Sol–Gel Synthesis of Ca_2.5Ag_0.3Yb_0.2Co₄O₉ Thermoelectric Materials: Mechanisms, Process Parameters, Structural Evolution, and Thermoelectrical Properties

This study meticulously investigates the synthesis and characterization of p-type Ca_2.5Ag_0.3Yb_0.2Co₄O₉ ceramic materials via the sol–gel method—a versatile and precise technique that yields homogeneous, finely grained powders. The synthesized materials were characterized using a range of techniques, including TG–DTA, FTIR, XRD, XPS, SEM, and TM, for comprehensive analysis. Thermoelectric performance was precisely evaluated by measuring the Seebeck coefficient, electrical resistivity, and power factor over a broad temperature spectrum. By incorporating Ag and Yb as dopants, the goal was to enhance electrical conductivity while preserving a high Seebeck coefficient, thereby boosting overall thermoelectric efficiency. At 800 °C, the p-type Ca_2.5Ag_0.3Yb_0.2Co₄O₉ ceramic material manifested a Seebeck coefficient of 262.03 µV/K, an electrical resistivity of 13.52 mΩ·cm, a thermal conductivity of 0.95 W/m·K, and a corresponding power factor of 0.51 mW/m·K². The results of this study offer vital insights into the ongoing evolution of high-performance thermoelectric materials for renewable energy transformation, particularly in the aviation sector, where optimizing waste heat recovery can significantly enhance overall operational efficiency.