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We study the temperature and pressure dependence of phase evolution in the 0.5MgO-0.5Y2O3 nanocomposite system using a diamond anvil apparatus in conjunction with in situ synchrotron energy dispersive x-ray diffraction at 7 GPa hydrostatic pressure. At (298 K, 7.0 GPa), structural transformations in the Y2O3 phase are observed, giving rise to the co-existence of its cubic, hexagonal, and monoclinic polymorphs together with cubic MgO. An increase in temperature to 1273 K causes the crystallinity of the Y2O3 hexagonal and monoclinic phases to increase. Isothermal and isobaric hold at (1273 K, 7.0 GPa) for 60 min results in yttrium dissolution in cubic MgO, causing ∼1.0% expansive volumetric lattice strain despite the large differences in the ionic radii of the cations. Cooling the nanocomposite to (298 K, 0 GPa) after a 60 min soak yields four phase co-existence among cubic MgO and cubic, hexagonal, and monoclinic Y2O3. The residual MgO unit cell volume expansion is 0.69% at 298 K, indicating solid solution formation at room temperature despite large differences in the ionic radii of Mg2+ and Y3+. The macroscopic shrinkage due to densification is 3% by volume. Thermodynamic considerations suggest that the relative molar partial volume of Y3+ in MgO is a negative quantity, indicating that the partial molar volume of Y3+ in the solid solution is smaller than its molar volume in the pure state. Aging of the nanocomposites for 240 h does not change the observed 4 phase co-existence. We propose a crystallographic model in which the observed volumetric expansion of the MgO unit cell is primarily attributed to two hydrostatic expansive strain components accompanying solid solution formation: (i) Coulomb repulsion among O2- ions in the immediate vicinity of Mg2+ vacancies, and (ii) misfit strain due to differences in ionic radii upon Y3+ substitution on Mg2+ sites. [ABSTRACT FROM AUTHOR]

Elastic and plastic strain evolution under four-point bending has been studied by synchrotron energy dispersive x-ray diffraction. Measured strain profiles across the specimen thickness showed an increasing linear elastic strain gradient under increasing four-point bending load up to ∼2 kN. The bulk elastic modulus of Ti–6Al–4V was determined as 118 GPa. The onset of plastic deformation was found to set in at a total in-plane strain of ∼0.008, both under tension and compression. Plastic deformation under bending is initiated in the vicinity of the surface and at a stress of 1100 MPa, and propagates inward, while a finite core region remains elastically deformed up to 3.67 kN loading. The onset of the plastic regime and the plastic regime itself has been verified by monitoring the line broadening of the (100) peak of α-Ti. The effective compression/tension stress-strain curve has been obtained from the scaling collapse of strain profile data taken at seven external load levels. A similar multiple load scaling collapse of the plastic strain variation has also been obtained. The level of precision in strain measurement reported herein was evaluated and found to be 1.5×10-5 or better. [ABSTRACT FROM AUTHOR]

A methodology is presented to characterize the crystallographic texture of atomic configurations on the basis of Euler angles. Texture information characterized by orientation map, orientation distribution function, texture index, pole figure and inverse pole figure is obtained. The paper reports the construction and characterization of the texture of nanocrystalline configurations with different grain numbers, grain sizes and percentages of preferred orientation. The minimum grain number for texture‐free configurations is ∼2500. The effect of texture on deducing grain size from simulated X‐ray diffraction curves is also explored as an application case of texture analysis. In addition, molecular dynamics simulations are performed on initially texture‐free nanocrystalline Ta under shock‐wave loading, which shows a ⟨001⟩ + ⟨111⟩ double fiber texture after shock‐wave compression. [ABSTRACT FROM AUTHOR]

The Ti-Ga co-doped zinc oxide (TGZO) thin films were deposited on glass substrates by radio frequency magnetron sputtering technique in an argon atmosphere. The effect of working pressure on the crystallinity, microstructure, morphology and optoelectrical properties of thin films was investigated by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, four-point probe and spectrophotometer. It is observed that all the deposited films are polycrystalline with a hexagonal wurtzite structure and highly textured along the c-axis perpendicular to the substrate surface. As the working pressure increases, the dislocation density, stress and resistivity decrease initially and then increase, while the crystallite size, average visible transmittance and figure of merit exhibit the reverse variation trend. The TGZO thin film deposited at the working pressure of 0.4 Pa possesses the best optoelectronic properties, with the largest crystallite size of 85.66 nm, the lowest dislocation density of 1.363 × 10 lines m, the minimum compressive stress of 0.232 GPa, the lowest resistivity of 6.715 × 10 Ω cm, the highest average visible transmittance of 88.24 % and the maximum figure of merit of 1.314 × 10 Ω cm. The optical energy-gaps of thin films were estimated by Tauc's law and observed to be in the range of 3.515-3.548 eV which are hardly affected by the working pressure. Furthermore, the optical parameters such as refractive index, extinction coefficient, dielectric constant and nonlinear optical susceptibility were determined by the method of optical spectrum fitting, and the dispersion behavior of refractive index was studied in terms of the Sellmeier's dispersion model. The results show that the microstructure and optoelectrical properties of the TGZO thin films are subjected to the working pressure. [ABSTRACT FROM AUTHOR]

We have constructed a pixelated germanium detector using a technique which has been shown to provide good isolation between adjacent pixels. In this work we present initial tests of the application of a low-noise CMOS ASIC to read out this detector. The detector has 64 pixels, each 0.5~\mm\times 5~\mm, arranged as a series of strips. It is connected by wire-bonds to two 32-channel application-specific integrated circuits (ASICs) which provide a complete photon-counting chain for every channel. Since the size of the pixel array is no longer restricted by the difficulties of instrumenting large channel-count conventional electronics, this development will open up the possibility of even larger arrays, similar to those offered by silicon detectors. [ABSTRACT FROM PUBLISHER]

A novel heteronuclear coordination polymer Cd(1,3-μ-SCN)Ni(CHN)(HO) ( I) has been prepared and characterized by elemental analysis, EDS analysis, PXRD and IR spectrum and single-crystal X-ray diffraction. The single-crystal X-ray diffraction analysis revealed that compound I crystallizes in a monoclinic system of space group C2/ m with a = 19.427(8), b = 9.622(3), c = 7.261(3) Å, β = 105.383(10)°. The compound exhibits a (6,3)-connected two-dimensional layer which is built up from the strict alternation of 6-connected {CdS6} octahedra and 3-connected {NiON} octahedra. [ABSTRACT FROM AUTHOR]

High quality Co-doped ZnO films with good reproducibility have been prepared under different oxygen partial pressure by radio-frequency magnetron sputtering. These films were characterized using numerous characterization techniques including X-ray diffraction, electrical transport, and magnetization measurements. The effect of oxygen partial pressure on the structural, magnetic, and electrical properties of Co-doped ZnO films has been systematically studied. It was found that the structural, magnetic, and electrical properties of Co-doped ZnO films are dependent on oxygen partial pressure. The saturated magnetization of Co-doped ZnO films rapidly increases with decreasing oxygen partial pressure, whereas the resistivity decreases with decreasing oxygen partial pressure. Our findings indicate that the magnetic and electrical properties of Co-doped ZnO films can be tuned by careful control of oxygen partial pressure. In addition, it was further demonstrated that the oxygen vacancy defect is absolutely necessary to induce ferromagnetic couplings in Co-doped ZnO films. [ABSTRACT FROM AUTHOR]

Abstract: Synchrotron based energy dispersive X-ray diffraction has been used to profile the strains around fatigue cracks in 4140 steel test specimens. In particular strain field comparisons were made on specimens prepared: with initial constant stress intensity fatigue; with this initial fatigue followed by a single overload cycle; and with this fatigue-overload sequence followed by an additional constant stress intensity fatigue. The strain profiles behind, at and in-front-of the crack tip are discussed in detail. Selected strain profiles measurements under in situ applied tensile stress are also presented. The technique of optical surface height profiling reveals surface depression effects which can be correlated with the interior strain profiles. [Copyright &y& Elsevier]

The article focuses on the instrumentation, mechanism and applicability of Diffraction Enhanced Imaging (DEI) in soft tissue imaging. It offers brief information on principles and concepts of DEI including the preparation of an imaging beam, the refraction and extinction as two sources of image contrast to radiography, and the stages of scanning. It also explores the DEI imaging in breast, cartilage, and lungs.

The use of bent asymmetric Laue crystals to sagittally focus high-energy synchrotron X-rays calls for an understanding of the mechanisms affecting X-ray diffraction by such crystals. The rocking-curve width, a measurable quantity directly related to the distortion of the lattice planes, is the necessary first step towards such an understanding. A model is formulated for assessing the rocking-curve widths of sagittally bent Laue crystals, considering the elastic anisotropy. A method for depth-resolved measurement of the rocking curves was also developed to verify the model. The model successfully explains the wide range of rocking-curve widths of a large number of reflections from silicon crystals with two different orientations. [ABSTRACT FROM AUTHOR]

We have developed a new X-ray imaging technique, diffraction enhanced imaging (DEI), which can be used to independently visualize the refraction and absorption of an object. The images are almost completely scatter-free, allowing enhanced contrast of objects that develop small angle scattering. The combination of these properties has resulted in images of mammography phantoms and tissues that have dramatically improved contrast over standard imaging techniques.This technique potentially is applicable to mammography and other fields of medical X-ray imaging and to radiology in general, as well as possible use in nondestructive testing and X-ray computed tomography. Images of various tissues and materials are presented to demonstrate the wide applicability of this technique to medical and biological imaging. [ABSTRACT FROM AUTHOR]

The lateral composition modulation in (InAs)[sub n]/(AlAs)[sub m] short-period superlattices was studied by means of synchrotron x-ray diffraction. By choosing specific diffraction vectors having a large component closely parallel to the modulation direction, we are able to observe a number of lateral satellite peaks around the zero-order short-period superlattice peak. A model, incorporating both composition and strain, is used to simulate the intensities of these satellites. Our results provide a quantitative fit and permit the evaluation of the composition amplitude. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Cd1-xZnxTe (CZT) substrates were studied to investigate their bulk and surface properties. Imperfections in CZT substrates affect the quality of Hg1-xCdxTe (MCT) epilayers deposited on them and play a role in limiting the performance of infrared (IR) focal plane arrays. CZT wafers were studied to investigate their bulk and surface properties. Transmission and surface x-ray diffraction techniques, utilizing both a conventional closed-tube x-ray source as well as a synchrotron radiation source, and IR transmission microspectroscopy, were used for bulk and surface investigation. Synchrotron radiation offers the capability to combine good spatial resolution and shorter exposure times than conventional x-ray sources, which allows for high-resolution mapping of relatively large areas in an acceptable amount of time. Information on the location of grain boundaries and precipitates was also obtained. The ultimate goal of this work is to understand the defects in CZT substrates and their effects on the performance and uniformity of MCT epilayers and then to apply this understanding to produce better infrared detectors. [ABSTRACT FROM AUTHOR]

Strain localization in the presence of a stress gradient is a phenomenon common to many systems described by continuum mechanics. Variations of this complex phenomenon lead to interesting nonlinear effects in materials/engineering science as well as in other fields. Here, the synchrotron based energy dispersive x-ray diffraction (EDXRD) technique is used for high spatial resolution profiling of both compression and tension induced strain localization in important materials/engineering problems. Specifically, compression induced strain localization in shot peened materials and tension induced strain localization in the plastic zones adjoining the faces of a fatigue crack are profiled. The utility of the EDXRD synchrotron technique for nondestructively cross-sectioning strain variations on small length scales (down to 10-20 jim) is described. While the strain field profiling relies on the shift of the Bragg lines, the data show that plastic deformation regions can also consistently be seen in the broadening of the Bragg peaks through the full width at half maximum parameter~ Quantitative correlations between the synchrotron based x-ray determined deformations and suiface deformations, as measured by optical surface height profiling, are also made. [DO!: 10.1115/1.2840962] [ABSTRACT FROM AUTHOR]

Two kinds of bed materials were used as bed materials when a biomass of cotton stalk was burnt in a circulation fluidized bed (CFB) combustion pilot plant (0.2 MW). After a long time operation, silica bed materials were found sintered while aluminous bed materials slightly changed. The particles of both kinds of bed materials were sampled and three instrumental approaches were performed (XRF, SEM/EDS, XRD) to identify the bed materials in order to find out the mechanics of agglomeration. The result shows that both of the bed materials were enriched with alkali metals but the changing speed of enrichment of aluminous particles was much slower than that of silica particles. The CFB could go steadily and well at least 72 h under our experimental condition when aluminous particles were used as bed material. Agglomeration of aluminous bed materials was reduced due to the protective element aluminous. [ABSTRACT FROM AUTHOR]

Hexagonal boron nitride was irradiated with 140 MeV protons to a fluence of ~6 1020p/cm2 at T irr ~200 °C. Isotropic graphite was also irradiated alongside h-BN under similar conditions and fluence to enable direct comparison of the two similar structures. The effects of proton irradiation on dimensional stability and microstructure were studied using precision dilatometry and energy dispersive Xray diffraction techniques revealing by direct comparison to graphite that h-BN can better resist radiation damage from bombardment when irradiated with protons impinging normal to the crystallographic planes or along the crystallographic c-axis. X-ray diffraction experiments also revealed a preferred orientation of the crystallites in bulk samples near the sample surface, an orientation influenced by irradiation. Thermal studies using differential scanning calorimetry and thermogravimetric analysis to 740 °C, augmented by precision dilatometry, provided evidence of subtle phase transitions attributed to residual w-BN in the matrix. Irradiation appears to induce shifting of such transitions. [ABSTRACT FROM AUTHOR]

Abstract: High-pressure resistivity and X-ray diffraction measurements were conducted on La0.85MnO3−δ at ∼6 and ∼7GPa, respectively. At low pressures the metal–insulator transition temperature (T MI) increases linearly up to a critical pressure, P * ∼3.4GPa, followed by reduction in T MI at higher pressure. Analysis of the bond distances and bond angles reveals that a bandwidth increase drives the increase in T MI below P *. The reduction in T MI at higher pressures is found to result from Jahn–Teller distortions of the MnO6 octahedra. The role of anharmonic interatomic potentials is discussed. [Copyright &y& Elsevier]

Abstract: High energy synchrotron X-ray diffraction measurements have been performed to provide quantitative microscopic guidance for modeling of fatigue crack growth. Specifically we report local strain mapping, along with in situ loading strain response, results on 4140 steel fatigue specimens exhibiting the crack growth retardation “overload effect”. Detailed, 2D, εyy -strain field mapping shows that a single overload (OL) cycle creates a compressive strain field extending millimeters above and below the crack plane. The OL strain field structures are shown to persist after the crack tip has grown well beyond the OL position. The specimen exhibiting the maximal crack growth rate retardation following overload exhibits a tensile residual strain region at the crack tip. Strain field results, on in situ tensile loaded specimens, show a striking critical threshold load, F c, phenomenon in their strain response. At loads below F c the strain response is dominated by a rapid suppression of the compressive OL feature with modest response at the crack tip. At loads above F c the strain response at the OL position terminates and the response at the crack tip becomes large. This threshold load response behavior is shown to exhibit lower F c values, and dramatically enhanced rates of strain change with load as the crack tip propagates farther beyond the OL position. The OL strain feature behind the crack tip also is shown to be suppressed by removing the opposing crack faces via an electron discharge cut passing through the crack tip. Finally unique 2D strain field mapping (imaging) results, through the depth of the specimen, of the fatigue crack front and the OL feature in the wake are also presented. [Copyright &y& Elsevier]