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Title: Pressure-induced Structural and Electronic Changes in alpha-AlH3

Abstract

Pressure-induced structural, electronic, and thermodynamic changes in {alpha}-AlH{sub 3} 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 H{sub 2} 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.

Authors:
; ; ; ; ;
Publication Date:
Research Org.:
Brookhaven National Laboratory (BNL) National Synchrotron Light Source
Sponsoring Org.:
Doe - Office Of Science
OSTI Identifier:
930601
Report Number(s):
BNL-80896-2008-JA
Journal ID: ISSN 1098-0121; TRN: US0901415
DOE Contract Number:
DE-AC02-98CH10886
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review B: Condensed Matter and Materials Physics; Journal Volume: 74
Country of Publication:
United States
Language:
English
Subject:
08 HYDROGEN; 43 PARTICLE ACCELERATORS; ALUMINIUM; ASYMMETRY; BRAGG CURVE; CRYSTAL LATTICES; DENSITY FUNCTIONAL METHOD; DIFFRACTION; FREE ENERGY; HYDROGEN; HYDROGENATION; PRESSURE DEPENDENCE; PRESSURE RANGE GIGA PA; SYNCHROTRON RADIATION; THERMODYNAMICS; X-RAY DIFFRACTION; national synchrotron light source

Citation Formats

Graetz,J., Chaudhuri, S., Lee, Y., Vogt, T., Muckerman, J., and Reilly, J.. Pressure-induced Structural and Electronic Changes in alpha-AlH3. United States: N. p., 2006. Web. doi:10.1103/PhysRevB.74.214114.
Graetz,J., Chaudhuri, S., Lee, Y., Vogt, T., Muckerman, J., & Reilly, J.. Pressure-induced Structural and Electronic Changes in alpha-AlH3. United States. doi:10.1103/PhysRevB.74.214114.
Graetz,J., Chaudhuri, S., Lee, Y., Vogt, T., Muckerman, J., and Reilly, J.. Sun . "Pressure-induced Structural and Electronic Changes in alpha-AlH3". United States. doi:10.1103/PhysRevB.74.214114.
@article{osti_930601,
title = {Pressure-induced Structural and Electronic Changes in alpha-AlH3},
author = {Graetz,J. and Chaudhuri, S. and Lee, Y. and Vogt, T. and Muckerman, J. and Reilly, J.},
abstractNote = {Pressure-induced structural, electronic, and thermodynamic changes in {alpha}-AlH{sub 3} 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 H{sub 2} 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.},
doi = {10.1103/PhysRevB.74.214114},
journal = {Physical Review B: Condensed Matter and Materials Physics},
number = ,
volume = 74,
place = {United States},
year = {Sun Jan 01 00:00:00 EST 2006},
month = {Sun Jan 01 00:00:00 EST 2006}
}
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