scholarly journals The Australian High Resolution Neutron Powder Diffractometer

1983 ◽  
Vol 36 (4) ◽  
pp. 507 ◽  
Author(s):  
CJ Howard ◽  
CJ Ball ◽  
RL Davis ◽  
MM Elcombe
Keyword(s):  
High Resolution ◽  
X Ray Diffraction ◽  
X Ray ◽  
Powder Diffractometer ◽  
Neutron Powder Diffractometer ◽  
Good Agreement

The high resolution neutron powder diffractometer installed on the AAEC HIFAR reactor at Lucas Heights is described. The resolution is in good agreement with predictions and, although below the most optimistic estimates, the intensities are usable. Examples are given of problems solved using the diffractometer which could not have been solved either by X-ray diffraction or by use of a conventional neutron powder diffractometer. Plans for diffractometer development are outlined.

Investigation of Residual Strains of the Second Kind in Plastically Deformed Metallic Materials

1994 ◽  
Vol 376 ◽  
Author(s):  
M. Vrána ◽  
P. Klimanek ◽  
T. Kschidock ◽  
P. Lukáš ◽  
P. Mikula
Keyword(s):  
High Resolution ◽  
Neutron Diffraction ◽  
Stacking Faults ◽  
Metallic Materials ◽  
Line Broadening ◽  
X Ray Diffraction ◽  
X Ray ◽  
Neutron Diffractometer ◽  
Residual Strains ◽  
Good Agreement

ABSTRACTInvestigation of strongly distorted crystal structures caused by dislocations, stacking-faults etc. in both plastically deformed f.c.c. and b.c.c. metallic materials was performed by the analysis of the neutron diffraction line broadening. Measurements were realized by means of the high resolution triple-axis neutron diffractometer equipped by bent Si perfect crystals as monochromator and analyzer at the NPI Řež. The substructure parameters obtained in this manner are in good agreement with the results of X-ray diffraction analysis.

HIGH-RESOLUTION ANGLE-RESOLVED PHOTOEMISSION STUDY OF η-MO4O11

2002 ◽  
Vol 09 (02) ◽  
pp. 1041-1045 ◽  
Author(s):  
H. FUJISAWA ◽  
H. KUMIGASHIRA ◽  
T. TAKAHASHI ◽  
R. KURITA ◽  
M. KOYANO
Keyword(s):  
High Resolution ◽  
Fermi Surface ◽  
Surface Topology ◽  
Photoemission Spectroscopy ◽  
Band Structure Calculation ◽  
X Ray Diffraction ◽  
X Ray ◽  
Angle Resolved Photoemission Spectroscopy ◽  
Photoemission Study ◽  
Good Agreement

We have performed high-resolution angle-resolved photoemission spectroscopy (ARPES) on a quasi two-dimensional (2D) conductor η- Mo 4 O 11. The band dispersions near E F and the Fermi-surface topology determined by ARPES show a qualitatively good agreement with the band-structure calculation, although the observed width of Mo 4d bands forming the Fermi surface is two-to-three times larger in the calculation. We have clearly identified two nesting vectors in the ARPES-derived Fermi surface, which show a good agreement with the CDW wave vectors obtained from X-ray diffraction experiments. The present ARPES results indicate that the CDW instability in η- Mo 4 O 11 is driven by "the hidden 1D Fermi-surface nesting" due to the quasi 1D chains in the crystal.

Curvature and strain in thick HVPE-GaN for quasi-substrate applications

2003 ◽  
Vol 798 ◽  
Author(s):  
Claudia Roder ◽  
Tim Böttcher ◽  
Tanya Paskova ◽  
Bo Monemar ◽  
Detlef Hommel
Keyword(s):  
High Resolution ◽  
Growth Temperature ◽  
Room Temperature ◽  
Biaxial Tension ◽  
Biaxial Compression ◽  
X Ray Diffraction ◽  
X Ray ◽  
Different Temperatures ◽  
Gan Film ◽  
Good Agreement

ABSTRACTUncracked HVPE-GaN layers of different thicknesses were investigated using high resolution x-ray diffraction at variable temperatures. The absolute lattice parameters as well as the wafer curvature were measured simultaneously at different temperatures. All samples were found to be under biaxial tension at growth temperature. At room temperature the GaN film is under biaxial compression while the substrate is tensile strained. A simulation of the stress and curvature of the heterostructures was performed for different thicknesses of the films and substrates and a good agreement was found with the experimentally determined values.

X-ray and neutron Rietveld quantitative phase analysis of industrial Portland cement clinkers

2004 ◽  
Vol 19 (3) ◽  
pp. 232-239 ◽  
Author(s):  
O. Pritula ◽  
Ľ. Smrčok ◽  
D. M. Többens ◽  
V. Langer
Keyword(s):  
High Resolution ◽  
Diffraction Data ◽  
Structural Data ◽  
Quantitative Phase Analysis ◽  
X Ray Diffraction ◽  
Rietveld Refinements ◽  
X Ray ◽  
Numerical Instabilities ◽  
Cement Clinkers ◽  
Good Agreement

Weight fractions of four dominant phases (C3S, C2S, C4AF, and C3A) present in five industrial clinkers were estimated by a series of neutron and X-ray Rietveld refinements. Calculated powder patterns were derived from the structural data for monoclinic and triclinic C3S, monoclinic C2S, orthorhombic C4AF, cubic C3A and MgO. Neutron diffraction data were collected with the high resolution E9 diffractometer (BENSC) using two different wavelengths, X-ray diffraction data with a high resolution transmission diffractometer. Elemental composition of the samples obtained by ESEM/EDX technique were in a good agreement with the data delivered by the producers. Convergence of the refinements was remarkably different for X-ray and for neutron data. Several refinements were not completed due to numerical instabilities. Neutron refinements were found to be more stable than X-ray, but there was not any notable difference in the final estimated phases’ compositions. Calculated absolute deviates of phases’ weight fractions were mostly within ±10%, which for the less abundant phases corresponded to relative deviations within ±50%. © 2004 International Centre for Diffraction Data.

A High Resolution Study of G.P. Zones in Aluminum - 4.2 at % Silver

1982 ◽  
Vol 40 ◽  
pp. 722-723 ◽  
Author(s):  
R. Gronsky
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
High Resolution ◽  
Computer Simulations ◽  
Structural Characteristics ◽  
X Ray Diffraction ◽  
X Ray ◽  
Transmission Electron ◽  
Resolution Study

The phenomenon of clustering in Al-Ag alloys has been extensively studied since the early work of Guinierl, wherein the pre-precipitation state was characterized as an assembly of spherical, ordered, silver-rich G.P. zones. Subsequent x-ray and TEM investigations yielded results in general agreement with this model. However, serious discrepancies were later revealed by the detailed x-ray diffraction - based computer simulations of Gragg and Cohen, i.e., the silver-rich clusters were instead octahedral in shape and fully disordered, atleast below 170°C. The object of the present investigation is to examine directly the structural characteristics of G.P. zones in Al-Ag by high resolution transmission electron microscopy.

Tubulin structure at intermediate resolution

1995 ◽  
Vol 53 ◽  
pp. 852-853
Author(s):  
K. H. Downing ◽  
S. G. Wolf ◽  
E. Nogales
Keyword(s):  
High Resolution ◽  
Structural Data ◽  
Therapeutic Drug ◽  
Zinc Ions ◽  
Two Dimensional ◽  
X Ray Diffraction ◽  
X Ray ◽  
Negative Stain ◽  
Functional Mechanisms ◽  
Tubulin Structure

Microtubules are involved in a host of critical cell activities, many of which involve transport of organelles through the cell. Different sets of microtubules appear to form during the cell cycle for different functions. Knowledge of the structure of tubulin will be necessary in order to understand the various functional mechanisms of microtubule assemble, disassembly, and interaction with other molecules, but tubulin has so far resisted crystallization for x-ray diffraction studies. Fortuitously, in the presence of zinc ions, tubulin also forms two-dimensional, crystalline sheets that are ideally suited for study by electron microscopy. We have refined procedures for forming the sheets and preparing them for EM, and have been able to obtain high-resolution structural data that sheds light on the formation and stabilization of microtubules, and even the interaction with a therapeutic drug.Tubulin sheets had been extensively studied in negative stain, demonstrating that the same protofilament structure was formed in the sheets and microtubules. For high resolution studies, we have found that the sheets embedded in either glucose or tannin diffract to around 3 Å.

A DFT study of spherands containing five anisyl groups — Highly preorganized to bind the alkali metal

2006 ◽  
Vol 84 (8) ◽  
pp. 1045-1049 ◽  
Author(s):  
Shabaan AK Elroby ◽  
Kyu Hwan Lee ◽  
Seung Joo Cho ◽  
Alan Hinchliffe
Keyword(s):  
Density Functional Theory ◽  
Binding Energy ◽  
Density Functional ◽  
Ionic Radius ◽  
Binding Energies ◽  
Cavity Size ◽  
X Ray Diffraction ◽  
Functional Theory ◽  
X Ray ◽  
Good Agreement

Although anisyl units are basically poor ligands for metal ions, the rigid placements of their oxygens during synthesis rather than during complexation are undoubtedly responsible for the enhanced binding and selectivity of the spherand. We used standard B3LYP/6-31G** (5d) density functional theory (DFT) to investigate the complexation between spherands containing five anisyl groups, with CH2–O–CH2 (2) and CH2–S–CH2 (3) units in an 18-membered macrocyclic ring, and the cationic guests (Li+, Na+, and K+). Our geometric structure results for spherands 1, 2, and 3 are in good agreement with the previously reported X-ray diffraction data. The absolute values of the binding energy of all the spherands are inversely proportional to the ionic radius of the guests. The results, taken as a whole, show that replacement of one anisyl group by CH2–O–CH2 (2) and CH2–S–CH2 (3) makes the cavity bigger and less preorganized. In addition, both the binding and specificity decrease for small ions. The spherands 2 and 3 appear beautifully preorganized to bind all guests, so it is not surprising that their binding energies are close to the parent spherand 1. Interestingly, there is a clear linear relation between the radius of the cavity and the binding energy (R2 = 0.999).Key words: spherands, preorganization, density functional theory, binding energy, cavity size.

Local atomic structure in tetragonal pure ZrO2nanopowders

2010 ◽  
Vol 43 (2) ◽  
pp. 227-236 ◽  
Author(s):  
Leandro M. Acuña ◽  
Diego G. Lamas ◽  
Rodolfo O. Fuentes ◽  
Ismael O. Fábregas ◽  
Márcia C. A. Fantini ◽  
...  
Keyword(s):  
Tetragonal Phase ◽  
Local Structure ◽  
X Ray Diffraction ◽  
X Ray ◽  
Atomic Structures ◽  
Crystallite Sizes ◽  
Exafs Study ◽  
The Difference ◽  
X Ray Absorption ◽  
Good Agreement

The local atomic structures around the Zr atom of pure (undoped) ZrO2nanopowders with different average crystallite sizes, ranging from 7 to 40 nm, have been investigated. The nanopowders were synthesized by different wet-chemical routes, but all exhibit the high-temperature tetragonal phase stabilized at room temperature, as established by synchrotron radiation X-ray diffraction. The extended X-ray absorption fine structure (EXAFS) technique was applied to analyze the local structure around the Zr atoms. Several authors have studied this system using the EXAFS technique without obtaining a good agreement between crystallographic and EXAFS data. In this work, it is shown that the local structure of ZrO2nanopowders can be described by a model consisting of two oxygen subshells (4 + 4 atoms) with different Zr—O distances, in agreement with those independently determined by X-ray diffraction. However, the EXAFS study shows that the second oxygen subshell exhibits a Debye–Waller (DW) parameter much higher than that of the first oxygen subshell, a result that cannot be explained by the crystallographic model accepted for the tetragonal phase of zirconia-based materials. However, as proposed by other authors, the difference in the DW parameters between the two oxygen subshells around the Zr atoms can be explained by the existence of oxygen displacements perpendicular to thezdirection; these mainly affect the second oxygen subshell because of the directional character of the EXAFS DW parameter, in contradiction to the crystallographic value. It is also established that this model is similar to another model having three oxygen subshells, with a 4 + 2 + 2 distribution of atoms, with only one DW parameter for all oxygen subshells. Both models are in good agreement with the crystal structure determined by X-ray diffraction experiments.

scholarly journals Dislocation Arrangement in a Thick LEO GaN Film on Sapphire

2000 ◽  
Vol 5 (S1) ◽  
pp. 97-103
Author(s):  
Kathleen A. Dunn ◽  
Susan E. Babcock ◽  
Donald S. Stone ◽  
Richard J. Matyi ◽  
Ling Zhang ◽  
...  
Keyword(s):  
High Resolution ◽  
Electron Diffraction ◽  
Threading Dislocations ◽  
X Ray Diffraction ◽  
Burgers Vector ◽  
X Ray ◽  
The Third ◽  
Dislocation Arrangement ◽  
Image Position ◽  
Gan Film

Diffraction-contrast TEM, focused probe electron diffraction, and high-resolution X-ray diffraction were used to characterize the dislocation arrangements in a 16µm thick coalesced GaN film grown by MOVPE LEO. As is commonly observed, the threading dislocations that are duplicated from the template above the window bend toward (0001). At the coalescence plane they bend back to lie along [0001] and thread to the surface. In addition, three other sets of dislocations were observed. The first set consists of a wall of parallel dislocations lying in the coalescence plane and nearly parallel to the substrate, with Burgers vector (b) in the (0001) plane. The second set is comprised of rectangular loops with b = 1/3 [110] (perpendicular to the coalescence boundary) which originate in the coalescence boundary and extend laterally into the film on the (100). The third set of dislocations threads laterally through the film along the [100] bar axis with 1/3<110>-type Burgers vectors These sets result in a dislocation density of ∼109 cm−2. High resolution X-ray reciprocal space maps indicate wing tilt of ∼0.5º.

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