Received 14 October 2013
Besides Li17Si4, Li16.42Si4, 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.
For details of the structural description of Li13Si4, see: Frank et al. (1975). For structural data for Li13Si4 based on computational methods, see: Chevrier et al. (2010). For details of the synthesis, thermodynamic properties and crystal structures of Li17Si4, Li16.42Si4 and Li15Si4, see: Zeilinger & Benson et al. (2013); Zeilinger & Kurylyshyn et al. (2013); Zeilinger & Baran et al. (2013). For further thermodynamic investigations on the Li-Si system, see: Thomas et al. (2013); Wang et al. (2013). The behavior of silicon as anode material upon lithiation/delithiation is described by Limthongkul et al. (2003) and Obrovac & Christensen (2004). For in-situ/ex-situ solid state NMR investigations of structural changes in silicon electrodes for lithium-ion batteries, see: Key et al. (2009, 2011).
Data collection: APEX2 (Bruker, 2008); cell refinement: SAINT (Bruker, 2008); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg, 2012); software used to prepare material for publication: publCIF (Westrip, 2010).
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: WM2778 ).
This work has been funded by the Fonds der Chemischen Industrie and the SolTech (Solar Technologies go Hybrid) program of the State of Bavaria.
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