Electron‐beam‐irradiation effects in bulk YBa₂Cu₃O_7−x

Irradiation effects on thin foils of bulk YBa₂Cu₃O_7−x have been studied in a transmission electron microscope using 100‐, 150‐, 200‐, 250‐, and 300‐keV electrons at 83 and 300 K. The disordering of the oxygen atoms and vacancies in the O(4) and O(5) sites in the Cu‐O planes during irradiation was monitored by measuring the splitting of the (11̄0) diffraction spots in the [001] diffraction pattern. The results show that YBa₂Cu₃O_7−x is insensitive to 100‐keV electron irradiation. Irradiation by higher‐energy electrons leads to irradiation‐induced oxygen disordering of the oxygen atoms and vacancies, mainly by single displacement events. The excellent fit of the data to a disordering model suggests that the displacement threshold energy for oxygen in YBa₂Cu₃O_7−x is around 18 eV and that irradiation‐assisted oxygen reordering occurs in YBa₂Cu₃O_7−x at 300 K, but not at 83 K.