Probing the glass transition structure of ZrF4-FLiNaK by solid-state MAS NMR

Abstract

BackgroundFluorozirconate glass (ZBLAN) refers to the main matrix material of the mid infrared fluoride fiber. Based on the formation of the glassy network structure, the quality of glass fiber products can be determined.PurposeThis study aims to investigate the phase transition structure of ZrF4-based glasses.MethodsZrF4-FLiNaK was used as an experimental model system to replace the ZBLAN glass. In addition, the nuclear magnetic resonance (NMR) technique was employed to study the structure of ZrF4-FLiNaK glass model systems. An analysis was conducted on the chemical shifts of 19F, 23Na and 7Li spectra with different concentrations of ZrF4 by using the NMR technique. Moreover, in order to characterize the movement behavior of Li+ ion, the full width at half maximum (FWHM) of 7Li signal was analyzed.ResultsExperimental results show the coordination structure of Zr4+ in the system tendes to be evolved in the order of [ZrF7]3-, [Zr6F31]7- and [ZrF6]2- with the increase of the ZrF4 concentration. Furthermore, the Zr-F-Zr bridge bond in the network structure is formed, and the eutectic salt phase transforms into glassy state under the concentration of ZrF4 reaching 25.0 mol%. Besides, K+, Na+ and Li+ ions acts as modifiers and fills the glass state to improve the stability of the network structure.ConclusionsThe mentioned results indicate the formation of the glassy network structure and the effect of the alkali metal cation. On that basis, this study can provide a theoretical reference for investigating the glass structure containing ZrF4 and improving the quality of the optical fiber product.

Keywords

• zrf4-flinak glass model
• solid-state nuclear magnetic resonance
• glassy network structure