Effective Decrease of the Thermal Conductivity Caused by Hf in Fe(V_0.955−xHf_0.045Ti_x)Sb Half-Heusler Phase

Abstract

The thermoelectric properties of the Fe(V_0.955−xHf_0.045Ti_x)Sb half-Heusler (HH) phase were studied in the temperature range from 300 to 800 K. We employed Hf- and Ti-substitutions for V in the FeVSb-based HH phase for reducing the lattice thermal conductivity and tuning the carrier concentration, respectively. The samples prepared with the composition of Fe(V_0.955−xHf_0.045Ti_x)Sb (0.000 ≤ x ≤ 0.075) consisted almost solely of the half-Heusler phase. We succeeded in significantly decreasing the lattice thermal conductivity κ_lat ≈ 2.1 W m⁻¹K⁻¹ for Fe(V_0.88Hf_0.045Ti_0.075)Sb while keeping appropriate carrier concentration for the optimized transport properties. However, the highest ZT value was not significantly increased but kept rather low at 0.55, mainly due to the reduction in the Seebeck coefficient. The mechanism leading to the reduction in Seebeck coefficient was revealed by the means of first principles band calculations.