Thermoelectric nanocomposite from the metastable void filling in caged skutterudite
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report a novel approach to realize the formation of well-distributed nanodispersions in n-type filled skutterudite through the manipulation of metastable void fillers by a designed sophisticated process of materials synthesis. Metastable Ga filling in CoSb3 is proved to happen at high temperature. The subsequent controlled annealing procedure drives Ga out of the crystal voids and finally leads to the homogeneous dispersion of GaSb nanodots with an average size of 11 nm in CoSb3 matrix. The grain size of nanodispersions can be manipulated by the controlled cooling procedure. The well-distributed nanodispersions are observed to enhance Seebeck coefficients and reduce lattice thermal conductivity at low temperature. Therefore, the thermoelectric performance of nanocomposite is improved in the whole temperature range. The highest figure of merit (ZT) is obtained to be 1.45 at 850 K, and an average ZT of 0.99 in 300850 K is achieved for Yb0.26Co4Sb12/ 0.2GaSb nanocomposite.
These authors contributed equally to the work. Address all correspondence to these authors. b) e-mail: [email protected] c) e-mail: [email protected] DOI: 10.1557/jmr.2011.90
Co4Sb12/InSb20 systems, also resulting in the size of dispersions or agglomerations always at hundred nanometers or larger. Since the nanoscattering effect is strongly dependent on the microstructure of nanocomposite, such as distribution, grain size, content of the nanoinclusions, and the interface matching of nanoinclusion with the matrix, introducing homogeneously dispersed nanoinclusions is the key factor to fabricate filled-skutterudite nanocomposite with enhanced TE performance. In filled skutterudites, filling atoms that possess weak bands with Sb atoms in the cage framework were regarded as effective scattering centers to phonons because of the “rattling” effects. Present researches have been only concentrated on the stable fillers, such as rare earth metals12,21 or alkaline earth metals,22,23 which fill the voids in the annealing period about 950–1080 K, and is thermodynamically stable in the application temperature range of CoSb3 (below 850 K). However, some special fillers, which can fill into the voids at high temperature but leave out the voids as temperature is lowered, may be ideal sources to form nanoinclusions in an in situ way. These elements may exist in pure element phase or filler-related nanoscale compounds. To realize this picture, three factors should be considered. (i) The filler atoms can be filled into the voids at high temperature, but the filled phase in not thermodynamically stable at low temperature. In other words, this filling behavior is in a metastable way; (ii) The nanoinclusions made from the fillers should be inert to the matrix of CoSb3 in the application temperature range (below 850 K); (iii) The metastable void filling, even the grain size of
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Ó Materials Research Society 2011
I. INTRODUCTION
Recent work on thermoelectric (TE) materials has demonstrated that nanosized dispersions in a matrix could introduce novel effects, such as ther
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