Electron and phonon transport in Co-doped FeV_(0.6)Nb_(0.4)Sb half-Heusler thermoelectric materials

The electron and phonon transport characteristics of n-type Fe_(1−x) Co_x V_(0.6)Nb_(0.4)Sb half-Heusler thermoelectric compounds is analyzed. The acoustic phonon scattering is dominant in the carrier transport. The deformation potential of E_(def) = 14.1 eV and the density of state effective mass m^* ≈ 2.0 m_e are derived under a single parabolic band assumption. The band gap is calculated to be ∼0.3 eV. Electron and phonon mean free paths are estimated based on the low and high temperature measurements. The electron mean free path is higher than the phonon one above room temperature, which is consistent with the experimental result that the electron mobility decreases more than the lattice thermal conductivity by grain refinement to enhance boundary scattering. A maximum ZT value of ∼0.33 is obtained at 650 K for x = 0.015, an increase by ∼60% compared with FeVSb. The optimal doping level is found to be ∼3.0 × 10^(20) cm^(−3) at 600 K.