Mechanism of the synthesis-temperature decrease for niobium-based superconducting coatings

The ion-plasma method was used to produce Nb-Sn and Nb-Al solid solution films supersaturated with tin and aluminum as compared to the equilibrium state. The lattice parameters were determined in a range of supersaturation concentrations of up to 25.5 at % Sn and 35.5 at % Al and shown to change from 0.3303 to 0.3352 and from 0.3303 to 0.3255 mn, respectively. As the concentrations exceeded the above values, arnorphization was observed in these systems. The threshold temperatures of synthesis of the intermetallics; were found to decrease to 500degreesC for the solid-solution specimens and to 400degreesC for the amorphous specimens in the Nb-Sn system and, respectively, to 750 and 600degreesC in the Nb-Al system. The compounds Nb3Sn and Nb3Al with an A 15 structure were produced on substrates of polycor and on copper ribbons; the degree of transformation was about 100%. The buffer layer of titanium nitride, which prevents aluminum diffusion into the copper substrate, also promotes the decrease of the threshold temperature because of the epitaxial growth of the Nb3Al phase on titanium nitride.