In situ measurement of electrical conductivity of alumina under electron irradiation in a high voltage electron microscope

Abstract

Radiation induced conductivity (RIC), thermally stimulated conductivity (TSC) and radiation induced electrical degradation (RIED) are major concerns of insulating ceramic materials under the effects of flux, electric field and temperature and may lessen their performance in fusion reactors. In situ measurements of the electrical conductivity of single crystal α-Al 2O3 (alumina) using the standard electric guarding technique has been performed under I MeV electron irradiation with an applied electric field of 93 kV/m at temperatures ranging from room temperature to 723 K. Experimental results imply that electronic excitation associated with radiation induced defects controls RIC of α-Al 2O 3 and show that TSC, especially the transient peak resulting from excess charges stored in defects, may affect the performance of α-Al 2O 3 in fusion reactors. A significant surface conductivity is confirmed from a 1 MeV electron dose of 3 × 10 22 e/m 2 (3.3 × 10 −5 dpa) but no substantial bulk degradation is found under irradiation up to a dose of 7.1 × 10 22 e/m 2 (7.7 × 10 -5 dpa) at 723 K. In conclusion, it is emphasized that RIC and RIED of α-Al 2O 3 are not severe for insulators in the International Thermonuclear Experimental Reactor (ITER) but TSC could limit their applications even to ITER.