Preparations of CaRuO<SUB>3</SUB> 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 (RRu/Ca) of 0.5 to 0.8 and at RRu/Ca=1.1 to 1.4, respectively. A non-stoichiometric solid solution range of bulk CaRuO3 body was first found in the RRu/Ca range between 0.7 and 1.0. The density increased with increasing RRu/Ca and the highest density was 97% at RRu/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 RRu/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 RRu/Ca=1.0. The dimensionless figure of merit (ZT) had the maximum at RRu/Ca=1.1, and the highest ZT value was 0.034 at 1020 K.