Primary and Secondary Phase Separation in CdF2-LiF-AlF3-PbF2 Glasses

Occurrence of primary and secondary phase separation in the CdF₂-LiF-AlF₃-PbF₂ glass system is observed. A primary phase separation, which is characterized by the formation of a small volume fraction of Cd-rich, Pb-deficient spheres whose size is on the order of 5μ is found to form upon cooling. A secondary phase separation initiates with precipitation of Pb-rich microspheres (about 4nm (40 Å) in diameter) in a Cd-rich matrix. The Pb-rich spheres develop with heat treatment 35°C above the glass transition temperature. They increase in volume fraction while changing composition and then grow slightly. As the material is further heat-treated, the Pb-rich regions crystallize. A pseudobinary model explaining the occurrence of both primary and secondary decomposition phenomena is presented.