THE BARIUM TITANO-DISILICATE BATISI2O7 - A STRUCTURAL INVESTIGATION BY VIBRATIONAL SPECTROSCOPY AND X-RAY-POWDER DIFFRACTION

Pure barium titanosilicate BaTiSi2O7 has been synthesized and investig ated by vibrational spectroscopy and X-ray diffraction. The Raman spec trum exhibits a high-frequency Ti-O vibration at 912 cm(-1) (identifie d by a 9 cm(-1) Ti-46-Ti-50 isotopic shift) which shows the existence of a short Ti=O bond, most probably included in a TiO5 pyramid as in t he similar compound Ba2TiSi2O8. BaTiSi2O7 is thus a titanyl metasilica te BaTiOSi2O6. The IR spectrum and the observed Si-28-Si-30 isotopic s hifts are compatible with the existence of Si4O12 rings as in the corr esponding vanadyl compound beta-BaVOSi2O6. In fact, the X-ray powder p attern is indexed by a monoclinic cell, a = 11.8831(7) Angstrom, b = 1 0.0067(5) Angstrom, c = 9.9156 Angstrom, beta = 93.832(6)degrees and p ossible relationships with the structure of beta-BaVOSi2O6 are pointed out and discussed. (C) 1998 Elsevier Science B.V. All rights reserved .