Two functionals approach in DFT for the prediction of thermoelectric properties of Fe2ScX (X = P, As, Sb) full-Heusler compounds

Abstract

In the quest for new thermoelectric materials with high power factors, full-Heusler compounds having flat band are found to be promising candidates. In this direction, Fe2ScX (X = P,As,Sb) compounds are investigated using mBJ for the band gap and SCAN to describe the electronic bands and phonon properties for thermoelectric applications. The band gaps obtained from mBJ are 0.81 eV, 0.69 eV and 0.60 eV for Fe2ScX compounds. The phonon dispersion, phonon density of states (DOS) and partial DOS are calculated. The phonon contributions to specific heat are obtained as a function of temperature under harmonic approximation. The electronic band structutre calculated from mBJ and SCAN functionals are qualitatively compared. The effective mass values are calculated at the band extrema from SCAN functional. The thermoelectric parameters are calculated for both hole and electron dopings under semiclassical theory. We use a simple, but reasonable method to estimate the phonon relaxation time (). Using the specific heat, estimated and slopes (phase velocity) of acoustic branches in the linear region, lattice thermal conductivity () at 300 K is calculated for three compounds. The obtained values of with constant are 18.2, 13.6 and 10.3 Wm−1 K−1, respectively. Finally, the temperature dependent figure of merit ZT values are calculated for optimal carrier concentrations in the doping range considered, to evaluate the materials for thermoelectric application. The ZT values for n-type Fe2ScX, in 900–1200 K, are 0.34–0.43, 0.40–0.48 and 0.45–0.52, respectively. While, the p-type Fe2ScX have ZT values of 0.25–0.34, 0.20–0.28 and 0.18–0.26, respectively in the same temperature range. The ZT values suggest that, Fe2ScX compounds can be promising materials in high temperature power generation application on successful synthesis and further reduction by methods like nanostructuring.