Analysis of metastable structures in quenched Cr-Ti alloys

1990 ◽  
Vol 48 (4) ◽  
pp. 144-145
Author(s):  
Wharton Sinkler ◽  
David E. Luzzi
Keyword(s):  
Diffuse Scattering ◽  
Eutectoid Temperature ◽  
Diffuse Intensity ◽  
Ti Alloys ◽  
Spatial Frequencies ◽  
Metastable Structures ◽  
Diffuse Form ◽  
Metastable Water ◽  
Bcc Phase ◽  
State Amorphization

Metastable water-quenched bcc Cr40Ti60 is reported to undergo solid state amorphization during sub-eutectoid temperature anneals. Electron diffraction of the metastable bcc phase reveals complex patterns of diffuse scattering indicating the presence of deviation, topological, chemical or both, from the ideally random solid solution. The hypothesis that the microstructure causing the diffuse scattering plays a role in the amorphization process is supported by studies in which an electron- irradiated bcc-based Cu-Ti alloy shows similar diffuse scattering just prior to irradiation-induced amorphization.Diffuse scattering is observed in all major zone axes of the as-quenched alloy except for (111). Analysis of the spatial frequencies of diffuse scattering maxima indicates that in spite of a clear directional relationship between the bcc matrix scattering and the diffuse scattering, at least some diffuse intensity maxima have spatial frequencies which are incommensurate with the bcc matrix. For instance, the streaked diffuse form along <11> in the (110) zone axis pattern (Fig. 1, arrow), which has been determined to be due to kinematical scattering, does not correspond to any possible bcc superlattice spacing along the [11] direction. This suggests that the microstructure of the as-quenched phase includes regions in which static displacements from the bcc equilibrium sites are encountered.

Metastable Structures in Quenched Cr-Ti and Electron Irradiated Cu-Ti Alloys

1989 ◽  
Vol 157 ◽  
Author(s):  
W. Sinkler ◽  
D.E. Luzzi
Keyword(s):  
Electron Diffraction ◽  
Amorphous Phase ◽  
Electron Irradiation ◽  
Structural Relaxation ◽  
Amorphous State ◽  
Eutectoid Temperature ◽  
Ti Alloys ◽  
Metastable Structures

ABSTRACTElectron diffraction and imaging are used to characterize and contrast the structures and microstructures of a metastable Cr-Ti phase formed after quenching and a metastable Cu-Ti phase formed during electron irradiation. In both phases, marked structural anisotropies are found which have characteristics common to both of these bcc-based materials. It has been reported in the literature that this quenched-in metastable Cr-Ti phase undergoes a spontaneous structural relaxation into the amorphous state during sub-eutectoid temperature anneals [1]. Despite the similarity of the present experiments to those reported in the literature, an amorphization transformation was not observed. It is argued that the amorphization of this material requires the stabilization of the amorphous phase by an impurity.

Analysis of diffuse scattering from the mineral mullite

1994 ◽  
Vol 27 (5) ◽  
pp. 742-754 ◽  
Author(s):  
B. D. Butler ◽  
T. R. Welberry
Keyword(s):  
Diffuse Scattering ◽  
Real Space ◽  
Order Parameters ◽  
Scattering Data ◽  
Local Order ◽  
Near Neighbour ◽  
Diffuse Intensity ◽  
Space Model ◽  
Least Squares Techniques ◽  
Space Volume

A full reciprocal-space volume of diffuse scattering data from a single-crystal of the mineral mullite, Al2(Al2 + 2x Si2 − 2x )O10 − x , x = 0.4, was collected. These data were analysed using least-squares techniques by writing an equation for the diffuse scattering that involves only the local order between vacancies on specific oxygen sites in the material. The effect of the large, but predictable, cation shifts on the diffuse intensity is taken account of in the coefficients of the oxygen-vacancy short-range-order intensities. This analysis shows that the vacancies are negatively correlated at the near-neighbour ½ 〈110〉, [110], 〈001〉 and 〈011〉 interatomic vectors and positively correlated along the 〈010〉, 〈101〉, ½ 〈112〉 and ½ 〈310〉 vectors. Subsequent Monte Carlo modelling of the structure based on these local-order parameters demonstrates that the structure of mullite is dominated by effective near-neighbour vacancy–vacancy repulsive interactions. A real-space model of mullite is presented that is approximately consistent with the measured local-order parameters.

Disorder in decagonal quasicrystals

2003 ◽  
Vol 218 (2) ◽  
Author(s):  
F. Frey ◽  
E. Weidner
Keyword(s):  
High Temperature ◽  
Neutron Diffraction ◽  
High Temperatures ◽  
Experimental Work ◽  
Diffuse Scattering ◽  
Diffuse Intensity ◽  
X Ray ◽  
Decagonal Quasicrystals ◽  
Ordered Alloys ◽  
Insight Into

AbstractComplementary neutron and x-ray diffuse scattering may provide insight into structural super-ordering and disordering of decagonal quasicrystals (d-phases), and, in consequence, into the formation and stability of aperiodically ordered alloys. Neutron diffraction makes a contrasting almost isoelectronic atomic species possible, as well as a separation of elastic and inelastic diffuse intensity contributions. Experimental work at high temperatures is comparatively unproblematic. The method suffers, however, from the difficulty in obtaining sufficiently sized mono-grain samples and a lack of dedicated neutron diffraction instruments. Recent results, with a main focus on high-temperature (<1000°C) investigations of disordered decagonal Al—Ni—Co phases are reported and some tentative models are discussed.

scholarly journals Measuring and modeling diffuse scattering in protein X-ray crystallography

2016 ◽  
Vol 113 (15) ◽  
pp. 4069-4074 ◽  
Author(s):  
Andrew H. Van Benschoten ◽  
Lin Liu ◽  
Ana Gonzalez ◽  
Aaron S. Brewster ◽  
Nicholas K. Sauter ◽  
...  
Keyword(s):  
Diffuse Scattering ◽  
Structure Refinement ◽  
Normal Modes ◽  
Coarse Grained ◽  
X Ray Diffraction ◽  
Diffuse Intensity ◽  
X Ray ◽  
Protein Motions ◽  
X Ray Crystallography ◽  
Standard Data

X-ray diffraction has the potential to provide rich information about the structural dynamics of macromolecules. To realize this potential, both Bragg scattering, which is currently used to derive macromolecular structures, and diffuse scattering, which reports on correlations in charge density variations, must be measured. Until now, measurement of diffuse scattering from protein crystals has been scarce because of the extra effort of collecting diffuse data. Here, we present 3D measurements of diffuse intensity collected from crystals of the enzymes cyclophilin A and trypsin. The measurements were obtained from the same X-ray diffraction images as the Bragg data, using best practices for standard data collection. To model the underlying dynamics in a practical way that could be used during structure refinement, we tested translation–libration–screw (TLS), liquid-like motions (LLM), and coarse-grained normal-modes (NM) models of protein motions. The LLM model provides a global picture of motions and was refined against the diffuse data, whereas the TLS and NM models provide more detailed and distinct descriptions of atom displacements, and only used information from the Bragg data. Whereas different TLS groupings yielded similar Bragg intensities, they yielded different diffuse intensities, none of which agreed well with the data. In contrast, both the LLM and NM models agreed substantially with the diffuse data. These results demonstrate a realistic path to increase the number of diffuse datasets available to the wider biosciences community and indicate that dynamics-inspired NM structural models can simultaneously agree with both Bragg and diffuse scattering.

scholarly journals Energy-filtered electron diffuse scattering of ferroelectrics PMN and PMN-xPT

2014 ◽  
Vol 70 (a1) ◽  
pp. C623-C623
Author(s):  
Jerome Pacaud ◽  
Wajdi Saidi ◽  
Ray Withers ◽  
Brahim Dkhil ◽  
Jian-Min Zuo
Keyword(s):  
Diffuse Scattering ◽  
Phonon Scattering ◽  
Relaxor Ferroelectrics ◽  
Charge Ordering ◽  
Diffuse Intensity ◽  
Sufficient Energy ◽  
Direct Lattice ◽  
Imaging Plates ◽  
Dielectric And Piezoelectric Properties

PbMb1/3Nb2/3O3 (PMN) and its solid solution (1-x)PbMb1/3Nb2/3O3-(x)PbTiO3 (PMN-xPT) are relaxor ferroelectrics which have attracted attention in the last few decades because of their very interesting dielectric and piezoelectric properties and have since be two of the most extensively studied. All the previous studies emphasized the role of the local structural fluctuations leading to local changes in symmetries [1] due to displacements of ions in the unit-cell. We studied PMN and PMN-xPT by electron diffuse scattering using an in-column energy filter and Imaging-Plates as detector. We found evidences for streaks of intensity along the [110]* direction as previously found in PbZn1/3Nb2/3O3 (PZN) with neutron diffraction [2]. Moreover, weak diffuse scattering sheets can be observed along (111)* reciprocal planes showing the existence of correlations along the [111] directions of the direct lattice. Figure 1 shows a diffraction pattern taken along [02-1] zone axis presenting both diffuse features. This can be related to the displacement of Pb ions along the diagonals of the cube found by simulation [3] but greatly complexify the analysis of the shape of the diffuse intensity. Compared to the neutron, electron diffraction has the advantage of two dimensional recording of diffuse scattering and eventually sensitivity to charge ordering but quantitative analysis is limited due to the complication of multiple scattering and the lack of sufficient energy resolution for the study of inelastic phonon scattering.

Time-resolved two-dimensional observation of the change in X-ray diffuse scattering from an alloy single crystal using an imaging plate on a synchrotron-radiation source

1990 ◽  
Vol 23 (6) ◽  
pp. 509-514 ◽  
Author(s):  
H. Iwasaki ◽  
Y. Matsuo ◽  
K. Ohshima ◽  
S. Hashimoto
Keyword(s):  
Synchrotron Radiation ◽  
Single Crystal ◽  
Diffuse Scattering ◽  
Structural Changes ◽  
Time Interval ◽  
Imaging Plate ◽  
Two Dimensional ◽  
Diffuse Intensity ◽  
Time Resolved ◽  
X Ray

Through the high sensitivity of an area-detector Imaging Plate and the high brilliance of synchrotron radiation, changes in two-dimensional intensity distribution of X-ray diffuse scattering from an AgZn single-crystal having the B2-type structure were observed successively during the structural transition from the β′ phase to the ζ phase. It has been shown in a series of patterns taken at a time interval of 600 s that a diffuse intensity sheet extending parallel to the (111) relplane gradually loses its intensity without a precursive modulation while weak diffraction spots from the nuclei of the ζ phase appear superimposed on the sheet with a definite positional relation to the diffraction spots from the β′ phase. Promising aspects as well as the limits of the method applied to time-resolved measurements of structural changes are discussed.

Disorder, structured diffuse scattering and the transmissionelectron microscope

2005 ◽  
Vol 220 (12) ◽  
Author(s):  
Ray L. Withers
Keyword(s):  
Electron Microscopy ◽  
Multiple Scattering ◽  
Solid Solutions ◽  
Diffuse Scattering ◽  
Disordered Materials ◽  
Diffuse Intensity ◽  
Modulation Wave ◽  
Distribution Shape ◽  
Flexible Framework ◽  
Diffuse Distribution

AbstractA review of the application of electron microscopy to disordered materials exhibiting sharp, highly structured diffuse intensity distributions is given from a modulation wave approach perspective. Structurally useful diffraction phenomena such as polarization, overall diffuse distribution shape and pseudo-extinction conditions are highlighted. The dangers of multiple scattering are emphasized before two particular such systems, substitutionally disordered solid solutions and inherently flexible framework structures are considered in more detail.

Formation of Metastable Structures and Amorphous Phases in cu-w Alloys Using the Triode Sputtering Technique

1988 ◽  
Vol 100 ◽  
Author(s):  
H. F. Rizzo ◽  
L. E. Tanner ◽  
M. A. Wall ◽  
T. B. Massalski ◽  
E. D. McClanahan
Keyword(s):  
Amorphous Alloys ◽  
Lattice Parameter ◽  
Near Neighbor ◽  
X Ray Diffraction ◽  
Amorphous Phases ◽  
Metastable Structures ◽  
Vegard’S Law ◽  
Wide Range ◽  
Bcc Phase ◽  
Near Neighbor Distance

ABSTRACTThe triode sputtering technique and a “split-target” arrangement were used to produce metastable crystalline and amorphous phases in the Cu-W system under essentially oxygen-free conditions. Large metastable extensions of solid solubility were observed both from the Cu (fcc) and W (bcc) sides of the phase diagram, and a wide range of metallic glass formation was observed, approximately between 30 and 65 at.% W. The thickness of the amorphous Cu-W phase (40–160 pm) that can be deposited without the formation of the metastable bcc phase appears to be dependent on the Cu-W alloy composition. On heating, the crystallization temperature of the amorphous alloys was higher than 350°C. The behavior of the lattice parameter and near-neighbor distance has been studied with x-ray diffraction, showing small positive deviations from an assumed Vegard's Law. Hardness measurements indicate that the metastable crystalline phases are relatively harder than the amorphous phase.

Multiple scattering and displacive modulation in the YBa2Cu3O7-δ system

1991 ◽  
Vol 49 ◽  
pp. 1082-1083
Author(s):  
Yimei Zhu ◽  
M. Suenaga ◽  
A.R. Moodenbaugh
Keyword(s):  
Diffraction Pattern ◽  
Multiple Scattering ◽  
Diffuse Scattering ◽  
Incident Beam ◽  
High Symmetry ◽  
Diffuse Intensity ◽  
Modulated Structure ◽  
Transmission Electron ◽  
Scattering Effects ◽  
Structure Modulation

Using transmission electron microscopy, structure modulation associated with electron multiple scattering and diffuse scattering in oxygen reduced, and Fe and Co doped YBa2Cu3O7_δ has been studied. The modulated structure (tweed) exhibits [110] and roughly-periodic lenticular domain images (see Fig.l) and cross-shaped diffuse intensity in diffraction (see Fig.2). The overall diffraction pattern in the [001] zone has a 4-fold symmetry with diffraction intensity which falls off monotonically from one Brillouin zone to the next. Superimposed over each Bragg spot seem to be two cross-streaks of equal length in the [110] and directions.However, for a diffraction pattern in a high symmetry Laue case, one must consider the possibility of multiple scattering effects, whereby a diffracted electron beam acts as an incident beam. This can complicate diffuse scattering phenomena, even in a thin crystal. Careful inspection of Fig.2 reveals that the shapes of the diffuse scattering are not all identical at all diffraction spots.

Intensity expression for short-range-order diffuse scattering with ordering energies in a ternary alloy system

1987 ◽  
Vol 20 (3) ◽  
pp. 182-186 ◽  
Author(s):  
S. Hashimoto
Keyword(s):  
Correlation Function ◽  
Ternary Alloy ◽  
Diffuse Scattering ◽  
Short Range ◽  
Short Range Order ◽  
Alloy System ◽  
Ternary Alloy System ◽  
Diffuse Intensity ◽  
X Ray ◽  
Intensity Expression

An X-ray partial diffuse intensity equation has been explicitly expressed as a function of ordering energies between different atomic species by referring to the description of the interatomic correlation function of de Fontaine [J. Phys. Chem. Solids (1973), 34, 1285–1304]. The expression suggests the appearance of a negative partial intensity. As an interesting example of its application, the calculation of the partial intensity for the disordered Cu2NiZn ternary alloy by means of the derived equation in terms of the ordering energies obtained theoretically by de Rooy, van Royen, Bronsveld & de Hosson [Acta Metall. (1980), 28, 1339–1347] is shown to lead to a distribution of diffuse scattering very similar to that given by experimental observations [Hashimoto, Iwasaki, Ohshima, Harada, Sakata & Terauchi (1985). J. Phys. Soc. Jpn, 54, 3796–3807].

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