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

Abstract

The electrical conductivity of undoped (125, 332 and 545 μm-thick) and Cr 3+ doped (332 μm-thick) α-Al 2O 3 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 Cr 3+ doping increases the electrical conductivity, it suppresses the radiation induced conductivity at higher ionization fields. The impurities in Cr 3+ doped α-Al 2O 3 are acting as trapping sites or recombination centers for carriers, affecting the electrical resistivity. The radiation induced conductivity in undoped α-Al 2O 3 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 Cr 3+ doped α-Al 2O 3 in the present study.