Electrical Breakdown Strength of Alumina at High Temperatures

The dc electrical strength of sapphire and poly crystalline alumina was studied up to 1400°C. The electrical strength was essentially identical for both materials. It was > 10⁶ V/cm at room temperature and decreased gradually with temperature up to 900°C (2.6×10⁵ V/ cm), then dropped rapidly to 2×10⁴ V/cm at 1400°C for a sample thickness of ∼ 100 μm. The electrical strength decreased with the sample thickness. It was inversely proportional to the thickness for samples thicker than ∼ 600 μm at 1200°C. The breakdown behavior was explained on the basis of a thermal breakdown model.