Transport properties of ZrNiSn-based intermetallics

Intermetallic compounds of the form MNiSn, where M is titanium, zirconium, or hafnium, are semiconductors with band gaps on the order of 0.2 electron volts. Due to their large conduction band masses, they show promise as thermoelectric materials with high figure of merit. In order to assess this potential, we have studied the thermoelectric properties of pure and doped ZrNiSn and Zr_0.5Hf_0.5NiSn mixed crystals. Upon doping with Sb the resistivity can be reduced by a factor of 20-40 with a reduction in the Seebeck coefficient of only a factor of two. The resulting power factors of doped samples at room temperature are comparable to those of state of the art thermoelectric materials. The thermal conductivity of Zr_0.5Hf_0.5NiSn is reduced strongly relative to ZrNiSn but must be reduced further to obtain a large figure of merit. The transport properties of these materials are very sensitive to annealing conditions