Glass crystallization by ion exchange: formation of NaNbO3 in thick films at the glass surface

Experimental results of studying a lithium–sodium high-temperature ion exchange in a lithium–niobium–silicate glass are presented. It has been discovered that the ion exchange brings forth glass crystallization. The crystals precipitating in the diffused layers and identified by X-ray diffraction (XRD) analysis are orthorhombic (and/or quasicubic) NaNbO3. Depending on the temperature–time conditions of the ion-exchange processing, surface glass-ceramic films of different thicknesses have been formed. The phenomenon and the conditions that produce it are discussed in terms of the theory of phase equilibria in liquid solutions. This work completes the topic (developed by the authors during the last few years) concerning the possibility to control any phase transformations in glasses (including liquid–liquid phase separation and crystallization) by the ion-exchange technique.