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A model automotive exhaust catalyst, consisting of 2.25 wt% Pd supported on initially high-surface-area (88 m 2 /g) cerium???zirconium mixed oxide (Ce 0.5 Zr 0.5 O 2), was studied by X-ray diffraction (XRD), thermogravimetric analysis (TGA), and transmission electron microscopy (TEM), following high-temperature (1150??C) redox aging. Spherical Pd particles with size varying from 30 to 80 nm in diameter were found to be embedded both within single grains and at interfaces between multiple grains of the mixed oxide. X-ray energy-dispersive spectroscopy (EDS) and microbeam electron diffraction show that these particles are pure Pd, with face-centeredcubic structure. These results, together with elemental distribution maps obtained by EDS imaging, provide detailed visualization of an encapsulation phenomenon previously reported on the basis of XRD and TGA measurements alone.

Phason-strained octagonal quasicrystal phases of Mo-Cr-Ni have been studied by electron diffraction and dark-field imaging. The shifting of some of the diffraction spots lowers the symmetry from eightfold to fourfold. Diffraction patterns of the orthogonal twofold axes show that the shifted spots are split along the fourfold axis. Discommensurations (DC’s) observed in dark-field images of split reflections are aligned perpendicular to the fourfold axis. We have found that the density of the DC’s in widely separated and adjacent regions may vary by more than 1 order of magnitude. The density of the DC’s is directly related to the separation of the splitting. The large difference in the density of DC’s in adjacent regions supports the interpretation that the DC’s in the Mo-Cr-Ni phases are due to the ordering of atomic species in the quasilattice. Our observations are consistent with some of the results of the two-dimensional octagonal random tiling model of Li, Park, and Widom.

Phason-strained octagonal quasicrystal phases of Mo-Cr-Ni have been studied by electron diffraction and dark-field imaging. The shifting of some of the diffraction spots lowers the symmetry from eightfold to fourfold. Diffraction patterns of the orthogonal twofold axes show that the shifted spots are split along the fourfold axis. Discommensurations (DC’s) observed in dark-field images of split reflections are aligned perpendicular to the fourfold axis. We have found that the density of the DC’s in widely separated and adjacent regions may vary by more than 1 order of magnitude. The density of the DC’s is directly related to the separation of the splitting. The large difference in the density of DC’s in adjacent regions supports the interpretation that the DC’s in the Mo-Cr-Ni phases are due to the ordering of atomic species in the quasilattice. Our observations are consistent with some of the results of the two-dimensional octagonal random tiling model of Li, Park, and Widom.

Phason-strained octagonal quasicrystal phases of Mo-Cr-Ni have been studied by electron diffraction and dark-field imaging. The shifting of some of the diffraction spots lowers the symmetry from eightfold to fourfold. Diffraction patterns of the orthogonal twofold axes show that the shifted spots are split along the fourfold axis. Discommensurations (DC’s) observed in dark-field images of split reflections are aligned perpendicular to the fourfold axis. We have found that the density of the DC’s in widely separated and adjacent regions may vary by more than 1 order of magnitude. The density of the DC’s is directly related to the separation of the splitting. The large difference in the density of DC’s in adjacent regions supports the interpretation that the DC’s in the Mo-Cr-Ni phases are due to the ordering of atomic species in the quasilattice. Our observations are consistent with some of the results of the two-dimensional octagonal random tiling model of Li, Park, and Widom.

Domains and discommensurations have been directly observed by transmission electron microscopy in some dark-field images using certain reflections in a Mn-Si-Al octagonal quasicrystal. The invisibility and visibility of domains and discommensurations separate the diffraction spots into basic and satellite reflections. The domains and discommensurations observed in satellite reflections are interpreted as due to the ordering of Si and Al atoms in the quasilattice of the quasicrystal. A simple model which gives satisfactory agreement with the experimental results is given.

Domains and discommensurations have been directly observed by transmission electron microscopy in some dark-field images using certain reflections in a Mn-Si-Al octagonal quasicrystal. The invisibility and visibility of domains and discommensurations separate the diffraction spots into basic and satellite reflections. The domains and discommensurations observed in satellite reflections are interpreted as due to the ordering of Si and Al atoms in the quasilattice of the quasicrystal. A simple model which gives satisfactory agreement with the experimental results is given.

Domains and discommensurations have been directly observed by transmission electron microscopy in some dark-field images using certain reflections in a Mn-Si-Al octagonal quasicrystal. The invisibility and visibility of domains and discommensurations separate the diffraction spots into basic and satellite reflections. The domains and discommensurations observed in satellite reflections are interpreted as due to the ordering of Si and Al atoms in the quasilattice of the quasicrystal. A simple model which gives satisfactory agreement with the experimental results is given.