Enhanced Thermoelectric Properties in p-Type Double Half-Heusler Ti_2−yHf_yFeNiSb_2−xSn_x Compounds

Double half-Heusler Ti₂FeNiSb₂-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 × 10²¹ cm⁻³ is achieved by doping Sn on the Sb site in a series of Ti₂FeNiSb_2−xSn_x (x = 0.2, 0.3, 0.4, and 0.5) samples. Combined with the further decreased lattice thermal conductivity by alloying with Hf₂FeNiSb₂, 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_1.6Hf_0.4FeNiSb_1.7Sn_0.3, indicating the promising applications of double half-Heusler compounds.