MICROSTRUCTURAL STUDY OF GROWTH OF A YBA2CU3O7-X LAALO3/YBA2CU3O7-X TRILAYERED FILM BY PULSED-LASER DEPOSITION/

The growth process of a YBCO/LaAlO3/YBCO trilayered film made by pulse d laser deposition has been studied by high resolution transmission el ectron microscopy (HRTEM). The high resolution images of the cross-sec tion samples have shown that a 7 nm layer of LaAlO3 has been grown epi taxially between c-axis oriented YBCO layers having the nominal thickn ess of 250 nm. A stacking fault in the LaAlO3 layer may introduce a st acking fault into the YBCO layer, which may form nucleation sites for a-axis oriented grains. A second phase had been formed at the interfac e between the LaAlO3 layer and the lower YBCO layer, which has been id entified by image simulation and energy dispersive x-ray (EDX) analysi s as a new tetragonal La-Al-Cu-O phase based on LaAlO3 in which some o f Al atoms have been replaced by Cu. The approximate lattice parameter s of the new phase are a = 0.38 nm and c = 0.76 nm. However, no second phase was found at the interface between the lower YBCO layer and the LaAlO3 substrate.