Effect of La³⁺, Ag⁺ and Bi³⁺ doping on thermoelectric properties of SrTiO₃: First-principles investigation

First principles calculations were applied to study the thermoelectric properties of La³⁺-, Ag⁺- and Bi³⁺- doped SrTiO₃. With the exception of Sr_0.9La_0.1TiO₃, the band gaps of Sr_0.8La_0.1Ag_0.1TiO₃, Sr_0.8La_0.1Bi_0.1TiO₃ and Sr_0.7La_0.1Ag_0.1Bi_0.1TiO₃ were higher than that of SrTiO₃. La³⁺, Ag⁺, and Bi³⁺ doping can cause an increase in electrical conductivity and power factor, and a decrease in thermal conductivity, which improves the ZT. The thermal conductivities of SrTiO₃, Sr_0.9La_0.1TiO₃, Sr_0.8La_0.1Ag_0.1TiO₃, Sr_0.8La_0.1Bi_0.1TiO₃ and Sr_0.7La_0.1Ag_0.1Bi_0.1TiO₃ successively decreased, while power factor and ZT increased. Sr_0.7La_0.1Ag_0.1Bi_0.1TiO₃, in particular, has the smallest thermal conductivity (2.237 W/m/K), the highest power factor (1.18 mW/(mK²)) and ZT (0.597) at 1200 K, 2.195 times larger than that of SrTiO₃ (0.272). In addition, the solid state reaction method was applied to prepare dense ceramics of 10 wt% Bi-doped and (Bi, Ag)-codoped Sr_0.9La_0.1TiO₃. It is demonstrated that (Bi, Ag)-codoped Sr_0.9La_0.1TiO₃ have improved power factors, thermal conductivities and ZT values. The calculations and experimental results are consistent. This work demonstrates a method of co-doping Bi³⁺, Ag⁺, and La³⁺ to enhance the thermoelectric performance of SrTiO₃.