KINETIC-STUDY OF DEFECT CLUSTERS IN THE MGO-AL2O3 SYSTEM UNDER ELECTRON-IRRADIATION AND OR ION-IRRADIATION

The kinetic behavior of defect clusters in MgO, alpha-Al2O3 and MgAl2O4 under electron irradiation has been examined through in-situ observation using high-voltage electron microscopy. Irradiation with 1 MeV electrons induces interstitial type dislocation loops in MgO and alpha-Al2O3. No loops are observed in MgAl2O4 during 1 MeV electron irradiation, but Ar+ ions with energy higher than 1 keV introduce loops. The loop kinetics in MgO is analogous to that for pure metals. Based on the kinetics, the migration energy of oxygen vacancies and the displacement threshold energy of oxygen ions are estimated to be 2.03 +/- 0.17 and 30 +/- 8 eV, respectively. Large nuclei of interstitial loops and/or a large number of vacant sites control the kinetic behavior of loops in alpha-Al2O3. The structural vacancies and large nucleation sites make the nucleation in MgAl2O4 difficult, and they are effective for designing radiation-resistant materials.