Research Article
Reduction of Lattice Thermal Conductivity in PbTe Induced by
Artificially Generated Pores
Jae-Yeol Hwang,
1
Eun Sung Kim,
1
Syed Waqar Hasan,
2
Soon-Mok Choi,
3
Kyu Hyoung Lee,
4
and Sung Wng Kim
2
1
Center for Integrated Nanostructure Physics, Institute for Basic Science (IBS), Sungkyunkwan University,
Suwon 440-746, Republic of Korea
2
Department of Energy Science, Sungkyunkwan University, Suwon 440-746, Republic of Korea
3
School of Energy, Materials and Chemical Engineering, Korea University of Technology and Education,
Cheonan 330-708, Republic of Korea
4
Department of Nano Applied Engineering, Kangwon National University, Chuncheon 200-701, Republic of Korea
Correspondence should be addressed to Kyu Hyoung Lee; khlee2014@kangwon.ac.kr and Sung Wng Kim; kimsungwng@skku.edu
Received 24 November 2014; Revised 25 February 2015; Accepted 25 February 2015
Academic Editor: Ram N. P. Choudhary
Copyright © 2015 Jae-Yeol Hwang et al. is is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Highly dense pore structure was generated by simple sequential routes using NaCl and PVA as porogens in conventional PbTe
thermoelectric materials, and the effect of pores on thermal transport properties was investigated. Compared with the pristine
PbTe, the lattice thermal conductivity values of pore-generated PbTe polycrystalline bulks were significantly reduced due to the
enhanced phonon scattering by mismatched phonon modes in the presence of pores (200 nm–2 m) in the PbTe matrix. We
obtained extremely low lattice thermal conductivity (∼0.56 W m
−1
K
−1
at 773 K) in pore-embedded PbTe bulk aſter sonication for
the elimination of NaCl residue.
1. Introduction
ermal energy can be directly converted into electrical
energy and vice versa through the flow of charge carriers
in solid-state without any moving parts using thermoelectric
(TE) materials [1, 2]; thus TE is focused as a key technology
for renewable energy harvesting and solid-state refrigeration.
Since the efficiency of TE device is directly determined by
the performance of TE materials (), which is defined as
=
2
/, where is the Seebeck coefficient, is
the electrical conductivity, and is the thermal conductivity
at a given absolute temperature , researches have been
mainly concentrated on discovering new concepts as well
as experimental approaches to enhance . Breaking the
trade-off between and by reducing the lattice thermal
conductivity (
latt
) is one of the most effective approaches due
to the relative easiness of controlling
latt
without significantly
affecting the carrier transport. In conventional TE materials
such as Bi
2
Te
3
, PbTe, and SiGe, the perturbations of structural
arrangements for enhancing phonon scattering through
nanostructuring and/or solid-solution alloying have been
shown to be one of the effective ways to minimizing
latt
[3–
8]. Recent experimental and theoretical results confirm that
reduced
latt
can be attained by the following mechanisms:
alloy scattering [3–6], resonant scattering [9–13], anharmonic
scattering [14], and interface scattering of phonons [15–17] or
their combination.
Noninvasive formation of phonon scattering centers is
another effective way to generate effective phonon scatter-
ing without altering the framework of TE materials and
introducing other elements. One promising approach is the
formation of nanoscale pore structure since such defect can
be effective phonon scattering centers without sacrificing
electronic transport properties ( and ). How to control the
dimension as well as distribution of pores is crucial to deter-
mine the frequency dependence of scattering mechanism for
heat-carrying phonons [7–9]. Practically, it is important to
make randomly distributed pores in the TE matrix through
Hindawi Publishing Corporation
Advances in Condensed Matter Physics
Volume 2015, Article ID 496739, 6 pages
http://dx.doi.org/10.1155/2015/496739