Electron microscopy of ceramic superconductors

Abstract

The microstructure of ceramic superconductors plays a crucial role in the transport properties of these materials. For example, it has been shown that high-angle grain boundaries can act as weak links and atomic scale defects can act as pinning centers. The nature and spatial distribution of such defects is related to the way in which the material is processed. Transmission electron microscopy (TEM) is an essential technique for understanding the relationship between microstructure, processing, and properties and for defect characterization. The advantage of TEM is that it is possible to combine various imaging modes with electron diffraction and other analytical techniques such as x-ray energy dispersive spectroscopy in order to obtain both structural and chemical information.Early measurements of critical current densities (Jc) across individual tilt grain boundaries in YBa2Cu3O7-δ (YBCO) thin films demonstrated that Jc decreased with increasing misorientation angle. More recently, however, it has been observed that this phenomenon may not be the case for all high-angle grain boundaries.