydrogen induced vacancy formation in metals and metal alloys has been of great interest during the past couple of decades. The main reason for this phenomenon, often referred to as the  superabundant vacancy formation, is the lowering of vacancy formation energy due to the trapping of hydrogen. By means of thermodynamics, we study the equilibrium vacancy formation in fcc metals (Pd, Ni, Co, and Fe) in correlation with the H amounts. The results of this study are compared and found to be in good agreement with experiments. For the accurate description of the total energy of the metal–hydrogen system, we take into account the binding energies of each trapped impurity, the vibrational entropy of defects, and the thermodynamics of divacancy formation. We demonstrate the effect of vacancy formation energy, the hydrogen binding, and the divacancy binding energy on the total equilibrium vacancy concentration. We show that the divacancy fraction gives the major contribution to the total vacancy fraction at high H fractions and cannot be neglected when studying superabundant vacancies. Our results lead to a novel conclusion that at high hydrogen fractions, superabundant vacancy formation takes place regardless of the binding energy between vacancies and hydrogen. We also propose the reason of superabundant vacancy formation mainly in the fcc phase. The equations obtained within this work can be used for any metal–impurity system, if the impurity occupies an interstitial site in the lattice.

2018 —

M.R. Staker, ICCF-21 (2018) (preprint).

Coupled Calorimetry and Resistivity Measurements, in Conjunction with an Emended and More Complete Phase Diagram of the Palladium – Isotopic Hydrogen System

Results of a calorimetric study established the energy produced, over and above input energy, from electrolytic loading of deuterium into Pd was 150 MJ/cc of Pd (14000 eV/Pd atom) for a 46 day period. High fugacity of deuterium was developed in unalloyed palladium via electrolysis (0.5 molar electrolyte of lithium deuteroxide, LiOD) with the use of an independent electromigration current. In situ resistivity measurements of Pd were used to assay activity of D in the Pd lattice (ratio of D/Pd) and employed as an indicator of phase changes. During this period, two run-away events were triggered by suddenly increasing current density resulting in 100 percent excess power (2.4 watts output with 1.2 watts input) and necessitating temporary cut back in electrolysis current. The average excess power (excluding run-away) ranged from 4.7 +/- 0.15 to 9.6 +/- 0.30 percent of input power while input power ranged from 2.000 to 3.450 watts, confirming the Fleischmann-Pons effect. The precision was: Power In = +/-.0005 W; ∆T = +/- .05oC; Power Out = +/-.015 W for an overall precision of +/- 0.5%. High fugacity was required for these results, and the triggered run-away events required even higher fugacity. Using thermodynamic energy balance, it was found that the energy release was of such magnitude that the source of the energy is from a nuclear source, however the exact reaction was not determined in this work. X-ray diffraction results from the recent literature, rules for phase diagram construction, and thermodynamic stability requirements necessitate revisions of the phase diagram, with addition of three thermodynamically stable phases of the superabundant vacancy (SAV) type. These phases, each requiring high fugacity, are: γ (Pd7VacD6-8), δ (Pd3VacD4 – octahedral), δ’ (Pd3VacD4 – tetrahedral). The emended Palladium – Isotopic Hydrogen phase diagram is presented. The excess heat condition supports portions of the cathode being in the ordered δ phase (Pd3VacD4 – octahedral), while a drop in resistance of the Pd cathode during increasing temperature and excess heat production strongly indicates portions of the cathode also transformed to the ordered δ’ phase (Pd3VacD4 – tetrahedral). A dislocation mechanism is presented for creation of vacancies and mobilizing them by electromigration because of their attraction to D+ ions which aids the formation of SAV phases. Extending SAV unit cells to the periodic lattice epiphanates δ as the nuclear active state. The lattice of the decreased resistance phase, δ’, reveals extensive pathways of low resistance and a potential connection to the superconductivity phase of PdH/PdD.

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