Microstructure, lattice parameters, and superconductivity of YBa 2 (Cu 1-x Fe x ) 3 O 7-δ for 0<=x<=0.33

摘要: Iron was substituted for copper in ${\mathrm{YBa}}_{2}$(${\mathrm{Cu}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Fe}}_{\mathrm{x}}$${)}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ 0\ensuremath{\le}x\ensuremath{\le}0.33. Superconducting transition temperatures and lattice parameters have been determined as a function of Fe content. The orthorhombic distortion \ensuremath{\Delta}${a}_{0}$=2(b-a)/(a+b) decreased to zero near x=0.03. Beyond x=0.03 the structure appears tetragonal. For compositions 0\ensuremath{\le}x\ensuremath{\le}0.15 superconducting critical temperature ${T}_{c}$ smoothly from ${T}_{c}$=90 K below 4.2 K. Transmission electron microscopy (TEM) revealed that spacing between twin boundaries \ensuremath{\sim}200 nm x=0 \ensuremath{\sim}20 x=0.02 before twins disappeared xg=0.03. sharp streaks TEM diffraction patterns were interpreted due boundary layers whose thickness varied \ensuremath{\sim}1 pure \ensuremath{\sim}2 (x=0.02) containing specimen. A tweed image associated diffuse along 〈110〉 directions pattern appeared xg0.015. This observation suggests consists fine (l5 nm) domains, each domain having twinlike crystallographic relation with its neighbors. Rietveld refinement powder neutron x=0.10 0.167 primarily on Cu ``chain'' site, every two atoms substituted, approximately one extra oxygen is incorporated Cu-O plane.