Thermoelectric properties of A-site deficient La-doped SrTiO3 at 100-900 °C under reducing conditions

Lanthanum doped strontium titanate is a potential n-type thermoelectric material at moderate and high temperatures. (La0.12Sr0.88)(0.95)TiO3 ceramics were prepared by two different routes, conventional sintering at 1500 degrees C and spark plasma sintering at temperatures between 925 and 1200 degrees C. Samples with grain size between 40 nm and 1.4 mu m were prepared and characterized with respect to their thermoelectric transport properties at temperatures between 100 and 900 degrees C under reducing conditions (H-2/H2O-buffer mixtures). The thermal conductivity was significantly reduced with decreasing grain size reaching a value of 1.3 W m(-1.)K(-1) at 600 degrees C for grain size of 40 nm and porosity of 19%. Electrical conductivity increased with increasing grain size showing a maximum of 500 S cm(-1) at 200 degrees C for a grain size of 1.4 mu m. The highest figure-of-merit (zT) was measured for samples with 1.4 mu m average grain size reaching 0.2 at 500 degrees C.