Observation and mechanism of local oxygen reordering induced by high-energy heavy-ion (U+,Au+,Xe+) irradiation in the high-TcsuperconductorYBa2Cu3O7−δ

Abstract

Transmission electron microscopy study reveals that high-energy $(>1\mathrm{GeV})$ heavy-ion (${\mathrm{U}}^{+},$ ${\mathrm{Au}}^{+},$ ${\mathrm{Xe}}^{+}$) irradiation in the $c$-axis direction of high-${T}_{c}$ superconductor ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ leads to the formation of aligned columnar defects, which are usually amorphous, and the associated volume expansion causes strain in surrounding matrix. Lobed ``bow-tie'' contrast is observed in both the [001] zone axis bright field and the high-resolution images of the regions surrounding the amorphous columns, the direction of which is rotated 90\ifmmode^\circ\else\textdegree\fi{} across a typical pre-existing twin boundary in ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}.$ Our study shows that this contrast is caused by local oxygen reordering in the $\mathrm{ab}$ planes that gives a 90\ifmmode^\circ\else\textdegree\fi{} reorientation of the orthorhombic unit cell in the affected area. The mechanism of resulting oxygen reordering in the $\mathrm{ab}$ planes for this area is reported here. A qualitative result on the form, the position, and the size of the oxygen reordering region distributed around an isolated track and between two or more tracks, is related to the orientation of the Cu-O chain direction of matrix and the energy of incident ions.