The Role of Ionized Impurity Scattering on the Thermoelectric Performances of Rock Salt AgPb_mSnSe_{2+ m}

This study reports on the successful synthesis and on the properties of polycrystalline AgPb_mSnSe_{2+ m} (m = ∞, 100, 50, 25) samples with a rock salt structure. Between ≈160 and ≈400 K, the dominant scattering process of the carriers in this system changes from acoustic phonon scattering in PbSe to ionized impurity scattering in AgPb_mSnSe_{2+ m}, which synergistically optimizes electrical and thermal transport properties. Thanks to the faint amount of AgSnSe₂, the Seebeck coefficient is enhanced by boosting the scattering factor, the electric conductivity is improved by the increase of the concentration of holes coupled to a limited degradation of their mobility, and the total thermal conductivity is reduced by suppressing bipolar thermal conductivity. Therefore, ZT of AgPb_mSnSe_{2+ m} (m = 50) reaches 1.3 at 889 K. The mechanism suggested in this study opens new paths to improve the thermoelectric performances of other families of materials.