Enhanced thermoelectric properties of La and Dy co-doped, Sr-deficient SrTiO3 ceramics

Sr-deficient La0.1DyxSr1-1.25(0.1+x)TiO3 (x = 0, 0.05, 0.075, 0.1) powders were synthesized via the sol-gel method, followed by sintering at 1550 °C under a reducing atmosphere of 5 vol% hydrogen in nitrogen. The composition, microstructure and thermoelectric properties of the La0.1DyxSr1-1.25(0.1+x)TiO3 ceramics were characterized to identify the influence of Sr deficiencies and co-doping on the thermoelectric performance of SrTiO3-based oxides. The results revealed that the main phase of the prepared ceramics was SrTiO3 with a cubic crystal structure, while a small amount of Dy2Ti2O7 appeared as the second phase in the samples when x = 0.075 and x = 0.1. With increasing Dy content, the grain size reduced remarkably from ∼20 μm (x = 0) to 2-5 μm (x = 0.1). Simultaneously, the electrical conductivity clearly increased with a slight increase in the absolute Seebeck coefficient, while the thermal conductivity clearly decreased, leading to a dimensionless figure of merit (ZT) with a high value of 0.29 at 500 °C for the La0.1Dy0.1Sr0.75TiO3 sample.