Dielectric breakdown, partial discharge and electrical microcracking in $BaTiO_3$

Abstract

Dielectric breakdown is one of the primary drawbacks for ceramic capacitors. The majority of ceramic capacitors are still fabricated with $BaTiO_3$. In ceramics, breakdown is caused by electrical discharges. Recently, the partial discharges in $BaTiO_3$ have been investigated. In order to investigate the correlations between partial discharge, breakdown, and microstructure of the ferroelectric ceramics, breakdown and partial discharge inception field were measured for $BaTiO_3$ ceramics which have different pore size distribution. The $BaTiO_3$ ceramics used in this study were sintered at either 1300℃, 1350℃, 1400℃ or 1450℃ to vary pore size distribution. Pore size of barium titanate ceramics increased with sintering temperature. The breakdown field and partial discharge inception field decreased with increase of sintering temperature. This means that the large pores in over-fired $BaTiO_3$, having relatively low inception voltage of partial discharge, lowered the breakdown field. Electrical microcracks have been observed in pole PZT and $BaTiO_3$ ceramics. It, however, has not been certain whether the microcracks occur at the grain boundaries or at the blocked domain boundaries. In order to clear it, grain size dependence of the electrical microcracking should be studied. High dc field was applied to $BaTiO_3$ ceramics which have different grain size. During poling of $BaTiO_3$, microcracks occur at the grain boundaries and propagate into the grains. The amounts of them become larger with increasing the extrinsic parameters such as poling field and time, or the intrinsic parameters such as tetragonality and grain size.