Structural phase transition in CaH{sub 2} at high pressures
- Department of Physics and Engineering Physics, University of Saskatchewan, Saskatoon, Saskatchewan, S7N 5E2 (Canada)
- Steacie Institute for Molecular Sciences, National Research Council of Canada, Ottawa, Ontario, K1A 0R6 (Canada)
- Laboratoire de physique des solides denses, Department of Physics, University of Ottawa, Ottawa, Ontario, K1N 6N5 (Canada)
- Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road Northwest, Washington, DC 20015 (United States)
- Canadian Light Source, University of Saskatchewan, Saskatoon, Saskatchewan, S7N 0X4 (Canada)
- Department of Physics, University of Guelph, Guelph, Ontario, N1G 2W1 (Canada)
The structural and vibrational properties of CaH{sub 2} have been examined up to 30 GPa at room temperature. Under ambient conditions, CaH{sub 2} has a Pnma (cotunnite-type) structure. A structural phase transformation was observed around 15 GPa and completed at 20 GPa. The high pressure structure is identified as hexagonal P6{sub 3}/mmc. First-principles calculations reproduced the first-order nature of the transition. Since P6{sub 3}/mmc is a supergroup of Pnma the structural change can be traced back to gradual displacements of the hydrogen atoms from the 4c positions in the cotunnite structure to the special 2a and 2d positions in the hexagonal structure. The observed phase transition pressure is much lower than that predicted for MgH{sub 2}.
- OSTI ID:
- 20957787
- Journal Information:
- Physical Review. B, Condensed Matter and Materials Physics, Vol. 75, Issue 13; Other Information: DOI: 10.1103/PhysRevB.75.134108; (c) 2007 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA); ISSN 1098-0121
- Country of Publication:
- United States
- Language:
- English
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