Effects Of Sintering Additives On Sintering Characteristics And Thermoelectric Properties Of LaCoO₃ Ceramics

LaCoO₃ oxide is one of the most promising p-type thermoelectric oxides. However, the sintering temperature of LaCoO₃ is too high to be co-fired with the low melting point metal in the process of preparation of thermoelectric devices, which will result in high cost of equipment and material. In this paper, sintering additives were added to reduce the sintering temperature.B₂O₃,B₂O₃-CuO and BBS were added to reduce the sintering temperature of LaCoO₃ ceramics by the conventional sintering. Microstructures and compositions were characterized by SEM and XRD. The electrical conductivity, Seebeck coefficient and thermal conductivity were studied from room temperature up to 500℃.The results indicate that B₂O₃ additives can not reduce the sintering temperature of LaCoO₃. B₂O₃-CuO composite can not only reduce the sintering temperature from 1200℃to 1000℃but also improve the thermoelectric properties by Cu doped. The electrical conductivity is significantly enhanced and the Seebeck coefficient is decreased by adding B₂O₃-CuO additives. The power factor of all the samples at different sintering temperatures is lager than that of the LaCoO₃ without B₂O₃-CuO additives. The thermal conductivity with same additives component decreases with the decrease of sintering temperature. By adding 2.5mass% B₂O₃-CuO and sintering at 1000℃, the ZT value can reach 0.073 at 100℃, which is 9 times larger than that of the LaCoO₃ without B₂O₃-CuO and 50% larger than that of the material sintered at 1100℃. Better thermoelectric properties are obtained under the lower sintering temperatures.BBS additives can significantly reduce the sintering temperature below to 950℃. The electrical conductivity is enhanced and the Seebeck coefficient is only a little changed by adding BBS additives. The power factor can reach to 1.03×10^-4W·m^-1·K^-2 with 3.0mass% BBS when sintering at 950℃. The thermal conductivity with same additives component decreases with the decrease of sintering temperature, and at the same sintering temperature the thermal conductivity decreases with the decrease amount of BBS additives. By adding 2.0mass% BBS sintering additives and sintering at 950℃, the ZT value can reach 0.035 at 400℃, which is 30% larger than that of the LaCoO₃ without BBS additives sintered at 1200℃.