Comparative study on the crack formations in the CeO2 buffer layers for YBCO films on textured Ni tapes and Pt tapes

Abstract

The crack formations in the CeO2 buffer layers on textured Ni tapes and Pt tapes, which were used for the substrates of the high T-c superconducting YBCO films, were comparatively studied. Since these two metallic tapes, which were textured by rolling and recrystallization, have very different properties of thermal expansion coefficients, lattice matching conditions, and chemical reactivities with the buffer layers, the comparisons of their buffer layer growth features were suggestive. Both Ni and Pt showed no salient reactive diffusion in the interface with the buffer layers. Numerous cracks were formed in the CeO2 buffer layer on Ni, while very few cracks were formed in the buffer layer on Pt. These results indicated it was unlikely that the effect of the thermal expansion coefficient differences of the films and the substrate caused the cracks. The CeO2 film deposited by the sputtering method on the thin template CeO2 film predeposited on Ni by e-beam evaporation, showed very few cracks. Detailed SEM observations indicated a possible relation between the cause of the crack formations and the lattice mismatching which seemed to distort the lattices and to produce the lattice defects. (C) 1998 Elsevier Science B.V. All rights reserved.