Electronic and thermoelectric behaviour of XCaB (X = Li, Na, K) half-Heusler alloys under strain

Abstract

Impact of isotropic strain (≤±10 %) on electronic and thermoelectric properties of XCaB (X = Li, Na, K) half-Heusler alloys is studied using DFT method. LiCaB possesses the maximum structural, dynamical and mechanical stability among the considered alloys. The alloys remain ferromagnetic and most of them also retain half-metallicity even in strained conditions. Inclusion of lattice thermal conductivity (κl) lowers the total figure of merit (ZTtot) to almost half (∼0.6 at 800K) of that of electronic figure of merit (ZTel) (∼1 at 200K). Ductility detests κl but favours ZTtot. Application of strain could tune electronic band structure and/or mechanical behaviour of LiCaB, KCaB increasing ZTtot to about 0.75, 0.67, respectively, at relatively larger compressive strains, except for a negligible change in NaCaB. Thus, required modifications in electronic and mechanical properties of XCaB alloys are beneficial for thermoelectric performance and can be achieved under appropriate strain application.