Quantum-chemical justification of the structure of fluorozirconate glasses

A number of fluorozirconate clusters of the general formula [ZrmFn]((4m - n)) and barium fluorozirconate clusters [BaZr2Fn]((10-n)) are studied by the quantum-chemical discrete variational X-alpha method. It is shown that the mean energies of fluorine ion addition for all structural units observed in real fluorozirconate crystals lies in a narrow range. The vibrational spectra are analyzed within the energy approach. It is demonstrated that the coordination number of zirconium in a number of barium fluorozirconate glasses is equal to seven or eight. The possible mechanism of structural transformations in binary fluorozirconate glass with a variation in its composition is proposed. The rigidity of different bonds in fluorozirconate clusters is investigated qualitatively. It is established that the rigidities of zirconium bonds with bridging and terminal fluoride ions level off in polymers, which is a prerequisite for the glass formation in fluorozirconate systems.