Sintering behavior and thermoelectric properties of LaCoO₃ ceramics with Bi₂O₃-B₂O₃-SiO₂ as a sintering aid

Recently, LaCoO₃ has received increasing attention as a promising thermoelectric oxide. However, its sintering temperature is too high from the practical point of view. This study investigated the effect of Bi₂O₃-B₂O₃-SiO₂ (BBS) as a sintering aid on the low-temperature sintering behaviors, microstructures and thermoelectric properties of LaCoO₃ ceramics. The XRD results revealed that the LaCoO₃ ceramics with 1-3 wt% BBS could form a single crystalline phase without visible secondary phases. The sintering temperature of LaCoO₃ ceramics was reduced remarkably from 1200 °C to 950°C by adding 3 wt% BBS, with a relative density higher than 95%. The process of densification and the appearance of rod-like grains in LaCoO₃ with BBS aids were observed by SEM. Meanwhile, the thermoelectric properties of LaCoO₃ ceramics were strongly dependent on the densification and microstructures. For the samples sintered at 1050°C, the electrical conductivity increased significantly with the increase of BBS content (x, wt%) up to x = 2.0, and the Seebeck coefficients were almost the same when the test temperatures were higher than 200°C. Moreover, the sample with x = 2.0 had the optimum thermoelectric properties with ZT = 0.05 at 400°C, which was about 66.7% higher than that of pure LaCoO₃ ceramics sintered at 1200°C, indicating that the addition of BBS could effectively promote the densification and further improve thermoelectric properties of LaCoO₃ ceramics without using complicated processes.