Structure of a Vapor-Quenched AgCu Alloy

Ag—52 at.% Cu films were prepared by coevaporation onto 0.005 in. thick vitreous silica plates held at liquid-nitrogen temperature. The interference function I(K), where K=4π sinθ/λ, was evaluated from the elastic x-ray scattering of the film and compared with I(K) of the liquid alloy, measured at 1000°C, and with a model I(K) based on fcc microcrystals containing 125 atoms. The Fourier transforms of K[I(K)—1] yielded the reduced distribution functions G(r) =4πr[ρ(r)—ρ0]V(r), where ρ(r) is the weighted atomic density at a distance r from any reference atom, ρ0 is the average atomic density, and V(r) is the size factor of the diffracting domains. Both I(K) and G(r) indicate that the alloy film cannot be characterized as amorphous but is micropolycrystalline with fcc structure. The size of the microcrystals can be estimated from G(r), i.e., from the value of r beyond which G(r) is zero within the scatter of the experimental points. A value of less than 16 Å has thus been found. I(K) and G(r) of the liquid alloy are characteristic of the close-packed liquid metals with a distance of less than 15 Å beyond which no short-range order can be detected.