Significant reduction in processing time for Ca_0.95Ce_0.05MnO₃ thermoelectric ceramics

Attrition-milling process has been applied to Ce-doped CaMnO3 precursors to obtain small grain-size powders. The use of Ce4+ as dopant instead a Rare Earth(3+) has allowed decreasing by 50% the atomic proportion of dopant, to obtain equivalent charge carrier concentration, which is required for attaining promising properties for thermoelectric applications. An impressive decrease in thermal processing time was achieved, together with an increase in thermoelectric performances, when compared to classically prepared materials. XRD and SEM analysis have confirmed that the final material is nearly single phase. Moreover, grain sizes and density increase with the sintering duration. These microstructural differences are reflected in a significant decrease in electrical resistivity, when compared to the samples prepared from ball-milled precursors (used as reference), without drastically modifying the Seebeck coefficient values. On the other hand, despite of their high electrical conductivity, thermal conductivity is decreased for short time sintered materials, leading to the highest ZT values at 800 degrees C (similar to 0.27) in samples sintered for 1 h at 1310 degrees C. These values are among the best reported in the literature, but they have been obtained in very short time using a simple, and easily scalable process. The suggested approach presented in this work appears particularly promising for large-scale production of oxide-based thermoelectric modules for power generation.