Received 12 July 2011
The mixed-valent titanium phosphate, Li2Ti2(PO4)3, has been prepared by the reactive halide flux method. The title compound is isostructural with Li2TiM(PO4)3 (M = Fe, Cr) and Li2FeZr(PO4)3 and has the same 3[Ti2(PO4)3]2- framework as the previously reported Li3-xM2(PO4)3 phases. The framework is built up from corner-sharing TiO6 octahedra and PO4 tetrahedra, one of which has 2 symmetry. The Li+ ions are located on one crystallographic position and reside in the vacancies of the framework. They are surrounded by four O atoms in a distorted tetrahedral coordination. The classical charge-balance of the title compound can be represented as Li+2(Ti3+/Ti4+)(PO43-)3.
The synthesis and structural characterization of stoichiometric Li2TiM(PO4)3 (M = Fe and Cr) and Li2FeZr(PO4)3 have been reported by Patoux et al. (2004) and Catti (2001), respectively. For related phosphates with general formula Li3-xM2(PO4)3 (0 x 1), see: Wang & Hwu (1991) for Li2.72Ti2(PO4)3. For Li batteries based on Li3-xM2(PO4)3 phases, see: Yin et al. (2003). For ionic conductivities of these phases, see: Sato et al. (2000). For ionic radii, see: Shannon (1976). For structure validation, see: Spek (2009).
Data collection: RAPID-AUTO (Rigaku, 2006); cell refinement: RAPID-AUTO; data reduction: RAPID-AUTO; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: locally modified version of ORTEP (Johnson, 1965); software used to prepare material for publication: WinGX (Farrugia, 1999).
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: WM2513 ).
This work was supported by the Priority Research Centers Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (NRF-2010-0029617). Use was made of the X-ray facilities supported by Ajou University.
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