Structural Phase Transition in CaH2 at High Pressures
The structural and vibrational properties of CaH2 have been examined up to 30GPa at room temperature. Under ambient conditions, CaH2 has a Pnma (cotunnite-type) structure. A structural phase transformation was observed around 15GPa and completed at 20GPa . The high pressure structure is identified as hexagonal P63/mmc . First-principles calculations reproduced the first-order nature of the transition. Since P63/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 MgH2 .
- 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:
- 930648
- Report Number(s):
- BNL-81085-2008-JA; PRBMDO; TRN: US200901%%161
- Journal Information:
- Physical Review B: Condensed Matter and Materials Physics, Vol. 75; ISSN 0163-1829
- Country of Publication:
- United States
- Language:
- English
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