INFLUENCE OF GRANULARITY ON THE CRITICAL-CURRENT DENSITY IN MELT-CASTPROCESSED BI2SR2CACU2OX

The microstructural analysis of melt-cast processed Bi2Sr2CaCu2Ox reve als the existence of grain boundaries on two different length scales. Plate-shaped crystal grains of approximately 10 mum length are texture d along the c direction on a scale of 200-300 mum, forming bundles of arbitrary orientation. To investigate the impact of the grain boundari es within and between bundles on the critical current density we have analysed the variation of the magnetic hysteresis with the sample size using different powder fractions and bulk material. It could be shown that the boundaries between the platelets within a bundle limit the o verall transport current density in bulk material, whereas the boundar ies between bundles do not further reduce its value. The results are i n agreement with a TEM analysis of the grain boundaries.