Enhanced Thermoelectric Properties in p-Type Double Half-Heusler Ti2-yHfyFeNiSb2-xSnx 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 approximate to 4.8 x 10(21) cm(-3) is achieved by doping Sn on the Sb site in a series of Ti2FeNiSb2-xSnx (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 approximate to 1.95 W m(-1) K-1 and a peak thermoelectric figure of merit (ZT) of approximate to 0.52 at 923 K are obtained in Ti1.6Hf0.4FeNiSb1.7Sn0.3, indicating the promising applications of double half-Heusler compounds.