Abstract
We report an in situ transmission electron microscopy study of damage evolution Eu—Ba—Cu—O and Gd—Ba—Cu—O ceramics under 50keV He ion irradiation. Our results on the irradiation-induced orthorhombic to tetragonal phase transformation (OTT) complement previous work. We report observations on the existence and evolution of defect clusters at 15 and 300 K, as well as the first evidence for the interaction of defects with pre-existing dislocations. We have also studied the dependence of the irradiation-induced amorphization threshold on the cation species and on the irradiation temperature. Taken together, these results lead us to propose the existence of at least two types of irradiation defects: an anionic defect (associated with oxygen) and a cationic defect. The former (which is mobile at 15 K) leads to defect clustering and interaction with dislocations; it is also related to the OTT. The latter is less mobile and is presumably instrumental in the amorphization process. We also point out that the occasional disproportionation (i.e. Cu2O formation) of the material is an artefact caused by long-term surface layer instability.