First-principles electronic structure, phonon properties, lattice thermal conductivity and prediction of figure of merit of FeVSb half-Heusler.

In this work, we have studied the electronic structure of a promising thermoelectric half-Heusler FeVSb using FP-LAPW method and SCAN meta-GGA including spin-orbit coupling. Using the obtained electronic structure and transport calculations we try to address the experimental Seebeck coefficientSof FeVSb samples. The good agreement between the experimental and calculatedSsuggests the band gap could be ~0.7 eV. This is supported by the obtained mBJ band gap of ~0.7 eV. Further, we study and report the phonon dispersion, density of states and thermodynamic properties. The effect of long range Coulomb interactions on phonon frequencies are also included by non-analytical term correction. Under quasi-harmonic approximation, the thermal expansion behaviour upto 1200 K is calculated. Using the first-principles anharmonic phonon calculations, the lattice thermal conductivity κphof FeVSb is obtained under single-mode relaxation time approximation considering the phonon-phonon interaction. At 300 K, the calculated κphis ~18.6 Wm-1K-1which is higher compared to experimental value. But, above 500 K the calculated κphis in good agreement with experiment. A prediction of figure of meritZTand efficiency for p-type and n-type FeVSb is made by finding out optimal carrier concentration. At 1200 K, a maximumZTof ~0.66 and ~0.44 is expected for p-type and n-type FeVSb, respectively. For p-type and n-type materials, maximum efficiency of ~12.2 % and ~6.0 % are estimated for hot and cold temperature of 1200 K and 300 K, respectively. A possibility of achieving n-type and p-type FeVSb by elemental doping/vacancy is also discussed. Our study is expected to help in further exploring the thermoelectric material FeVSb.