J. Appl. Cryst. (2001). 34, 484-492 [ doi:10.1107/S0021889801008809 ]
Abstract: Single crystals of Cu-41.5 at.% Ni-16 at.% Fe have been studied by small-angle and large-angle X-ray scattering in order to determine the displacements induced by the disc-like precipitates formed during decomposition. The small-angle X-ray scattering (SAXS) patterns gave information on the size and the organization of the precipitates, while the scattering near Bragg peaks allows a determination of the distortions of the lattice created by these precipitates. The variations of the atomic scattering factors of Fe, Ni and Cu (for the large-angle measurements) were used to determine both the partial structure functions (`chemical' data) and the partial displacements. The precipitates were found to be enriched in Fe and Ni, which induced a contraction of the lattice, while the depleted matrix (mainly Cu) was dilated. This succession of compressed and dilated regions is very stable and prevents a single precipitate from growing much in this direction during coarsening. This can explain why a single precipitate tends to grow mainly in the orthogonal directions, where the extension of the displacements is smaller than the precipitated region.
Keywords: anomalous small/large-angle X-ray scattering; Cu-Ni-Fe alloy; nanoprecipitates; lattice distortion; partial structure functions.
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