Journal
JOURNAL OF ALLOYS AND COMPOUNDS
Volume 353, Issue 1-2, Pages 74-85Publisher
ELSEVIER SCIENCE SA
DOI: 10.1016/S0925-8388(02)01324-5
Keywords
rare earth compounds; hydrogen absorbing materials; metal hydrides; electronic structure; enthalpy
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Density functional calculations of the electronic structure and enthalpy of formation DeltaH of LaNi5 and LaNi5H7 are reported. Single-crystal elastic constants and Voigt-Reuss-Hill polycrystalline moduli were calculated for both materials using a stress-based least-squares fitting methodology. We obtain DeltaH(0K) = -40 kJ/mol H-2 for the hydride at zero temperature. Incorporating a Debye estimate of the phonon contribution we find DeltaH(298 K)similar to-39 kJ/mol/H-2, a value that compares favorably with experimental determinations of -32 to -35 kJ/mol/H-2. Our results indicate that the H-Ni and H-La interactions in the hydride are primarily metallic with a small ionic component. The calculated elastic moduli are in excellent accord with single-crystal measurements on LaNi5 and with available data for polycrystalline samples of the parent and hydride. (C) 2002 Elsevier Science B.V. All rights reserved.
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