Effects of Fe and Ni substitutions on the 1-2-4 structure of YBCO superconductors studied by high-resolution transmission electron microscopy

Abstract

Structures and defects of YBa 2Cu 4O y (1-2-4) type of superconductors, doped with Fe as well as Ni, are examined by HRTEM and the results are compared with those of the Co-substituted system reported previously. By Fe substitution, a part of the (CuO) 2 double chain layers of the 1-2-4 structure is replaced with (CuO) single chain layers, as was the case in Co substitution. The single chains are induced rather randomly by Fe substitutions, while ordered structures such as 2-4-7 or 3-6-11 were obtained by Co substitutions. Contrary to Fe and Co substitutions, Ni substitution has little structural effects on the 1-2-4 structure.