Pressure and temperature dependence of structural and elastic properties of FeSe superconductor by first-principles calculation

Abstract

Structural and elastic properties of iron selenium (FeSe) superconductor at high pressure and temperature are important for understanding their superconductivity characteristics. In this study we report the first-principles calculation and the quasi-harmonic approximation (QHA) for exploring structural properties, thermodynamic properties and elasticity of FeSe over a wide pressure and temperature range. The obtained results exhibit that the elastic constants and modulus increase with the applied pressure, which is properly interpreted from the view of microelectronic profile. A transition from ductile to brittle of the FeSe is revealed at about 6 GPa, and the elastic anisotropy is found to be enhanced slightly with the pressure. A thermodynamic framework that relies on the QHA is utilized to evaluate the temperature dependence of the FeSe’s crystal volume. Combined the volume coefficient of thermal expansion and the first-principles elastic theory, the temperature-dependent mechanical properties of FeSe are achieved. The results show the elastic modulus increase gradually with temperature, and a three-dimensional graph of FeSe’s volume is illustrated numerically.