Nanocrystalline Thermoelectric Ca₃Co₄O₉ Ceramics by Sol−Gel Based Electrospinning and Spark Plasma Sintering

A novel technique is developed to process nanocrystalline Ca 3 Co 4 O 9 ceramics with much enhanced thermoelectric properties. Nanocrystalline Ca 3 Co 4 O 9 nanofibers are synthesized first using sol−gel based electrospinning, and then consolidated into bulk ceramics by spark plasma sintering with preferred grain orientation distribution and without substantial grain growth. The nanofiber-sintered ceramic has a grain size much smaller than that sintered from sol−gel synthesized powders with improved texture, and has simultaneously enhanced Seebeck coefficient, electric conductivity, and thermal resistivity, resulting in substantial enhancement in thermoelectric figure of merit ZT . This technique is promising for high-efficiency thermoelectric conversion of waste heat directly into electricity.