Direct experimental analysis of the relation between the grainstructure and the distribution of critical current density inYBa2Cu3Ox coated conductors

Abstract

We present a relatively simple experimental method to correlate the grain structure ofYBa2Cu3Ox coated conductors with spatial variations of the critical current density on a macroscopicscale. Variations of the current density on a micrometre scale are visualized withmagneto-optical imaging, using the flux trapped by colonies of grains to quantify thedegree of connectivity. Integrating these trapped flux profiles over larger distances yieldsdirect information of the critical current distribution on a millimetre scale, providedthat contributions from negative return flux in colony boundaries are properlyeliminated. Flux polarity is determined using the wavelength dependence of the Verdetconstant. The validity of this analysis is demonstrated by comparing the resultswith direct transport data on the lateral current distribution, measured with themagnetic knife technique. The combination of both experiments shows that thecritical current density is suppressed over several millimetres of conductor length atareas where a large number of high-angle grain boundaries or defects are present.