COMPARATIVE-STUDY ON THE CRACK FORMATIONS IN THE CEO2 BUFFER LAYERS FOR YBCO FILMS ON TEXTURED NI TAPES AND PT TAPES

The crack formations in the CeO2 buffer layers on textured Ni tapes an d Pt tapes, which were used for the substrates of the high T-c superco nducting YBCO films, were comparatively studied. Since these two metal lic tapes, which were textured by rolling and recrystallization, have very different properties of thermal expansion coefficients, lattice m atching 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 th ermal expansion coefficient differences of the films and the substrate caused the cracks. The CeO2 film deposited by the sputtering method o n the thin template CeO2 film predeposited on Ni by e-beam evaporation , showed very few cracks. Detailed SEM observations indicated a possib le relation between the cause of the crack formations and the lattice mismatching which seemed to distort the lattices and to produce the la ttice defects. (C) 1998 Elsevier Science B.V. All rights reserved.