Elastic constants, electronic properties and thermoelectric response of LiAlX (X=C, Si, Ge, and Sn) half-Heusler compounds

Since they have become indispensable in various technological applications and a powerful source for generating energy in thermoelectric devices, Lithium-based alloys are the central topic of many experimental and theoretical reports. Hence, LiA1X(X = C, Si, Ge, Sn) materials represent the main research in this study. Different interesting properties such as the effect of pressure on the band gaps as well as the elastic parameters and the thermoelectric efficiency of these materials were investigated using the full potential linearized augmented plane wave (FP-LAPW) method. LiAlX alloys were found to be semiconducting with indirect band gaps. When studying the mechanical properties, we realized that LiAlC alloy remains stable against a wide range of pressure changes (90 GPa), while the rest three systems preserve their mechanical stability in a moderate range of 40, 50 and 30 GPa, respectively. The semiconducting band gap for each possible transition have been calculated in a range of different pressures using both GGA and mBJ-GGA approximations. The results revealed a decaying trend of the indirect gap along Gamma-X direction with increase of pressure. High values of the power factor were achieved and a large figure of merit (almost 0.7 for all systems) was calculated at 600 K, which makes these Li-based alloys very auspicious in the thermoelectric field applications.