“…It is assumed that the initiation of breakdown happens, due to a sudden destabilization of trapped charges [1][2][3], which causes a current flow through the material. The breakdown strength, E b , defined as breakdown voltage, V b , per sample thickness, t, is reported to be dependent on the microstructure [2][3][4], sample thickness [5][6][7][8][9] and loading condition [8,[10][11][12]. The influence of the porosity [2,[13][14][15], grain size [2-4, 13, 15-17], purity and secondary phase [2-4, 6, 7] on the breakdown strength have been investigated.…”