Effect of substitution on the transport properties of the half-Heusler alloy ZrNiSn

Substituted semiconductor alloys exhibit effects due to doping and disorder. To focus on the effect of disorder on transport properties, we have investigated isoelectronic Zr/sub 1-x/Hf/sub x/NiSn (x=0.0-0.3) and heavily substituted Zr/sub 0.5/Hf/sub 0.5/Ni/sub 0.7/Pd/sub 0.3/Sn/sub 0.95/, half Heusler alloys. Upon substitution, Zr/sub 1-x/Hf/sub x/NiSn alloys exhibit resistivity ratios R=/spl rho//sub 4.2K///spl rho//sub 295K/ as large as /spl sim/300 and thermally activated conduction in the temperature range 100-295K. At 4.2K, the (Zr,Hf)NiSn alloys possess carrier densities of /spl sim/10/sup 16/ to 10/sup 18/ cm/sup -3/ and carrier mobilities in the range /spl sim/100-350 cm/sup 2//V-s. The opposite signs exhibited by the Hall coefficient and thermopower, along with the saturation of resistivity at low temperature in ZrNiSn and Zr/sub 0.5/Hf/sub 0.5/Ni/sub 0.7/Pd/sub 0.3/Sn/sub 0.95/ alloys indicate band overlapping. Various scenarios of bandgap structures are discussed.