Microstructures and transport properties: A comparison between grain boundaries artificially produced in YBa2Cu3Ov bicrystal thin films and bulk crystals

Abstract

In order to establish the link between grain boundary (GB) structures and transport properties in superconducting materials, electromagnetic measurements and detailed microstructural studies of carefully prepared GBs are required. Frequently, artificially induced GBs prepared by thin film deposition onto bicrystal substrates are used for such studies. Recently, transmission electron microscopy (TEM) studies have revealed a meandering configuration for GBs in YBa2Cu3Oy (YBCO) thin films grown on [001] tilt SrTiO3 bicrystal substrates (Fig. la). The deviation of the meandering GBs away from the underlying substrate GBs varies from a few tens to hundreds of nanometers. We have demonstrated that the magnitude of the meander in terms of amplitude and wavelength can be reduced by lowering the film deposition rate. The meandering GBs were shown to consist of various straight facets which are a few tens to hundreds of nanometers in length. It is possible that the various segments have very different current transport behavior due to a variable misfit dislocation density. Thus, an unambiguous correlation between the microstructure and global transport properties is difficult to attain.