On the conflicting roles of ionizing radiation in ceramics

Ionizing radiation can produce competing effects in ceramic materials. It is well established that ionizing radiation can produce displacement damage via radiolysis in alkali halides and some other ceramics. At high stopping powers (electronic dE/dx > 5-50 keV/nm, depending on the material), additional displacement damage via inelastic collision processes can also be created in the vicinity of the ion track (swift-heavy-ion displacement damage). On the other hand, ionizing radiation can promote the recovery of displacement damage in many ceramic insulators by enhancing the mobility of point defects (ionization-induced diffusion). Therefore, under different irradiation conditions (electronic stopping powers), ionizing radiation can lead to either a substantial enhancement or suppression of radiation resistance in ceramics. The microstructures of SiC, Al₂O₃, MgO, MgAl₂O₄, Si₃N₄ and AlN were examined by transmission electron microscopy (TEM) following irradiation with ion beams ranging from 1 MeV H⁺ to 710 MeV Bi⁺. The oxides and Si₃N₄ were found to be susceptible to ionization-induced diffusion. In these materials, high fluxes of ionizing radiation produced coarsening of dislocation loops and cavities, and inhibited low-temperature amorphization. At high electronic stopping powers, displacement damage was produced in the ion tracks in the oxides and Si₃N₄ that could not be attributed to normal elastic collision processes. The amorphous ion track diameter in Si₃N₄ associated with 710 MeV Bi ion irradiation was 3.5 nm. AlN and SiC were resistant to swift-heavy-ion-track displacement damage up to electronic stopping powers of 34 keV/nm.