Glass ceramic dielectrics: Energy storage and breakdown

The possible use of glass ceramics as high energy density capacitors in heart defibrillators and hybrid automotive vehicles is explored. Glass ceramics, lead sodium niobate silicate (PNNS), barium sodium niobate silicate (BNNS) and barium titanate silicate (BTS), allow the development of dielectrics with various permittivity values ranging from 20 to 700. Glasses were formed by melt-rolling the respective constituents which were then crystallized by reheating the glass at higher temperatures. Heat treatment schedules were formulated based on DTA results. A spectrum of crystalline phases, ranging from perovskites, tungsten bronzes and pyrochlores to fresnoites, were generated within the various glass matrices. Disadvantages, such as difficult glass formability, less control over crystallization due to multiphase formation etc., associated with high permittivity PNNS and BNNS glass ceramics served as the motivating factor for exploring low permittivity glass ceramics. BTS glass ceramics exhibit excellent stability in permittivity, high resistivity and low loss over the measured range of temperature. Thin samples with pristine surfaces are required for achieving high breakdown strength values. Investigation of the crystallization kinetics of BTS glass would provide further insight into exploring glass nano-composites, analogous to polymer nano-composites.