Preparation and characterization of dielectric glass-ceramics in Na2O–PbO–Nb2O5–SiO2 system

Glass-ceramics in the Na2O–PbO–Nb2O5–SiO2 system have been synthesized to produce bulk materials with nanometer-sized crystals grown in a glass phase via roll-quenching followed by controlled crystallization. X-ray diffraction studies indicate that Pb2Nb2O7, NaNbO3 and PbNb2O6 phases are formed from the as-quenched glass in temperature range from 750 to 900 °C. Pb2Nb2O7 crystallizes at 750 °C and disappears at 850 °C, NaNbO3 is the primary phase at 850 °C, while PbNb2O6 is formed at a higher temperature of 900 °C. The dielectric properties of the glass-ceramics formed through controlled crystallization have a strong dependence on the phase assemblages that are developed during heat treatment. The highest dielectric constants (> 600) were found in samples annealed at 850 °C for 3 h. Microstructural observation shows that randomly oriented, nanometer-sized crystalline are found with residual glass concentrated at crystallite boundaries. Further studies by scanning tunneling electron microscopy (STEM) in conjunction with energy dispersive spectroscopy (EDS) reveals inhomogeneous distribution of NaNbO3 and PbNb2O6 in the sample annealed at 850 °C for 3 h and these phases contribute to the high dielectric constant.