Pressure-induced structural and electronic changes in α-Al H3

J. Graetz, S. Chaudhuri, Y. Lee, T. Vogt, J. T. Muckerman, J. J. Reilly

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Abstract

Pressure-induced structural, electronic, and thermodynamic changes in α-Al H3 were investigated using synchrotron x-ray powder diffraction and density-functional theory. No first-order structural transitions were observed up to 7 GPa. However, increasing Bragg peak asymmetry with pressure suggests a possible monoclinic distortion at moderate pressures (1-7 GPa). The pressure-volume relationship was fit to the Birch-Murnaghan equation of state to give a bulk modulus of approximately 40 GPa. The reduced cell volume at high pressure is accommodated by octahedral tilting and a decrease of the Al-H bond distance. Ab initio calculations of the free energy indicate that hydrogenation becomes favorable at H2 pressures above 0.7 GPa at 300 K. Electronic density of states calculations reveal a slight decrease in the band gap with pressure but no evidence of an insulator-to-metal transition predicted by previous high-pressure studies. Calculated Mulliken charges and bond populations suggest a mixed ionic and covalent Al-H bond at 1 atm with an increase in covalent character with pressure.

Original languageEnglish
Article number214114
JournalPhysical Review B - Condensed Matter and Materials Physics
Volume74
Issue number21
DOIs
Publication statusPublished - Dec 1 2006

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ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics

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