Half-Heusler compounds hold great promise for thermoelectricity due to their excellent thermal stability and electronic transport properties. This study unveils the physical characteristics of half-Heusler compounds XCoSi (X = V, Nb, Ta) as potential materials for thermoelectric using the Quantum ESPRESSO and PHONOPY codes with PBEsol-GGA correlation functional. The electronic band structure calculations revealed the semiconducting nature of the compounds with an indirect band gap (X \(\rightarrow \) W) of size 0.55 eV, 0.84 eV, and 1.25 eV for VCoSi, NbCoSi, and TaCoSi, respectively. The XCoSi(X=V, Nb, Ta) compounds demonstrate dynamic and mechanical stability, with ionic bonds and predicted ductility of these alloys. Additionally, critical parameters for thermoelectric application are computed, including the Seebeck coefficient (S), electrical conductivity ( \(\sigma \) ), thermal conductivity ( \(\kappa \) ), and the figure of merit (ZT). At room temperature, both p-type and n-type XCoSi (X = V, Nb, Ta) exhibit figure of merit values close to unity: 0.96 for VCoSi, 0.98 for NbCoSi, and 0.99 for TaCoSi, based solely on the electronic contribution to thermal conductivity. Including the lattice thermal conductivity provides a more accurate assessment of the thermoelectric potential of XCoSi (X = V, Nb, Ta). Among them, VCoSi shows greater potential for thermoelectric applications compared to TaCoSi and NbCoSi.
