Effect of Bromine on NaF Crystallization in Photo‐Thermo‐Refractive Glass
Effect of Bromine on NaF Crystallization in Photo‐Thermo‐Refractive Glass
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DOI：
10.1111/j.1551-2916.2011.04691.x
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发表时间：
2011-09
影响因子：
3.9
通讯作者：
G. P. Souza;V. Fokin;C. A. Baptista;Edgar Dutra Zanotto;J. Lumeau;L. Glebova;L. Glebov
中科院分区：
文献类型：
--
作者：
G. P. Souza;V. Fokin;C. A. Baptista;Edgar Dutra Zanotto;J. Lumeau;L. Glebova;L. Glebov
光热折射（PTR）玻璃是一种Na 2 O-K2 O-ZnO-Al 2 O3-SiO2硅酸盐光学玻璃，它还含有氟、少量溴和在UV范围内产生光敏性的掺杂剂。PTR玻璃在UV暴露后经历NaF纳米晶体的结晶，然后进行热处理，导致永久的折射率变化。在这项研究中，我们只探索了未暴露于紫外线的玻璃中的热活化转变，我们表明溴降低了NaF的溶解度，即，增加了NaF的过饱和度，从而增加了结晶的热力学驱动力。这一特征导致结晶NaF的最大体积分数随着母体玻璃中溴含量的降低而降低。随着等温处理时间的增加，玻璃化转变温度，Tg的演变揭示了两个并发过程之间的相互作用，液-液相分离，导致Tg下降，和Br-控制的NaF结晶，在相反的方向上起作用的最小值。在较低的溴含量的玻璃，更少和更大的晶体出现和表面引发的结晶占主导地位。一个表面层的F-耗尽的玻璃印迹残余宏观应力，这是不减轻退火。
Photo-thermo-refractive (PTR) glass is a Na2O–K2O–ZnO–Al2O3–SiO2 silicate optical glass which also contains fluorine, a small amount of bromine, and dopants that yield photo-sensitivity in the UV range. PTR glass undergoes crystallization of NaF nanocrystals after UV-exposure followed by thermal treatment, resulting in permanent refractive index change. In this study, where we explore only the thermally activated transformations in the UV-unexposed glass, we show that bromine decreases the solubility of NaF, i.e., increases the super-saturation of NaF thus increasing the thermodynamic driving force for crystallization. This feature causes a decrease in the maximum volume fraction of crystallized NaF with decreasing bromine content in the parent glass. The evolution of the glass transition temperature, Tg, with increasing isothermal treatment time revealed a minimum resulted from interplay between two concurring processes, liquid–liquid phase separation that led to decrease in Tg, and Br-controlled NaF crystallization that acted in the opposite direction. In glasses with lower bromine content, fewer and larger crystals appeared and a surface-initiated crystallization was dominant. A surface layer of F-depleted glass imprinted residual macro-stresses, which were not alleviated by annealing.