Electron-beam-irradiation effects in bulk YBa,Cu, OTB-X

Irradiation effects on thin foils of bulk YBa, Cu, 0, _ x have been studied in a transmission electron microscope using lOO-, 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 0( 5) sites in the Cu-0 planes during irradiation was monitored by measuring the splitting of the (li0) diffraction spots in the [OOl ] diffraction pattern. The results show that YBa, Cu, 0, _ x is insensitive to lOO-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 YBa, Cu, 0, _ x is around 18 eV and that irradiation-assisted oxygen reordering occurs in YBa, Cu, 0, _ x at 300 K, but not at 83 K.