Grain structure and thermal transport properties of TiNiSn1-xSbx and Ti1-yZryNiSn0.95Sb0.05 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 (κL) in Ti1-yZryNiSn0.95Sb0.05 via mass fluctuation scattering (y>20%) is observed. However, small amounts of Sb (x≤5%) in TiNiSn1-xSbx do not yield similar results. A non-systematic increase in κL in the TiNiSn1-xSbx series was observed, even with the amounts (x≤5%) of Sb-doping. Extensive investigations of the grain structure in these materials show that there is a direct correlation between κL 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.