Irradiation spectrum and ionization-induced diffusion effects in ceramics

There are two main components to the irradiation spectrum which need to be considered in radiation effects studies on nonmetals, namely the primary knock-on atom energy spectrum and ionizing radiation. The published low-temperature studies on Al2O3 and MgO suggest that the defect production is nearly independent of the average primary knock-on atom energy, in sharp contrast to the situation for metals. On the other hand, ionizing radiation has been shown to exert a pronounced influence on the microstructural evolution of both semiconductors and insulators under certain conditions. Recent work on the microstructure of ion-irradiated ceramics is summarized, which provides evidence for significant ionization-induced diffusion. Polycrystalline samples of MgO, Al2O3, and MgAl2O4 were irradiated with various ions ranging from 1 MeV H+ to 4 MeV Zr+ ions at temperatures between 25 and 650 degrees C. Cross-section transmission electron microscopy was used to investigate the depth-dependent microstructural of the irradiated specimens. Dislocation loop nucleation was effectively suppressed in specimens irradiated with light ions, whereas the growth rate of dislocation loops was enhanced. The sensitivity to irradiation spectrum is attributed to ionization-induced diffusion. The interstitial migration energies in MgAl2O4 and Al2O3 are estimated to be ≤0.4 eV and ≤0.8 eV, respectively for irradiation conditions where ionization-induced diffusion effects are expected to be negligible