The barium titano-disilicate BaTiSi2O7:: a structural investigation by vibrational spectroscopy and X-ray powder diffraction

Pure barium titanosilicate BaTiSi2O7 has been synthesized and investigated by vibrational spectroscopy and X-ray diffraction. The Raman spectrum exhibits a high-frequency Ti-O vibration at 912 cm(-1) (identified 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 the similar compound Ba2TiSi2O8. BaTiSi2O7 is thus a titanyl metasilicate BaTiOSi2O6. The IR spectrum and the observed Si-28-Si-30 isotopic shifts are compatible with the existence of Si4O12 rings as in the corresponding vanadyl compound beta-BaVOSi2O6. In fact, the X-ray powder pattern is indexed by a monoclinic cell, a = 11.8831(7) Angstrom, b = 10.0067(5) Angstrom, c = 9.9156 Angstrom, beta = 93.832(6)degrees and possible relationships with the structure of beta-BaVOSi2O6 are pointed out and discussed. (C) 1998 Elsevier Science B.V. All rights reserved.