Sol–gel fabrication of thermoelectric P-type Ca_2.5Ag_0.3Ce_0.2Co₄O₉ materials for aerospace applications

The article provides a comprehensive description of the synthesis and characterization of Ca_2.5Ag_0.3Ce_0.2Co₄O₉ semiconducting ceramics for potential application in thermoelectric generators, particularly in the aerospace industry. These materials were synthesized using the sol–gel method, with distilled water serving as the solvent and citric acid monohydrate incorporated into expedited gel formation. The pH and turbidity values of solutions were monitored through a pH meter and turbidimeter, respectively. The produced xerogel was subjected to drying at 200°C for 2 h in an air atmosphere to remove residual moisture and volatile by-products. The desiccated powders were then heat-treated at 800°C for 2 h under ambient air conditions, yielding the final Ca_2.5Ag_0.3Ce_0.2Co₄O₉ compound. Thermal processing of the resulting pellets was carried out at 900°C for 24 h to fabricate bulk samples. Comprehensive characterization was performed to assess thermal, structural, microstructural, and thermoelectric behaviors via DTA-TG, XRD, XPS, SEM, and TM machines. It was found that at 800°C, a maximum power factor of.24 mW/m·K² was achieved, derived from a Seebeck coefficient of 214.30 µV/K and electrical resistivity of 19.05 mΩ·cm at the same temperature. The synthesized ceramic materials exhibit promising thermoelectric efficiency, making them suitable for thermoelectric generator production.