Effect of Bromine on NaF Crystallization in Photo-Thermo-Refractive Glass

    Authors

    G. P. Souza; V. M. Fokin; C. A. Baptista; E. D. Zanotto; J. Lumeau; L. Glebova;L. B. Glebov

    Comments

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    Abbreviated Journal Title

    J. Am. Ceram. Soc.

    Keywords

    X-RAY-DIFFRACTION; OPTICAL-PROPERTIES; Materials Science, Ceramics

    Abstract

    Photo-thermo-refractive (PTR) glass is a Na(2)O-K(2)O-ZnO-Al(2)O(3)-SiO(2) 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, T(g), with increasing isothermal treatment time revealed a minimum resulted from interplay between two concurring processes, liquid-liquid phase separation that led to decrease in T(g), 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.

    Journal Title

    Journal of the American Ceramic Society

    Volume

    94

    Issue/Number

    9

    Publication Date

    1-1-2011

    Document Type

    Article

    Language

    English

    First Page

    2906

    Last Page

    2911

    WOS Identifier

    WOS:000295215900038

    ISSN

    0002-7820

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