Synthesis, sintering, and thermoelectric properties of the solid solution La1–xSr x CoO3±δ (0 ≤ x ≤ 1)

In this work, we synthesized cubic perovskite ceramics of the whole La1–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 PFmax = 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, La1–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.