Superconducting Critical Temperatures of Niobium Recovered from Megabar Dynamic Pressures

摘要

Nb was processed and recovered intact from high dynamic pressures in the range 0.6 to 1.2 Mbar. Pressure and effective-plastic-strain histories were calculated using a finite-element hydrodynamic computer code. Recovered specimens were characterized by x-ray diffraction, metallography, Vicker's hardness, and electrical resistivity ratio. The superconducting transition temperature T/sub c/ was found to be weakly sensitive to shock-induced defects. The maximum change observed in T/sub c/ was a decrease of 0.035 deg K in the specimen shocked to a maximum pressure of 0.6 Mbar. Shock processing of V sub 3 Si at 1 Mbar was recently reported by Stewart et al. to depress T/sub c/ 1.8 deg K from the initial value of 16.4 deg K. These results indicate that shock-induced defects and disorder have a relatively weak effect on the T/sub c/ of equilibrium phases and suggest that shock-synthesized metastable superconductors might have T/sub c/'s close to intrinsic values for the ordered material. (ERA citation 10:037111)