Chemical solution preparation and in-depth structural, microstructural, and thermoelectric characterization of Ca _2.5 Ag _0.3 Dy _0.2 Co ₄ O ₉ semiconducting materials

The thermoelectric performance of Ca3Co4O9-based materials has been limited in the development of thermoelectric conversion devices due to their relatively low conversion efficiency. In this study, Ca2.5Ag0.3Dy0.2Co4O9 was synthesized via double Ca-site doping via a sol-gel method to modify the microstructure and enhance the thermoelectric properties for aerospace applications. The method enabled precise control over processing parameters, allowing nanostructuring and morphology tuning. Key synthesis steps included drying, combustion, calcination at 800°C, and sintering at 900°C. Thermal, structural, and chemical analyses, including DTA-TG, FTIR, XRD, and XPS, confirmed phase formation and dopant incorporation, while SEM revealed the expected grain morphology. Co-doping with Ag and Dy significantly improved the Seebeck coefficient and power factor. The material exhibited a Seebeck coefficient of 214.27 µV/K, electrical resistivity of 17.15 mΩ cm, and a peak power factor of 0.27 mW/m·K2 at 800°C, highlighting its thermoelectric potential.