MICROCRACKS OBSERVED IN EPITAXIAL THIN-FILMS OF YBA2CU3O7-DELTA AND GDBA2CU3O7-DELTA

Microcracking of epitaxially c-oriented YBa2Cu3O7-delta and GdBa2Cu3O7 -delta thin films is observed to preferentially occur on buffered, R-c ut sapphire substrates of 3 in diameter in comparison to smaller subst rates and other substrate materials such as MgO, SrTiO3, and LaAlO3. T he area density and the crystallographic appearance of the crack patte rn can vary considerably across a given surface, from sample to sample , and in dependence on the temperature treatment. These dependencies i ndicate the crack behaviour to be seriously affected by the microstruc ture. The latter is studied by optical, electron, and atomic force mic roscopy. Cross-sectioning TEM reveals cracks to locally separate the H TSC him from the buffer layer. Optical microscopy using transmitted po larized light is found to be a straightforward, sensitive survey metho d to observe the microcracking behaviour.