CRITICAL-CURRENT DISTRIBUTION OF HOT ISOSTATICALLY PRESSED PBMO6S8 WIRES

The PbMo6S8 Chevrel phase has an important potential for the construction of ultra-high-field superconducting coils. The critical current density of hot isostatically pressed (HIP) PbMo6S8 wires with a stainless steel matrix and a molybdenum diffusion barrier was investigated in fields up to 25 T. The field dependence of J(c) is considerably improved in the high-field regime by going from a 990-degrees-C, 4 h to a 1225-degrees-C, 4 h HIP treatment at 110 MPa. However, a drop of J(c) at ususually low fields as 15 T was observed. The appearance of a double peak in the critical current distribution, obtained by dV2/dI2 suggests that the origin of such a behavior is a strongly reduced effective upper critical field B(c2)*, presumably at grain boundaries. A detailed analysis of the critical current distribution reveals that only a few percent of the wire is in a dissipative state at an electric field criterion of 1 mu V cm-1, indicating that the used HIP parameters are not yet optimized.