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

Abstract Ca 3 Co 4 O 9 (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·K 2 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 Δ T = 190 K. Graphical abstract