MICROSTRUCTURE OF ION-IRRADIATED CERAMIC INSULATORS

Cross-section transmission electron microscopy was utilized to examine the radiation-induced microstructural changes in Al2O3, MgO, Si3N4 and MgAl2O4 after irradiation with a wide variety of energetic ion beams. The relative influence of ionizing and displacive radiation was studied by systematically varying the mass and energy of the bombarding ions between 1 MeV H+ and 4 MeV Zr3+ ions. The measured ion ranges were between 1 and 15% greater than the ranges calculated by the TRIM code, with the largest discrepancies occurring for intermediate mass ions. The implanted ions exerted a strong influence on the overall microstructural evolution of the irradiated ceramics. Numerous microstructural features (e.g., amorphization, colloids) were produced in the implanted ion regions which could not be produced in irradiated regions that were well separated from the implanted ions. The microstructural evolution in regions welt separated from the implanted ions was found to depend strongly on the mass and energy of the bombarding ion. Light ion irradiation produced a significant enhancement in point defect diffusion (evidenced by defect free zones at the surface and adjacent to internal defect sinks) compared to heavy ion irradiation at the same damage rate. Similarly, irradiation with a given ion at a higher flux generally produced an increased amount of observable diffusion. In some cases such as 1 MeV proton irradiation, observable defect clusters did not form. This suppression in defect cluster formation may be due to the high amount of point defect recombination associated with ionization enhanced diffusion that occurs during energetic light ion irradiation.