Optimization of high temperature thermoelectric properties of Ca₃Co₄O₉ ceramics prepared by solid phase sintering with clay as a mineralizer

Ca₃Co₄O₉ is an environmentally friendly high-temperature oxide thermoelectric material, known for its excellent stability at elevated temperatures and low decomposition rate. In this study, Ca₃Co₄O₉ ceramics were prepared via a solid-phase method. Various clay mineralizers, characterized by their unique charge properties and ion-exchange capabilities, were innovatively introduced to enhance both the sintering process and the thermoelectric performance of the resulting ceramics. Experimental results indicate that the inclusion of bentonite as a mineralizer promotes the conversion of Co⁴⁺ to Co³⁺, thereby enhancing the Seebeck coefficient of the samples. At a temperature of 600 °C, the sample containing 4 % bentonite exhibits a power factor of 126.74 μW/K²·m, representing an increase of approximately 14.62 % compared to the pure phase sample produced in this study. Furthermore, the dimensionless figure of merit (ZT) has doubled from the previously reported value of 0.04–0.08. At 800 °C, the ZT value reaches 0.16, with a thermal conductivity of 1.25 W/(m·K). The addition of this novel raw material not only enhances the thermoelectric properties but also helps reduce production costs, demonstrating the material's potential for widespread applications in areas such as waste heat recovery and aerospace.