Susceptibility, crystal-structure, and Mössbauer study of the high-temperature superconductor YBa2Cu3O7−δ doped with iron

Abstract

Resistance and ac susceptibility measurements, ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ Mössbauer spectroscopy, and powder x-ray crystal-structure refinements were used to study the high-temperature superconductor $\mathrm{Y}{\mathrm{Ba}}_2{\left({\mathrm{Cu}}_{1-x}{\mathrm{Fe}}_x\right)}_3{\mathrm{O}}_{7-\delta }$. The superconducting transition temperature decreased as the Fe content was increased. The crystal structure is markedly orthorhombic for $x=0\mathrm{}$, but the cell parameters $a$ and $b$ are nearly equal for $0.015<x<\mathrm{}0.100\mathrm{}$. In addition, the difference between $a$ and $b$ decreases systematically with Fe content; they are equal at $x=0.100\mathrm{}$. The Mössbauer spectra above about 10 K consist of three doublets; their site assignments are proposed. Measurements of the ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ recoil-free fraction as a function of temperature yielded a Debye temperature of about 455 K. Below 10 K, magnetic ordering of iron was observed.