Er1-yCayBa2Cu3-x(Fe, Zn)(x)O7-delta superconductors: a study of microstructure and resistive transitions in a dc magnetic field

We report an investigation of structure by x-ray diffraction, microstructur e by atomic force microscopy (AFM) and broadening of resistive transitions in high de magnetic fields (0-20 kOe) in Er1-yCayBa2Cu3-x(Fe, Zn)(x)O7-delt a (y = 0.1, 0.2; and 0 less than or equal tox less than or equal to0.20) ce ramic 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 siz e 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 sub stitution has no effect; and (3) Fe substitution enhances it. We show that these results can be interpreted in terms of a thermally activated flux mot ion (TAFM), and the effect of various dopants on the properties like pinnin g barrier and anisotropy.