Effects of pores on dielectric breakdown of alumina ceramics under AC electric field

The relationship between pores and dielectric breakdown strength of alumina ceramics has been investigated. Alumina specimens with different internal pores in size and quantity were obtained with polyvinyl alcohol (PVA) granules additives being removed after sintering. Pores inside the ceramic samples were characterized by density measurement and micro computed tomography (Micro Cr) analysis. We tested the breakdown strength of different alumina sheets under AC electric field, with the same electrodes and voltage loading methods being adopted. The experimental results indicated that the dielectric breakdown strength of alumina specimens decreased with the increment of their thickness. Interestingly, a great deal of large pores influences the breakdown strength significantly. And the breakdown channel passes through the large hole when there is a large hole in the sample. Small pores have little effects on the insulating properties. Further discussion and analysis reveal that the measured results of breakdown strength conform to the Weibull distribution. In addition, the experimental results can be well explained by space charge injection models and electric field simulation.