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 (?-quartz) solid-solution nano crystals corresponding to ?-LiAlSi2O6. This structure yields a more compact ?-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: ?-quartz?????Coesite I?????Coesite II. The measured transition pressures are consistent with the larger cell volume attained in the ?-LiAlSi2O6 yielding a wider metastability pressure range of the ?-quartz-type phase.

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