THE STRUCTURE OF TERNARY FLUOROZIRCONATE GLASSES

Ternary fluorozirconate glasses in the systems ZrF4-BaF2-NaF and ZrF4- BaF2-LiF have been prepared by quenching mixtures of pure salts in sea led platinum capsules from 650 degrees C. The glass samples have been examined by IR and Raman spectroscopy. The principal IR and Raman band s assigned to Zr-F stretching vibrations decrease in frequency with in creasing F/Zr ratio as reported for fluorozirconate melts. The counter cations (Ba, Na, Li) in the glasses have a minor influence on the Ram an bands, but a larger effect on the IR bands which correspond to asym metric stretching vibrations. There is a systematic shift in stretchin g frequencies between the glasses and the corresponding liquids. We pr opose a structural model of these glasses involving a decrease in the coordination number of Zr with increasing temperature. This model, inv olving Zr coordination changes above T-g, associated with breaking of Zr-F-Zr bridging groups, provides an explanation of the observed high degree of fragility of fluorozirconate melts.