A new class of materials with promising thermoelectric properties: MNiSn (M = Ti, Zr, Hf)

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 hare been prepared and investigated for their thermoelectric properties. With thermopowers of about -200 mu V/K and resistivities of a few m Omega cm, power factors S-2/rho as high as 38 mu W/K(2)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 Zr1-xHfxNiSn, Zr1-xTixNiSn, and Hf1-xTixNiSn were formed. The figure of merit of Zr0.5Hf0.5NiSn at 700 K (ZT = 0.41) exceeds the end members ZrNiSn (ZT = 0.26) and HfNiSn (ZT = 0.22).