Revision of the Li₁₃Si₄ structure

Besides Li₁₇Si₄, Li_16.42Si₄, and Li₁₅Si₄, another lithium-rich representative in the Li-Si system is the phase Li₁₃Si₄ (trideca­lithium tetra­silicide), the structure of which has been determined previously [Frank et al. (1975). Z. Naturforsch. Teil B, 30, 10-13]. A careful analysis of X-ray diffraction patterns of Li₁₃Si₄ revealed discrepancies between experimentally observed and calculated Bragg positions. Therefore, we redetermined the structure of Li₁₃Si₄ on the basis of single-crystal X-ray diffraction data. Compared to the previous structure report, decisive differences are (i) the introduction of a split position for one Li site [occupancy ratio 0.838 (7):0.162 (7)], (ii) the anisotropic refinement of atomic displacement parameters for all atoms, and (iii) a high accuracy of atom positions and unit-cell parameters. The asymmetric unit of Li₁₃Si₄ contains two Si and seven Li atoms. Except for one Li atom situated on a site with symmetry 2/m, all other atoms are on mirror planes. The structure consists of isolated Si atoms as well as Si-Si dumbbells surrounded by Li atoms. Each Si atom is either 12- or 13-coordinated. The isolated Si atoms are situated in the ab plane at z = 0 and are strictly separated from the Si-Si dumbbells at z = 0.5.