| Y1Ba2Cu30 7_15 has a structural characteristic of two
inequivalent Cu-site, Cu(l) 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 29 =33° confrrms
the phase transformations. The critical transition temperature
(TJ 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(l) sites
in the basal plane, while Ni occupies Cu (II) sites in Cu02
plane. These observations are substantiated by the earlier
reports on ordering of magnetic moments. |
