The vibrational spectra of MgO-Al₂O₃-SiO₂ glasses containing TiO₂

Abstract

The infrared spectra from a series of MgO-Al₂O₃-SiO₂ glasses containing TiO₂ are consistent with the existence of a phase-separated structure consisting of a high silica phase and a high modifier phase of metasilicate composition. The invariance of the spectra throughout the range of pre-crystallization heat treatments and compositions precludes the possibility of significant changes in the average number of non-bridged oxygen ions per silica tetrahedron either during “nucleation” treatments or upon the addition of TiO₂ to the base glass. The Raman spectra from the same series of glasses consist of two main high-frequency bands, at 1000 and 910 cm⁻¹ which change markedly in relative intensity as TiO₂ is added to the base glass, and several subsidiary bands at lower frequencies. It is suggested that the high-frequency bands arise from two dissimilar metasilicate-type structures which are the pre-cursors of the major crystalline phases which precipitate upon devitrification of the glasses, namely cordierite in the low titania glasses (rings of [SiO₄]²⁻ tetrahedra), and a pyroxene similar to enstatite in the high titania glasses (chains of [SiO₄]²⁻ tetrahedra).