Thermoelectric properties of electron doped SrO(SrTiO3)n (n=1,2) ceramics

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公開日
2009-05-18
資源種別
journal article
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  • Copyright (2009) American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior per　mission of the author and the American Institute of Physics.
DOI
  • 10.1063/1.3117943
公開者
American Institite of Physics

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説明

Crystal structure and thermoelectric properties of Nb^5+- and Ln^3+-(rare earth: La^3+, Nd^3+, S^3+, and Gd^3+) doped SrO(SrTiO3)n (n=1,2) ceramics, which were fabricated by conventional hot-pressing, were measured to clarify the effects of Ti^4+- and Sr^2+-site substitution on the thermoelectric properties. The thermal conductivities are very close between the n=1 and 2 phases either doped with Nb5^+ or Ln^3+ and decreased by ~60% at room temperature and ~30% at 1000 K as compared to that of SrTiO3, which is likely due to an enhanced phonon scattering at the SrO/ (SrTiO3)n (n=1,2) interfaces. The density of states effective mass md *(1.8.2.4 m0) and consequently the Seebeck coefficient \midS\mid in Nb^5+-doped samples are fairly smaller than those reported for SrTiO3, which probably resulted from a deterioration of DOS due to the formation of the singly degenerate a1g (Ti3dxy) orbital as the conduction band bottom, which should be induced by the distortion of TiO6 octahedra in (SrTiO3)n layers. However, in the Ln^3+-doped SrO(SrTiO3)2, the TiO6 octahedra were found to be restored, in contrast to the Nb5^+-doped, with a gradually increasing O.Ti.O bond angle in the (100) plane at high temperatures, which would lead to the formation of triply degenerate Ti 3d-t2g (dxy, dyz, and dxz) orbitals to cause a significant enhancement in md*(7.5 m0 at 1000 K) and consequently in \midS\mid . Accordingly, the maximum dimensionless figure of merit ZT~0.24 obtained in 5%-Gd^3+-doped SrO(SrTiO3)2 at 1000 K is about 70% larger than that of Nb-doped SrO(SrTiO3)2 (ZT1000 ~K0.14).

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