Nanocomposite Dielectrics in PbO–BaO–Na₂O–Nb₂O₅–SiO₂ System with High Breakdown Strength for High Voltage Capacitor Applications

Nanocomposite dielectrics in 6PbO–4BaO–20Na₂O–40Nb₂O₅–30SiO₂ system were prepared via melt-quenching followed by controlled crystallization. X-ray diffraction studies reveal that Pb₂Nb₂O₇, Ba₂NaNb₅O₁₅, NaNbO₃ and PbNb₂O₆ phases are formed from the as-quenched glass annealed in temperature range from 700°C to 850°C. Ba₂NaNb₅O₁₅, Pb₂Nb₂O₇ crystallizes at 700°C and then Pb₂Nb₂O₇ disappears at 850°C, while PbNb₂O₆ and NaNbO₃ are formed at 850°C. Microstructural observation shows that the crystallized particles are nanometer-sized and randomly distributed with glass matrix being often found at grain boundaries. The dielectric constant of the nanocomposites formed at different crystallization temperatures shows good frequency and electric field stability. The breakdown strength is slightly decreased when the glass-ceramics thickness is varied from 1 mm to 4 mm. The corresponding energy density could reach 2.96 J/cm³ with a breakdown strength of 58 kV/mm for thickness of 1 mm.