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

Abstract

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.

Ba substitution for enhancement of the thermoelectric properties of LaCoO3 ceramics (0⩽x⩽0.75)

“…Kun et al [37] found that, for the same Ba content, S exhibits a value close to our value, whereas for lower Ba content (1%), a higher value of S (≈ 400 µV•K -1 ) was measured. This is similar to the values measured in La 1-x Sr x CoO 3 compounds but for higher substitutant content (x = 0.05) [23].…”

“…Indeed, measurements of the electrical conductivity show that the ceramics substituted by Ba display a high electric conductivity at low temperatures. This value is slightly lower than the optimum electrical conductivity in La 1−x Sr x CoO 3 , which is σ max ≈ 3×10 5 S•m -1 at 330 K for x = 0.3 [23]. However, it is consistent in terms of substitutant content.…”

“…This step has been repeated twice after manual grinding. Finally, the calcined samples were pressed into pellets, and sintered for 12 h in air at 1673 K [23].…”

“…Indeed, on the contrary to all the other cobalt oxides that present high thermoelectric properties at high temperatures, Androulakis et al [19] have reported in La 1-x Sr x CoO 3 (x = 0.05), the highest thermoelectric properties for an oxide at 300 K (ZT = 0.18). Therefore, Sr substituted LaCoO 3 ceramics have been largely studied [20][21][22][23] and the optimum value for thermoelectric properties is obtained for x = 0.05. Moreover, Bousnina et al [23] have shown that the substitution can be realized up to x = 0.8 without any addition and up to x = 1 for an additional substitution of 3% Si for Co.…”

“…Therefore, Sr substituted LaCoO 3 ceramics have been largely studied [20][21][22][23] and the optimum value for thermoelectric properties is obtained for x = 0.05. Moreover, Bousnina et al [23] have shown that the substitution can be realized up to x = 0.8 without any addition and up to x = 1 for an additional substitution of 3% Si for Co.…”