Effects of Sn-Doping on the Thermoelectric Properties of Famatinite

Various Sn-doped famatinite (Cu 3 Sb 1− y Sn y S 4 , 0 ≤ y ≤ 0.1) specimens were prepared by employing a mechanical alloying and hot-pressing method. The phase transitions, microstructures, and thermoelectric properties, i.e., the electrical conductivity, Seebeck coefficient, power factor, thermal conductivity, Lorenz number, and figure of merit, were examined. The famatinite phase with a tetragonal structure was stable below its melting point, as no secondary phases were present; however, it transformed to skinnerite Cu 3 SbS 3 at higher temperatures. Sn doping reduced the melting point from 817 K (Cu 3 SbS 4 ) to 815 K (Cu 3 Sb 0.92 Sn 0.08 S 4 ). Hot-pressed compacts exhibited relative densities of 97.1–99.5%. Because Sn replaced at Sb sites, the a -axis slightly reduced, and the c -axis increased. Cu 3 SbS 4 exhibited non-degenerate semiconductor behavior, and possessed a low dimensionless figure of merit ( ZT ) of 0.1 at 623 K; these phenomena were products of the power factor of 0.14 mW m −1 K −2 and thermal conductivity of 0.62 W m −1 K −1 . Conversely, the Sn-doped specimens exhibited degenerate semiconductor characteristics. As the Sn content increased, the electrical and thermal conductivities and power factor increased, whereas the Seebeck coefficient decreased. The thermoelectric performance was significantly enhanced by Sn doping. The highest ZT (0.67 at 623 K) was obtained for Cu 3 Sb 0.92 Sn 0.08 S 4 , and it was a product of implementing a power factor of 0.94 mW m −1 K −2 and thermal conductivity of 0.86 W m −1 K −1 .