Thermoelectric Properties of Undoped and Doped ( Ti 0.75 Sn 0.25 ) O 2

Thermoelectric properties of undoped and doped ( Ti 0.75 Sn 0.25 ) O 2 were investigated for high‐temperature thermoelectric conversion application. Nano‐composites were formed by annealing above 1000°C. Outside the spinodal dome, ilmenite‐type SnTiO 3 precipitated from the rutile structure. Thermoelectric properties were measured in the temperature range from room temperature to 1000°C. ( Ti 0.75 Sn 0.25 ) O 2 was doped with both acceptor and donor dopants. Both undoped and doped ( Ti 0.75 Sn 0.25 ) O 2 exhibit n ‐type electrical behavior independent of the type of the dopant. The electrical conductivity was enhanced three orders of magnitude by donor doping with Nb 2 O 5 or Ta 2 O 5 ; achieving a maximum of 546 S/m at 850°C. The increase in electrical conductivity was accompanied by reduction of the absolute Seebeck coefficient. Seebeck coefficient reduction of −600 μV/K was observed between undoped and 4% Ta 2 O 5 doped samples. The solid solution and doping reduced the thermal conductivity to <4 W/mK, far below the parent materials TiO 2 and SnO 2 . Lattice thermal conductivity decreased with increasing temperature, achieving 1.9 W/mK at 900°C for 4% Ta 2 O 5 doping. No further reduction in thermal conductivity was observed in annealed samples containing nano‐sized SnTiO 3 precipitates. Dimensionless figure of merit ( ZT ) attained was <0.1.