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,±(2/5,0) and (0,±(1/2,0) have been observed in annealed ${\mathrm{Ba}}_2$ ${\mathrm{YCu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ with 0.3≲δ≲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.