Determination of the Distortion Field in Binary Alloys

Abstract

The distortion field induced by a substitutional defect in a simple metal has been calculated from lattice statics, using Shaw’s optimized model potential in combination with a screening function suggested by Vashishta and Singwi. Using this procedure, interactions of arbitrary range can be taken into account. In order to test the validity of the theory, the diffuse elastic cross-section, which is directly related to the Fourier transform of the distortion field, was measured experimentally with the help of a neutron scattering technique. The system under investigation was Al containing a few at% Mg. A comparison of the experimental data with the predictions of the pseudopotential concept gave quantitative agreement for a limited, but nevertheless continuous, range of momentum transfer vector. Furthermore, qualitative agreement was obtained throughout the entire experimental range. Supplementary virtual force model calculations gave, even by simulating forces upto the fourth nearest neighbour shell, no satisfactory description of the experimental cross-section.