Low lattice thermal conductivity and promising thermoelectric figure of merit of Zintl type TlInTe2

Abstract

Thallium compounds have appeared as a new class of advanced thermoelectric (TE) materials owing to their extremely low lattice thermal conductivity. Using a first-principles approach and Boltzmann transport theories, we investigate the electronic and phonon transport properties of a ternary thallium telluride, TlInTe₂. Unlike the Bi₂Te₃ and PbTe used in current TE devices, a multi-valley band structure with intrinsic degeneracy is obtained for TlInTe₂, which contributes to its high Seebeck coefficient and relatively high power factor. Also, because of its weak bonding stiffness and strong phonon anharmonicity, TlInTe₂ has an extremely low lattice thermal conductivity of about 0.37 W m⁻¹ K⁻¹ at room temperature, which is almost one third of the values for Bi₂Te₃ and PbTe. Consequently, competitive ZT values of 1.78 and 1.84 are obtained at 300 K for p- and n-doped TlInTe₂, respectively, indicating that thallium compounds are promising TE materials for practical applications.