[en] Cross section transmission electron microscopy was utilized to examine the radiation-induced microstructural changes in oxide ceramics after irradiation with a wide variety of ion beams. The microstructure showed a strong dependence on ion mass and energy. The microstructural results have been correlated with the calculated depth-dependent partitioning between ionization an displacement damage. This correlation indicates that defect clusters do not form in MgAl₂O₄ if the ratio of energy deposited into electronic ionization to atomic displacements is greater than about 10. The corresponding ratio needed to suppress defect cluster formation in MgO and Al₂O₃ is 500 to 1000. Additional microstructural evidence obtained on the irradiated ceramic specimens suggest that the physical mechanism responsible for the lack of defect clusters in highly ionizing radiation environments is associated with ionization-enhanced diffusion (IED), which promotes annihilation of the point defects created by displacement damage during the irradiation. The most important parameter for IED is the ratio of ionizing to displacive radiation, since this is roughly proportional to the amount of ionization per dpa. However, the absolute magnitude of the ionizing radiation flux is also important