Grain structure and thermal transport properties of TiNiSn/sub 1-x/Sb/sub x/ and Ti/sub 1-y/Zr/sub y/NiSn/sub 0.95/Sb/sub 0.05/ half-Heusler alloys

Thermal conductivity of two series of Ti-based half-Heusler alloys have been investigated and compared. A significant reduction in the lattice thermal conductivity (/spl kappa//sub L/) in Ti/sub 1-y/Zr/sub y/NiSn/sub 0.95/Sb/sub 0.05/ via mass fluctuation scattering (y>20%) is observed. However, small amounts of Sb (x/spl les/5%) in TiNiSn/sub 1-x/Sb/sub x/ do not yield similar results. A non-systematic increase in /spl kappa//sub L/ in the TiNiSn/sub 1-x/Sb/sub x/ series was observed, even with the amounts (x/spl les/5%) of Sb-doping. Extensive investigations of the grain structure in these materials show that there is a direct correlation between /spl kappa//sub L/ and the average grain size in these materials. These results are in good agreement with the theoretical predictions of Goldsmid et al. Theoretical calculations relating to the phonon mean free path in both the series of compounds would also be presented and discussed.