Preparation and thermoelectric properties of rare-earth-metal-doped SrO(SrTiO3)n oxides

Rare-earth-metal-doped (Sr0.95R0.05)3Ti2O7 (R=Nd, Eu) bulk samples were prepared by a conventional solid state reaction and Spark Plasma Sintering (SPS). The effect of calcining temperature Tcal and atmosphere on the phase composition of samples were investigated. The results show that (Sr0.95R0.05)3Ti2O7(R=Eu) samples with pure Ruddlesden–Popper (RP) phases can be obtained at Tcal=1500 oC in the atmosphere consisting of mixture H2 and Ar with their volume ratio of 5:95. Thermoelectric property measurements (300K-1000K) indicate that both the electrical resistivity ρ and the absolute value of thermopower S increase with elevating temperature, showing a typical behavior of a degenerate semiconductor. In comparison, the Eu-doped samples have larger dimensionless figure of merit (ZT) than the Nd-doped samples at the temperatures below 550K. The largest ZT of (Sr0.95Nd0.05)3Ti2O7 obtained in the present study is 0.087 (at 919K).