Microstructural inhomogeneities in chemically derived Ba₂YCu₃O_7−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 Ba₂YCu₃O_7−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.