Diffuse Streaks Research Articles

An electron diffraction and Monte Carlo simulation study of diffuse scattering in Pb(Zr,Ti)O3

Transverse polarized diffuse streaks have been recordedviatransmission electron microscopy for a range of Pb(Zr1−xTix)O3ceramics spanning the entire phase diagram from the rhombohedral phase (x= 0.3), through the monoclinic morphotropic phase boundary region (MPB;x= 0.48) to the tetragonal phase (x = 0.7). Although the same type of streaks are observed over the whole composition range, they are strongest and most distinct in the rhombohedral phase and diminish in clarity as the MPB is approached. The streaks have been shown to correspond to diffuse planes of scattering in three dimensions and are oriented normal to the (cubic) 〈111〉cdirections. A Monte Carlo computer simulation model has been developed that convincingly reproduces the observed diffraction patterns in the rhombohedral phase. In this model the displacements of Pb ions in chains running along each of the 〈111〉cdirections are directed along the chain and are strongly correlated from cell to cell. There is no evidence of lateral correlation, indicating that neighbouring chains are essentially independent.

Structural origin of the x-ray diffuse scattering in(CH3)4NCdCl3and related compounds

The local structure of ${({\text{CH}}_{3})}_{4}{\text{NCdCl}}_{3}$ (TMCC) has been determined by a configurational-bias reverse Monte Carlo method applied to x-ray diffuse scattering data. The following two phases have been analyzed and refined: phase I at 293 K, $P{6}_{3}/m$ space group, $a=9.139(1)\text{\AA{}}$, and $c=6.723(1)\text{\AA{}}$; and phase ${\text{I}}^{\ensuremath{'}}$ at 410 K, $P{6}_{3}/mmc$ space group, $a=9.235(1)\text{\AA{}}$, and $c=6.742(1)\text{\AA{}}$. A model dividing the ${\text{CdCl}}_{6}$ octahedral chains into elementary blocks has been implemented in order to take into account the coupling between the orientation of the ${({\text{CH}}_{3})}_{4}\text{N}$ molecules and the local deformations of the octahedral chains. The resulting structures contain subchains of ${\text{CdCl}}_{6}$ octahedra that are shifted longitudinally away from their average positions. The subchain lengths can be described by a Poisson-like distribution with an average length of roughly six unit cells. X-ray diffuse scattering effects observed on the $hk0$ plane require the existence of transverse subchain displacements. An additional correlation between the transverse and longitudinal shifts of the subchains was needed in order to explain the weak modulation effects and diffuse streaks observed on the planes perpendicular to ${c}^{\ensuremath{\ast}}$.

Modulated Structures and Atomic Ordering in InPySb1-y Layers Grown by Organometallic Vapor Phase Epitaxy

Modulated structure in organometallic vapour phase epitaxially grown InPSb(001) layers has been investigated using transmission electron microscopy (TEM) and transmission electron diffraction (TED). TEM results show that a fine scale modulated contrast (15–20 nm) and a fine scale speckled contrast (∼5 nm) are simultaneously present. In addition, a fine needle-like contrast (∼1.5–2.1 nm) is present. TED patterns show that (111) and (111) CuPt-type ordered variants are present. Diffuse streaks along the [110] direction are also observed in the [110] TED pattern and found to be associated with the needle-like contrast. A possible model involving segregation of atoms associated with rows of missing dimers in the surface reconstruction or the presence of antiphase boundaries (APBs) and domain boundaries in CuPt-type ordered regions present in the layers is suggested to explain the origin of the needle-like contrast.

Turbulent blood flow plays an essential localizing role in the development of atherosclerotic lesions in experimentally induced hypercholesterolaemia in rats

Taking into account that atherosclerosis is a focal disease and high levels of plasma cholesterol are closely correlated with its pathogenesis, it is a challenge to explain how equal concentrations of cholesterol bathing the endothelium can produce local, rather than global, effects on arteries. The focal distribution of atherosclerotic lesions has been considered to be dependent, at least in part, on hydrodynamic factors. The present study was carried out to further test the hypothesis that these forces are an important localizing factor in rats feeding a hypercholesterolaemic diet and submitted to infra-diaphragmatic aortic constriction. These animals develop a normotensive prestenotic region with laminar blood flow that serves as control for a normotensive poststenotic region with turbulent blood flow. Our findings clearly demonstrated that the combination of turbulent blood flow and low wall shear stress (WSS) in the presence of hypercholesterolaemia and oxidative stress creates conditions to the formation of focally distributed incipient atherosclerotic lesions observed in the poststenotic segment. In contrast, only diffuse fatty streaks could be observed in the normotensive prestenotic segment with laminar blood flow and normal WSS in the presence of hypercholesterolaemia and oxidative stress. Although haemodynamic forces are not by themselves responsible for the pathogenesis of atherosclerosis, they prime the local vascular wall in which the lesion develop. Further studies are required to establish how haemodynamic forces are detected and transduced into chemical signalling by the cells of the artery wall and then converted into pathophysiologically relevant phenotypic changes.

Chronic Polymyositis Associated with Disseminated Sarcocystosis in a Captive-born Rhesus Macaque

A 2-year-old, captive-born, clinically healthy male, rhesus macaque, was euthanatized as part of an experimental study. At necropsy, diffuse pale streaking of the trunk, lumbar, and limb muscles were noted macroscopically. On histology, numerous elongated cysts that contained crescent-shaped basophilic spores were found in the fibers of skeletal muscles. Scattered affected myofibers were degenerate and accompanied by eosinophilic-to-granulomatous inflammation. Sarcocysts had prominent villus-like projections with the morphology of a type 11 sarcocyst wall similar to Sarcocystis neurona but possessing many more villus microtubules than is reported for S. neurona. In addition, bradyzoites were very long, up to approximately 12 microm in length. The protozoa were consistent with a Sarcocystis sp., based on histology and ultrastructure, however, a definitive identification of the species was not possible. Nonspecific immunohistochemical crossreaction with Sarcocystis cruzi antisera was observed. The 18S ribosomal deoxyribonucleic acid sequence showed 91% similarity to Sarcocystis hominis, 90% similarity to Sarcocystis buffalonis, and 89% similarity to Sarcocystis hirsuta. Interestingly, the ITS1 sequence showed very little homology to any sequence in GenBank, suggesting that this is possibly a unique Sarcocystis sp. Sarcocystosis is often considered an incidental finding, particularly in wild-caught animals, with little clinical significance. However, as demonstrated in this report and others, disseminated sarcocystosis can occur in captive-born rhesus macaques with or without clinical signs. In some cases interference with research results can occur; including death in fulminant cases.

Determination of stacking fault densities in 3C‐SiC crystals by diffuse X‐ray scattering

AbstractThick 3C‐SiC single crystals grown by continuous‐feed physical vapor transport (CF‐PVT) are studied by high‐resolution X‐ray reciprocal space mapping. These crystals contain Shockley‐type stacking faults (SFs) lying in the {111} planes, which give rise to diffuse intensity streaks along the 〈111〉 directions. An approach is presented that allows to determine, in combination with the simulation of transverse scans, the SF density from the simulation of the diffuse intensity streaks. SF densities as low as 0.4 × 103 cm–1 could be detected in high‐quality CF‐PVT grown crystals. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Complex disorder in β-NH4Fe2(PO4)2: deciphering from a five-dimensional formalism

A new mixed-valent iron ammonium phosphate, beta-NH(4)Fe(2)(PO(4))(2), has been synthesized. The diffuse scattering observed on the diffraction patterns implies complex disorder phenomena and prevents a direct structure resolution. The latter can be solved by generating an artificially ordered orthorhombic structure, using a five-dimensional approach and performing partial integration of the diffuse streaks. In the artificially ordered structure, hexagonal tunnels, delimited by FeO(6) octahedra, perpendicular to the directions [011] and [01(over)1] can then be seen; they are filled either by [FeP(2)O(10)](infinity) zigzag ribbons or by NH(4)(+) cations. It is shown that the disordering originates from the shifting of adjacent (100) tunnel slices of the structure with respect to each other along [011], allowing the formation of either new commensurate (superstructure) or incommensurate modulations, or even complete disorder along a. The close relationships with the ordered monoclinic form alpha-NH(4)Fe(2)(PO(4))(2) are also explained by this description.

Superstructure of Challis mordenite with doubled monoclinic unit cell

A new superstructure was found in mordenite (Na 5.59 Ca 1.80 Al 9.19 Si 38.81 O 96 ·nH 2 O) from Challis Valley, Idaho-a zeolite widely used in previous studies. The occurrence of the superstructure reflections were observed in 12 specimens from two rock samples, at the midpoint of layers in the oscillation photographs around the a* and b* axes, but not around the c* axis. The apparent 2a, 2b, and c axes are orthogonal. In spite of yielding an apparent orthorhombic cell, careful observation of the intensities revealed that the superstructure is monoclinic with twice the volume of the orthorhombic cell: a’ = 27.356(9), b’ = 27.356(9), c’ = 7.517(2) Å, γ′ = 97.14(4)°, and V′ = 5582(4) Å 3 . The presence of the superstructure was examined for specimens from ten other localities and a synthetic sample but there was no evidence for extra spots of the superstructure, indicating that the occurrence is not common. The large displacement factors of O8 oxygen, and its associated 180° T-O-T angle that is energetically unfavorable, are basic to the mordenite structure. In the monoclinic superstructure the O8 oxygen is decomposed into several asymmetric O atoms by the symmetry reduction. The large displacement smearing of O8 oxygen perpendicular to the straight T-O-T, are explained by the superposition of decomposed O atoms. The extra spots are predominantly observed in the reciprocal planes with l = odd in the same way as diffuse streaks. The observation of extra spots and diffuse streaks suggests that there are three kinds of domains in the mordenite, one in the ordered form and two others in the random form of c/2 linear displacements. The domain in the ordered form represents the superstructure. Thus, we propose a model for the superstructure in which the c/2 displacement occurs alternatively in the two basic unit cells slightly modified in the superstructure, yielding the periodic arrangements.

TEM investigation of the microporous compound VSB-1: Building units and crystal growth mechanisms

Surface fine structure and structural defects in the open framework material VSB-1 have been investigated by electron microscopy. Crystal growth phenomena are proposed by a building unit model: (i) a unit is formed by two building units; (ii) they are linked to form first channels; and (iii) the whole network is grown via a layer-by-layer growth mechanism. A planar defect was observed in high-resolution transmission electron microscope (HRTEM) image taken with the [0001] incidence, and diffuse streaks related to the presence of defects were observed in a series of electron diffraction (ED) patterns. The microstructure model derived from the defect structure gives information on crystal growth. These defects highlight an open site that could be the pillar of a new crystal growth process. The study of defects and crystal growth is important in understanding physical properties such as catalytic or magnetic properties, and in synthesising a new open framework structure.

Martensitic transformation in FePd alloy revealed by synchrotron radiation

Synchrotron radiation experiments were performed for the precursor study of the martensitic transformation in Fe 68.6Pd 31.2 (numbers indicate at.%) alloy. Tunable wavelength is one of advantages of synchrotron radiation and was utilized in the present work. Six wavelengths, which give various penetration depths and give information from various depths, were chosen for observing the transformation behavior. Oscillation photographs with various wavelengths were taken at several temperatures above the martensitic transformation temperature. Those oscillation photographs showed splitting of Bragg reflections and 〈1 1 0〉 diffuse streaks and also showed a wavelength dependence. Thus the transformation mechanism was discussed from a viewpoint of precursor phenomenon and incomplete phonon softening features.

Ultraviolet Luminescence from Defect Complexes in the Twin Boundaries of K-Feldspar

The ultraviolet (UV) emission at 290 nm has been studied by thermoluminescence (TL), cathodoluminescence (CL), and radioluminescence (RL) techniques in a natural K-feldspar with intermediate microcline X-ray diffraction pattern. Electron microprobe analyses (EMPA) give the chemical formula K0.98Na0.02Al1.02Si2.98O8. An irregular submicroscopical twinning has been observed from transmission electron microscopy (TEM) images. Selected area electron diffraction (SAED) patterns along the [001] zone axis evidence the triclinic character of this feldspar (γ* angle ≈ 91°) and exhibit a double spot splitting, associated with the presence of discrete twin-domains, interconnected by diffuse streaks. The 29Si MAS NMR spectrum demonstrates that the appearance of this UV emission cannot be explained by distinct T−O−T geometry of the local structure in comparison with other triclinic K-feldspars. The close association between twinning and the UV band in the K-feldspar points to charge trapping and light emissions from c...

Structural phase transition of monoclinic crystals of hen egg-white lysozyme

Two monoclinic crystals (space group P2(1)) of hen egg-white lysozyme, a type I crystal grown at room temperature in a D2O solution with pD 4.5 containing 2%(w/v) sodium nitrate and a type II crystal grown at 313 K in a 10%(w/v) sodium chloride solution with pH 7.6, were each transformed into another monoclinic crystal with the same space group by dehydration-induced phase transition. Changes in X-ray diffraction were recorded to monitor the progress of the crystal transformation, which started with the appearance of diffuse streaks. In both crystals, the intensity of h + l odd reflections gradually weakened and finally disappeared on completion of the transformation. X-ray diffraction in the intermediate state indicated the presence of lattices of both the native and transformed crystals. In the native type I crystal, two alternate conformations were observed in the main chain of the region Gly71-Asn74. One conformer bound a sodium ion which was replaced with a water molecule in the other conformer. In the transformed crystal, the sodium ion was removed and the main-chain conformation of this region was converted to that of the water-bound form. The transformed crystal diffracted to a higher resolution than the native crystal, while the peak width of the diffraction spots increased. Analysis of the thermal motion of protein molecules using the TLS model has shown that the enhancement of the diffraction power in the transformed crystal is mainly ascribable to the suppression of rigid-body motion owing to an increase in intermolecular contacts as a result of the loss of bulk solvent.

Observation of a Strongly Nested Fermi Surface in the Shape-Memory AlloyNi0.62Al0.38

The Fermi surface topology of the shape-memory alloy Ni0.62Al0.38 has been determined using Compton scattering. A large area of this Fermi surface can be made to nest with other areas by translation through a vector of approximately 0.18[1,1,0](2pi/a), which corresponds to the wave vector associated with martensitic precursor phenomena such as phonon softening and diffuse streaking in electron diffraction patterns. This observation is compelling evidence that these phenomena are driven by the enhanced electron-lattice coupling due to the Fermi surface nesting.

Evolution of product phase assemblages during thermal decomposition of muscovite under strong disequilibrium conditions

We investigated the thermal decomposition of muscovite in natural granite powders heated to 1175 °C for durations from 5 min to 68 h, at 1 bar, paying special attention to the early stages of decomposition. This study shows that muscovite is completely transformed after 5 min. Muscovite pseudomorphs consist of glass, mullite, and Al-rich oxides. For short durations (5 and 40 min), the Al-rich phase was identified by XRD, electron diffraction, and TEM microanalysis as γ-Al2O3 containing 4-8 wt% FeO (total Fe), probably a few weight percents of MgO, and possibly up to 10 wt% SiO2. Faint superstructure spots and diffuse streaks observed in electron-diffraction patterns suggest vacancy or trace elements ordering in the γ-Al2O3 defect spinel structure. γ-Al2O3 displays an unexpected acicular morphology, elongated along three directions at 120° in the basal (001)musc planes and parallel to lateral faces of the former muscovite. Mullite forms rods elongated in the basal (001)musc planes along a direction at 90° from one set of γ-Al2O3 needles. The γ-Al2O3 structure appears to be a metastable phase that is replaced by corundum for longer durations.

The characterization of synthetic and natural single crystal diamonds by X-ray diffraction

Natural and synthetic single crystal diamonds (types Ia, Ib, IIa and IIb) have been characterized by measurements of the X-ray integrated scattering intensity, lattice parameter and diffuse scattering. We found a drastic increase of X-ray integrated scattering intensity for natural and B-doped diamond crystals. Synthetic type IIa diamond was also measured for comparison. Measurements of the lattice parameters have been made at room temperature by using the X-ray bond method. We found that the lattice parameter is smallest for natural diamond and largest for the B-doped diamond. Diffuse scattering experiments were performed using a four circle diffractometer at room temperature. We measured the diffuse scattering for (4 0 0) Bragg reflection for the four types of crystals. The scattering intensity of the natural crystals diffuses asymmetrically to form a streak along the [1 0 0] direction parallel to the reciprocal lattice vector. These results suggest the existence of the nitrogen atom platelets on (1 0 0) plane in the natural diamond. We also found the diffuse streaks along the [ 1 ˙ 0 0 ] direction for (4 0 0) Bragg reflection for the B-doped crystal, suggesting that boron atoms are likely to form precipitates on the (1 0 0) plane.

Structural disorder of a new zeolite-like lithosilicate, K2.6Li5.4[Li4Si16O38]·4.3H2O

The framework structure of the synthetic microporous lithosilicate RUB-30 (K(2.6)Li(5.4)[Li4Si16O38].4.3H2O) is similar to that of the fibrous zeolites such as natrolite, edingtonite and thomsonite, since all their frameworks include the same secondary structural building unit, the so-called 4-1 T5O10 cluster of tetrahedra. Unique to the structure of RUB-30, each 4-1 unit consists of a LiSi4O10 moiety within which the single [LiO4] tetrahedron is strictly segregated from the other four [SiO4] tetrahedra. The connection of neighboring 4-1 units through edge-sharing [LiO4] tetrahedra results in a new framework topology. The present work reports an ;average' structure of RUB-30 solved by synchrotron X-ray single-crystal diffraction data collected at a second-generation source. A superstructure with a x 2b x c (relative to the subcell quoted above) could be seen in X-ray diffraction data collected with better resolution and higher brightness at a third generation source. Diffuse streaks along k with l = odd and unusual superstructure hkl reflections, with k = odd and l = odd only, indicate a more complicated real structure of the material. To explain this observation we propose two different structure types which are statistically, but coherently, intergrown in RUB-30.

Phase Transformation and Magnetic Properties in Ni52FexMn21−xGa27 Alloys

Effect of chemical composition was investigated on martensitic transformation temperatures, Curie temperature, magnetization for Ni52FexMn21−xGa27 alloys. X-ray diffraction patterns revealed that all the samples were in a single Heusler (L21) phase state at room temperature. Forward and reverse martensitic transformation temperature, M* and A*, decreased with Fe content, x, up to 15 mol% and then turned to increase by further addition of Fe. Composition dependence of the Curie temperature exhibited a reversed tendency compared with M*. The structure of martensite was 10M for the alloys with x<15 and a mixture of 14M and 10M for x=20. Electron diffraction patterns of L21 phase exhibited intense diffuse streaks on cooling, which were longer than those observed in ternary Ni–Mn–Ga.

Microfocus X-ray scattering investigations of eggshell nanotexture

The avian eggshell is a highly ordered calcitic bioceramic composite, with both inorganic and organic constituents. The interactions between the inorganic and organic components within the structure are poorly understood but are likely to occur at the nanometre level. Thus structural variation at this level may impinge on the overall structural integrity and mechanical performance of the eggshell, and therefore analysis at this level is fundamental in fully understanding this ordered structure. In this study, structural changes in the mineral crystallites were investigated by microfocus small-angle X-ray scattering (microSAXS) using synchrotron radiation. Small-angle X-ray scattering (SAXS) can be used to investigate structures on the nanometre scale such as size, shape, arrangement and internal porosity. A microfocused X-ray beam, 1.5 microm vertically by 7 microm, was used to produce vertical linear scans of the eggshell section. SAXS patterns were taken from the eggshell membrane (inner surface of the eggshell) to the cuticle (outer surface of the eggshell). This allowed textural variations within the eggshell to be mapped. The scattering intensity profile was then used to derive the dimension of scattering objects that define the nanotexture. The nanotexture observed may result from the presence of the organic matrix, which is embedded as intracrystalline particles producing voids within the calcified framework of large (>1 microm) calcite crystals. Porod analysis revealed the average size of a scattering interface to be approximately 4.5 nm with small changes that had a depth-dependent variation. These were largest at the mammillary layer/membrane boundary. The palisade layer displayed a small upward trend in size of scattering object. Parallel scans showed that the textural variations observed within the palisade layer are significant and indicate local subtextures. In addition, many of the patterns exhibit diffuse scattering streaks that could result from reflectivity from the larger crystallite interfaces. Changes in the orientation of diffuse streaks were observed within the different layers, the membranes, mammillary layer, palisade layer, vertical crystal layer and cuticle, indicating certain preferred orientations of the crystallites within the layers. The nanotextural variations that are apparent could have implications at the macroscopic level of the resulting eggshell.

Nano-sized domains related to dielectric anomaly in YFe2O4-δ

We examined microstructures related to the charge ordering in YFe2O4-delta, by transmission electron microscopy. It is found that two types of characteristic diffuse scatterings appear at room temperature. One is characteristic diffuse streaks elongated along the [0001] direction through the (1/3 1/3 2/3 0)-type reciprocal positions and the other is diffuse spots at (1/3 - eta 1/3 - eta 2/3 + 2eta 0)-type incommensurate positions (eta approximately 0.066). Real-space images revealed that the former diffuse scattering is related to nano-domains due to the charge ordering and the latter one is related to those due to vacancy ordering. The presence of the nano-sized domains should be strongly related to the dielectric anomalies found in YFe2O4-delta.

Identification of soft phonon modes in Ge–Sb–Te using electron diffraction

The atomistic structure of crystalline Ge–Sb–Te thin film for phase-change optical recording was investigated using transmission electron microscopy and nanobeam electron diffraction. Nonradial diffuse streaks were observed in electron diffraction patterns obtained from laser-induced crystalline phases of Ge–Sb–Te thin films. The intensities of the diffuse streaks were pronounced in particular directions in this alloy. The diffuse streaks were due to low-frequency transverse lattice waves that occur along directions perpendicular to the near neighbor zigzag atomic chains.