Schmidmair, D.; Kahlenberg, V.; Perfler, L.; Tribus, M.; Hildebrandt, J.; Többens, D.M.: On the ambient pressure polymorph of K2Ca3Si3O10 - An unusual mixed-anion silicate and its structural and spectroscopic characterization. Journal of Solid State Chemistry 228 (2015), p. 90-98
10.1016/j.jssc.2015.04.019

Abstract:
An ambient pressure polymorph of K2Ca3Si3O10 has been synthesized via solid state reactions. Single-crystal X-ray diffraction experiments show, that this new modification crystallizes in the triclinic space group P-1. The structure was solved by direct methods and subsequently refined. A special feature of the crystal structure is the coexistence of two different types of silicate anions. Isolated [SiO4]-tetrahedra as well as [Si4O12]-vierer single rings occur in the ratio 2:1, resulting in the crystallochemical formula K4Ca6[SiO4]2[Si4O12]. To the best of our knowledge, this is the first example of an oxo-silicate where insular and cyclic silicate anions appear concomitantly. Further characterization of this new compound was carried out by electron microprobe analysis and Raman spectroscopy. DFT calculations were employed (i) to assign Raman bands to certain vibrational modes and (ii) to determine the relative stabilities of the monoclinic high-pressure and the triclinic ambient pressure polymorph of K2Ca3Si3O10.