INFLUENCE OF OH- ION POINT-DEFECT COMPLEXES ON THE ELECTRON-IRRADIATION DAMAGE RESPONSE OF MGO CRYSTALS

Microstructural evolution and radiation damage kinetics have been stud ied in a wide variety of MgO single crystals by in-situ observations u nder electron irradiation in a high-voltage electron microscope. Elect ron irradiation induces interstitial dislocation loops, no defect clus ters and bubbles in MgO crystals, depending on the source and the hist ory of the crystals. We have found evidence that the presence of struc tural vacancies in MgO may suppress the nucleation and growth of dislo cation loops during electron irradiation, thereby enhancing the radiat ion resistance of this ceramic. The vacancies that appear to promote r adiation tolerance in MgO are related to the incorporation of OH- ions in the crystal lattice. In fact, these vacancies are actually point-d efect complexes, consisting of one or two OH- ions residing on O latti ce sites, together with a vacancy on a Mg site. These configurations y ield either a fully charge-compensated point defect complex ((OHVMg)-V -.'' HO.)(X) or a singly charged point-defect complex ((OHVMg)-V-.'')' .