Effect of Plastic Deformation and Annealing Temperature on Superconducting Properties

Abstract

Single crystals and polycrystals of Nb and Re were deformed in tension at room temperature. The critical field was found in both cases to increase with deformation and in the case of Nb the increase was as large as 150%. The change in critical field is related to the increase in plastic deformation. Annealing the plastically deformed sample restored the original critical field. The transition temperature in Nb was not affected either by the deformation or the annealing treatment. These experimental results can be explained theoretically if one assumes that in a hard superconductor the current is carried by filaments. The filaments may be identified with dislocations.The transition temperature of Re was found to depend on the annealing temperature and in some cases on plastic deformation. The transition temperature is higher, the higher the annealing temperature before plastic deformation. Plastic deformation does not affect the transition temperature in the cases where the transition is sharp. However, when the transition is broad, plastic deformation raises the transition temperature and sharpens the transition region. These results can be interpreted in terms of the equilibrium number of vacancies at the annealing temperature.