Mössbauer, Raman, and DTA Studies on the Structure of BaF2–ZrF4–FeF2 Glasses

Structural studies on the ternary BaF2–ZrF4–FeF2 glasses have been performed to elucidate the local structure of the ZrF4-based glasses which are known to be excellent in the optical transparency and the electric conductivity due to F− ion. Mössbauer and Raman measurements reveal that iron (Fe2+ and Fe3+) plays a structural role similar to that of Ba2+ ion surrounded by eight fluorine atoms at the interstitial site of one- or two-dimensional zigzag chains composed of ZrF6 octahedra. Raman and DTA measurements reveal that the increase in the fraction of BaF2 causes an increase in the coordination number of Zr from 6 to 7. Mössbauer measurements of 25BaF2·65ZrF4·10FeF2 glass at lower temperatures lead to a conclusion that the glass undergoes a phase transition at 225±5K, of which structural change is easily reflected in the isomer shift, quadrupole splitting, and the absorption area. This is supported by the DTA measurement of the same sample at lower temperatures, i.e., the DTA curve consists of two exothermic peaks and a wide endothermic peak observed at about 220–230 K and 180–210 K, respectively.