Epitaxial growth of A15 Nb3Si

Films of niobium-rich Nb3Si have been grown epitaxially on polycrystalline, A15 Nb3Ir using electron beam evaporation. The use of epitaxy has allowed formation of A15 Nb3Si under deposition conditions in which it normally would not form. The Nb3Si has been made niobium-rich in order to match lattice parameters with the Nb3Ir. Some samples have then been brought toward stoichiometry by gradually lowering the evaporation rate of the Nb. The use of this compositional grading technique has been found to enhance the Tc´s relative to the epitaxial films by in some cases more than 6 K. Tconsets, measured resistively, have been found up to 13.2 K. The effects of varying the thickness of the graded layer have been studied, and Tc´s have been found to continue to increase after the graded layer has been brought to 25 at. % Si.