Synthesis of superconducting Nb 3 Sn coatings on Nb substrates

Abstract

In the present work the electrochemical and thermal syntheses of superconducting Nb 3 Sn films are investigated. The Nb 3 Sn phase is obtained by electrodeposition of Sn layers and Cu intermediate layers onto Nb substrates followed by high temperature diffusion in inert atmosphere. Electrodeposition was performed from aqueous solutions at current densities in the 20-50 mA cm -2 range and at temperatures between 40°C and 50°C. Subsequent thermal treatments were realized to obtain the Nb 3 Sn superconductive phase. Glow discharge optical emission spectrometry demonstrated that after thermal treatment interdiffusion of Nb and Sn occurred across a thickness of about 13 μm. Scanning electron microscopy allowed accurately measuring the thickness of the Nb 3 Sn phase, whose average for the various types of film samples was between 5.7 and 8.0 μm. X-ray diffraction patterns confirmed the presence of a cubic Nb 3 Sn phase (A15 structure) having (210) preferred orientation. The maximum obtained T c was 17.68 K and the B c20 ranged between 22.5 and 23.8 T. With the procedure described in the present paper, coating complex shapes cost-effectively becomes possible, which is typical of electrochemical techniques. Furthermore, this approach can be implemented in classical wire processes such as 'jelly roll' or 'rod in tube', or directly used for producing superconducting surfaces. The potential of this method for superconducting radiofrequency structures is also outlined.