Critical currents and pinning mechanisms in Chevrel-phase superconductors: materials science issues

Critical current densities and pinning mechanisms in lead (PMS) and tin (SMS) molybdenum sulfides are reviewed with the emphasis on materials science problems. In both compounds, pinning at grain boundaries is dominant only in fine-grained materials and in the low-field regime. In coarser grained materials, additional pinning behaviors (the maximum pinning force density F/sub p/ at the reduced field b/sub m/=0.4-0.55 and 0.7) are reproducibly observed and can be related to pinning at intragrain defects (planar defects, oxide precipitates, and point-like defects). The difference in the critical currents in PMS and SMS is discussed and related to the difference in the extent of stress-induced structural transformation at grain boundaries.