Influence of Fuel Composition in Solution Combustion Synthesis on the Structure and Thermoelectric Properties of La-Doped SrTiO3

High-temperature thermoelectric SrTiO₃ powders, including La-doped (Sr_0.95La_0.05)TiO₃, were synthesized using solution combustion synthesis. It was found that using urea as the organic fuel leads to the formation of a polyphase material consisting of 80 wt % SrTiO₃ and 20 wt % TiO₂ along with Sr₂TiO₄. The introduction of a fuel mixture of urea and glycine into the reaction solution significantly improved homogeneity of the powder, increasing the proportion of the target phase to 95 wt %. Spark plasma sintering further homogenized the powder, reducing amount of the impurity phase TiO₂ to less than 5 wt %. The study demonstrated that doping, phase composition, and porosity have a significant impact on the thermoelectric properties of SrTiO₃. The presence of TiO₂ secondary phase and porosity was shown to regulate the material’s electrical and thermal conductivities. La doping affected the charge carrier concentration, and together with the other factors, enabled the production of a dense (Sr_0.95La_0.05)TiO₃ sample with a figure of merit ZT ≈ 0.23 at 950 K. The findings underscore the significance of controlling phase composition, doping, and defect structure to enhance the thermoelectric performance of SrTiO₃, paving the way for the design of energy-efficient materials applicable in thermal energy conversion technologies.