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A misfit layer sulfide (BiS)1.2(TiS2)2 with a natural superlattice structure has been shown to be a promising thermoelectric material, but its high carrier concentration should be reduced so as to further optimize the thermoelectric performance. However, ordinary acceptor doping has not succeeded because of the non-parabolic band structure. In this paper, we have successfully doped chromium ions into the Ti sites, which can maintain or even enhance the high effective mass of electrons so as to effectively improve ZT value. X-ray diffraction analysis, coupled with X-ray photoelectron spectroscopy, shows that chromium has been substituted into titanium sites in TiS2 layers and confirms its ionic state. The chromium doping has successfully reduced the carrier concentration with the subsequent reduction of electrical conductivity. Unlike other acceptor dopants (alkaline earth metals), chromium also enhances Seebeck coefficient and the effective mass, which can possibly be attributed to the formation of additional resonant states near Fermi level. Though the power factor does not improve, the significant reduction in the electronic part of the thermal conductivity leads to a measurable improvement in ZT.


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Thermoelectric performance enhancement of (BiS)1.2(TiS2)2 misfit layer sulfide by chromium doping

Show Author's information Yulia Eka PUTRIaChunlei WANa,bRuizhi ZHANGcTakao MORIdKunihito KOUMOTO*,a,b( )
Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan
CREST, Japan Science and Technology Agency, Tokyo 102-0075, Japan
Department of Physics, State Key Laboratory of Photoelectric Technology and Functional Materials (Culture Base), Northwest University, Xi’an 710069, China
National Institute for Materials Science (NIMS), Tsukuba 305-0044, Japan

Abstract

A misfit layer sulfide (BiS)1.2(TiS2)2 with a natural superlattice structure has been shown to be a promising thermoelectric material, but its high carrier concentration should be reduced so as to further optimize the thermoelectric performance. However, ordinary acceptor doping has not succeeded because of the non-parabolic band structure. In this paper, we have successfully doped chromium ions into the Ti sites, which can maintain or even enhance the high effective mass of electrons so as to effectively improve ZT value. X-ray diffraction analysis, coupled with X-ray photoelectron spectroscopy, shows that chromium has been substituted into titanium sites in TiS2 layers and confirms its ionic state. The chromium doping has successfully reduced the carrier concentration with the subsequent reduction of electrical conductivity. Unlike other acceptor dopants (alkaline earth metals), chromium also enhances Seebeck coefficient and the effective mass, which can possibly be attributed to the formation of additional resonant states near Fermi level. Though the power factor does not improve, the significant reduction in the electronic part of the thermal conductivity leads to a measurable improvement in ZT.

Keywords:

thermoelectric, misfit layer sulfide, spark plasma sintering, electrical conductivity, thermal conductivity
Received: 08 December 2012 Revised: 15 January 2013 Accepted: 16 January 2013 Published: 06 April 2013 Issue date: March 2013
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Publication history

Received: 08 December 2012
Revised: 15 January 2013
Accepted: 16 January 2013
Published: 06 April 2013
Issue date: March 2013

Copyright

© The author(s) 2013

Acknowledgements

The authors thank Prof. Saki Sonoda from Kyoto Institute of Technology (KIT) for her generous advice.

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