Enhanced Thermoelectric Properties in p‐Type Double Half‐Heusler Ti 2− y Hf y FeNiSb 2− x Sn x Compounds

Double half‐Heusler Ti 2 FeNiSb 2 ‐based compounds, which can be regarded as a combination of 17‐electron TiFeSb and 19‐electron TiNiSb, have a lower intrinsic thermal conductivity due to the smaller group velocity phonons and the disordered scattering by Fe/Ni. An enhanced room‐temperature Hall carrier concentration of ≈4.8 × 10 21  cm −3 is achieved by doping Sn on the Sb site in a series of Ti 2 FeNiSb 2− x Sn x ( x  = 0.2, 0.3, 0.4, and 0.5) samples. Combined with the further decreased lattice thermal conductivity by alloying with Hf 2 FeNiSb 2 , a low lattice thermal conductivity of ≈1.95 W m −1  K −1 and a peak thermoelectric figure of merit (ZT) of ≈0.52 at 923 K are obtained in Ti 1.6 Hf 0.4 FeNiSb 1.7 Sn 0.3 , indicating the promising applications of double half‐Heusler compounds.