Sodium niobate-based glass-ceramics: Dependence of crystallization temperature on phase evolution, refractive index and dielectric properties

Transparent glass-ceramics (GCs) containing NaNbO3 as the major crystalline phase have been synthesized at low temperatures of 750 and 800 degrees C, which were confirmed from XRD, TEM and FESEM analysis. Johnson-Mehl-Avrami-Erofeev-Kolmogorov (JMAK) model fitting approach of conversion versus time at temperatures from 800 to 900 degrees C gives an average value of the Avrami index (n) similar to 3 which points towards the predominant bulk nucleation and growth. Interestingly, an increase of non-linear third order optical susceptibility of the GCs has been observed, when compared with the base glass, due to progressive evolution of the non-centrosymmetric NaNbO3 crystal phase upon crystallization. The dielectric constant (at 1 kHz) increases five-fold from the base glass (17.6) to the GC samples up to 93.6 for the sample heat-treated at 850 degrees C for 5 h. The dissipation factor decreases from the base glass (5.11 x 10(-3)) to the GC samples up to a minimum value of 8.79 x 10(-5).