The thermal and mechanical properties of Li-based Half Heusler alloys LiAlZ(Z = Si, Ge) using Quasi-Harmonic Approach

Abstract

Using the Density Functional Density (DFT) method coupled with a Quasi-Harmonic Approximation (QHA), we studied the structural stability and thermal properties of Li-based Half Heusler alloys LiAlZ (Z= Si and Ge). The obtained results show that type I for both compounds is the most stable of all the examined structural phase types i (i = I, II, III) and have semiconductor behavior with narrow indirect band gaps. The study of the elastic constants and phonon curves confirmed that these compounds are mechanically and dynamically stable. The obtained results of total free energy are considered while estimating the thermal properties as the lattice parameters, volume thermal expansion, heat capacity, electronic and entropy in the range of temperature from 0 K to 1000 K. The thermal properties show that half Heuslers LiAlZ are thermodynamically stable, and the vibrational contribution is dominant compared to configurational and electronic contributions in the heat capacity and entropy. In contrast, the vibrational contribution is very small to the configurational and electronic free energy contributions.