In this work, we synthesized cubic perovskite ceramics of the whole La_1–xSr _x CoO₃ (0 ≤ x ≤ 1) solid solution for the first time. Synthesis was carried out by solid state reaction and conventional sintering to reach dense ceramics. For x > 0.8, it was necessary to substitute 3% cobalt by silicon to stabilize the cubic perovskite structure. Electrical conductivity increased with Sr content to reach 3×10⁵ S∙m^–1 at 330 K for x = 0.3. However, the optimum electrical properties have been found for x = 0.05 at 330 K with PF_max = 3.11×10^–4 W∙m^–1∙K^–2. Indeed, the Seebeck coefficient was decreasing when x increased to reach values close to 0 for x ≥ 0.3. Thermal conductivity was low at low temperature (≈ 2.5 W∙m^–1∙K^–1) and increased up to 6.5 W∙m^–1∙K^–1 when temperature increased. As the highest power factor was reached at low temperature as well as the lowest thermal conductivity, La_1–xSr _x CoO₃ compounds with low x values appeared as very promising thermoelectric materials around room temperature, on the contrary to layered cobalt oxides. For high x values, Seebeck coefficient values close to zero made these materials unsuitable for thermoelectric applications.

In the present work, dense perovskite ceramics were successfully prepared from a series of La_1–xBa_xCoO₃ solid solutions in the range of substitution 0 ⩽ x ⩽ 0.75 using solid state reaction and conventional sintering. Structural properties of La_1–xBa_xCoO₃ were systematically investigated and thermoelectric properties were measured in the temperature range of 330–1000 K. The results show that the thermoelectric properties of Ba-substituted LaCoO₃ depend on x. Indeed, at 330 K, electrical conductivity presents an optimum value for x = 0.25 with a value of σ_max ≈ 2.2×10⁵ S·m⁻¹ whereas the Seebeck coefficient decreases when x and/or the temperature increases. The Ba-substituted LaCoO₃ samples exhibit p-type semiconducting behaviour. The best power factor value found is 3.4×10⁻⁴ W·m⁻¹·K⁻² at 330 K for x = 0.075, which is 10% higher than the optimum value measured in La_1–xSr_xCoO₃ for x = 0.05. The thermal diffusivity and thermal conductivity increase with increasing temperature and Ba concentration. La_1–xBa_xCoO₃ shows a maximum figure of merit (ZT = 0.048) for x = 0.05 at 330 K, 25% higher than the best value in La_1−xSr_xCoO₃ compounds.