Effects of Lattice Defects on Critical Current of Hard Superconducting Nb

TL;DRAbstract

The effects of lattice defects on the critical current behavior of superconducting Nb in D.C. applied fields have been studied. The concentrations of lattice defects were varied by a various combination of cold work and heat treatment and the changes of these concentrations were estimated by measurements of the electrical resistivity and Vicker’s hardness, and observations by means of electron and optical microscopy. The disappearance of some point deffects takes place at about 150°C, but no appreciable change in critical current was observed. The disappearance of dislocations in heavily cold worked Nb begins at about 400°C, and the rate of dislocation disappearance becomes smaller at higher temperatures. It was observed by electron microscopy that during annealing at 900°C grain growth took place and in grown-up grains the dislocation density was very low. Comparison of the change in the density of dislocations and grain boundaries with the critical current behavior shows that the dis

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