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Title: Structural Phase Transition in CaH2 at High Pressures

Abstract

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 .

Authors:
; ; ; ; ; ; ; ;
Publication Date:
Research Org.:
Brookhaven National Laboratory (BNL) National Synchrotron Light Source
Sponsoring Org.:
Doe - Office Of Science
OSTI Identifier:
930648
Report Number(s):
BNL-81085-2008-JA
Journal ID: ISSN 0163-1829; PRBMDO; TRN: US200901%%161
DOE Contract Number:  
DE-AC02-98CH10886
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review B: Condensed Matter and Materials Physics; Journal Volume: 75
Country of Publication:
United States
Language:
English
Subject:
08 HYDROGEN; ATOMS; HYDROGEN; PHASE TRANSFORMATIONS; CALCIUM; national synchrotron light source

Citation Formats

Tse,J., Klug, D., Desgreniers, S., Smith, J., R. Flacau, R., Liu, Z., Hu, J., Chen, N., and Jiang, D. Structural Phase Transition in CaH2 at High Pressures. United States: N. p., 2007. Web. doi:10.1103/PhysRevB.75.134108.
Tse,J., Klug, D., Desgreniers, S., Smith, J., R. Flacau, R., Liu, Z., Hu, J., Chen, N., & Jiang, D. Structural Phase Transition in CaH2 at High Pressures. United States. doi:10.1103/PhysRevB.75.134108.
Tse,J., Klug, D., Desgreniers, S., Smith, J., R. Flacau, R., Liu, Z., Hu, J., Chen, N., and Jiang, D. Mon . "Structural Phase Transition in CaH2 at High Pressures". United States. doi:10.1103/PhysRevB.75.134108.
@article{osti_930648,
title = {Structural Phase Transition in CaH2 at High Pressures},
author = {Tse,J. and Klug, D. and Desgreniers, S. and Smith, J. and R. Flacau, R. and Liu, Z. and Hu, J. and Chen, N. and Jiang, D.},
abstractNote = {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 .},
doi = {10.1103/PhysRevB.75.134108},
journal = {Physical Review B: Condensed Matter and Materials Physics},
number = ,
volume = 75,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}