Preparation and properties of SiC nanopowder/Ca₃Co₄O₉₊ composite thermoelectric ceramics by spark plasma sintering

Ca3Co4O9+delta compound thermoelectric ceramics with different SiC content were successfully prepared by spark plasma sintering. The effects of different SiC content on the phase structure, microstructure and thermoelectric properties of the Ca3Co4O9+delta composite thermoelectric ceramics were studied systematically. The experimental results show that SiC nanoparticles are evenly distributed in Ca3Co4O9+delta thermoelectric ceramics. The phase structure of Ca3Co4O9+delta thermoelectric ceramics is not changed by the composition of SiC nanoparticles. The grain size of composite ceramics gradually decreases with the increase of the composition amount of SiC nanoparticles. The electrical properties of SiC/Ca3Co4O9+delta composite thermoelectric ceramics show that the compound of SiC nanopowder has little effect on the Seebeck coefficient of composite thermoelectric ceramics. The conductivity of SiC/Ca3Co4O9+delta composite thermoelectric ceramics increases first and then decreases with increasing compound content of SiC. The thermal conductivity of the Ca3Co4O9+delta composite thermoelectric ceramics was first decreasing and then increasing with the increase compound content of SiC nanoparticle. A certain amount of SiC nanopowder enhances the carrier concentration of composite ceramics, produces more grain boundaries in ceramics, enhances phonon scattering, which improves the electrical conductivity and reduces thermal conductivity of composite ceramics. When the SiC content is 0.06 wt%, the conductivity and thermal efficiency of the SiC and Ca3Co4O9+delta composite thermoelectric ceramics are optimized simultaneously. When the temperature is 973 K, the ZT value of the composite thermoelectric ceramics reaches 0.21 at 923 K, which is 61.5% higher than that of the Ca3Co4O9+delta thermoelectric ceramics.