Ab Initio Study of Novel Quaternary Heusler LiTiRhZ (Z = Si, Ge, Sn) Compounds for Thermoelectric Application

Abstract

Quaternary Heusler LiTiRhZ (Z = Si, Ge, Sn) compounds are investigated for mechanical and thermodynamic stability and their suitability as potential thermoelectric materials in a high-temperature range. The density functional theory and Boltzmann transport equations have been used for the calculations of structural, electronic, phonon dynamics, elastic, and thermoelectric properties. The compounds exhibit indirect band gaps of 1.076, 1.132, and 1.032 eV in LiTiRhZ (Z = Si, Ge, Sn), respectively, confirming their semiconducting nature. The negative formation energies and high melting points (~1800 K) suggest structural stability and experimental feasibility. Elastic and phonon calculations confirm mechanical and dynamical stability, along with ductile and anisotropic behavior. For a better understanding of thermodynamic properties, free energy, entropy, and specific heat at constant volume are also investigated up to 1000 K temperature. We obtained the increasing nature of power factor in all studied compounds, indicating the high value of figure of merit (ZT), particularly in the high-temperature region, with LiTiRhSi achieving a maximum ZT ~ 0.69 at 1000 K, showing its potential for high-temperature thermoelectric applications. The higher and stable values of ZT as compared to the other reports in the high-temperature range may provide strong support for experimental research on the studied compounds.