Glasses and glass-ceramics in the oxyfluoride ternary system Pb(PO3)2-WO3-PbF2

Glasses were prepared by the melt-quenching method in the ternary system Pb(PO3)2-WO3-PbF2 and doped with Er3+ in order to prepare luminescent transparent glass-ceramics. This work focused on thermal and structural characterization of tungsten lead-phosphate glasses and crystallization study for preparing transparent glass-ceramics. Thermal properties such as thermal stability and crystallization behavior upon heating were investigated by DSC in function of PbF2 content. For low PbF2 concentrations, only one crystallization peak due to Pb3(PO4)2 is observed whereas samples containing more than 15% of PbF2 present another exothermic event at lower temperatures related with precipitation of PbF2, Pb2P2O7 and Pb2OF2. Structural investigations by Raman spectroscopy suggest that PbF2 modifies the tungsten-phosphate network through the formation of P―F and P―O―Pb bonds but the average network connectivity remains almost constant. A crystallization study has been performed by DSC to investigate the dominant crystallization mechanisms in these glasses and it has been established that Pb3(PO4)2 is nucleated on the surface whereas PbF2, Pb2P2O7 and Pb2OF2 crystallize dominantly from the glassy bulk. Transparent glass-ceramics containing nanosized PbF2 crystallites were also prepared by suitable heat-treatment on the glass sample containing 20% of PbF2 and Raman microscopy of these glass-ceramics supports the crystallization mechanisms determined by DSC. ► Simultaneous bulk crystallization at low temperature and surface crystallization at high temperature in lead-tungsten fluorophosphate glasses. ► Controlled crystallization of β-PbF2 nanosized crystallites and transparent glass-ceramics. ► Crystallization mechanisms probed by surface Raman microscopy.