Investigation on Structural, Electronic, and Thermoelectric Properties of Half-Heusler Compounds TiXSb (X = Si, Ge) under Pressure Based on Density Functional Theory (DFT)

Abstract

Based on density functional theory, structural, electronic, and thermoelectric properties of TiXSb (X = Si, Ge) at pressures of 0, 5, 10, and 15 GPa have been investigated. Structural properties at 0 GPa are in accord with other theoretical and experimental works. In electronic properties at 0 GPa, Ti-d² orbitals have main contributions near the Fermi energy in valence band and in conduction band. According to our calculations, as shown in diagrams of electronic density of states at different pressures, peaks in the valence band move to more negative energies when the pressure increases. However, in the conduction band, they move to more positive energies. This occurs as a result of decreasing stability of the system due to increase in pressure. In this study, we also calculated the thermoelectric properties such as Seebeck coefficient, thermal conductivity divided by relaxation time, electrical conductivity divided by relaxation time, and figure of merit, at pressures of 0, 5, 10, and 15 GPa, in the temperature range of 100–900 K (contribution of phononic thermal conductivity was ignored as low).