Diffraction evidence for oxygen-vacancy ordering in annealed Ba_{2}YCu_{3}O_{7-δ} (0.3≲δ≲0.4) superconductors

Abstract

Diffuse streaks centered at q=(0,\ifmmode\pm\else\textpm\fi{}(2/5,0) and (0,\ifmmode\pm\else\textpm\fi{}(1/2,0) have been observed in annealed ${\mathrm{Ba}}_{2}$${\mathrm{YCu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ with 0.3\ensuremath{\lesssim}\ensuremath{\delta}\ensuremath{\lesssim}0.4, which has a ${T}_{c}$ of 60 K and a Meissner effect equivalent to the 90 K phase. We interpret the presence of the diffuse streaking as a result of short-range oxygen vacancy ordering. The vacancy ordering has a short correlation length along the copper-oxygen chains (b direction) and a long correlation length perpendicular to the chains along the a direction. The ordered structure is completely uncorrelated parallel to the c axis.