La and Sm Co-doped SrTiO3-delta Thermoelectric Ceramics

The thermoelectric properties of Sr1-xLax/2Smx/2TiO3-δ (0.05 ≤ x ≤ 0.30) ceramics have been investigated with compositions batched, synthesised by solid state reaction and sintered in 5% H2/N2 at 1500 °C for 6 hrs. All X-ray diffraction patterns were fully indexed according to a cubic perovskite phase. Scanning electron microscopy revealed homogeneous grain structure in the ceramics and confirmed relative density ≥ 89%. The electrical conductivity (σ) of x ≤ 0.15 displayed metallic behaviour with σ < 1000 S/cm, whereas x ≥ 0.20 were semiconducting with σ < 250 S/cm. The Seebeck coefficient of all compositions was negative indicating n-type behaviour. Within this series, x = 0.20 displayed the lowest thermal conductivity of ∼ 3 W/m.K (at 973 K), x = 0.10 displayed the highest power factor of 1400 μW/K2.m (at 573 K) and overall x = 0.15 had the highest dimensionless figure of merit (ZT) of 0.24 (at 875 K).