Structural inhomogeneities in thin epitaxial films of YBa2Cu3O7-δ and their effects on superconducting properties

Structural inhomogeneities in thin single-crystal films of YBa2Cu3O7-δ are characterized using high resolution X-ray diffraction. Results of these measurements show a distribution in the c-axis lattice parameter and variations in the integrated intensities of (00) diffraction peaks. Both effects can be interpreted as due to a variance in the oxygen content. Films prepared under identical growth conditions, when subjected to different post-annealing treatments showed varying structural and superconducting properties. A film with 7-δ close to 7.0 had a transition temperature (Tc) of 91 K, a width (ΔTc) of 0.6 K, and a critical current density (Jc) of 6.5 x 106 A/cm2, whereas a film in which the oxygen content varied between 6.86 and 6.96 had a Tc of 87 K, a ΔTc of 0.5 K, and a Jc of 8.17 x 106 A/cm2. For each of the samples measured, the full width at half maximum (FWHM) of the (006) diffraction peak ranged between 340 and 2100 arc-seconds and was dependent on the method of preparation and the substrate. The Jcs of these films were not sensitive to the quality of the film, as determined from the FWHM of the (006) peak, and the oxygen content, as determined from the (005) to (006) integrated intensity ratio. High resolution X-ray topographs showed uniform microstructure of the films, indicating that oxygen distribution is finely dispersed in the film. (orig.)