Displacements induced by different nanoprecipitates: a SAXS and WAXS anomalous study on Cu–Ni–Fe and Cu–Ni–Co single crystals

Abstract

Single crystals of different Cu-Ni-Co and Cu-Ni-Fe alloys, forming spheroid or plate-like precipitates during decomposition, have been studied by small-angle (SAXS) and wide-angle X-ray scattering (WAXS). The SAXS patterns gave information on the sizes and the organization of the precipitates, while the scattering near Bragg peaks allowed a determination of the distortions of the lattice created by these precipitates. The variations of the SAXS spectra with the atomic scattering factors of Co (or Fe) and Ni were used to determine the composition variation between matrix and precipitates (i.e. the 'chemical' term), while those of the WAXS spectra enabled the determination of the displacements in the matrix and in the precipitates. The precipitates were found to be enriched in respectively Co and Ni, or Fe and Ni, inducing a local contraction of the lattice, while the matrix (mainly Cu) was of course depleted in the same elements, and its lattice was dilated. These precipitates are piled up along one of the three h100i 'soft' directions. The variations of the deformation field with the precipitate sizes (along both directions parallel and orthogonal to the pile-up orientation), and with the distance between precipitates have been determined. From the knowledge of such variations, it was possible to modify the respective deformation fields in such a way that the respective precipitates have the same sizes, but with a different geometry, and then to isolate what was induced solely by the geometry of a precipitate. Moreover, these experiments yielded the determination of the secondary components of the displacement field (displacements orthogonal to the pile-up direction), which were found to be weak compared with the primary one (parallel to the same direction). Finally, from the variation of the aspect ratio of the precipitates with the aging duration, it was possible to estimate the surface energy of the precipitates, and a comparison between SAXS and WAXS results shows the applicability of this new approach to the decomposition process.

Evolution of electrochemical interfaces in solid oxide fuel cells (SOFC): a Ni and Zr resonant anomalous ultra-small-angle X-ray scattering study with elemental and spatial resolution across the cell assembly

“…Anomalous USAXS measurements made close to two wellseparated absorption-edge X-ray energies have interrogated the evolution of SOFC microstructures during service life, and quantied the inuence of sulfur in the fuel on anode microstructure degradation. These studies differ from other recent anomalous SAXS studies using multiple X-ray absorption edges, 47,48 which have characterized discrete scattering particles within a uniform matrix. By contrast, SOFC microstructures are complex and heterogeneous in nature, with each phase having boundaries with multiple other phases.…”

Anomalous grazing incidence small-angle X-ray scattering of carbon-encapsulated Au and Cu clusters

“…Of course, if the scattering q ranges of the two kinds of clusters have no or little overlap, this will facilitate the analysis. We can nevertheless predict the limit for overlapping signals: in all our previous ASAXS experiments (Simon & Lyon, 1994;Lyon et al, 2005 and papers quoted therein), the limit of precision (or of systematic error) was about 1-2%. This limit was reached in the model case of the binary C-Cu system with relative contrast variations in the range AE15%, and also in the case of the C-Au-C trilayer containing both Au nanoclusters and additional defects.…”

Contribution of synchrotron radiation to small-angle X-ray scattering studies in hard condensed matter

“…The theoretical approaches are recent (reviewed by Fratzl et al, 1999): few experiments exist on single crystals. Cu 70 Ni 23 Co 7 (at.%) Lyon et al, 2005) undergoes phase separation into an Ni-Co-rich phase and a Cu-rich phase: since the bulk parameter of the Ni-Co phase is smaller than that of the Cu phase, there are lattice strains in both phases. The anisotropy of the lattice constants induces a pile-up along the weak h100i directions.…”