Substitution of 3d Metals for Cu in Y1Ba2Cu3O7-δ

Abstract

Y1Ba2Cu3O7-δ has a structural characteristic of two inequivalent Cu-site, Cu(I) and Cu(II), of different oxygen co-ordinations. The contrasting effect of substitution for Cu in these two sites is of considerable interest. The dopants Fe, Co and Ni are considered here for substituting Cu. Unit cell parameters obtained by X-ray diffraction analysis were used to estimate change in orthorhombicity with substitution content which shows 0 →T phase transformations at x < 0.1. The merging of the characteristic split peak of orthorhombic/tetragonal at 20 ≈33° confirms the phase transformations. The critical transition temperature (Tc) determined by the temperature dependent electrical resistivity measurements using the standard four probe technique exhibits depression with dopant content. The results of variation of orthorhombicity and Tc with substitution indicate that Fe and Co substitutes occupy the Cu-sites of analgous oxygen co-ordination, i. e. Cu(I) sites in the basal plane, while Ni occupies Cu (II) sites ...