Fabrication and thermoelectric properties of heavily rare-earth metal-doped SrO(SrTiO3)n (n = 1, 2) ceramics

To clarify the effect of substitutional electron doping on the thermoelectric figure of merit (ZT = S2σTκ−1) of Ruddlesden–Popper phase SrO(SrTiO3)n (or Srn+1TinO3n+1), measurements were conducted for several thermoelectric parameters, e.g. electrical conductivity (σ), Seebeck coefficient (S) and thermal conductivity (κ), of (Sr1−xREx)n+1TinO3n+1 (n = 1 or 2, RE (rare earth): La or Nd, x = 0.05 and 0.1) dense ceramics prepared by a conventional solid-state reaction and hot-pressing technique. Crystal structures of the resultant ceramics were represented as (Sr1−xREx)n+1 TinO3n+1 evaluated by powder X-ray diffraction followed by the Rietveld analysis. All the ceramics exhibited electrical conductivity and the σ values simply depended on the dopant concentration, indicating that both La3+ and Nd3+ ions act as electron donors. The |S| values increased with temperature due to decrease in the chemical potential. Significant reduction of the κ values was observed as compared to cubic-perovskite SrTiO3. The ZT value increased with temperature and reached 0.15 at 1000 K for (Sr0.95La0.05)3Ti2O7.