High-performance Thermoelectric Materials Prepared by MG or MA Technique

Abstract

We have examined the thermoelectric properties of Co_1-xFe_xSb₃ ternary system and CoSb₃-FeSb₂ composite system. The Seebeck coefficient and the electrical resistivity are generallyreduced by the substitution for Co by Fe. The thermal conductivity is also reduced by the substitution especially at high iron content region. These behaviors of the thermoelectric properties in the samples with low iron content are ascribed to the substituted Fe, while those in the samples with high iron content are ascribed to the precipitated FeSb₂ (Fe_0.73Co_0.27Sb₂) compound. Co_0.75 Fe_0.25Sb₃ has a maximum value of figure of merit of 4.8×10^-4 K^-1 at 773K. For the purpose of more reducing of the thermal conductivity, we have prepared the CoSb₃-FeSb₂ composite where the FeSb₂ particles are dispersed in the CoSb₃ matrix by MG (mechanical grinding) technique. The thermal conductivity of the composite is smaller than that of Co_1-xFe_xSb₃. The electrical resistivity of the composite increases with increasing MG time, but it is smaller than that of CoSb₃ at high temperature. The decrease of the thermal conductivity and the less increase of the electrical resistivity are ascribed to the enhancement of the phonon scattering caused by the dispersed FeSb₂ in the matrix and the low electrical resistivity of FeSb₂, respectively. As a result, the composite whose molar ratio of CoSb₃ to FeSb₂ is 0.7 to 0.3 and MG time is 25h has a maximum value of figure of merit of 6.1×10^-4 K^-1 at 756K. This value is larger than the maximum value of 4.8×10^-4 K^-1 for Co_1-xFe_xSb₃ system.