Thermoelectric properties of Sr-Ru-O compounds prepared by spark plasma sintering

Sr-Ru-O in the ratio of Ru to Sr (R-Ru/(Sr)) from 0.5 to 1.2 were prepared by spark plasma sintering (SPS) and the effect of composition on the electrical conductivity (sigma), thermal conductivity (kappa) and Seebeck coefficient (S) was investigated. All compositions yielded dense sintered mass with around 90-100% of a theoretical density. SrRuO3 and Sr2RuO4 in a single phase were obtained at R-Ru/Sr = 1.0 and 0.5, respectively. The second phases were identified, i.e., RuO2 and Ru at R-Ru/(Sr) > 1.0 and Sr3Ru2O7 and Sr2RuO4 at R-Ru/Sr < 1.0. The or increased with increasing R-Ru/Sr in the R-Ru/Sr range from 0.8 to 1.2 at room temperature exhibiting a metallic behavior, whereas the sigma showed a semiconducting behavior at RRu/Sr = 0.5. The K was around 2 to 7 Wm(-1) K-1 at R-Ru/Sr = 0.8 to 1.2 at room temperature and slightly increased with increasing temperature and R-Ru/Sr. The K decreased with increasing temperature at R-Ru/Sr = 0.5. The S was around 25-40 pV K-1 at room temperature, almost independent of compositions. The S slightly decreased with temperature at RRu/Sr = 0.8 to 1.0, whereas the S increased with temperature and showed a maximum around 500 to 600 K at RRu/Sr = 1.2. The S significantly decreased with increasing temperature at RRu/Sr = 0.5. The highest dimensionless figure of merit (ZT) was 0.06 at R-Ru/Sr = 1.2 at 600K.