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Materials 2016, 9(7), 570; doi:10.3390/ma9070570

Crystal Structures and Mechanical Properties of Ca2C at High Pressure

1
School of Physics and Optoelectronic Engineering, Xidian University, Xi’an 710071, China
2
School of Microelectronics, Xidian University, Xi’an 710071, China
3
College of Physics and Optoelectronic Technology, Baoji University of Arts and Sciences, Baoji 721016, China
*
Authors to whom correspondence should be addressed.
Academic Editor: Martin O. Steinhauser
Received: 17 May 2016 / Revised: 17 June 2016 / Accepted: 6 July 2016 / Published: 14 July 2016
(This article belongs to the Special Issue Computational Multiscale Modeling and Simulation in Materials Science)
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Abstract

Recently, a new high-pressure semiconductor phase of Ca2C (space group Pnma) was successfully synthesized, it has a low-pressure metallic phase (space group C2/m). In this paper, a systematic investigation of the pressure-induced phase transition of Ca2C is studied on the basis of first-principles calculations. The calculated enthalpy reveals that the phase transition which transforms from C2/m-Ca2C to Pnma-Ca2C occurs at 7.8 GPa, and it is a first-order phase transition with a volume drop of 26.7%. The calculated elastic constants show that C2/m-Ca2C is mechanically unstable above 6.4 GPa, indicating that the structural phase transition is due to mechanical instability. Both of the two phases exhibit the elastic anisotropy. The semiconductivity of Pnma-Ca2C and the metallicity of C2/m-Ca2C have been demonstrated by the electronic band structure calculations. The quasi-direct band gap of Pnma-Ca2C at 0 GPa is 0.86 eV. Furthermore, the detailed analysis of the total and partial density of states is performed to show the specific contribution to the Fermi level. View Full-Text
Keywords: pressure-induced phase transition; first-principles calculations; Ca2C pressure-induced phase transition; first-principles calculations; Ca2C
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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Wei, Q.; Zhang, Q.; Zhang, M. Crystal Structures and Mechanical Properties of Ca2C at High Pressure. Materials 2016, 9, 570.

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