Lowering of lattice thermal conductivity through strain application on LiCaB half-heusler alloys in presence of aliovalent doping

Abstract

In this study, we have used DFT method to investigate the impact of aliovalent doping and strain on the electronic and thermoelectric properties of LiCaB half-Heusler alloy. Doping of Mg, Ca (divalent) and In (trivalent) atoms in the X-site of LiCaB at various concentrations has been explored. The results show significant reduction in κ_l due to increased phonon scattering caused by the heaviest dopant In. The lowest κ_l is recorded to be 1.25 W/mK (800 K) for Li_0·75In_0·25CaB, marking a ∼79% reduction compared to the pristine alloy (5.94 W/mK). Application of isotropic strain further reduced the κ_l of Li_0·75In_0·25CaB, significantly by 64% to 0.45 W/mK (800 K). Such lowering in κ_l has resulted in reduced κ_tot, which in turn influenced the transport properties. In particular, the total figure of merit (ZT_tot) of pristine LiCaB (0.56) increased by ∼5% in Li_0·75In_0·25CaB (0.59) and this enhancement could even be boosted up to ∼36% with ZT_tot of 0.80 when the doped system was introduced with compressive strain of 8%. Accordingly, the conversion efficiency (η) of LiCaB increased by ∼23% in Li_0·75In_0·25CaB, which was subsequently augmented by ∼13% in strained Li_0·75In_0·25CaB. These findings highlight the possibility of improvement in performance of thermoelectric materials through combined approach of aliovalent doping and strain application.