Crystalline lithium disilicate, Li2Si2O5 (LS2c) is usually produced at atmospheric pressure by suitable heat treatment of the glass with the same Stoichiometric composition (LS2g). At this pressure, the orohombic phase of lithium disilicate is thermodynamically stable. The heat treatment of LS2g under high pressure induces the crystallisation of lithium metasilicate Li2SiO3 (LSm) phase, which remains metastable after pressure release. In this work, distinct heat treatment under high pressure were chosen to produce lithium metasilicate crystals with different grain sizes embedded in the glass matrix: smaller than 10um, about 100um and larger than 100um. Thermal stability of this set of samples was investigated during subsequent heat treatments at atmospheric pressure. All samples were analyzed by XRF, Raman spectroscopy and optical microscopy.
