The isothermal section of the phase diagram of Li–La–Ge ternary system at 400 °C

Abstract

The isothermal section of the phase diagram of Li–La–Ge ternary system at 400 °C in the 30–100 at.% Ge concentration range was built and formation of seven ternary compounds were observed. For all ternary compounds: τ1–LiLa2Ge6−x (Cmmm space group, LiPr2Ge6 structure type), τ2–LiLaGe2 (Pnma, LiCaSi2), τ3–Li2La2Ge3 (Cmcm, Li2Ce2Ge3), τ4–Li8La7Ge10 (Cmmm, own structure type), τ5–Li12La11Ge16 (Immm, own structure type), τ6–Li4La3Ge4 (Immm, Gd3Cu4Ge4) and τ7–LiLa4Ge4 (Pnma, LiTm4Ge4) the crystal structures are known. The Li2La2Ge3, Li12La11Ge16, Li8La7Ge10 and Li4La3Ge4 ternary phases form the homologous series which is based on the simple Al2MgCu and AlB2 structure types. The crystal structures of LixLa5Ge3 phase, which formed by incorporation of lithium atoms into octahedral voids of La5Ge3 binary phase, was studied more precisely by X-ray powder diffraction and electrochemical investigation. According to electronic structure calculations using the tight-binding linear muffin-tin orbital-atomic spheres approximations (TB–LMTO–ASA) method the strong covalent Ge–Ge interactions were established.