Crystallization Behavior of Glasses in the ZrF4–BaF2–LaF3–AlF3–NaF and HfF4–BaF2–LaF3–AlF3–NaF Systems Modified with Chlorine and Bromine Ions

Abstract

We have prepared glasses in the ZrF₄–BaF₂–LaF₃–AlF₃–NaF (ZBLAN) and HfF₄–BaF₂–LaF₃–AlF₃–NaF (HBLAN) systems in which fluorine anions are partially replaced by chlorine and bromine anions. Structural changes in the chlorine-substituted glasses have been investigated by Raman spectroscopy and their crystallization behavior has been studied by differential thermal analysis and X-ray diffraction. The results demonstrate a characteristic decrease in glass transition temperature (T_g) and the precipitation of fine-particle crystalline chloride and bromide phases in a temperature range well below the crystallization temperature (T_x) of the fluoride analogues. We have identified phases that crystallize during heat treatment of the glasses at various temperatures.