Evaluation of soft chemistry methods to synthesize Gd-doped CaMnO3-d with improved thermoelectric properties
Ceramics of Ca0.96Gd0.04MnO3−d are prepared via different soft chemistry methods and the solid state route. The phase formation processes of the synthesized powders are compared, and the effects of powder morphology and sintering behavior on the microstructure and thermoelectric properties of the ceramics are investigated. Ceramic powders with particle size of 110 nm are obtained from soft chemistry routes. These powders show excellent phase purity and shrink at lower temperatures compared to solid state route powders. Dense ceramics with 1 µm mean grain size, homogeneous dopant distribution and good thermoelectric properties are obtained after sintering at 1200 °C. Soft chemistry synthesized samples show a figure of merit ZT = 0.14 at 700 °C. This is higher than the figure of merit of solid state route ceramics, due to a more homogeneous microstructure, better densification and, hence, improved electrical properties. The soft chemistry synthesis methods provide ceramics with comparable thermoelectric performances.