Oxygen order-disorder phenomena in YBa2Cu3O(7-delta) as observed by electron microscopy

The structural features associated with the ordering of oxygen in YBa2Cu3O(7-delta) as studied by electron microscopy are presented noting that the simplest among these phenomena is the twinning resulting from the tetragonal to orthorhombic phase transition. Results from a number of 'in situ' experiments conducted in the electron microscope suggest that domain ordering and narrowing occur by the propagation of twinning dislocations. Models are proposed for twinning disclocations and it is shown that the ordering stresses resulting from the T-O transformation induce the so-called synchroshear glide motion of such dislocations along twin interfaces, thereby causing their lateral shift. Vacancy ordered structures are discussed including the orthorhombic II structure and various diffraction patterns. Crystallographic shear planes are also observed and analyzed.