Structural inhomogeneity and twinning inYBa2Cu3O7−δsuperconductors: High-resolution transmission electron microscopy measurements

Abstract

The superconducting properties of ${\text{YBa}}_{2}{\text{Cu}}_{3}{\text{O}}_{7\text{\ensuremath{-}}\ensuremath{\delta}}$ (YBCO) are strongly dependent on atomic structure and composition. While the average structures of YBCO are well documented, the local oxygen concentration and ordering have received much less attention owing to the difficulty of experiments and analysis. We examined several samples of YBCO by quantitative high-resolution transmission electron microscopy and geometric phase analysis to determine their local atomic structure and symmetry. Our results reveal that adjacent domains separated by the (110) interfaces, commonly considered to be twin domains, can have different ${a}_{o}/{b}_{o}$ ratios. The domains, therefore, do not retain the ideal twinned configuration commonly expected for this system. Assuming the ${a}_{o}/{b}_{o}$ ratio is proportional to oxygen concentration, we suggest that these domains result from inhomogeneous oxygen distribution. Multiple measurements in both bulk and thin-film samples indicate that YBCO can consist of different phases, which may yield locally variable superconducting properties.