Ab Initio Prediction of Large Thermoelectric Effect in Distorted Heusler Alloy Ti-Fe-Sb Compound

The thermoelectric figure of merit of the Heusler alloy TiFe$_{1.5}$Sb was investigated by first-principles calculations of lattice thermal conductivity. The electronic thermal conductivity, electrical conductivity, and Seebeck coefficient are calculated by semi-classical Boltzmann transport theory. TiFe$_{1.5}$Sb was found to be thermally and dynamically stable, as confirmed by its phonon dispersion. Additionally, the small phonon band gap between acoustic and optical modes enhances phonon scattering, leading to a low lattice thermal conductivity of 0.703 W/mK at 300 K. Our study also reveals that TiFe$_{1.5}$Sb is a non-magnetic semiconductor. Notably, it demonstrates a significant longitudinal thermoelectric effect, with a Seebeck coefficient of 359.4 $\mu$V/K at 300 K. The combination of low lattice thermal conductivity and a high Seebeck coefficient results in a high thermoelectric figure of merit (ZT) of 0.88 and 0.91 at 300 K and 500 K, respectively. These findings highlight the considerable potential of TiFe$_{1.5}$Sb as a promising material for thermoelectric device applications.