Evidence for Local Atomic Strain in Pb-Doped Heavy-Metal Fluoride Glasses

Near-edge and extended x-ray absorption fine structure (NEXAFS and EXAFS) measurements have been made as a function of Pb dopant concentration to study the changes in local geometric and electronic structure in several heavy-metal fluoride glasses (Zr/Ba/La/Al/Na, or ZBLAN). A strong correlation is found between the observed glass instability for Pb concentrations > 10% and the structural changes that are measured exclusively around the Ba atoms. Implications of these novel findings are examined in light of the present understanding of these complex glass systems.