Crystal Site Occupancy of Alloying Elements in Polycrystalline Nb3Sn Superconductors By Electron Channeling

Abstract

Many of the crystallographic problems encountered in materials science require techniques that can be used on small volumes of materials, e.g., in VLSI semiconductors, thin films, and the composite materials used in high magnetic field superconductors. In recent years several sensitive and accurate microcrystallographic techniques, based on diffraction of 100-keV electrons, have been developed. For example, convergent beam electron diffraction is a powerful technique to determine the symmetry of microcrystals and electron channeling techniques for the location of dilute elements in the crystal unit cell.We shall here deal with the application of the electron channeling technique called ALCHEMI (Atom Location by Channeling Enhanced Microanalysis) to study composite materials by determining the crystal sites of small amounts of alloying elements in Nb3Sn made by the bronze process. This is a problem of considerable interest in conjunction with the development of high magnetic field superconductors, because small amounts of certain alloying elements increase the upper critical magnetic field significantly.