Establishing the correlation between microstructure and current transport in high temperature superconductors has long been a challenge, especially for real-world conductors that have complex microstructures. In some cases, the presence of defects can block current flow, while in other cases it is the absence of defects that leads to poor flux pinning and reduced critical currents. In this work, we address these issues in high temperature superconducting wires and attempt to establish the correlation between current flow and microstructural and crystallographic defects by using an array of characterization tools that bridge length scales to address local variations. We have used the coordinated application of Raman microscopy, scanning electron microscopy, spectral imaging, and transmission electron microscopy to study representative specimens of "coated conductor" superconducting tapes. Detailed studies of microstructure are guided by magneto-optical imaging that reveals localized information about superconducting behavior, and highly site-specific specimen preparation is achieved using focused ion beam sectioning. These studies have identified specific microstructural and chemical defects that can be correlated with field-dependent critical current density. We have also explored the evolution of microstructure as a function of processing. Following the evolution of microstructure provides new insight that provides a better understanding of how key defects form and how they influence properties. These results will illustrate many of the capabilities available in the Electron Microscopy Center at Argonne, and a brief overview of future capabilities will also be presented.
ANL Physics Division Colloquium Schedule