Analysis of structural and electronic properties of NiTiZ (Z = Si, Ge, Sn and Sb) under high-pressure using ab initio calculations

Abstract

The present study investigates the pressure dependencies of the structural and the thermoelectric properties of the half-Heusler alloys NiTiZ (Z = Si, Ge, Sn and Sb) using the first-principle density functional study. The fully relaxed samples demonstrate a semiconducting characteristic with an increase of the energy-gaps in NiTiZ (Z = Si, Ge and Sn) with pressure whereas the metallic character prevails in NiTiSb throughout the entire range of the pressure considered. The computed equilibrium lattice constants are in excellent agreement with the available experimental and theoretical data. A detailed calculation and analyses of the thermoelectric properties of the above half-Heuslers have been performed. Moreover, among the above half-Heuslers, the dimensionless figure of merit of the semiconducting alloys is maximum for NiTiSn. In case of NiTiGe, we observe a gradual increase in its figure-of-merit value with pressure.