Synthesis and Characterization of P-type Ca_2.5Ag_0.3Er_0.2Co₄O₉ Semiconducting Materials for Thermoelectric Generators

P-type Ca_2.5Ag_0.3Er_0.2Co₄O₉ ceramic materials were synthesized using the sol–gel method and characterized for their thermoelectric properties. The phase formation and structural integrity were confirmed using thermogravimetry–differential thermal analysis (TG-DTA), Fourier-transform infrared spectroscopy (FTIR), and x-ray diffraction (XRD). Microstructural analysis via scanning electron microscopy (SEM) revealed a well-densified grain morphology, while x-ray photoelectron spectroscopy (XPS) provided insights into the oxidation states of constituent elements. The thermoelectric performance was evaluated by measuring the Seebeck coefficient, electrical resistivity, and power factor over a range of temperatures. The optimized Ca_2.5Ag_0.3Er_0.2Co₄O₉ composition exhibited enhanced thermoelectric properties due to improved carrier transport and phonon scattering effects induced by Er and Ag doping. These results suggest the potential of Ca_2.5Ag_0.3Er_0.2Co₄O₉ as a promising candidate for high-temperature thermoelectric generators in waste heat recovery applications, particularly in aerospace environments.