Electron microscopic studies of local structures of high temperature YBa2Cu3O7-x superconductor

Abstract

The local structural characteristics of the high temperature superconducting material YBa2Cu3O7-x (YBCO) have been explored employing electron microscope technique. Two special structural characteristics have been obtained. One of these corresponds to a significant local area variation of the c periodicity (∼11.6 to ∼11.8 Å) and the other relates to the domain formation. It has been suggested that the variation of the c periodicity originates due to cation disorder in the chain -Ba-Ba-Y-Ba-Ba-(e.g. -Ba-Ba-Ba-Y-Ba- and -Ba-Ba-Cu-Ba-Y-). The domain formation which represents an important result of the present investigation originates due to ordering of oxygen vacancies on alternative equivalent set of sites in different crystal regions. A domain model together with the inherent defect lamellae has been advanced and the oxygen stoichiometries obtained by different workers e.g. 6.81 and 6.90, have been shown to be a natural artifact of oxygen ordering and domain formation. It has been suggested that the various reported short lived-near room temperature forms of YBCO and related phases may correspond to highly ordered versions of YBa2Cu3O7-x with x=0 or x → 0. © 1988.