Preparation methods and parameters for the optimization of superconducting and mechanical properties of Chevrel phase wires

The Chevrel phase compounds based on SnMo6S8, PbMo6S8 and Pb1,2-xSnxMo6S8 were prepared using HIP-prereacted, partly HIP-prereacted starting materials or unreacted powder mixtures. The application of various powder metallurgical methods for fabricating improved superconducting monofilamentary wires supplied an enhancement of the critical current densities up to the highest presently known values of Jc (4,2 K)=2.108 Am-2 and Jc (1,8 K)=3,5.108 Am-2. This is mainly due to an improved flux pinning behavior which correlates with the average grain diameter of the Chevrel phase material. A considerable reduction of the necessary reaction time and a correlated reduction of the grain growth were observed as a consequence of the significant diminuation of the impurity content (O2, C) in the samples. Using microstructural investigations by means of Auger electron spectroscopy, inhomogeneities in the Chevrel phase compounds could be specified. The results of these analysis indicate future possibilities for improving the performance of Chevrel phase wires. The wire configuration developed in this work is oriented towards technical application. The Chevrel phase is enclosed in a Ta or Nb barrier material separating it from a stabilizing Cu section which is in turn enclosed by a stainless steel jacket for mechanical stabilization, thus yielding a fully stable superconducting wire. (orig.)