High-Temperature Thermoelectric Behaviors of Fine-Grained Gd-Doped CaMnO₃Ceramics

Gd-doped CaMnO3 were synthesized by two methods: a coprecipitation route and a conventional solid-state reaction. The ceramic samples obtained by the coprecipitation method possess nanometer-scale grains but the grain sizes by the solid-state reaction route are several micrometers. Our results show that the electrical conductivity is slightly decreased with a decreasing grain size, which indicates that fine-grained ceramics can maintain good electrical property. However, thermal conductivity values of the fine-grained sample are relatively low due to the enhancement of grain boundary scattering. The highest dimensionless figure of merit ZT=0.24 has been obtained at 973 K in the air for fine-grained Ca0.96Gd0.04MnO3, suggesting that they can be a promising candidate of n-type material for high-temperature thermoelectric application.