Microstructural inhomogeneities in chemically derived Ba2YCu3O7−x thin films: Implications for flux pinning

Abstract

A gradient in the density of polytypoidal stacking faults was observed through the thickness of chemically derived epitaxial Ba2YCu3O7−x (BYC) films on (001) LaAlO3. Cross-sectional TEM studies indicated that films of less than 100 nm thickness were faulted, with a high density of polytypoidal stacking faults. A decrease in stacking fault density in thicker films (300-500 nm thick) was found with increasing distance from the most defective layer near the film/substrate interface. An abrupt transition from highly faulted material near the substrate to essentially stacking fault-free BYC in the upper part of the films was observed in several cases. The present observations are compared with the previously reported1 decrease in critical current density with increasing thickness of these films. Possible implications for flux pinning in BYC thin films are discussed.