A new semiconducting full Heusler Li2BeX (X = Si, Ge and Sn): first-principles phonon and Boltzmann calculations

The Full Potential-Linearized Augmented Plane Wave (FP-LAPW) is employed into density functional theory (DFT) within WIEN2k package to explore and investigate the thermoelectric, mechanical, electronic and structural properties of full-Heusler alloys Li2BeX (X = Si, Ge and Sn) were explored. The exchange and correlation potential are treated by different approximations: the generalized gradient approximation with Perdew-Burke-Ernzerhof scheme (GGA-PBE) and Tran-Blaha modified Becke-Johnson (mBJ-GGA). The results achieved for the electronic properties show that these compounds are semiconductor in nature with an indirect band gap, of values: 0.60 eV, 0.55 eV and 0.24 eV for Li2BeSi, Li2BeGe and Li2BeSn, respectively. In addition, these materials are mechanically stable owing to the fact that the conditions required for this mechanical stability satisfy Born's criteria, and are of a brittle nature due to the calculated values of the ratios (B/G), on the other hand, these compounds are dynamically stable due to the non-presence of negative frequencies following the detailed study of phonons. These compounds are characterized by a high figure of merit (ZT) (close to unity) and high Seebeck coefficient (S), making them promising candidates for thermoelectric applications.