Oxygen Deficiencies at Defects in YBa₂CU₃O_7-δ as Determined by High Resolution Parallel Electron Energy Loss

Abstract

There has been considerable discussion on the exact nature of the pinning defects in the high temperature ceramic superconductors, and the YBa₂Cu₃O_7-δ (Y123) structure in particular. High resolution parallel electron energy loss spectrometry (PEELS) allows for fine spatial resolution (<17 nm) and fast acquisition times to probe the oxygen content of defects (i.e., dislocations, stacking faults, twin boundaries and grain boundaries), all which have been proposed as potential pinning sites or weak-links. Oxygen deficiencies up to 13% were measured at twin boundaries, and 20% at grain boundaries while stacking faults showed an increase in oxygen and copper content. Regions of low oxygen (0.5 < δ < 1) were usually confined to an area within approximately 50 nm of the defect, which is within the spatial resolution of the measurements. Examination of the fine structure of the oxygen K-edge suggests that the oxygen holes are absent at the twin and grain boundaries.