Characterization of Nb<inf>3</inf>Sn diffusion layer (A-15) material

Microstructural characterization of Nb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Sn diffusion layers grown by Sn-vapor reaction with single crystal Nb substrates has been carried out using Auger and X-ray spectroscopy, X-ray and reflection electron diffractometry, and scanning electron microscopy. The layers exhibit preferred crystallographic orientation traceable to the underlying Nb-substrate orientation. The <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\langle 111 rangle</tex> -Nb-substrate layers differ substantially from all other-Nb-direction layers. In particular, they exhibit surface-like composition profiles over several hundred angstroms into the bulk, a very rough micro-structure including numerous microcracks, and a surface superconducting transition temperature of < 1 K. Non- <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\langle 111 rangle</tex> -Nb-substrate layers with 1 μm columnar grain structure and surface T <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> 's ∼ 18 K appear to have breaking stresses far in excess of bulk polycrystalline Nb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Sn.