A Raman study of the pressure-induced densification of SiO2-based glass-ceramics

Abstract

Here we report a structural characterization study of glass-ceramics as a function of pressure by Raman spectroscopy. We selected a glass-ceramics of Li2O–Al2O3–nSiO2 (n ≈ 8) doped with ZrO2 and TiO2. This composition induces slight structural modification in Si–O and Si–O–Si bonds in the glass matrix that are crucial to stabilize metastable hexagonal SiO2 (β-quartz) solid-solution nano crystals corresponding to γ-LiAlSi2O6. This structure yields a more compact β-quartz-type phase that eventually stabilizes it in wider pressure range than pure SiO2. Raman spectroscopy allows to unravel at least two pressure-induced structural phase transitions at about 6 and 15 GPa that could not be previously revealed by x-ray diffraction. We show that the phase-transition sequence can tentatively be described in terms of SiO2-type structure as: β-quartz → Coesite I → Coesite II. The measured transition pressures are consistent with the larger cell volume attained in the γ-LiAlSi2O6 yielding a wider metastability pressure range of the β-quartz-type phase.