Using Imaging Raman Microscopy to Explore Phase Evolution in Composite Ceramic Superconductors

Abstract

Raman microspectroscopy and imaging Raman microscopy have proven to be powerful tools for studying the evolution and spatial distribution of chemical phases in the bismuth-based (BSCCO) and thallium-based (TBCCO) families of high-critical-temperature (high- Tc) superconducting ceramics. These techniques have been applied to compressed/sintered powders and silver-clad composite conductors in conjunction with scanning electron microscopy and energy dispersive x-ray spectroscopy. Many important insights have been gained about the identity, size, shape, orientation, and spatial distribution of the various nonsuperconducting secondary phases (NSPS) that form and dissipate during heat treatment of the BSCCO and TBCCO silver-clad composite tapes. The resuIts have aHowed us to determine key mechanistic features that influence the formation of the super- conducting phases as heat treatment progresses, incIuding the location of lead-rich NSPS and the identification of the constituent phases in certain NSP agglomerations that tend to resist dissipation as high-Tc phase formation proceeds to completion.