First principle studies on lattice thermal conductivity and thermoelectric properties of ScCu(S,Se,Te)2

Abstract

This study is aimed at evaluating the structural stability, lattice thermal conductivity, transport properties and the thermoelectric figure of merit of scandium copper chalcogenides (denoted by ScCuX2) based on first principles. At the apex of this work, we explored the transport properties by solving Boltzmann transport equations in a relaxation time approximation to obtain transport coefficients of interest which were then integrated with lattice thermal conductivity in order to establish the values of the dimensionless figure of merit (ZT), which dictate not only the possibility of using a given material as a major component in the design of thermoelectric system but also indicates how efficient it is in converting thermal to electrical energy, where values of ZT around unity are preferred.At room temperature (300 K), the values of the averaged lattice thermal conductivity obtained are 1.58, 1.28 and 1.47 W/mK for ScCuS2, ScCuSe2 and ScCuTe2 respectively which are promising for thermoelectric applications where minimal values of lattice thermal conductivity are desirable. We also evaluated the Debye temperatures as well as transverse and longitudinal sound velocity in ScCuX2 compounds. In addition, group velocities, phonon lifetimes and mean free paths were explored in order to uncover the mechanisms of thermal transport in these ternaries. Our study provides important new insights into heat transport and phonon scattering mechanisms in ScCuX2 ternary compounds. From our findings, among the three ternary compounds, ScCuSe2 has the highest value of dimensionless figure of merit of 0.65 at high temperatures (1000 K) when the majority charge carriers are holes having a carrier concentration of 1019 cm−3.