CRYSTALLISATION BEHAVIOUR AND MICROSTRUCTURE OF ErF3 NANOCRYSTALS IN AN OXYFLUORIDE GLASS

The crystallisation of ErF3 nanocrystals in oxyfluoride glass with the composition 55SiO2.20Al2O3.15Na2O.10ErF3 (mol%) was observed after heat treatment above the glass transition temperature. The crystallisation mechanism of this glass was substantiated by microstructural and compositional changes in the crystalline phase. Investigations, using dilatometry, XRD, TEM and DSC, showed that a maximum crystal size of 20 nm was obtained after varying the heat treatment time and temperature. TEM images of the as-annealed glass before heat treatment showed no phase separation after quenching the melt. However, after heat treatment for 10 h at 620 C, ordered regions of dark contrast (0.5 nm) with respect to the matrix appeared. These regions are believed to be associated with the onset of nucleation of the fluorite phase.