Critical current and temperature of filamentary niobium tin as a function of reaction conditions

The critical temperature of filamentary niobium tin as determined by reaction conditions has been measured along with critical current as a function of field at different temperatures in the range 4.2 to 18°K. Using diffusion couples able to provide compound of less than stoichiometric amounts of tin, a minimum in Tc and a maximum in Jc has been established and it is shown that the optimum reaction depends on the operating temperature of the composite. A hypothesis is advanced explaining results in terms of changes in the position of niobium and copper in the compound lattice.