Enhanced mid-temperature thermoelectric performance of textured SnSe polycrystals made of solvothermally synthesized powders

This work revealed that the thermoelectric properties of textured SnSe polycrystals, which are made of solvothermally synthesized powders with a preferred orientation grown along the (400) plane, can be enhanced, especially in the range of mid-temperatures. The electrical conductivity for the sintered sample is greatly improved in the whole measured temperature range, attributed to the high carrier concentration and unique mobility change. This results in a large power factor combined with the moderate Seebeck coefficient, especially in the range of 300-650 K, which exceeds 5 mu W cm(-1) K-2 at 423 K and even larger than 6 mu W cm(-1) K-2 at 521 K. Benefiting from the enhanced electrical conductivity and the low total thermal conductivity (<1 W m(-1) K-1 in the range of 300 to 773 K), a higher ZT value than that reported for undoped single crystals was achieved in a relatively wide mid-temperature range, which reached 0.44 at 522 K and 0.5 at 573 K, and then showed weak temperature dependence in the range from 573 to 700 K. Above 700 K, the ZT value increased with temperature and a maximum value of nearly 0.6 was obtained at the maximum measured temperature of 773 K for the SnSe sample without any deliberate doping.