Hybrid microwave processing of Ca3Co4O9 thermoelectrics

In this study, hybrid microwave sintering of Ca3Co4O9 thermoelectric materials was implemented for the first time. Thermoelectric properties of samples sintered in different conditions and in conventional electrical furnace, using the same temperatures and dwell times, were assessed and compared. Microwave processing was found to promote densification and grain texturing in Ca3Co4O9 bulk ceramics, leading to a significant increase of the electrical conductivity. Seebeck coefficient and thermal conductivity were essentially unaffected by the microstructural changes. Prolonged exposure to microwave radiation at 800 °C led to partial phase decomposition and consequent formation of Ca3Co2O6 and Co3O4 impurities, with minor effect on the charge transport. Still, the significant presence of residual porosity suggests the need for further optimization of powder and microwave processing conditions.