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 $H_{c2\mathrm{}}$ (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 $H_{c2\mathrm{}}$ are in good agreement with calculated values based on the BCS and Ginsberg-Landau-Abrikosov-Gor'kov theories and with our resistivity measurements.