Infrared and Raman spectroscopy of mullite-type Bi2Ga 4O9

Abstract

Mullite-type Bi2Ga4O9 single-crystals were grown by the top-seeded solution growth (TSSG) method and investigated by vibrational spectroscopy. Polarised IR specular reflectance and attenuated total reflectance (ATR) spectra, as well as polarised micro-Raman spectra were acquired at room temperature. Powder IR spectra of sol-gel-derived samples were also recorded. Using model calculations and comparison to other mullite-type compounds, bands at ∼ 850 - 400 cm-1 could be assigned to stretching and bending vibrations of the structural GaO4 and GaO 6 units. Low-energetic modes were attributed to motions involving Bi atoms. The IR spectra of Bi2Ga4O9 display close similarities to those of the mullite-type alkali gallates (9Ga 2O3 · Rb2O), while their differences to those of mullite sensu stricto (3Al2O3 · 2SiO 2 and 2Al2O3 · SiO2, repectively) are assigned to Si-O stretching vibrations of the corresponding tetrahedral units. © 2008 WILEY-VCH Verlag GmbH & Co. KGaA.