The effect of mechanical twinning on the <i>T</i> <i>c</i> of vanadium

The effects of unidirectional and sign-alternating torsional deformation at 4.2 °K on the superconducting transition temperature of vanadium have been studied. A nonmonotonic variation of Tc with the degree of deformation was found: The initial sharp growth was replaced by a gradual decrease but Tc remained above the initial value up to destruction of the sample. The maximum growth of Tc was 0.43 °K. The structure of the sample surface was studied and it was shown that the deformation of vanadium during its initial stages occurs largely by mechanical twinning. It is concluded that the reason for the increase of Tc for vanadium is the appearance of twin layers with a high compressive stress in the neighborhood of their boundaries during the process of low-temperature deformation.

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