Preparation and analysis of Ca_2.6/2.5/2.4Ag_0.3Y_0.1/0.2/0.3Co₄O₉ semiconductor materials for thermoelectric devices in possible aerospace uses

This study focuses on the fabrication and characterization of Ca_2.6/2.5/2.4Ag_0.3Y_0.1/0.2/0.3Co₄O₉ ceramics for potential thermoelectric applications in the aerospace sector. The materials were synthesized via a sol-gel route using citric acid monohydrate as a gelation agent, with precursors dissolved in distilled water. The turbidity and pH of the solutions were monitored to ensure sol stability. Following gelation, the xerogels were dried at 200 °C for 2 h to remove residual moisture and volatiles. The dried powders were then calcined in air at 800 °C for 2 h to induce phase formation, and the resulting powders were sintered at 900 °C for 24 h to produce bulk p-type semiconductor pellets. A comprehensive characterization was conducted using DTA-TG, FTIR, XRD, XPS, SEM, and thermoelectric property measurements. FTIR, XRD, and XPS analyses confirmed the formation of phase-pure Ca₃Co₄O₉-based structures with successful Ag and Y doping. SEM revealed microstructures with well-developed grain morphologies. Thermoelectric measurements at 800 °C showed a Seebeck coefficient of 227.90 μV/K, electrical resistivity of 12.74 mΩ cm, and a maximum power factor of 0.41 mW/m·K². These findings suggest that the synthesized ceramics are promising candidates for use in high-temperature thermoelectric generators, particularly in aerospace applications.