Crystallization Behavior and Dielectric Properties of Ferroelectric Glass-ceramics Containing BNN and NN Crystals

Abstract

Glass samples with compositions of 16Na2O-8BaO-26Nb2O5-50SiO2 (mol%) were prepared using the melt-quenching method and then heat-treated under different temperatures and times. The resulting crystallization behavior was then studied through X-ray diffraction and scanning electron microscopy, and the dielectric properties were measured using an impedance analyzer in the frequency range 10 Hz–10 MHz. The experimental results showed that all of the obtained glass-ceramic samples heat treated using different temperatures and times contained mixed-crystalline phases between Ba2NaNb5O15 (BNN) with tungsten-bronze structure and NaNbO3 (NN) with a perovskite structure. The crystals of these two phases were distributed randomly throughout the bulk glass-ceramics at the nano-scale. The plots of the dielectric constant versus the measurement temperature reveal a serial phase transition with a complex mechanism of the dielectric relaxation. The serial phase transition is related to the dielectric response of both the BNN and the NaNbO3 crystals. Also, the presence of the BNN phase tended to lower the Curie's temperature. The dielectric spectroscopic investigations revealed that a dipolar polarization mechanism is responsible for the dielectric contribution of the bulk glass-ceramics. The presence of the BNN phase gave the ferroelectric glass-ceramics higher dielectric constants. The dielectric properties of the glass-ceramics were found to be highly sensitive to changes in treatment conditions. An increase in treatment temperature gave rise to glass-ceramics with larger crystallites and higher dielectric permittivity but an increase in treatment time also allowed the glass matrix to be annealed with the effect being a lower dielectric permittivity and lower phase transition levels.