Raman spectroscopic study of benitoite-type compounds

Raman scattering measurements were performed in the benitoite-type BaTiSi3O9, BaZrSi3O9, BaSnSi3O9 and tetragermanate-type BaGe4O9 phases in order to elucidate the spectroscopic and structural features of D2/vG(T3O9)-type compounds (expressed by Smith's notation) with the GO6 octahedral unit isolated by the T3O9 ring. The Raman band assignments in middle and high wavenumber region wes also carried out. In addition, the wavenumber of antisymmetric stretching vibration mode, νas, for Si-O-G bond was calculated by means of combination of the simple molecular model and Badger's rule, and compared with the experimental results. It was suggested that the νas was governed by the force constant of T-Oax bond, which was connected with the G4+.