Evaluation of BaTiS₃ for Thermoelectric Applications by Using First Principles Theory

BaTiS₃ is a semiconductor with a band gap of about 0.5 eV and very strong transport anisotropy for both electron and hole conduction. The conduction band minimum is very dispersive with a small effective mass and large mobility because of split-off dz² band contribution. The optical phonons are relatively soft, and the ground state non-centrosymmetric phase is favorable by just about 1 mev/fu over the centrosymmetric phase, indicating possibility of phase intermixing and reduced thermal conductivity at finite temperatures. Electrons can be doped easily for instance by an external dopant La. The possibility of large electrical conductivity with a tunable thermal conductivity by external doping and phase intermixing makes this compound excellent candidate for thermoelectric applications. By using the first principles density functional theory and linearized Boltzmann transport theory, we calculate electrical conductivity, thermal conductivity and the Seebeck coefficient and report reasonable thermoelectric figure of merit, ZT, of about 0.4 at 800K for n-type BaTiS₃. Additional possibility to enhance the figure of merit by doping, phase intermixing and band engineering is discussed.