Intricate Li-Sn Disorder in Rare-Earth Metal-Lithium Stannides. Crystal Chemistry of RELiSn (RE = La-Nd, Sm; x < 0.3) and EuLiSn ( x ≈ 2.0).

Reported are the syntheses, crystal structures, and electronic structures of six rare-earth metal-lithium stannides with the general formulas RELiSn (RE = La-Nd, Sm) and EuLiSn. These new ternary compounds have been synthesized by high-temperature reactions of the corresponding elements. Their crystal structures have been established using single-crystal X-ray diffraction methods. The RELiSn phases crystallize in the orthorhombic body-centered space group Immm (No. 71) with the ZrCuSi structure type (Pearson code oI22), and the EuLiSn phase crystallizes in the orthorhombic base-centered space group Cmmm (No. 65) with the CeLiGe structure type (Pearson code oC50). Both structures can be consdered as part of the [RESn] [RELiSn] homologous series, wherein the structures are intergrowths of imaginary RESn (AlB-like structure type) and RELiSn (MgAlCu-like structure type) fragments. Close examination the structures indicates complex occupational Li-Sn disorder, apparently governed by the drive of the structure to achieve an optimal number of valence electrons. This conclusion based on experimental results is supported by detailed electronic structure calculations, carried out using the tight-binding linear muffin-tin orbital method.