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

Transparent glass-ceramics (GCs) containing NaNbO ₃ as the major crystalline phase have been synthesized at low temperatures of 750 and 800 °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 °C gives an average value of the Avrami index ( n) ∼ 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 NaNbO ₃ 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 °C for 5 h. The dissipation factor decreases from the base glass (5.11 × 10 ⁻³) to the GC samples up to a minimum value of 8.79 × 10 ⁻⁵.