Strain induced improvement and consistency in thermoelectric performance of Mg and In co-doped LiCaB half-Heusler alloy

This study explores the combined effects of co-doping and external strain on electronic and thermoelectric properties of LiCaB half-Heusler alloy using DFT method. Out of the two co-doped configurations, In -doped Li 0.75 Mg 0.25 CaB ( In 0.25 Li 0.50 Mg 0.25 CaB ) and Mg- doped Li 0.75 In 0.25 CaB ( Mg 0.25 Li 0.50 In 0.25 CaB ), the former is found to be more stable. It retains half-metallicity of its pristine state Li 0.75 Mg 0.25 CaB but exhibits modified electronic band structure with a reduced band gap and hence enhanced power factor ( PF ). Co-doping of heavier element such as In in Mg pre-doped LiCaB results in substantial reduction of lattice thermal conductivity ( κ l ) caused by significant phonon-defect scattering. The reduced κ l , supported by adequate PF , leads to notable increment of ∼87% in the total figure of merit ( ZT tot ) (0.73) at 800K compared to Li 0.75 Mg 0.25 CaB . There is further suppression in κ l when In 0.25 Li 0.50 Mg 0.25 CaB alloy is subjected to -8% strain and accordingly, another ∼16% improvement in ZT tot (0.85) is obtained. In addition to this, the alloy displays notable thermoelectric response even at room temperature, as indicated by a tremendous jump in ZT tot from 0.40 to ∼0.71 under achievable tensile strain limit of 6%. Interestingly, the thermoelectric efficiency of In 0.25 Li 0.50 Mg 0.25 CaB is improved and remains consistent over a wide range of temperature under tensile strain conditions. The corresponding conversion efficiency ( η ) boosts up as compared to the unstrained alloy. These findings highlight the synergistic role of co-doping and strain for tuning thermoelectric properties of half-Heusler materials in ways desired for practical applications. • In doping reduces κ l of Li 0.75 Mg 0.25 CaB increasing ZT tot from 0.39 to 0.73 at 800K • -8% strain further suppresses κ l of In 0.25 Li 0.50 Mg 0.25 CaB and ZT tot becomes 0.85 • In , Mg co-doped LiCaB alloy exhibits ZT tot of ∼0.71 at 300K under 6% strain. • The co-doped alloy maintains high ZT tot over wide temperature and strain ranges.