Preparations of CaRuO₃ Body by Plasma Sintering and Its Thermoelectric Properties

Abstract

Dense CaRuO₃ body was synthesized by spark plasma sintering (SPS) using CaCO₃ and RuO₂ powders. The second phases of CaO and RuO₂ were identified at the Ru to Ca molar ratio in the source powder (R_Ru/Ca) of 0.5 to 0.8 and at R_Ru/Ca=1.1 to 1.4, respectively. A non-stoichiometric solid solution range of bulk CaRuO₃ body was first found in the R_Ru/Ca range between 0.7 and 1.0. The density increased with increasing R_Ru/Ca and the highest density was 97% at R_Ru/Ca=1.4. The electrical conductivity (σ) decreased with increasing temperature, showing a metallic conduction behavior. The σ increased from 1×10⁵ to 5×10⁵ Sm⁻¹ with increasing R_Ru/Ca at room temperature (RT). The Seebeck coefficient (S) was around 25 to 35 μVK⁻¹ from RT to 1023 K independent of composition, exhibiting a p-type conduction. The thermal conductivity (κ) slightly increased with increasing temperature and showed the lowest value at R_Ru/Ca=1.0. The dimensionless figure of merit (ZT) had the maximum at R_Ru/Ca=1.1, and the highest ZT value was 0.034 at 1020 K.