The structural behavior of zirconolite (CaZrTi2O7) under reducing conditions at high temperature has been studied, mainly by scanning electron microscopy (SEM) and x-ray diffraction (XRD), but also with x-ray absorption spectroscopy, thermogravimetry, and electron paramagnetic resonance. The partial reduction of Ti4+ to Ti3+, associated with a reducing atmosphere heat treatment, led to the initial formation of perovskite (CaTiO3) as a second phase. As the concentration of Ti3+ in the zirconolite increased, so did the amount of perovskite until the zirconolite was totally transformed into a fluorite structured phase. Analysis of the reduced zirconolites showed them to be consistently deficient in Ca and enriched in Zr, in proportion to the concentration of Ti3+. To determine how electroneutrality was preserved in these reduced zirconolites, a series of zirconolites were prepared in air using In3+ and Ga3+ as models for Ti3+. These samples were then investigated by neutron and x-ray diffraction, SEM, solid state nuclear magnetic resonance (NMR), and nuclear quadrupole resonance (NQR). 71Ga MAS NMR studies of the Ga substituted zirconolite exhibited a narrow resonance at ˜13 ppm which was attributed to six-coordinate Ga incorporated in a trace perovskite phase. Broadline 71Ga NMR and 69/71Ga NQR were required to characterize the Ga incorporated in the zirconolite. The resultant quadrupolar parameters of CQ = 30.0 ± 0.05 MHz and η = 1.0 ± 0.03 indicate that the Ga site is in a highly distorted environment which would suggest that it is located on the five-coordinate Ti site within the zirconolite lattice. These results were complemented by Rietveld refinement of the neutron diffraction data from the In-doped zirconolite sample, which was optimal when all the In was located on the five-coordinate Ti site with the excess Zr located on the Ca site. It would therefore appear that charge compensation for the presence of Ti3+ in zirconolite is effected via the substitution of an appropriate amount of Zr on the Ca site. The Ti3+-stabilized fluorite structure was readily oxidized back to a single phase zirconolite upon heating in air.

The Crystal Structure Analysis On The Low- And High-Temperature Phases Of Y4Al2O9 By High-Temperature Neutron Diffraction Revealed A Martensitic Phase Transformation At Around 1380°C. A Diffusionless Cooperative Movement Of Atoms At Transition Was Demonstrated.

Rietveld refinement using neutron, laboratory X-ray, and synchrotron powder diffraction data of NIST SRM clinker 8488 was performed. Quantitative phase analysis (QPA) results were compared between data, and with other studies. QPA results for the main phases in the clinker were found to be in agreement between the different data used here, and in and other studies, although the QPA of the tricalcium silicate polymorphs was shown to be inconsistent. The QPA results for the tricalcium aluminate phase varied between data types, and the neutron data were unable to distinguish this phase. (c) 2006 International Centre for Diffraction Data.

A new powder diffractometer aiming for high angular, and thus high reciprocal space, resolution is being constructed within the Neutron Beam Instrumentation Project at the upcoming Australian Neutron Source OPAL, near Sydney. The neutron flux at the sample can be expected to be up to 107 n/cm2/s. With an array of 128 position sensitive detectors, each equipped with a 30 cm high Söller collimator of 5 arc min acceptance this instrument will have one of the highest performances of its kind. In addition to classical applications in powder diffraction, the quasi two-dimensional detector will be used for rapid texture measurements, where high separation of peaks is necessary. Even single crystal reciprocal space mapping is envisaged. The article compiles an overview of the design, status of the project and potential research activities.

We found an unusual negative thermal expansion in the simple perovskite MnF3 below the Neel point, where the spins are ordered in an A-type magnetic structure. The structure of MnF3 has been studied between 5 and 500 K using powder neutron and synchrotron diffraction. The structure remains monoclinic C2/c over the entire temperature range. We have found that the interplay of spin and orbital ordering is sufficient to result in a large positive magnetovolume effect without charge ordering. This expansion is reminiscent of the Invar effect observed in certain alloys.

PO BOX 78087, MERILINE POSTAL OUTLET, 1460 MERIVALE RD, OTTAWA, CANADA, ONTARIO, K2E 1B1

The lattice parameters, cell volume, and structure of a sample of phase pure triclinic tricalcium silicate were determined using in situ, high‐temperature synchrotron powder diffraction and full‐profile Rietveld refinement. The temperature range covered was from ambient to 740°C. Evidence of superstructure was found. The T2 type structure with disordered SiO4 tetrahedra was observed, and an average structure for the subcell (P, a= 11.7416(2) Å, b= 14.2785(2) Å, c= 13.7732(2) Å, α= 105.129(1)°, β= 94.415(1)°, and γ= 89.889(1)°) is presented. Differential thermal analysis and X‐ray fluorescence was also performed.

For Abstract see ChemInform Abstract in Full Text.

The existence of intracrystalline proteins and amino acids in calcium oxalate monohydrate was demonstrated by X-ray synchrotron diffraction studies. Their presence has implications for the destruction of calcium oxalate crystals formed in the urinary tract and the prevention of kidney stones.Introduction: Although proteins are present in human kidney stones, their role in stone pathogenesis remains unknown. This investigation aimed to characterize the nature of the relationship between the organic and mineral phases in calcium oxalate monohydrate (COM) crystals grown in human urine and in aqueous solutions of proteins and amino acids to clarify the function of proteins in urolithiasis.Methods: COM crystals were grown in human urine and in aqueous solutions containing either human prothrombin (PT), Tamm-Horsfall glycoprotein (THG), aspartic acid (Asp), aspartic acid dimer (AspAsp), glutamic acid (Glu), glutamic acid dimer (GluGlu), or gamma-carboxyglutamic acid (Gla). Controls consisted of COM crystals precipitated from pure inorganic solutions or from human urine that had been ultratiltered to remove macromolecules. Synchrotron X-ray diffraction with Rietveld whole-pattern peak fitting and profile analysis was used to determine nonuniform crystal strain and crystallite size in polycrystalline samples.Results: Crystals precipitated from ultratiltered urine had lower nonuniform strain than those grown in urine or in aqueous PT solution. Nonuniform strain was much lower in crystals grown in distilled water or in the presence of THG. For the amino acids, the highest nonuniform strain was exhibited by crystals grown in Gla solution, followed by Glu. Crystallite size was inversely related to nonuniform strain, with the effect being significantly less for amino acids than for macromolecules.Conclusions: Selected proteins and amino acids associated with COM crystals are intracrystalline. Although their incorporation into the mineral bulk would be expected to affect the rate of crystal growth, they also have the potential to influence the phagocytosis and intracellular destruction of any crystals nucleated and trapped within the renal collecting system. Crystals impregnated with protein would be more susceptible to digestion by cellular proteases, which would provide access to the crystal core, thereby facilitating further proteolytic degradation and mineral dissolution. We therefore propose that intracrystalline proteins may constitute a natural form of defense against renal stone formation.

Abstract The high-resolution powder diffractometer (HRPD) at the HIFAR reactor has been a reliable research tool for over twenty years in a number of configurations [1]. The diffractometer shares beamline 4H1 with the higher intensity, medium-resolution powder diffractometer. The design of the HRPD is based on that of DIA at the Institut Laue Langevin. It uses a simple Ge single crystal monochromator with a fixed take-off angle of 120°. The monochromator provides monochromatic beams of neutrons at a number of wavelengths by rotation around [1 −1 0], the most commonly requested being λ = 1.32, 1.49, and 1.88Å. This monochromator will shortly be replaced with a focusing monochromator at the same take-off angle. The detector system consists of 24 3He detectors that can cover the angular range 5 < 2θ < 155° at step intervals of 0.05°. The best resolution of the diffractometer is Δd/d = 2 × 10−3. Typically it takes approximately twenty-four hours to collect a pattern, and a representative pattern is shown in Figure 1.

The structure of the n=4 Aurivillius oxide BaBi4Ti4O15 has been studied at room temperature using powder neutron diffraction, and from 300 to 1000 K using synchrotron X-ray diffraction methods. The structure is orthorhombic (space group A21am) at 300 K and transforms to a tetragonal (I4/mmm) structure near 700 K.

Variations in the structure of gamma-alumina (gamma-Al2O3), derived from well-crystalline boehmite, calcined at various temperatures in air were investigated. Consistent distribution of cation coordination, similar to69% octahedral and similar to31% tetrahedral, was observed for material calcined between 500 and 900 degreesC. Gamma alumina was found to be present between 450 and 750 degreesC. Its structure was tetragonally distorted but showed a reduced tetragonal distortion with increasing temperature. A cubic gamma-Al2O3 phase was never detected. Above 750 degreesC, delta-Al2O3 was not observed, but instead a new phase was identified and designated gamma-prime-alumina (gamma'-Al2O3). Similarly to delta-Al2O3, gamma'-Al2O3 was determined to be a triple cell of gamma-Al2O3 and was described using the P (4) over bar m2 space group. The cation ordering in this structure is more obvious than that for gamma-Al2O3, with fewer site positions being occupied with increasing calcination temperature.

gamma-alumina (gamma-Al2O3) derived from boehmite has historically been described as having a cubic spinel structure with Fd (3) over barm symmetry, despite reports of tetragonal distortion in the structure. Based on neutron diffraction, transmission electron microscopy, and magic angle spinning NMR data, we propose a tetragonal model for the structure of boehmite-derived gamma-Al2O3 with I4(1)/amd space group symmetry, a maximal subgroup of Fd (3) over barm. It is also demonstrated that an accurate average structural model cannot be achieved if the cations are restricted to spinel positions.

From X-ray fluorescence analysis via scanning electron microscopy (SEM), there was no evidence of Zr occupation of the Ca site of zirconolite (CaZrTi2O7). Mg can inhabit both the Ca and Ti sites as shown by solid-state magic-angle spinning and high-field static nuclear magnetic resonance measurements. Microstructural. work indicated that approximately 0.1 formula units of divalent or trivalent Fe, Mn, Co and Ni can also inhabit Ca sites. From SEM, Al substituted into zirconolite with appropriate charge compensators being present can inhabit Ti sites but not the Ca sites. A Rietveld analysis of the powder neutron diffraction patterns showed that Al enters the fivefold Ti site preferentially to the sixfold Ti sites.

The crystal structure of kingite, Al-3(PO4)(2)(F,OH)(2).8(H2O,OH), a secondary mineral from a Cambrian-Precambrian phosphate deposit at Tom's Quarry, near Kapunda, South Australia, has been determined from a powder sample using synchrotron X-ray diffraction data. The structure was determined ab initio by direct methods and refined to R-Bragg = 0.022 and R-wp = 0.039 using the Rietveld method. The triclinic structure was solved and refined in the space group P (1) over bar1, a = 9.377(1), b = 10.113(1), c = 7.138(1) Angstrom, alpha = 97.60(1), beta = 100.88(1), gamma = 96.01(1)degrees, V = 653.0(1) Angstrom(3), Z = 2. The structure of kingite contains finite strings of three corner sharing Alphi(6) octahedra (where phi represents O, OH-, F-, or H2O). These strings are cross-linked via PO4 tetrahedra to produce layers that are perpendicular to [100]. The layers are linked via hydrogen bonding through H2O located in the interlayer space. Kingite is shown to have a different stoichiometry to that reported earlier. The relationship of kingite to the structures of wavellite, Al-3(PO4)(2)(OH)(3).5H(2)O, and mitryaevaite, Al-5(PO4)(2)[(P,S)O-3(OH,O)](2)F-2(OH)(2)(H2O)(8).6.48H(2)O, are briefly discussed.

During the first few hydrogenation–dehydrogenation cycles of virgin LaNi5, the absorption plateau pressure drops sharply, accompanied by powdering of the starting intermetallic. We looked for an explanation of this phenomenon in the microstructural features of the metal that can be studied via diffraction. Five complete absorption–desorption cycles were conducted in an unbroken sequence, with neutron powder diffraction patterns being recorded in cycles 1, 2 and 5. We found that, after activation, the drop in absorption plateau pressure correlates with increasing coherency of the phase transformation in the c-direction, translating to lower elastic strain energy associated with the transformation. The total microstrain in the dehydrided metal is essentially constant after cycle 1. These findings afford a partial understanding of the pressure behaviour in the first few cycles, but the mechanism by which the lattice coherency develops remains to be explained.

The compounds formed by the hydration of single-phase samples of the mixed, solid solution, Ca/Sr aluminates, Ca 3− x Sr x Al 2 O 6 , 3≤ x ≤0 have been studied using high-resolution synchrotron powder diffraction. Hydration of these mixed metal aluminates generally resulted in the formation of at least two hydrogarnet phases, one Ca-rich and the other Sr-rich. The structures of these hydrogarnets have been refined from neutron or synchrotron powder X-ray diffraction (XRD) data. A simple solubility model to explain the phase separation is presented.

The crystal structure of SrRuO3 at high temperatures has been studied at fine temperature intervals using high-resolution synchrotron diffraction. It has been shown that SrRuO3, orthorhombic in space group Pnma, at room temperature, changes by a continuous transition to a structure in Imma at about 685 K, then by a discontinuous transformation to tetragonal I4/mcm at about 825 K, and finally, continuously, to cubic at near 950 K.