Synthesis,sintering,and thermoelectric properties of the solid solution La_(1–x)Sr_(x)CoO_(3±δ)(0≤x≤1)

In this work, we synthesized cubic perovskite ceramics of the whole La_(1–x)Sr_xCoO_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_xCoO_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.

In this work, we synthesized cubic perovskite ceramics of the whole La1-xSrxCoO3±δ（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 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-xSrxCoO3 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.