利用固体魔角旋转核磁共振研究ZrF_(4)-FLiNaK的玻璃相变结构

Probing the glass transition structure of ZrF_(4)-FLiNaK by solid-state MAS NMR

氟锆酸盐玻璃(Fluorozirconate glass,ZBLAN)是制作中红外氟化物光纤的主要基质材料。本研究以ZrF_(4)-FLiNaK作为模型体系,利用核磁共振技术分析了^(19)F、^(23)Na和^(7)Li谱的化学位移随不同ZrF_(4)浓度的变化趋势,揭示了该复合熔盐体系固化过程中氟锆酸根离子的结构随着ZrF_(4)配比增加逐渐向[ZrF_(7)]^(3-)、[Zr_(6)F_(31)]^(7-)和[ZrF_(6)]^(2-)的演变过程。当ZrF_(4)浓度达到25.0 mol%时,发生了共晶盐相到玻璃结构的相变过程,体系中形成了Zr-F-Zr桥键的玻璃态网络结构,而当ZrF_(4)浓度超过56.0 mol%时,可能会导致玻璃态稳定性的降低。另外研究发现体系中的碱金属K^(+)、Na^(+)和Li^(+)离子在玻璃态结构中主要作为修饰剂,起到填充作用,用于提高网络结构的稳定性。这些结果指出了玻璃态网络结构的形成过程和碱金属阳离子的作用,为研究含ZrF_(4)玻璃结构及提高光纤品质提供理论参考。

[Background]Fluorozirconate 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.[Purpose]This study aims to investigate the phase transition structure of ZrF_(4)-based glasses.[Methods]ZrF_(4)-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 ZrF_(4)-FLiNaK glass model systems.An analysis was conducted on the chemical shifts of ^(19)F,^(23)Na and ^(7)Li spectra with different concentrations of ZrF_(4) by using the NMR technique.Moreover,in order to characterize the movement behavior of Li^(+) ion,the full width at half maximum(FWHM)of ^(7)Li signal was analyzed.[Results]Experimental results show the coordination structure of Zr^(4+)in the system tendes to be evolved in the order of[ZrF_(7)]^(3-),[Zr_(6)F_(31)]^(7-) and[ZrF_(6)]^(2-) with the increase of the ZrF_(4) 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 ZrF_(4) 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.[Conclusions]The 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 ZrF_(4) and improving the quality of the optical fiber product.