Topological phonons and low lattice thermal conductivity of Li2CaX (X = Sn and Pb) type Heusler compounds

The topological phonons, electronic structure, and transport properties of Li2CaX (X = Sn and Pb) have been investigated using first-principles. Topological phononic states are facilitated by Dirac-like band crossings observed in optical phonon branches, which are ensured by calculated surface states in the (001) plane. Li2CaPb has very low lattice thermal conductivity(������������), as evidenced by shorter phonon lifetime, acoustic phonon mode dispersion, and low Debye temperature. The value of ������������is low at high temperatures due to Dirac-like crossings in optical phonon branches exhibiting non-trivial topological properties. The inclusion of hybrid functional transits Li2CaPb into an indirect bandgap semiconductor. Li2CaPb has a figure of merit of 0.15 for holes and 0.2 for electrons at 500 K. Topological phonons combined with promising transport features in Li2CaX (X = Sn and Pb) may be desirable for future device applications.