Er_1-yCa_yBa₂Cu_3-x(Fe, Zn)_xO_7-δsuperconductors: a study of microstructure and resistive transitions in a dc magnetic field

Abstract

We report an investigation of structure by x-ray diffraction, microstructure by atomic force microscopy (AFM) and broadening of resistive transitions in high dc magnetic fields (0-20 kOe) in Er 1−y Ca y Ba 2 Cu 3−x (Fe, Zn) x O 7−δ (y = 0.1, 0.2; and 0 x 0.20) ceramic superconductors. The XRD shows that the presence of Ca does not alter the known effect of Fe/Zn substitution on the structure of the pure (y = 0) system. Substitution of both Fe and Zn leads to a decrease in the grain size and micro-hardness. Interesting results were obtained on the influence of various dopants on the broadening of resistive transitions in dc magnetic fields, in general: (1) an increase in Ca content suppresses it; (2) Zn substitution has no effect; and (3) Fe substitution enhances it. We show that these results can be interpreted in terms of a thermally activated flux motion (TAFM), and the effect of various dopants on the properties like pinning barrier and anisotropy.