Stabilization of the tetragonal phase and superconducting behavior in $R{\mathrm{Ba}}_2{\left({\mathrm{Cu}}_{1-x}{\mathrm{Fe}}_x\right)}_3{\mathrm{O}}_y$ ($R=\mathrm{Y},\mathrm{G}\mathrm{d}$; $0\le x\le 0.15$)

The structure and superconductivity for $\mathrm{Y}{\mathrm{Ba}}_2{\left({\mathrm{Cu}}_{1-x}{\mathrm{Fe}}_x\right)}_3{\mathrm{O}}_y$ and $\mathrm{Gd}{\mathrm{Ba}}_2{\left({\mathrm{Cu}}_{1-x}{\mathrm{Fe}}_x\right)}_3{\mathrm{O}}_y$ ceramics ($0\le x\le 0.15$) have been studied by x-ray diffraction and resistivity measurements. In each family of materials (but more rapidly in the Gd ceramics), increasing Fe substitution leads to the stabilization of the tetragonal perovskite structure and suppression of superconductivity, apparently owing to pair breaking by the Fe moments. Anomalous behavior at higher Fe substitution is attributed to the combined influence of Gd and Fe moments.