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

Yifeng Wang, Kyu Hyoung Lee, Hiromichi Ohta, Kunihito Koumoto

Research output: Contribution to journalArticle

60 Citations (Scopus)

Abstract

Crystal structure and thermoelectric properties of Nb5+ - and Ln 3+ -(rare earth: La3+, Nd3+, Sm3+, and Gd3+) doped SrO (SrTiO3)n (n=1,2) ceramics, which were fabricated by conventional hot-pressing, were measured to clarify the effects of Ti4+ - and Sr2+ -site substitution on the thermoelectric properties. The thermal conductivities are very close between the n=1 and 2 phases either doped with Nb5+ or Ln3+ 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 S in Nb5+ -doped samples are fairly smaller than those reported for SrTiO 3, which probably resulted from a deterioration of DOS due to the formation of the singly degenerate a1g (Ti 3 dxy) orbital as the conduction band bottom, which should be induced by the distortion of TiO 6 octahedra in (SrTiO3)n layers. However, in the Ln3+ -doped SrO (SrTiO3)2, the TiO 6 octahedra were found to be restored, in contrast to the Nb 5+ -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 d xz) orbitals to cause a significant enhancement in md (∼7.5 m0 at 1000 K) and consequently in S. Accordingly, the maximum dimensionless figure of merit ZT∼0.24 obtained in 5% -Gd3+ -doped SrO (SrTiO 3) 2 at 1000 K is about 70% larger than that of Nb-doped SrO (SrTiO3)2 (ZT1000 K ∼0.14).

Original languageEnglish
Article number103701
JournalJournal of Applied Physics
Volume105
Issue number10
DOIs
Publication statusPublished - 2009 Jun 11

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ceramics
orbitals
hot pressing
Seebeck effect
deterioration
figure of merit
conduction bands
electrons
thermal conductivity
rare earth elements
substitutes
crystal structure
augmentation
causes
room temperature
scattering

All Science Journal Classification (ASJC) codes

  • Physics and Astronomy(all)

Cite this

Wang, Yifeng ; Lee, Kyu Hyoung ; Ohta, Hiromichi ; Koumoto, Kunihito. / Thermoelectric properties of electron doped SrO (SrTiO3) n (n=1,2) ceramics. In: Journal of Applied Physics. 2009 ; Vol. 105, No. 10.
@article{6b24501afa5c4450817dda3215f3c27e,
title = "Thermoelectric properties of electron doped SrO (SrTiO3) n (n=1,2) ceramics",
abstract = "Crystal structure and thermoelectric properties of Nb5+ - and Ln 3+ -(rare earth: La3+, Nd3+, Sm3+, and Gd3+) doped SrO (SrTiO3)n (n=1,2) ceramics, which were fabricated by conventional hot-pressing, were measured to clarify the effects of Ti4+ - and Sr2+ -site substitution on the thermoelectric properties. The thermal conductivities are very close between the n=1 and 2 phases either doped with Nb5+ or Ln3+ 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 S in Nb5+ -doped samples are fairly smaller than those reported for SrTiO 3, which probably resulted from a deterioration of DOS due to the formation of the singly degenerate a1g (Ti 3 dxy) orbital as the conduction band bottom, which should be induced by the distortion of TiO 6 octahedra in (SrTiO3)n layers. However, in the Ln3+ -doped SrO (SrTiO3)2, the TiO 6 octahedra were found to be restored, in contrast to the Nb 5+ -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 d xz) orbitals to cause a significant enhancement in md (∼7.5 m0 at 1000 K) and consequently in S. Accordingly, the maximum dimensionless figure of merit ZT∼0.24 obtained in 5{\%} -Gd3+ -doped SrO (SrTiO 3) 2 at 1000 K is about 70{\%} larger than that of Nb-doped SrO (SrTiO3)2 (ZT1000 K ∼0.14).",
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Thermoelectric properties of electron doped SrO (SrTiO3) n (n=1,2) ceramics. / Wang, Yifeng; Lee, Kyu Hyoung; Ohta, Hiromichi; Koumoto, Kunihito.

In: Journal of Applied Physics, Vol. 105, No. 10, 103701, 11.06.2009.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Thermoelectric properties of electron doped SrO (SrTiO3) n (n=1,2) ceramics

AU - Wang, Yifeng

AU - Lee, Kyu Hyoung

AU - Ohta, Hiromichi

AU - Koumoto, Kunihito

PY - 2009/6/11

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N2 - Crystal structure and thermoelectric properties of Nb5+ - and Ln 3+ -(rare earth: La3+, Nd3+, Sm3+, and Gd3+) doped SrO (SrTiO3)n (n=1,2) ceramics, which were fabricated by conventional hot-pressing, were measured to clarify the effects of Ti4+ - and Sr2+ -site substitution on the thermoelectric properties. The thermal conductivities are very close between the n=1 and 2 phases either doped with Nb5+ or Ln3+ 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 S in Nb5+ -doped samples are fairly smaller than those reported for SrTiO 3, which probably resulted from a deterioration of DOS due to the formation of the singly degenerate a1g (Ti 3 dxy) orbital as the conduction band bottom, which should be induced by the distortion of TiO 6 octahedra in (SrTiO3)n layers. However, in the Ln3+ -doped SrO (SrTiO3)2, the TiO 6 octahedra were found to be restored, in contrast to the Nb 5+ -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 d xz) orbitals to cause a significant enhancement in md (∼7.5 m0 at 1000 K) and consequently in S. Accordingly, the maximum dimensionless figure of merit ZT∼0.24 obtained in 5% -Gd3+ -doped SrO (SrTiO 3) 2 at 1000 K is about 70% larger than that of Nb-doped SrO (SrTiO3)2 (ZT1000 K ∼0.14).

AB - Crystal structure and thermoelectric properties of Nb5+ - and Ln 3+ -(rare earth: La3+, Nd3+, Sm3+, and Gd3+) doped SrO (SrTiO3)n (n=1,2) ceramics, which were fabricated by conventional hot-pressing, were measured to clarify the effects of Ti4+ - and Sr2+ -site substitution on the thermoelectric properties. The thermal conductivities are very close between the n=1 and 2 phases either doped with Nb5+ or Ln3+ 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 S in Nb5+ -doped samples are fairly smaller than those reported for SrTiO 3, which probably resulted from a deterioration of DOS due to the formation of the singly degenerate a1g (Ti 3 dxy) orbital as the conduction band bottom, which should be induced by the distortion of TiO 6 octahedra in (SrTiO3)n layers. However, in the Ln3+ -doped SrO (SrTiO3)2, the TiO 6 octahedra were found to be restored, in contrast to the Nb 5+ -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 d xz) orbitals to cause a significant enhancement in md (∼7.5 m0 at 1000 K) and consequently in S. Accordingly, the maximum dimensionless figure of merit ZT∼0.24 obtained in 5% -Gd3+ -doped SrO (SrTiO 3) 2 at 1000 K is about 70% larger than that of Nb-doped SrO (SrTiO3)2 (ZT1000 K ∼0.14).

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