The Effect of Superconducting Transition on Plastic Properties of Lead and Lead Alloys

The flow stress change Δτ associated with superconducting transition has been measured on lead and lead alloy crystals against the kind and the concentration of solute atoms as well as the amount of deformation and temperature. Δτ increases with applied stress rapidly in the beginning and slowly in later stages of deformation. The temperature dependence of Δτ cannot simply be expressed as proportional to (1- B s / B n ), where B n and B s are the electronic drag coefficients of a dislocation in normal and superconducting states, respectively. Δτ of lead alloys is dominantly affected by the size misfit between solute and solvent atoms. As to the solute concentration c , Δτ∝ c n , where n is first about 1/2 but increases with deformation. These results are discussed theoretically by taking account of the influence of the electron viscosity on both terms of the activation energy and the attempt frequency in the rate equation describing the thermally activated motion of a dislocation.