Structural and dynamical studies of fluorozirconate glass
Abstract
Fluorozirconate glass structure was studied by comparison with fluorozirconate crystal data and by the molecular dynamics computer simulation technique. A detailed tabulation of the bond lengths and angles in crystalline fluorozirconates of known structure yielded general trends regarding the effects of bridging, countercation size, and countercation charge. These observations were applied to the interpretation of analogous solid-state effects on the vibrational frequencies of fluorozirconate glasses and crystals. Spectroscopic evidence for the occurrence of double fluoride bridges (edge-bridging) between Zr atoms in the glasses is presented, and a general treatment based on Badger's rule is used to estimate the characteristic symmetric stretching frequencies, $\nu\sb{\rm s}$, of various ZrF$\sb{\rm n}$ groups in the presence of divalent and monovalent countercations. New vibrational spectra of $\alpha$-ZrF$\sb4$, MgZrF$\sb6$, Ba$\sb2$ZrF$\sb8$, $\beta$-BaZr$\sb2$F$\sb{10}$, $\alpha$-BaZr$\sb2$F$\sb{10}$, and Ba$\sb3$ZrF$\sb{10}$ are presented and incorporated into the method. The factors affecting $\nu\sb{\rm s}$ are outlined and discussed in detail. Complications of estimated frequencies are used to deduce local structure around Zr ions in binary barium fluorozirconate glasses and in fluorozirconate melts containing lithium and sodium ions. It is concluded that the presence of 8-coordinate Zr in some barium fluorozirconate glasses is not inconsistent with the results of Raman spectroscopy. The viscosity and activation energy for viscous flow of fluorozirconate melts were calculated by molecular dynamics computer simulation and compared with experimental results for fluorozirconates, as well as with simulated results for silica melts. Vibrational spectra of fluorozirconate glasses and crystals were also simulated by this technique.
Degree
Ph.D.
Advisors
Angell, Purdue University.
Subject Area
Chemistry
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