Defect formation, distribution and size reduction of Y2BaCuO5 in melt-processed YBCO superconductors

High critical current density (J(c)) in high temperature superrranducting m elt-processed Y-Ba-Cu-O (YBCO), which consists of a superconducting YBa2Cu3 O7-y (Y123) phase matrix containing discrete Y2BaCuO5 (Y211) inclusions, ca n be achieved by control of the grain microstructure during processing. Y12 3 grain growth rate, Y211 particle size, morphology, distribution and densi ty and the chemistry of the peritectically molten liquid are key parameters in the processing of this material and effectively determine its microstru cture. In addition, YBCO processed with excess Y211 generates defects at th e Y123/Y211 interface which form effective flux pinning sites and hence enh ance J(c). The effect of addition of Y211 on the sample microstructure, its distribution and refinement by chemical doping are discussed in detail in this review.