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Ba substitution for enhancement of the thermoelectric properties of LaCoO3 ceramics (0≤x≤0.75)
Journal of Advanced Ceramics 2019, 8 (4): 519-526
Published: 04 December 2019
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In the present work, dense perovskite ceramics were successfully prepared from a series of La1−xBaxCoO3 solid solutions in the range of substitution 0 ≤ x ≤ 0.75 using solid state reaction and conventional sintering. Structural properties of La1−xBaxCoO3 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 σmax ≈ 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 La1-xSrxCoO3 for x = 0.05. The thermal diffusivity and thermal conductivity increase with increasing temperature and Ba concentration. La1−xBaxCoO3 shows a maximum figure of merit (ZT = 0.048) for x = 0.05 at 330 K, 25% higher than the best value in La1-xSrxCoO3 compounds.

Open Access Research Article Issue
Synthesis, sintering, and thermoelectric properties of the solid solution La1–xSrxCoOδ (0 ≤ x ≤ 1)
Journal of Advanced Ceramics 2018, 7 (2): 160-168
Published: 28 March 2018
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In this work, we synthesized cubic perovskite ceramics of the whole La1–xSrxCoO3 (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–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.

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