Optimization of Solid-State-Reactions of Calcium Cobaltite Ca3Co4O9
- Calcium cobaltite is a promising p-type oxide thermoelectric material for high temperature applications due to its high figure of merit between 600 °C and 900 °C in air. The solid-state-reaction is well known for large scale powder synthesis of functional materials. As a high temperature process, the powder synthesis consumes a lot of energy. In different studies, different synthesis conditions were used for the preparation of calcium cobaltite powder. This study showed that a higher energy input (elevated temperatures, longer dwell times, or repeated calcinations) during powder synthesis does not increase but decrease the Seebeck coefficient and the electrical conductivity. The same correlation was determined for the densification. As a higher energy input leads to a larger grain size and therefore to a reduced sinter activity, it can be concluded that the thermoelectric properties are correlated with the sinter activity of the powder. These results can be used to minimize the energyCalcium cobaltite is a promising p-type oxide thermoelectric material for high temperature applications due to its high figure of merit between 600 °C and 900 °C in air. The solid-state-reaction is well known for large scale powder synthesis of functional materials. As a high temperature process, the powder synthesis consumes a lot of energy. In different studies, different synthesis conditions were used for the preparation of calcium cobaltite powder. This study showed that a higher energy input (elevated temperatures, longer dwell times, or repeated calcinations) during powder synthesis does not increase but decrease the Seebeck coefficient and the electrical conductivity. The same correlation was determined for the densification. As a higher energy input leads to a larger grain size and therefore to a reduced sinter activity, it can be concluded that the thermoelectric properties are correlated with the sinter activity of the powder. These results can be used to minimize the energy demand for the powder synthesis of Ca₃Co₄ O₉.…