Boosting the thermoelectric performance of Ca3Co4O9 ceramics through optimized precursor powder particle size

Abstract Ca₃Co₄O₉ (CCO349) is a promising p-type thermoelectric ceramic oxide with high thermoelectric power factor PF, and reasonable thermoelectric figure-of-merit zT. CCO349 bulk ceramics were prepared from precursor powders with average particle sizes d ₅₀ ranging from about 10 µm to 0.5 µm, and conventional sintering at 920 °C. Remarkably, ceramics made from powders with optimum d ₅₀ of 1 µm exhibit enhanced electrical conductivity σ _⊥ and power factor PF _⊥ of 11,100 S/m and 340 µW/m·K² at 800 °C, respectively. The ceramics exhibit anisotropic microstructures with Lotgering factors larger than 0.9, and anisotropic thermoelectric properties: the electrical conductivity σ _⊥ and power factor PF _⊥ are higher by 90% and 110% as compared to σ _‖ and PF _‖ at 800 °C, respectively, and the zT _⊥ reaches nearly 0.16 at 800 °C. Moreover, a transverse thermoelectric device was fabricated based on alternating layers of CCO349 and silver with a power output of 5 mW at ΔT = 190 K. Graphical abstract