This work reports the synthesis and electrical characterisation over a range of oxygen partial pressures (10^–20–1 atm) of the A-site deficient perovskites Sr_1–3x/2La_xTiO_3–δ, with a view to establishing their potential as anode materials for solid oxide fuel cells. Single phase samples were observed for synthesis in air for 0≤x≤0.6, and the materials remained phase pure for both high and low oxygen partial pressures at the measurement temperature of 930 °C. Good electrical conductivity, which increased with increasing La content, was observed on reduction in low oxygen partial pressures, with values as high as 7 S cm^–1 [ P(O₂)= 10^–20 atm], similar to values observed for the related system, Sr_1–x/2Ti_1–xNb_xO_3–δ, examined previously. The conductivity of the fully reduced samples showed metallic character from 100 to 930 °C. As the oxygen partial pressure was raised, the conductivity dropped, showing an approximate [P(O₂)]^–1/6 dependence for porous samples. New samples, Sr_{1–y/2–3x/2}La_xTi_1–yNb_yO_3–δ, with both La and Nb substitutions, were also studied, and these phases showed similar electrical behaviour. Further results for the Sr_1–x/2Ti_1–xNb_xO_3–δsystem are presented and compared with the La doped systems.

Donor-substituted strontium titanate ceramics demonstrate one of the most promising performances among n-type oxide thermoelectrics. Here we report a marked improvement of the thermoelectric properties in rare-earth substituted titanates Sr_0.9R_0.1TiO_3±δ (R = La, Ce, Pr, Nd, Sm, Gd, Dy, Y) to achieve maximal ZT values of as high as 0.42 at 1190 K < T < 1225 K, prepared via a conventional solid state route followed by sintering under strongly reducing conditions (10%H₂–90%N₂, 1773 K). As a result of complex defect chemistry, both electrical and thermal properties were found to be dependent on the nature of the rare-earth cation and exhibit an apparent correlation with the unit cell size. High power factors of 1350–1550 μW m⁻¹ K⁻² at 400–550 K were observed for R = Nd, Sm, Pr and Y, being among the largest reported so far for n-type conducting bulk-ceramic SrTiO₃-based materials. Attractive ZT values at high temperatures arise primarily from low thermal conductivity, which, in turn, stem from effective phonon scattering in oxygen-deficient perovskite layers formed upon reduction. The results suggest that highly-reducing conditions are essential and should be employed, whenever possible, in other related micro/nanostructural engineering approaches to suppress the thermal conductivity in target titanate-based ceramics.