Environmental Stability of High Tc Superconducting Ceramics

Abstract

The discovery of high Tc superconductivity in layered cuprate ceramics has so far led to the identification of about 35 distinct superconducting cuprate systems, the latest of which is the 133 K superconducting system Hg-Ba-Ca-Cu-O. For most of their proposed applications, high Tc ceramics have to be resistant to environmental degradation both with respect to atmospheric water vapor, e.g., in storage, and to liquid water (produced by condensation on warm-up from cryogenic conditions). The presence of CO2 is an important factor in both environments. Increasing environmental stability involves improving the processing methods to eliminate pores, cracks, and other macroscopic defects (e.g., highly leachable impurity phases) which are prevalent in materials prepared by solid-state sintering. Furthermore, protective coatings and hermetic seals are necessary in many applications involving films because of small film thickness. (Wires are usually drawn inside metal tubes, which provide protection.)