Effect of pressure on the mechanical and dynamical stability of NaAlSi

ABSTRACT

The effects of pressure on the mechanical and dynamical stability of NaAlSi have been fully investigated by first-principles calculations within the generalised gradient approximation (GGA). The obtained results show that the optimised lattice constants, atomic positions and elastic constants at ambient pressure are in good agreement with the available experimental and theoretical data. The lattice constants decrease monotonically with increasing pressure. The elastic constant C₁₁, C₁₂, C₁₃, C₃₃ and C₆₆ increase while C₄₄ decreases with increasing pressure. It is found that NaAlSi is mechanically unstable when the pressure is above 25.97 GPa. The phonon-dispersion curves along several high symmetry lines are obtained. The phonon frequencies at the Z point decrease with increasing pressure and completely soften to zero at 27.52 GPa, further confirming the structural instability of NaAlSi.

KEYWORDS:

• Structural properties
• mechanical stability
• dynamical stability
• high pressures
• NiAlSi

Acknowledgements

The authors acknowledge support from Dr X. Gonze and his coworkers for providing their version of the ABINIT code. The authors would like to gratefully acknowledge financial support from the National Natural Science Foundation of China (NSFC) [grant number: 51506018] and the Chongqing Science and Technology Commission [grant number: cstc2015jcyjA50025].

Disclosure statement

No potential conflict of interest was reported by the authors.