Topical review defect formation, distribution and size reduction of Y_2BaCuO_5 in melt-processed YBCO superconductors

摘要

High critical current density (J_c) in hightemperature superconducting melt-processed Y-Ba-Cu-O (YBCO),which consists of a superconducting YBa_2Cu_3O_(7-x)(Y123)phase matrix containing discrete Y_2BaCuO_5(Y211) inclusions,can be achieved by control of the grain microstructure duringprocessing. Y123 grain growth rate, Y211 particle size,morphology, distribution and density and the chemistry of theperitectically molten liquid are key parameters in the processing ofthis material and effectively determine its microstructure. Inaddition, YBCO processed with excess Y211 generates defects atthe Y123/Y211 interface which form effective flux pinning sitesand hence enhance J_c. The effect of addition of Y211 on thesample microstructure, its distribution and refinement by chemicaldoping are discussed in detail in this review.