Tailoring Ca3Co4O9 microstructure and performances using a transient liquid phase sintering additive

A flexible, adaptable, economical and easily scalable processing route, allowing microstructural control, is presented. It involves classical solid state sintering method and addition of liquid promoting compound. Controlled porosity and high thermoelectric performance have been attained in Ca3Co4O9 by K2CO3 additions, drastically improving the sintering procedure. K2CO3 behaves as transient liquid phase, providing microstructural benefits, vanishing during sintering. Electrical resistivity was improved by enhanced grains connectivity and growth. Significant increase in Seebeck coefficient at high temperatures has been produced while lattice thermal conductivity was unaffected. The best ZT value, estimated at 800 °C, assuming the thermal conductivity value at 140 °C, is 0.35 for 5 wt.% K2CO3 samples. These values are significantly higher than that obtained in highly-dense textured materials at the same temperature. The results suggest that this approach is very effective for preparing highly-performing Ca3Co4O9-based thermoelectric materials with relatively high porosity to control thermal conductivity.