A high-resolution 19{sup left}F NMR spectroscopic study of barium fluorozirconate glasses and related crystals

摘要

Fluorozirconate glasses have attracted considerable attention not only for their transparency in the infrared, but also due to their high fluorine ion conductivities and extreme fragility in the viscosity-temperature relationship. We report on structural studies of binary BaF{sub}2-ZrF{sub}4 glasses with 58-78 mol% ZrF{sub}4 using high-resolution magic-angle-spinning 19{sup left}F NMR. High-speed 19{sup left}F MAS NMR allows us to resolve at least three unique fluorine environments in these binary glasses. These fluorine environments are attributed to one type of bridging fluorine, between corner-sharing Zr-F coordination polyhedra, and two types of non-bridging fluorine (NBF), one of which is bonded to one Zr and one Ba atom while the other is bonded to one Zr and two Ba atoms. The concentration of the first type of NBF increases with decreasing ZrF{sub}4 concentration, while that of the second type is essentially independent of glass composition. These assignments have been made on the basis of detailed 19{sup left}F NMR studies of a wide variety of crystalline fluorozirconates with known crystal structures. A comparison between the glass and crystal 19{sup left}F NMR spectra rules out any significant concentration of edge-shared Zr-F polyhedra in these binary glasses. The Zr atoms in all glasses are found to be coordinated to ～7.8 ± 0.2F atoms.