Synthesis and Characterization of P-type Ca2.5Ag0.3Er0.2Co4O9 Semiconducting Materials for Thermoelectric Generators

P -type Ca 2.5 Ag 0.3 Er 0.2 Co 4 O 9 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 2.5 Ag 0.3 Er 0.2 Co 4 O 9 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 2.5 Ag 0.3 Er 0.2 Co 4 O 9 as a promising candidate for high-temperature thermoelectric generators in waste heat recovery applications, particularly in aerospace environments.