Thermoelectric properties of alkaline earth ruthenates prepared by SPS

• Published in: Materials science & engineering. B, Solid-state materials for advanced technology Solid-state materials for advanced technology, 2009-04, Vol.161 (1), p.71-75
• Main Authors: Keawprak, Nittaya, Tu, Rong, Goto, Takashi
• Format: Article
• Language: English
• Subjects: BaRuO 3; CaRuO 3; Spark plasma sintering; Sr 2RuO 4; SrRuO 3; Thermoelectric property
• ISSN: 0921-5107; 1873-4944
• DOI: 10.1016/j.mseb.2008.12.026

Alkaline earth ruthenates ARuO 3 ( A = Ca, Sr and Ba) and Sr 2RuO 4 in a single phase were obtained at molar ratio of Ru to A, R Ru/ A = 1.0 and 0.5, respectively. A non-stoichiometric solid solution range was identified in the Ca–Ru–O system at R Ru/Ca = 0.7–1.0. The relative densities of CaRuO 3, SrRuO 3, BaRuO 3 and Sr 2RuO 4 compacted by spark plasma sintering (SPS) were 82%, 95%, 97% and 96%, respectively. The electrical conductivity ( σ) of ARuO 3 showed a metallic behavior whereas Sr 2RuO 4 exhibited a semiconducting behavior. The σ increased in the order of Sr 2RuO 4, BaRuO 3, CaRuO 3 and SrRuO 3. The Seebeck coefficient ( S) of ARuO 3 was around 25–40 μV K −1 and almost independent of temperature whereas that of Sr 2RuO 4 decreased with increasing temperature. The thermal conductivity ( κ) of ARuO 3 slightly increased with increasing temperature, whereas that of Sr 2RuO 4 decreased with increasing temperature. SrRuO 3 showed much higher κ than the other compounds. The highest dimensionless figure of merit (ZT) values of ARuO 3 were around 0.02–0.025 at 1023 K whereas Sr 2RuO 4 was 0.001 at 600 K.