急冷法で作った化合物 (Bi_1-xSb_x)₂(Te_1-ySe_y)₃の熱伝導率

抄録

A number of (Bi_1-xSb_x)₂(Te_1-ySe_y)₃ compounds were prepared from melts of stoichiometric composition by the quenched technique. Thermal conductivity was determined at room temperature by a comparison method, and the lattice thermal conductivity was obtained by using the observed values of the Seebeck coefficient and electrical conductivity which are reported by Yokota et al. in the preceding paper.The lattice thermal conductivity at high temperature is derived by using the Ktemens-Callaway theory. It is assumed that the reciprocal relaxation times depend on the fourth power of phonon frequency ω in the scattering process due tostrain and mass point defects and on ω² in normal and umklapp process of the three phonon anharmonic scatter. In many compounds, experimental values of the lattice thermal conductivity agree with values calculated from the above theory. It is found that the lattice thermal conductivity is mainly governed by strain scatter rather than mass defect scatter. In the case of the compounds rich in Sb₂Se₃, experimental values are smaller than those calculated from the above theory. Additional phonon scatter by localized mode of point defects, as discussed by Wagner, is used to explain the experimental data. The experimental values of the lattice thermal conductivity of intrinsic materials are not particularly large relative to that of other compounds. Therefore, it seems that ambipoler diffusion has no effect on thermal conductivities ofintrinsic materials, since capture centers of electron and hole are considered to exist in those compounds.