磁性离子Fe和Ni替代YBCO体系的结构特征和载流子局域化

为阐明磁性离子在不同替代位置对YBCO体系超导电性的影响机制，利用正电子湮没及相关实验手段结合数值模拟，系统研究了Fe和Ni掺杂的YBa₂Cu₃O_7-δ体系. 结果表明，Fe和Ni离子在替代过程中均以离子团簇的形式进入晶格. 当离子进入CuO₂面时，由于团簇改变了周围的电子结构，造成电子的局域化，并直接影响了电子对的配对和输运，因而强烈抑制了体系的超导电性.而当掺杂离子进入Cu-O链区时，它们同样通过团簇的形式改变周围关键词：YBCO超导体磁性离子替代正电子湮没数值模拟

Characteristics of structure and carrier localization in YBCO systems doped with magnetic ions Fe and Ni

To make clear the physical mechanism of substitution by the magnetic ions Fe and Ni in different sites in YBCO systems, the positron annihilation technology (PAT) and simulated calculations are utilized to systemically investigate the compounds YBa₂Cu_3-x（Fe，Ni）_xO_7-δ（x=0.0—0.5）. The results obtained show that the doping ions Fe and Ni form different kinds of ion clusters and enter the crystal lattice. When occupying Cu(2) sites in CuO₂ planes, the ions gather into double square and/or other clusters, which results in a strong electronic localization and would directly affect the pairing and transportation of carriers, so the superconductivity is suppressed dramatically. While ions substitution for Cu(1) through gathering hexamer and/or other clusters, this induces the localization of holes and weakens the function of carrier reservoir; thus carriers cannot easily transfer to CuO₂ planes. However, in this case, the pairing and transportation of carriers are not affected directly, thus the superconductivity will be suppressed weakly. On the other hand, the present results indicate the suppression of superconductivity has no direct correlation with the magnetism of Fe and Ni ions itself.