Current distributions of grain boundaries in differently processedmelt-textured YBa2Cu3O7

Abstract

The local current density distribution of grain boundaries indifferently processed melt-textured YBa2Cu3O7-δ (YBCO) isinvestigated by a magneto-optical technique and inversion of Biot-Savart'slaw. By correlating the local current density with the microstructure revealedby a scanning electron microscope, we are able to distinguish the depressionof the critical current density jc at clean grain boundaries (GBs) fromthat occurring at normal phases and cracks at and in the vicinity of GBs.The GBs are formed by different multi-seeding melt-growth processes using anon-stoichiometric precursor which is optimized with respect to the bulkcritical current. In order to obtain GBs with extended regions free of normalphases and with large critical current densities the amount of liquid phaseand the density of Y2BaCuO5 particles has to be controlled. Theproperties of GBs can be tailored by both controlling the amount of liquidphase and the seed distance. The related changes in the growth andmicrostructure are analysed and we show how to grow extended GBs almost freeof normal phases with optimized critical current densities in multiple-seededmelt-growth YBCO.