Microstructure of epitaxially oriented superconducting YBa2Cu3O7−<i>x</i> films grown on (100) MgO by metalorganic decomposition

Abstract

The microstructure in epitaxially oriented thin films of YBa2Cu3O7−x grown on (100) MgO by metalorganic decomposition has been studied by transmission electron microscopy and ion channeling. The as-prepared films consisted of single-crystal platelets lying flat on the MgO surface. The majority of the crystallites showed perfect alignment of their c axis with the [100] axis of MgO, while some crystallites were found to have a misorientation of up to 7.5°. Images of the interfacial regions showed good epitaxial growth to within one lattice spacing of the MgO substrate. He++ channeling measurements as a function of energy from 1 to 4.5 MeV indicated a 0.51° spread in crystallite orientation. Extrapolation of the channeling measurements to the limit of zero crystallite spread gave a minimum yield of 0.20 for bulk YBa2Cu3O7−x , which is much larger than the value reported for single crystals. The large backscattering yield is attributed to the grain boundaries in the film. A relatively strain-free interface was indicated by channeling results.