Enhanced thermoelectric performance of SmS by Se alloying and Y doping

Rare-earth sulfide SmS is verified to be a potential high-temperature thermoelectric material. However, the relatively high thermal conductivity limits its performance. Although Se alloying can effectively reduce the thermal conductivity, the bandgap becomes wider at the same time and more carrier concentration is required to optimize the electrical performance. A series Sm1-xYxS0.77Se0.23 (x =0, 0.03, 0.05, 0.07, 0.1) was synthesized by ball-milling combined hot-pressing. X-ray powder results showed all Y-doped samples of Sm1-xYxS0.77Se0.23 contains tiny Sm₃S₄ phase. When x < 0.1, carrier concentration and electrical conductivity increased obviously, while the Seebeck coefficient changed slightly and remained at a temperature over 850 K. The maximum power factor of Sm0.97Y0.03S0.77Se0.23 reaches 1.42 mW/m K² at 1023 K. The thermal conductivity of Sm1-xYxS0.77Se0.23 (x <0.1) increased a little due to the increase of electron thermal conductivity but still smaller than pristine. The maximum zT 1.11 was obtained at 1023K, which is about 68% higher than that of pristine SmS.