Effects of specimen thickness and impurity on the conductivity of alumina under electron irradiation

The electrical conductivity of undoped (125, 332 and 545 μm-thick) and Cr3+ doped (332 μm-thick) α-Al2O3 single crystals was measured under electron irradiation at temperatures from 300 to 723 K. The conductivity under the ITER environment is found to be less than the limiting conductivity of 10−4 S/m required for insulators in ITER. Although the Cr3+ doping increases the electrical conductivity, it suppresses the radiation induced conductivity at higher ionization fields. The impurities in Cr3+ doped α-Al2O3 are acting as trapping sites or recombination centers for carriers, affecting the electrical resistivity. The radiation induced conductivity in undoped α-Al2O3 increases with increasing specimen thickness, which is explained in terms of the increase of energy absorption with increasing specimen thickness. No radiation induced electrical degradation was found in both undoped and Cr3+ doped α-Al2O3 in the present study.