Structural study on peculiar high-pressure behavior of fluorozirconate glass in permanent densification

A 55ZrF4 . 17BaF(2). 23NaF . 5EuF(3) glass was densified under 1.5, 3.0, 4. 5, 6.0, and 9.0 GPa at 250 degreesC by using a 6-8 multi-anvil-type high-pr essure apparatus. The densities of permanently densified glasses increased until exhibiting a maximum value around 3.0 GPa and then gradually decrease d with further increasing pressure. Local structures around Zr4+, Eu3+, and Ba2+ in the undensified and densified glasses were investigated by means o f Raman spectroscopy, Eu3+ fluorescence spectroscopy, and Zr-K, Eu-L-III, a nd Ba-L-III EXAFS spectroscopy. The EXAFS analyses revealed that the local structure around Ba2+ changed remarkably with applied pressure, giving a pr essure dependence similar to that of density, while the local structures ar ound Zr4+ and Eu3+ hardly changed. Therefore, it is concluded that the stru ctural change around Ba2+ which is explained by a structural relaxation in the F- coordination environments around Ba2+ under releasing applied pressu re, is an origin of a peculiar high-pressure behavior observed in the prese nt glass. (C) 2001 Elsevier Science Ltd. All rights reserved.