Grain size dependence of critical current densities in hot isostatically pressed SnMo/sub 6/S/sub 8/

The dependence of critical current density on the heat treatment and microstructure of SnMo/sub 6/S/sub 8/ was systematically studied. Powders with minimal initial oxygen contamination were processed by hot isostatic pressing at 800 degrees C to produce a sample having a mid-point inductive critical temperature of 14.2 K, a magnetization critical current density of 820 A/mm/sup 2/ (9 T, 4.2 K) and electromagnetically nongranular behavior. The microstructure was controlled by varying subsequent heat-treatment temperature and time and was examined by scanning and transmission electron microscopies. In each sample grains appeared well connected and ranged over two orders of magnitude in size, with average grain sizes being between 0.2 and 0.5 mu m. Critical current density decreased with increasing annealing temperature and time and at fields <8 T was inversely proportional to the grain size. These results show that Chevrel phase materials are not intrinsically weakly coupled and that grain boundaries are sites of Abrikosov vortex pinning.<>