Boltzmann transport calculation of thermoelectric properties in Ag₂Se_1-xTe_x (x = 0.0 and 0.5)

We calculated the thermoelectric properties of the Ag-based chalcogenides Ag₂Se and Ag₂Se_0.5Te_0.5 (AST) at room temperature using the Boltzmann transport equations within the density functional theory. We confirmed that the power factor S 2 σ and electronic figure-of-merit ZT_e of the Ag₂Se_0.5Te_0.5 compound can be enhanced by hole doping as compared with Ag₂Se due to enhancement of the Seebeck coefficient and electrical conductivity. The localized electrons introduced by Te doping give rise to heavy valence bands and a small band gap near the Fermi energy. We also investigated the thermoelectric properties of the compounds in terms of the two-band model within the assumption of arbitrary isotropic band dispersions. We suggest that the hole doping in the AST compound can produce a good candidate for p-type thermoelectric material by controlling the effective mass of valence band and small band gap opening. Using large atomic size elements for chemical potential tuning and isostructural substitution in Ag₂Se related chalcogenides can be a good route to increase the thermoelectric performance.