Phase transformations, crystal and magnetic structures of high-pressure hydrides of d-metals

Antonov, V.E.

doi:10.1016/s0925-8388(01)01532-8

Cited by 125 publications

(90 citation statements)

References 22 publications

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“…Such a kind of peculiarity in the phonon spectrum, which is known as the Kohn anomaly, was also found experimentally [20] and theoretically [21]. It is well known that palladium hydride adopts the fcc structure [22] where hydrogen atoms occupy octahedral sites of palladium matrix (Fig.2). The calculated enthalpy of formation of ideal PdH turned out to be -0.53 eV which is almost two times lower than the value of -0.25 eV obtained in Ref.…”

Section: Resultssupporting

confidence: 55%

Dynamic stability of palladium hydride: An ab initio study

Isaeva

Бажанов

Isaev

et al. 2011

International Journal of Hydrogen Energy

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We present results of our ab initio studies of electronic and dynamic properties of ideal palladium hydride PdH and its vacancy ordered defect phase Pd 3 VacH 4 with L1 2 crystal structure proposed theoretically and found experimentally. Quantum and electronic properties of these hydrides, such as phonon dispersion relations and the vacancy formation enthalpies have been studied. Dynamic stability of the defect phase Pd 3 VacH 4 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.

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Section: Resultssupporting

confidence: 55%

Dynamic stability of palladium hydride: An ab initio study

Isaeva

Бажанов

Isaev

et al. 2011

International Journal of Hydrogen Energy

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“…1) A systematic investigation of the phase diagram of transition metalhydrogen (M-H) alloys under extended pressure-temperature conditions (p(H 2 ) 6 GPa, T 400 C) was performed by a Russian group, by combination of in situ resistometry and Xray diffraction (XRD) of recovered specimens, and the results were described in their review papers. 2,3) We have succeeded in taking a step forward by developing techniques of in situ XRD under more extended p(H 2 )-T conditions, and reported the phase diagrams for Cr-H, 4) Mn-H, 5) Fe-H 6) and Ni-H 7) systems. For the Mo-H system at high hydrogen pressures, the Russian group showed that an hcp hydride of a nearly stoichiometric composition [H]/[Mo] % 1 was formed, 8,9) and the bcc ()-hcp (") boundary was located at 250 C, 2 GPa increasing to 450 C, 5 GPa.…”

Section: Introductionmentioning

confidence: 99%

The Phase Diagram of Mo-H Alloys under High Hydrogen Pressures

Fukai

Mizutani

2003

Mater. Trans.

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The phase diagram of the Mo-H system was determined by in situ X-ray diffraction using synchrotron radiation up to 1200 C and the hydrogen pressure to p(H 2 ) = 5.3 GPa. Three phases were found to exist; a bcc phase () of low hydrogen concentrations at low hydrogen pressures, and two high-pressure phases, an hcp (") phase at lower temperatures and an fcc () phase at higher temperatures, both having a nearly stoichiometeric composition of x = [H]/[Mo] $ 1. A gradual lattice contraction observed in the fcc phase indicates the formation of superabundant Mo-atom vacancies (vacancy-hydrogen clusters).

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“…The analysis of available experimental data allows to formulate two important contradictions between the obtained results and their interpretation: (i) the claimed nickel hydride exists in a wide range of hydrogen concentration that can even exceed H/M  1.0 (e.g., [12]); (ii) this nickel hydride has the same f.c.c. crystal structure as the parent nickel and differs only by the increased lattice parameter of about 6%, as it follows from the X-ray diffraction measurements (e.g., [14]).…”

Section: Introductionmentioning

confidence: 98%

“…Being transition element and because of similarities between the general view of the Ni-H and Pd-H phase diagrams (where the miscibility gap area is present), nickel became an object of particularly intensive researches (e.g., [1][2][3][4][5][6][7][8][9][10][11][12][13][14]). A conclusion about the formation of nickel hydride was derived based on the non-diffusive character of hydrogen desorption kinetics [1][2][3].…”

Section: Introductionmentioning

confidence: 99%

“…The high-pressure hydrogen charging allows the thermodynamic study of nickel-hydrogen system with construction of the T-P and T-C phase diagrams for hydride formation and its decomposition (e.g., [12,13]). A common result is that, with increasing temperature, the concentration range of the two-phase coexistence decreases, which is a sign of a crown, i.e.…”

Section: Introductionmentioning

confidence: 99%

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Precipitation Reactions in Nickel—Hydrogen System: ab initio Study

Teus¹

2016

Metallofiz. Noveishie Tekhnol.

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A type of precipitation reactions in the nickel-hydrogen system is studied by means of first-principle atomic calculations. The concentration dependence of solution enthalpy is calculated, and its second derivative is shown to be negative within the hydrogen-to-nickel ratios, H/Ni, of 0.03-0.75. This result suggests that a spinodal decomposition of the solid solution occurs resulting in formation of the hydrogen-rich and hydrogen-depleted phases. The obtained hydrogen concentrations in these conjugated phases are in consistency with the available experimental data. The effects of hydrogen concentration on the electronic structure and its correlation with thermodynamic stability of phases confirm that spinodal decomposition in the nickelhydrogen system has the electronic origin. The obtained results are at variance with the widely accepted concept of the nickel hydride.Key words: spinodal decomposition, nickel-hydrogen system, hydride, ab initio calculations.Тип реакцій виділення в системі нікель-водень досліджено за допомогою розрахунків із перших принципів. Розраховано концентраційну залеж-ність ентальпії розчинення, а також показано, що її друга похідна є від'ємною в діяпазоні відношень водень-метал, H/Ni, від 0,03 до 0,75. Це означає, що має місце спинодальний розпад твердого розчину із форму-ванням збагаченої та збідненої воднем фаз. Одержані значення концент-рацій водню в цих спряжених фазах узгоджуються з експериментальни-ми даними. Вплив концентрації водню на електронну структуру, а також кореляція з термодинамічною стабільністю фаз підтверджують, що спи- S. M. TEUSнодальний розпад у системі нікель-водень має електронну природу. Оде-ржані результати знаходяться у протиріччі з широко розповсюдженою концепцією гідриду ніклю.Ключові слова: спинодальний розпад, система нікель-водень, гідрид, ро-зрахунки із перших принципів.Тип реакций выделения в системе никель-водород изучен при помощи расчётов из первых принципов. Рассчитана концентрационная зависи-мость энтальпии растворения, а также показано, что её вторая производ-ная является отрицательной в диапазоне отношений водород-металл, H/Ni, от 0,03 до 0,75. Это свидетельствует о том, что имеет место спино-дальный распад твёрдого раствора с формированием обогащённой и обед-нённой водородом фаз. Полученные значения концентраций водорода в этих сопряжённых фазах находятся в согласии с экспериментальными данными. Влияние концентрации водорода на электронную структуру и корреляция с термодинамической стабильностью фаз подтверждают, что спинодальный распад в системе никель-водород имеет электронную при-роду. Полученные результаты находятся в противоречии с широко рас-пространённой концепцией гидрида никеля.Ключевые слова: спинодальный распад, система никель-водород, гид-рид, расчёты из первых принципов.

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Phase transformations, crystal and magnetic structures of high-pressure hydrides of d-metals

Cited by 125 publications

References 22 publications

Dynamic stability of palladium hydride: An ab initio study

Dynamic stability of palladium hydride: An ab initio study

The Phase Diagram of Mo-H Alloys under High Hydrogen Pressures

Precipitation Reactions in Nickel—Hydrogen System: ab initio Study

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