Deuterium occupation of tetrahedral sites in palladium

K. G. McLennan, E. MacA. Gray, and J. F. Dobson
Phys. Rev. B 78, 014104 – Published 9 July 2008

Abstract

The long-standing controversy over the occupation by hydrogen of tetrahedral interstices in palladium has been addressed experimentally and theoretically. Using the highest resolution neutron powder diffractometer available, diffraction profiles were recorded from single-phase samples obtained by loading Pd with deuterium in situ at 310°C, at D2 pressures up to 90 bar. Rietveld profile analysis showed that a model including tetrahedral occupancy was necessary to properly fit the experimental diffraction profiles. The maximum absolute tetrahedral occupancy was found at a deuterium-to-metal atomic ratio of 0.6, where about one-third of all D atoms were in tetrahedral sites. At the lowest and highest D concentration, the tetrahedral fraction approached zero. The energy of formation was calculated, based on density-functional theory, for numerous configurations of octahedral and tetrahedral interstitials in a supercell, which modeled stoichiometries Pd8Hn such that n=1,2,8. For Pd8H3, the minimum formation energy was found with 1–2 tetrahedral atoms. For all other stoichiometries, the minimum formation energy was 0–1 tetrahedral atoms. Thus, the calculations are in excellent qualitative agreement with experiment and support the reality of tetrahedral occupancy.

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  • Received 10 September 2007

DOI:https://doi.org/10.1103/PhysRevB.78.014104

©2008 American Physical Society

Authors & Affiliations

K. G. McLennan*,†, E. MacA. Gray, and J. F. Dobson

  • Nanoscale Science and Technology Centre, Griffith University, Brisbane 4111, Australia

  • *Corresponding author: CSIRO Energy Technology, QCAT, GPO Box 883, Kenmore QLD 4069, Australia; keith.mclennan@csiro.au; Tel.: +61 7 3327 4127; Fax: +61 7 3327 4455;
  • Present address: CSIRO Energy Technology, QCAT, Pullenvale 4069, Australia.

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Vol. 78, Iss. 1 — 1 July 2008

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