IRRADIATION EXPERIMENTS ON HIGH-TEMPERATURE SUPERCONDUCTOR THIN-FILMS

Thin single crystalline REBaCuO films (RE = rare earth) grown in diffe rent 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 w ere performed. The superconducting properties degrade and the unit cel l expands under H+ and He+ irradiations. The loss of superconductivity is not directly connected with an orthorhombic to tetragonal phase tr ansformation for proton irradiated films as in oxygen deficient sample s. In alpha-axis grown films irradiated with protons we observed the f ormation 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 pl ane of the unit cell. This is thought to be strongly correlated with t he observed metal-insulator transition due to carrier concentration re duction in the CuO2 planes. Distinct X-ray intensity variations indica te atomic displacements in the cationic sublattices. At higher fluence s (i.e. 0.02 dpa) an amorphization process sets in, probably driven by strain in the irradiated films.