STRUCTURAL INHOMOGENEITIES IN THIN EPITAXIAL-FILMS OF YBA2CU3O7-DELTAAND THEIR EFFECTS ON SUPERCONDUCTING PROPERTIES

Structural inhomogeneities in thin single-crystal films of YBa2Cu3O7-d elta are characterized using high resolution X-ray diffraction. Result s of these measurements show a distribution in the c-axis lattice para meter and variations in the integrated intensities of (OOl) diffractio n peaks. Both effects can be interpreted as due to a variance in the o xygen content. Films prepared under identical growth conditions, when subjected to different post-annealing treatments showed varying struct ural and superconducting properties. A film with 7-delta close to 7.0 had a transition temperature (T-c) of 91 K, a width (Delta T-c) of 0.6 K, and a critical current density (J(c)) of 6.5 x 10(6) A/cm(2), wher eas a film in which the oxygen content varied between 6.86 and 6.96 ha d a T-c of 87 K, a Delta T-c of 0.5 K, and a J(c) of 8.17 x 10(6) A/cm (2). For each of the samples measured, the full width at half maximum (FWHM) of the (006) diffraction peak ranged between 340 and 2100 are-s econds and was dependent on the method of preparation and the substrat e. The J(c)s of these films were not sensitive to the quality of the f ilm, as determined from the FWHM of the (006) peak, and the oxygen con tent, as determined from the (005) to (006) integrated intensity ratio . High resolution X-ray topographs showed uniform microstructure of th e films, indicating that oxygen distribution is finely dispersed in th e film. (C) 1997 Elsevier Science S.A.