Physical properties of Li-based LiPd₂M Heusler compounds (M = Si, Ge, Sn)

We synthesized and studied LiPd₂M, M = Si, Ge and Sn, Heusler-type compounds. All three compounds crystallize in the cubic Fm-3m crystal structure with estimated lattice parameters a = 5.9016 Å (LiPd₂Si), 6.0105 Å (LiPd₂Ge) and 6.2642 Å (LiPd₂Sn). The compounds were characterized by means of magnetic susceptibility, heat capacity and resistivity. For LiPd₂Ge bulk transition was confirmed by a large HC anomaly at T_c = 1.96 K. Fitting the HC data yields γ = 5.8 mJ mol^-1 K^-2 and Θ_D = 244 K. The electron-phonon coupling λ_e-p= 0.53 implies weak-coupling superconductivity. Electronic structure, phonons and electron-phonon interaction functions were computed using the density functional theory. LiPd₂Ge exhibits the strongest electron-phonon coupling within the studied series, in agreement with the observation of superconductivity. In all the compounds a phonon soft mode is found in the Γ-K direction, and it is most pronounced in the case of the superconducting LiPd₂Ge, which suggests its correlation with the electron-phonon interaction.