Thermoelectric Properties of Tl-Doped SnSe: A Hint of Phononic Structure

Polycrystalline samples with composition Sn 1− x Tl x Se (for x = 0 to 0.04) have been synthesized from elements of 5 N purity at elevated temperatures. The phase purity of the products was verified by x-ray diffraction analysis. Samples for measurement of transport properties were prepared by hot pressing. The samples were then characterized by measurement of electrical conductivity, Hall coefficient, Seebeck coefficient, and thermal conductivity over the temperature range from 300 K to 725 K. All samples demonstrated p -type conductivity. Tl markedly enhanced the carrier concentration. We discuss the influence of Tl substitution on the free carrier concentration and thermoelectric performance. Investigation of the thermoelectric properties showed an order-of-magnitude improvement, with ZT reaching 0.6 at 725 K. We discuss the distinctive nature of the thermal conductivity of SnSe.