IRRADIATION EXPERIMENTS ON HIGH-TEMPERATURE SUPERCONDUCTOR THIN-FILMS

Thin single crystalline REBaCuO films (RE = rare earth) grown in different orientations ([100], [001], [110]) were irradiated with 300 keV H+ and He+ ions at room temperature. Investigations of the ion-induced changes of the transport and especially of the structural properties were performed. The superconducting properties degrade and the unit cell expands under H+ and He+ irradiations. The loss of superconductivity is not directly connected with an orthorhombic to tetragonal phase transformation for proton irradiated films as in oxygen deficient samples. In alpha-axis grown films irradiated with protons we observed the formation of a new root 2a(c)x root 2a(c)x3a(c)(a(c) approximate to 3.8 Angstrom) superstructure induced by oxygen reordering in the basal plane of the unit cell. This is thought to be strongly correlated with the observed metal-insulator transition due to carrier concentration reduction in the CuO2 planes. Distinct X-ray intensity variations indicate atomic displacements in the cationic sublattices. At higher fluences (i.e. 0.02 dpa) an amorphization process sets in, probably driven by strain in the irradiated films.