Dielectric Properties of Ferroelectric Glass-Ceramics of the Na2O-K2O-Nb2O5-Al2O3-SiO2 System with Partial Substitution of K2O for Na2O

Substitution of K2O for Na2O content was performed in ferroelectric glass-ceramics of the Na2O-Nb2O5-Al2O3-SiO2 system and its effect on crystallization process and the associated properties were investigated. Conventional melt quenching method was employed for parent glass production. Phase identification shows that NaNbO3 perovskite phase is crystallized spontaneously during quenching along with other two phases, NaNbO8 and phase of the sodium alumino silicate compound. No evidence of complex phases occurring due to presence of K2O. However, the results of dielectric measurements revealed complex phase transition from room temperature up to 400 degrees C. First order transition can be observed in range 150 degrees C-250 degrees C. While the main transition seen in dielectric-temperature plot is at 380 degrees C with dielectric constant of 1370 (at 1 kHz). This is associated to transition of NaNbO3 from orthorhombic to perovskite cell with cubic symmetry. Higher dielectric loss is observed at higher temperature. It is also noted that entering of K2O content reduce dielectric constant of the glass-ceramics system.