Dielectric breakdown of alumina single crystals

The bulk breakdown behaviour of alumina single crystals with two different crystal orientations, { 1   1   2 ¯   0 } -plane (single crystal A) and {0 0 0 1} -plane (single crystal C), have been studied. Therefore, plan-parallel single crystal samples were electrically loaded until dielectric breakdown was achieved. For each crystal orientation, a characteristic breakdown channel direction through the sample could be defined. In C-oriented crystals the breakdown channel originated parallel to the c-axis. For A-oriented crystals, however, the breakdown channel crossed the sample in an oblique direction; the angle between crystal surface and breakdown channel was 60°. Here, the breakdown channel crossed the sample along an A-plane. Although the breakdown channel paths of A and C crystals are different, the observed breakdown strength are identical within the scatter range.