Superconducting Technetium-Tungsten Alloys

The transition temperatures, critical fields, electrical resistivities, and crystalline structures of a series of technetium-tungsten alloys containing up to 60 at.% technetium are reported. T_c increases monotonically to 7.9°K and H_c2 (at 4.2°K) to 43.5 kG for 60 at.% technetium. The samples are single-phase solid solutions up to 40 at.% Tc, but a sigma phase is present at higher concentrations. The measured values of H_c2 are in good agreement with calculated values based on the BCS and Ginsberg-Landau-Abrikosov-Gor'kov theories and with our resistivity measurements.