Study of crystallization in lithium silicate glasses using high-voltage electron microscopy

Abstract

Abstract The early stages of crystallization in a lithium disilicate glass were studied by high-voltage transmission electron microscopy and diffraction at 1000 kV, using thin sections prepared from the bulk material. Heat treatment of the glass in the range 450°-500°C produced large numbers of internally-nucleated lithium disilicate crystals. These consisted of small faceted single-crystal plates parallel to (010) planes and elongated along [001]. Within the crystals, regions of a darker contrast and distinct shape were observed, which contained a high defect concentration. The presence of planar growth-faults in the crystals was indicated by streaking of the diffraction spots. New branches formed on many of the crystals, probably by a twinning mechanism. The regular nature of this branching explains the morphology of crystallization observed after prolonged growth. The effect of an addition of P2O5to the glass composition on the crystal morphologies was also studied.