Effect of composition and neutron irradiation on the upper critical field of Nb3Pt

The upper critical field H/sub c/2(T) of the A15 compound Nb/sub 100-x/Pt/sub x/(19< or = x < or = 29.1) has been measured as a function of temperature T for various compositions and levels of irradiation with fast reactor neutrons. Compositions ranging from 19 to 29 at. % Pt and neutron fluences up to 16 x 1018 n/cm2 (E > 1 Me V) were studied. A stoichiometric sample that had been rapidly quenched from the liquid (splat-cooled) was also investigated. For the unirradiated samples, T/sub c/ exhibits a maximum of 10.4 K at the stoichiometric composition, while both H/sub c/2(0) and dH/sub c/2(T)/dT/sub T/ = T/sub c/ attain their maximum values on the Pt-rich side of stoichiometry. The irradiated samples show a decrease of H/sub c/2(0) with increasing neutron fluence. The results are discussed in terms of antisite disorder and a strong correlation is obtained between decreasing H/sub c/2(0) and increasing disorder of the Nb atomic sites