First principle studies on electronic and thermoelectric properties of Fe$_{2}$TiSn based multinary Heusler alloys

TL;DR

This study uses first-principles calculations to explore the electronic and thermoelectric properties of Fe$_{2}$TiSn based multinary Heusler alloys, revealing their potential for efficient energy conversion at high temperatures.

Contribution

It provides a detailed computational analysis of stability, electronic structure, and thermoelectric performance of substituted Fe$_{2}$TiSn alloys, highlighting their high ZT values.

Findings

Alloys are mechanically and dynamically stable.

High ZT value of 0.81 at 900 K for specific alloy compositions.

TB-mBJ functional predicts higher ZT than PBE-GGA.

Abstract

The alloys with 8/18/24 valence electron count (VEC) are promising candidates for efficient energy conversion and refrigeration applications at low as well as high temperatures. The full potential linearized augmented plane wave method as implemented in WIEN2k code was used to investigate electronic structure and TE transport properties with the PBE$-$GGA and TB$-$mBJ exchange potentials and Boltzmann transport theory. The calculated single crystal elastic constants, phonon dispersion and phonon density of states confirm that these systems are mechanically and dynamically stable. The TE transport properties is calculated by including the lattice part of thermal conductivity ($\kappa_{L}$) obtained from two methods one from the calculated elastic properties calculation ($\kappa^{elastic}_{L}$) and the other from phonon dispersion curve ($\kappa^{phonon}_{L}$). The strong phonon$-$phonon scattering by large mass difference/strain fluctuation of isovalent/aliovalent substitution at Ti/Sn sites of Fe$_{2}$TiSn reduces the lattice thermal conductivity which results in high \textit{ZT} value of 0.81 at 900\,K for Fe$_{2}$Sc$_{0.25}$Ti$_{0.5}$Ta$_{0.25}$Al$_{0.5}$Bi$_{0.5}$. The comparative analysis of TE transport properties using the band structures calculated with the PBE$-$GGA and TB$-$mBJ functional shows that the \textit{ZT} value obtained from TB$-$mBJ scheme is found to be significantly higher than that based on PBE$-$GGA. The calculated relatively low lattice thermal conductivity and high \textit{ZT} values suggest that isovalent/aliovalent substituted Fe$_{2}$TiSn are promising candidates for medium to high temperature waste heat recovery.