Li 2 Si 3 O 7 : Crystal structure and Raman Spectroscopy * Hannes Kr¨ uger † , Volker Kahlenberg Institut f¨ ur Mineralogie und Petrographie Leopold-Franzens-Universit¨at 6020 Innsbruck, Austria Reinhard Kaindl Christian-Doppler-Laboratory for Advanced Hard Coatings at the Institute of Mineralogy and Petrography University of Innsbruck, Austria 2006 Abstract The crystal structure of metastable Li 2 Si 3 O 7 was determined from single crystal X-ray diffraction data. The orthorhombic crystals were found to adopt space group P mca with unit cell parame- ters of a = 19.648(3) ˚ A, b =5.9969(8) ˚ A and c = 4.8691(6) ˚ A. The content of the cell is Z = 4. The obtained structural model was refined to a R-value of 0.035. The structure exhibits silicate sheets, which can be classified as {uB ,2,1 2 ∞ }[Si 6 O 14 ] using the silicate nomenclature of Liebau. The layers are build up from zweier single chains running parallel to c. Raman spectra are presented and compared with other silicates. Furthermore the structure is discussed versus Na 2 Si 3 O 7 . 1 Introduction Crystalline lithium silicates are of special impor- tance for certain areas of materials science and solid state chemistry. Recent fields of applications include, for example, glass-ceramics (H¨oland & Beall 2002), CO 2 absorbing materials (Essaki, Nak- agawa, Kato & Uemoto 2004) and solid electrolytes in lithium batteries (Jackowska & West 1983, Kho- * accepted for publication in Journal of Solid State Chem- istry, http://dx.doi.org/10.1016/j.jssc.2006.12.015 † Email: Hannes.Krueger@uibk.ac.at rassani & West 1984). With this regard it is in- teresting to note that the historically first devel- oped glass-ceramic was based on Li 2 Si 2 O 5 (Stookey 1953). In addition to studies of the crystalline com- pounds numerous investigations were aimed to elu- cidate the glass formation and the crystallisation behaviour in the binary glasses of the system Li 2 O– SiO 2 (Vogel 1963, McMillan 1979, James 1985). Furthermore, the binary glasses have been also used as comparatively simple model systems to under- stand the internal structure, short range ordering and ion transport mechanisms in amorphous sys- tems (Beier & Frischat 1984, Habasaki & Hiwatari 2004, Lammert, Kunow & Heuer 2003, Soltay & Henderson 2005). According to the phase diagram (Levin, Rob- bins & McMurdie 1969) three thermodynamically stable crystalline phases have to be distinguished: Li 4 SiO 4 , Li 2 SiO 3 and Li 2 Si 2 O 5 , respectively. The crystal structures of these compounds are known for a long time. However, there are indications that metastable phases such as Li 2 Si 3 O 7 can be obtained as well. The crystallisation of Li 2 Si 3 O 7 from a stoichiometric glass was firstly reported by Matveev & Velya (1959). A more detailed study was carried out by West & Glasser (1970), who gave optical data, IR spectra as well as in- dexed X-ray powder data along with a sugges- tion for the space group P bcm or P ca2 1 de- termined from single crystal X-ray photographs. 1