The quantum chemical study of the fluoride and oxyfluoride glass structure

We illustrate the use of the results of quantum chemical DV-X, method toget her with spectroscopic data for investigating the structure of fluorozircon ate and oxyfluoroniobate glasses. The calculations of the electron structur e and stability of some complex fluorides and oxyfluorides simulating the g roups found or assumed in the glasses: AlF4- AIF(6)(2-), AlF63-, ZrF5-, ZrF 62-, ZrF73-, ZrF84-, NbOF52-, NbO2Fnk- and model systems on their basis are presented. We established that polymer fluoride glass networks are built f rom polyhedra formed by molecular ions unstable against dissociation. An in crease of stability of these ion structures occurs when they are connected by bridging bonds and formed in networks. We show that ZrF7 and ZrF8 polyhe dra form fluorozirconate glasses, AlF6 polyhedra form the glass networks ob tained from the liquids consisting of AlF63- and NbOF52- molecular ions and the glasses based on NbO2F can be obtained without a second glass former. We confirmed these computations by obtaining NbO2F-BaF2 and NbO2F-BaF2-KF g lass compositions. These glass compositions are composed of distorted NbO2F 3 octahedra connected by oxygen bridges. (C) 1999 Elsevier Science B.V. All rights reserved.