Thermoelectric properties of metal-hexaborides

Thermoelectric properties of some metal hexaborides, MB₆ (M=Ca, Sr, Ce, Sm, and Yb), were examined from room temperature to 1073 K. Seebeck coefficients of the divalent hexaborides (CaB₆, SrB₆, and YbB₆) were large and negative ranging from -100 to -270 μV/K at 1073 K, while those of trivalent and intermediate-valent hexaborides (CeB₆ and SmB₆) were as small as several μV/K within the temperature range measured. Electrical conductivity of SrB₆ 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 CaB₆ with maintaining large negative Seebeck coefficient.