High-resolution electron microscopy investigations of stacking faults in Y_1Ba_2Cu_3O_7-δ metalorganic chemical vapor deposited thin films

摘要

New structural planar defects in Ba-deficient Y_1Ba_2Cu_3O_7-δ (YBCO) (l: 1.6:3) thin films grown on NdGaO_3 and SrTiO_3, substrates by metalorganic chemical vapor deposition have been observed by means of high-resolution electron microscopy. The defects are associated with perturbations of the YBCO "l:2:3" stacking sequences along the c direction, which give rise to structural variants with locally "2:5:7" "3:4:7," or "4:6:10" cationic stoichiometries. The defects can be consistently interpreted as CuO-YO-CuO/CuO conversions or YO/BaO (BaO/YO) interconversions in the (a,b) planes and extending over a few nanometers along the c axis. Structural models based on image matching with simulations are proposed for two particular cases. It is thought that these structural imperfections can be effective sites of flux pinning.