Influence of deformation defects on properties of normal and superconducting niobium

The temperature dependence of resistivity is analyzed in the interval 9.5–310 K for a niobium single crystal in the initial state, after a strong plastic deformation by rolling at 20 K and annealings between 423 and 533 K, and the superconducting transition temperature is measured. The results are processed by using a model taking into account the intra- and interband electron scattering as well as the effects associated with the electron lifetime during scattering by defects and thermal phonons. The calculations carried out in terms of the Friedel model reveal that an increase in the dislocation density and the redistribution of the vacancy-oxygen complexes upon annealing reduces the Fermi energy and the width of the d-band and lowers its center of gravity. It is concluded that the enhancement of anisotropy of the Fermi surface, which is accompanied by the constriction of the d-band and the emergence of soft phonon modes, plays a leading role in the enhancement of superconductivity of niobium with dislocations.

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