Thermoelectric properties of Ag8Tl2Te5 and AgTl3Te2

Thermoelectric properties of ternary silver thallium tellurides: Ag8T12Te5 and AgT13Te2 were studied above room temperature to slightly below the melting temperature. As for Ag8T12Te5, the effects of Te content on the thermoelectric properties were also studied by characterizing the samples of Ag8T12Tex (x = 5.0, 5.1, 5.2). Both compounds show positive Seebeck coefficient (S). Ag8T12Te5 indicates semiconductor-like behavior, while AgT13Te2 shows metallic one. Both the electrical resistivity ( ) and S of Ag8T12Tex decrease with increasing x, which indicates that the carrier concentration increases with x. Although the amount of Te of Ag8T12Tex strongly influences the electrical resistivity and Seebeck coefficient, the thermal conductivity ( ) values are at a similar level. The of Ag8T12Te5 and AgT13Te2 are very low, especially those of Ag8T12Tex are extremely low, approximately 0.35 Wm-lK-1 around room temperature. The maximum values of the dimensionless figure of merit ZT (=S2T/ ) of Ag8T12Te5.2 and AgT13Te2 were 0.54 at 567 K and 0.06 at 515 K, respectively.