High Band Degeneracy Contributes to High Thermoelectric Performance in p-Type Half-Heusler Compounds

Half-Heusler (HH) compounds are important high temperature thermoelectric (TE) materials and have attracted considerable attention in the recent years. High figure of merit zT values of 0.8 to 1.0 have been obtained in n-type ZrNiSn-based HH compounds. However, developing high performance p-type HH compounds are still a big challenge. Here, it is shown that a new p-type HH alloy with a high band degeneracy of 8, Ti-doped FeV_(0.6)Nb_(0.4)Sb, can achieve a high zT of 0.8, which is one of the highest reported values in the p-type HH compounds. Although the band effective mass of this system is found to be high, which may lead to a low mobility, its low deformation potential and low alloy scattering potential both contribute to a reasonably high mobility. The enhanced phonon scattering by alloying leads to a reduced lattice thermal conductivity. The achieved high zT demonstrates that the p-type Ti doped FeV_(0.6)Nb_(0.4) Sb HH alloys are promising as TE materials and offer an excellent TE performance match with n-type ones for high temperature power generation.