Intra- and intergrain critical current in PbMo/sub 6/S/sub 8/ sintered samples

To study the mechanisms limiting the critical current in the superconductor lead-molybdenum-sulfide, powders having a narrow distribution of T/sub c/ and B/sub c2/ have been synthesized. The absence of a broadening in the specific heat jump at the superconducting transition in a magnetic field indicates that the distribution of the critical field over the grains is very narrow. For all the samples, B/sub c2/ lies between 50 and 60 T (at T=0 K), whereas the critical current density displays a sharp decrease at a pseudocritical field which can be half of the calorimetric value of B/sub c2/. This reflects the poor quality of the grain interfaces, which limits the intergrain critical current. On a cold-pressed sample, it was possible to determine the intragrain critical current, which is estimated to be one order of magnitude higher than the best intergrain value. Therefore, an appreciable improvement in critical current density is expected if good superconducting links between grains can be achieved.