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

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

doi:10.1063/1.3117943

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

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

Department of Materials Science and Engineering

Research output: Contribution to journal › Article › peer-review

67 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 d_xy) 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- t_2g (d_xy, d_yz, 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 language	English
Article number	103701
Journal	Journal of Applied Physics
Volume	105
Issue number	10
DOIs	https://doi.org/10.1063/1.3117943
Publication status	Published - 2009

Bibliographical note

Funding Information:
We all the authors are deeply indebted to Dr. Hideki Hyuga and Dr. Hideki Kita at National Institute of Advanced Industrial Science and Technology (AIST), Japan, for their technical support in hot-pressing process and to Dr. Katsuhiko Inaba (Rigaku Co.) for his great job of high temperature XRD measurements. Meanwhile, the first author would like to express his heartfelt gratitude to Nature COE program and Global COE program of Nagoya University for their financial support during the research.

All Science Journal Classification (ASJC) codes

Physics and Astronomy(all)

Access to Document

10.1063/1.3117943

Cite this

@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).",

author = "Yifeng Wang and Lee, {Kyu Hyoung} and Hiromichi Ohta and Kunihito Koumoto",

note = "Funding Information: We all the authors are deeply indebted to Dr. Hideki Hyuga and Dr. Hideki Kita at National Institute of Advanced Industrial Science and Technology (AIST), Japan, for their technical support in hot-pressing process and to Dr. Katsuhiko Inaba (Rigaku Co.) for his great job of high temperature XRD measurements. Meanwhile, the first author would like to express his heartfelt gratitude to Nature COE program and Global COE program of Nagoya University for their financial support during the research.",

year = "2009",

doi = "10.1063/1.3117943",

language = "English",

volume = "105",

journal = "Journal of Applied Physics",

issn = "0021-8979",

publisher = "American Institute of Physics Publising LLC",

number = "10",

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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

N1 - Funding Information: We all the authors are deeply indebted to Dr. Hideki Hyuga and Dr. Hideki Kita at National Institute of Advanced Industrial Science and Technology (AIST), Japan, for their technical support in hot-pressing process and to Dr. Katsuhiko Inaba (Rigaku Co.) for his great job of high temperature XRD measurements. Meanwhile, the first author would like to express his heartfelt gratitude to Nature COE program and Global COE program of Nagoya University for their financial support during the research.

PY - 2009

Y1 - 2009

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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