Thermoelectric properties of metal-hexaborides

Thermoelectric properties of some metal hexaborides, MB/sub 6/ (M=Ca, Sr, Ce, Sm, and Yb), were examined from room temperature to 1073 K. Seebeck coefficients of the divalent hexaborides (CaB/sub 6/, SrB/sub 6/, and YbB/sub 6/) were large and negative ranging from -100 to -270 /spl mu/V/K at 1073 K, while those of trivalent and intermediate-valent hexaborides (CeB/sub 6/ and SmB/sub 6/) were as small as several /spl mu/V/K within the temperature range measured. Electrical conductivity of SrB/sub 6/ was the largest among the divalent hexaborides, and the dimensionless figure-of-merit of it reached to approximately 0.3 at 1073 K. Substitution of part of Ca sites with Yb reduced thermal conductivity of CaB/sub 6/ with maintaining large negative Seebeck coefficient.