Synthesis, sintering, and thermoelectric properties of the solid solution La _{1– x} Sr _x CoO _{3± δ} (0 ≤ x ≤ 1)

Abstract

In this work, we synthesized cubic perovskite ceramics of the whole La _{1– x} Sr _x CoO ₃ (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 3×10 ⁵ 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– x} Sr _x CoO ₃ 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.