Daniela Seiler

Glass ceramics as dielectrics for high power capacitors

These glass ceramics are produced in a two-step process. In a first step a transparent glass with a solely amorphous structure is molten. In a second and independent step crystallites are grown in such glasses by applying a well defined time-temperature profile. By growing nanosized crystallites with ferro- or para-electric phases, pore free dielectric materials with very high homogeneity and high dielectric strength are obtained. In the current paper we present two types of such material. The first one (i), PoweramicTM-P2200, has a ferroelectric crystalline phase and has a dielectric constant of H= 220 together with a positive temperature coefficient. It exhibits excellent dielectric properties for temperatures up to 200°C. The second material (ii), PoweramicTM-NP0 (preliminary naming), has a dielectric constant of H= 40, a true NP0 temperature characteristic and shows very useful dielectric properties for temperatures up to 300°C. Such glass ceramics have further very high dielectric breakdown strength of up to 85 kV/mm measured on 200 Πm thick samples. The application of this new material class for high power capacitors is discussed.