Crystallization in Lead Tungsten Fluorophosphate Glasses

The glass forming ability was investigated in the codoped Er³⁺/Yb³⁺ ternary system NaPO₃-WO₃-PbF₂ with increasing amounts of PbF₂. It has been found that glass samples can be obtained for PbF₂ contents ranging from 0 mole% to 50 mole% for the codoped samples and an undoped sample containing 60% of lead fluoride could also be vitrified. Thermal properties of the most PbF₂ concentrated glasses exhibit strong dependence of the composition with a decrease of the glass transition temperatures and thermal stabilities against devitrification with increasing the lead fluoride content. These glass samples were heat-treated near the crystallization peaks and the X-ray diffraction measurements pointed out that the dominant phase which precipitates from the glass samples containing 40% and 50% of PbF₂ is the lead fluorophosphate phase Pb₅F(PO₄)₃ whereas the sample containing 60% of PbF₂ exhibits a preferential bulk crystallization of cubic lead fluoride β-PbF₂.

glasses; phosphate; lead fluoride