A Raman study of the pressure-induced densification of SiO 2 -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 Li 2 O–Al 2 O 3 – n SiO 2 ( n ≈ 8) doped with ZrO 2 and TiO 2 . 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 SiO 2 ( β -quartz) solid-solution nano crystals corresponding to γ -LiAlSi 2 O 6 . This structure yields a more compact β -quartz-type phase that eventually stabilizes it in wider pressure range than pure SiO 2 . 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 SiO 2 -type structure as: β -quartz → Coesite I → Coesite II. The measured transition pressures are consistent with the larger cell volume attained in the γ -LiAlSi 2 O 6 yielding a wider metastability pressure range of the β -quartz-type phase.