MICROSTRUCTURAL INHOMOGENEITIES IN CHEMICALLY DERIVED BA2YCU3O7-X THIN-FILMS - IMPLICATIONS FOR FLUX-PINNING

A gradient in the density of polytypoidal stacking faults was observed through the thickness of chemically derived epitaxial Ba2YCu3O7-x (BY C) films on (001) LaAlO3. Cross-sectional TEM studies indicated that f ilms of less than 100 nm thickness were faulted, with a high density o f polytypoidal stacking faults. A decrease in stacking fault density i n thicker films (300-500 nm thick) was found with increasing distance from the most defective layer near the film/substrate interface. An ab rupt transition from highly faulted material near the substrate to ess entially stacking fault-free BYC in the upper part of the films was ob served in several cases. The present observations are compared with th e previously reported(1) decrease in critical current density with inc reasing thickness of these films. Possible implications for flux pinni ng in BYC thin films are discussed.