INTRAGRAIN AND INTERGRAIN CRITICAL CURRENT IN PBMO6S8 SINTERED SAMPLES

To study the mechanisms limiting the critical current in the superconductor lead-molybdenum-sulfide, powders having a narrow distribution of T(c) and B(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(c2) lies between 50 and 60 tesla (at T = 0 K), whereas the critical current density displays a sharp decrease at a pseudo-critical field which can be half of the calorimetric value of B(c2). This reflects the poor quality of the grain interfaces which limits the intergrain critical current. On a cold pressed sample, we were able 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.