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 (κ_L) in Ti_1-yZr_yNiSn_0.95Sb_0.05 via mass fluctuation scattering (y>20%) is observed. However, small amounts of Sb (x≤5%) in TiNiSn_1-xSb_x do not yield similar results. A non-systematic increase in κ_L in the TiNiSn_1-xSb_x 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 κ_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.