A New Class of Materials with Promising Thermoelectric Properties: MNiSn (M = Ti, Zr, Hf)

Abstract

TiNiSn, ZrNiSn and HfNiSn are members of a large group of intermetallic compounds which crystallize in the cubic MgAgAs-type structure. Polycrystalline samples of these compounds have been prepared and investigated for their thermoelectric properties. With thermopowers of about −200 µV/K and resistivities of a few mΩcm, power factors S²/p as high as 38 ΩW/K² cm were obtained at 700 K. These remarkably high power factors are, however, accompanied by a thermal conductivity which is too high for applications. In order to reduce the parasitic lattice thermal conductivity, solid solutions Zr_l−xHf_xNiSn, Zr_l−xTi_xNiSn, and Hf_l−xTi_xNiSn were formed. The figure of merit of Zr_0.5Hf_0.5NiSn at 700 K (ZT = 0.41) exceeds the end members ZrNiSn (ZT = 0.26) and HfNiSn (ZT = 0.22).