Influence of Fe impurities on the Y-Ba-Cu-O superconducting system

Abstract

We have studied the influence of Fe impurities in high-temperature superconductors of the type ${\mathrm{Y}}_{1.2}{\mathrm{Ba}}_{0.8}\mathrm{Cu}{\mathrm{O}}_{4\ensuremath{-}\ensuremath{\delta}}$ and $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ on the critical temperature as measured by the resistance transition. The chemical compositions of the different phases have been determined using a scanning electron microscope and electron-probe microanalysis. We find that for low concentrations Fe substitutes for Cu in the superconducting phase. The transition temperature decreases linearly as a function of the Fe concentration, in remarkable analogy with the situation in conventional superconductors with paramagnetic impurities.