Thermoelectric properties of divalent hexaborides

Thermoelectric and transport properties of divalent hexaborides (MB₆: M=Ca, Sr, Ba) were examined to discuss the possibility of further improvement in their thermoelectric performance. Hall measurements showed that carrier concentration of the BaB₆ was the highest among the three hexaborides and that of CaB₆ was the lowest. Substitution of part of the alkaline earth metals with one of the others changed the carrier concentration. As the carrier concentration increased, Seebeck coefficient increased and electrical conductivity decreased, while the carrier mobility was almost unchanged. These results suggest that the thermoelectric properties of the divalent hexaborides depend largely on the carrier concentration. Consequently, such a substitution enables us to control Seebeck coefficient and electrical conductivity of the hexaborides, and will also be effective to reduce the lattice heat conduction due to the alloying effect.