Effects of substitution of O by S and Cu by Fe on superconductivity in YBa2Cu3O7

Abstract

The single-phase high-$T_c$ superconductors $\mathrm{Y}{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-x}{\mathrm{S}}_x$ and $\mathrm{Y}{\mathrm{Ba}}_2{\mathrm{Cu}}_{3(1-y)\mathrm{}}{\mathrm{Fe}}_{3y}{\mathrm{O}}_7$ have been prepared and studied by dc magnetometry. Y${\mathrm{Ba}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_6$S has a larger unit cell than Y${\mathrm{Ba}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_7$, and yet has the same $T_c$; its phase transition is sharper and displays full Meissner effect. Substitution of Cu by Fe leads to a sharp decrease in $T_c$.