Pressure-induced Structural and Electronic Changes in alpha-AlH3
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.
- Research Organization:
- Brookhaven National Lab. (BNL), Upton, NY (United States). National Synchrotron Light Source
- Sponsoring Organization:
- Doe - Office Of Science
- DOE Contract Number:
- DE-AC02-98CH10886
- OSTI ID:
- 930601
- Report Number(s):
- BNL-80896-2008-JA; TRN: US0901415
- Journal Information:
- Physical Review B: Condensed Matter and Materials Physics, Vol. 74; ISSN 1098-0121
- Country of Publication:
- United States
- Language:
- English
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