Preparation of AgNPs/Ca3Co4O9 nanocomposites with enhanced thermoelectric performance

Ca3Co4O9 polycrystalline thermoelectric ceramics with small amounts of silver nanoparticles (AgNPs) have been fabricated by spark plasma sintering (SPS) directly from the mixture of AgNPs prepared by wet chemical method and Ca3Co4O9 powders synthesized by solid-state reaction. The effects of AgNPs introducing on the morphology and thermoelectric properties have been investigated in detail. By this route, we achieve a lower thermal conductivity due to the increased phonon scattering, decreasing from 3.1 W/m(Ca3Co4O9) to 1.6 W/m(AgNPs/Ca3Co4O9) at 700 K. Besides, the nano-sized AgNPs effectively strengthen the p-type Ca3Co4O9 grain orientation (from 0.5 to 0.7), leading to a significant enhancement of the electrical conductivity. As a result, the Ca3Co4O9 sample containing 2.0 vol% AgNPs exhibits an exceedingly enhanced ZT value at 700 K, which is about 5 times higher than that of pure bulk Ca3Co4O9. The results demonstrate that introducing nanoparticles as a second nano-phase is a promising route to optimize the thermoelectric performance of Ca3Co4O9.