scholarly journals Anomalous reflexions in X-ray patterns

1941 ◽  
Vol 179 (976) ◽  
pp. 1-7 ◽  
Keyword(s):  
Simple Theory ◽  
Monochromatic Radiation ◽  
X Ray Diffraction ◽  
Satisfactory Explanation ◽  
Characteristic Radiation ◽  
X Ray ◽  
Diffraction Patterns ◽  
Ray Patterns

The presence on X-ray diffraction patterns of anomalous reflexions, that is to say, reflexions which cannot be accounted for by the simple theory of diffraction, is almost a commonplace. Many of these effects are no doubt to be ascribed to imperfections in the specimen, strains, etc., but even after these have been taken into account there remain streaks and spots for which there is no satisfactory explanation. The observation of effects of the type considered here is by no means novel; Friedrich (1913) recorded them as radial streaks running through the Laue spots in a photograph of KCl. The extra spots are generally very weak compared with the normal Laue reflexions and indeed may not be observed at all unless the photographs are somewhat over-exposed. They are most easily observed on Laue photographs taken with a tube emitting a characteristic radiation such as the K radiation of Cu or Ag, and their study will be greatly facilitated by the use of powerful sources of monochromatic radiation.

The structure of bacterial flagella: the packing of the polypeptide chains within a flagellum

1961 ◽  
Vol 260 (1303) ◽  
pp. 558-573 ◽  
Keyword(s):  
Point Of View ◽  
X Ray Diffraction ◽  
Detailed Structure ◽  
Satisfactory Explanation ◽  
X Ray ◽  
Bacterial Flagella ◽  
Diffraction Patterns ◽  
Polypeptide Chains ◽  
Ray Patterns ◽  
Single Flagellum

The X-ray diffraction patterns from specimens of bacterial flagella taken by Astbury, Weibull and others consist essentially of three sets of reflexions, two sets on the meridian and one set on the equator. The equatorial set gives information on the packing arrange-merit of the polypeptide chains within a single flagellum. This paper is concerned with the interpretation in terms of a physical model of the equatorial diffraction from flagella from Proteus vulgaris for which the published diffraction data are most detailed. The polypeptide chains are all assumed to be in the α -helical form though the meridional diffraction gives some indication that a smaller ‘cross- β ’ component may also be present. The separation (121 Å) between the flagella in the X-ray specimens is inferred from the spacings of the equatorial reflexions and two alternative models (model I and model II) for the detailed structure of a flagellum are inferred from the intensity data. The structures proposed are similar in outline but differ in detail and postulate that a flagellum is composed of a number of identical interwoven filaments which themselves comprise a limited number of α -helices in a centred hexagonal or pseudo-hexagonal array. In model I the flagella are assumed to be in contact in the X-ray specimens and the structure comprises three filaments of diameter 56 Å each containing 19 single α -helices. In model II the flagella are not in contact and each of the seven filaments of diameter 33 Å contains seven α -helices; the diameter of the flagellum on this model is about 100 Å. The equatorial X-ray patterns from the two models are calculated in detail including effects due to the packing of the flagella within an X-ray specimen, for comparison with the observed diffraction. Both calculated patterns give a satisfactory explanation of the spacings of the observed reflexions and show reasonable agreement with the experimental intensities. The relative merits of the two models are discussed from the diffraction point of view and in conjunction with available data from electron microscopy. The diffraction pattern from model II is in better agreement with the experimental results than the pattern from model I but the latter agreement may be improved if the hexagonal packing of the α -helices within a filament is slightly modified; a cylindrical lattice is considered from this point of view. It is concluded that, at the present time, there is insufficient evidence to differentiate between the two models of a flagellum presented.

Structure and X-ray reference diffraction patterns of (Ba6−xSrx)R2Co4O15 (x = 1, 2) (R = lanthanides)

2013 ◽  
Vol 28 (3) ◽  
pp. 212-221 ◽  
Author(s):  
W. Wong-Ng ◽  
G. Liu ◽  
Y.G. Yan ◽  
J.A. Kaduk
Keyword(s):  
General Structure ◽  
Unit Cell ◽  
X Ray Diffraction ◽  
Unit Cell Parameters ◽  
Powder Diffraction File ◽  
Coordination Environment ◽  
X Ray ◽  
Cell Parameters ◽  
Diffraction Patterns ◽  
Ray Patterns

The structure and X-ray patterns of two series of barium lanthanide cobaltates, namely, Ba4Sr2R2Co4O15 (R = La, Nd, Sm, Eu, Gd, and Dy), and Ba5SrR2Co4O15 (R = La, Nd, Sm, Eu, and Gd) have been determined. These compounds crystallize in the space group P63mc; the unit-cell parameters of Ba4Sr2R2Co4O15 (R from La to Dy) decrease from a = 11.6128(2) Å to 11. 5266(9) Å, c = 6.869 03(11) to 6. 7630(5) Å, and V = 802.23(3) Å3 to 778.17(15) Å3, respectively. In the Ba5SrR2Co4O15 series (R = La to Gd), the unit-cell parameters decrease from a = 11.735 44(14) Å to 11.619 79(12) Å, c = 6.942 89 (14) Å to 6.836 52(8) Å, and V = 828.08(3) Å3 to 799.40(2) Å3. In the general structure of (Ba6−xSrx)R2Co4O15, there are four Co ions per formula unit occupying one CoO6 octahedral and three CoO4 tetrahedral units. Through corner-sharing of these polyhedra, a larger Co4O15 unit is formed. Sr2+ ions adopt both octahedral and 8-fold coordination environment. R3+ ions adopt 8-fold coordination (mixed site with Sr), while the larger Ba2+ ions assume both 10- and 11-fold coordination environments. The samples were found to be insulators. X-ray diffraction patterns of these samples have been determined and submitted to the Powder Diffraction File (PDF).

scholarly journals EFFECT OF VARIOUS PRETREATMENTS ON X-RAY DIFFRACTION PATTERNS OF CLAY FRACTIONS OF PODZOLIC B HORIZONS

1981 ◽  
Vol 61 (2) ◽  
pp. 311-316 ◽  
Author(s):  
C. WANG ◽  
H. KODAMA ◽  
N. M. MILES
Keyword(s):  
Amorphous Material ◽  
Clay Sample ◽  
X Ray Diffraction ◽  
X Ray ◽  
Freeze Dried ◽  
Amorphous Si ◽  
Chemical Pretreatments ◽  
Diffraction Patterns ◽  
Ray Patterns ◽  
Identification And Quantification

The objective of this study was to compare the effects of various pretreatments on the X-ray identification and quantification of clay-sized minerals from some podzolic B horizons. After soil samples were treated with H2O2 to remove organic matter, clay fractions were dispersed, separated, and freeze-dried. A portion of each clay sample was subjected to the following pretreatments: ultrasonic bath, extraction by citrate-dithionite, extraction by 0.5 N NaOH, and extraction by Tiron. Oriented slides were used for identification and quantification of clay minerals after each pretreatment. The X-ray patterns for ultrasonically dispersed samples were used as a basis for evaluating the effectiveness of the three chemical pretreatments. Tiron pretreatment was found to be the most suitable method for removal of amorphous material from clay separates of podzolic B horizons. The traditional citrate-dithionite method was not effective in removing amorphous Si from clays. The 0.5 N NaOH method is not recommended because it resulted in significant destruction of phyllosilicates and it was not effective in removing amorphous Fe.

In Situ Hydration of Sulfoaluminate Cement Mixtures Monitored by Synchrotron X-Ray Diffraction

2018 ◽  
Vol 930 ◽  
pp. 153-157
Author(s):  
Cleusa M. Rossetto ◽  
Rodrigo Uchida Ichikawa ◽  
Luís Gallego Martinez ◽  
Geraldo L. Carezzato ◽  
Alexandre M.G. Carvalho ◽  
...  
Keyword(s):  
Calcium Ions ◽  
Rietveld Analysis ◽  
Deionized Water ◽  
Monochromatic Radiation ◽  
X Ray Diffraction ◽  
X Ray ◽  
Calcium Sulfoaluminate ◽  
Crystalline Precipitate ◽  
Diffraction Patterns

Mixtures of calcium sulfoaluminate and Portland clinkers with gypsum were hydrated with deionized water. The pastes were introduced in 0.7 mm borosilicate capillary tubes and kept at 40 oC while diffraction patterns were collected every 35 s for approximately 3 hours with a monochromatic radiation of 12 keV at the XRD1 beamline of the Laboratório Nacional de Luz Síncrotron (LNLS) in Campinas, SP - Brazil. The main crystalline phases (C2S, C3S, ettringite, ye’elemite and gypsum) involved in the hydration were quantified by Rietveld analysis. The most noticeable fact was the absence of portlandite as a crystalline precipitate, most likely due to the capture of calcium ions to form ettringite.

Evaluation of Freezing Methods by Low Temperature X-Ray Diffraction

1977 ◽  
Vol 35 ◽  
pp. 330-333
Author(s):  
T. Gulik-Krzywicki ◽  
M.J. Costello
Keyword(s):  
Biological Materials ◽  
Molecular Organization ◽  
X Ray Diffraction ◽  
Glass Capillary ◽  
X Ray ◽  
Rate Dependent ◽  
Before And After ◽  
Freeze Etching ◽  
Diffraction Patterns ◽  
Set Up

Freeze-etching electron microscopy is currently one of the best methods for studying molecular organization of biological materials. Its application, however, is still limited by our imprecise knowledge about the perturbations of the original organization which may occur during quenching and fracturing of the samples and during the replication of fractured surfaces. Although it is well known that the preservation of the molecular organization of biological materials is critically dependent on the rate of freezing of the samples, little information is presently available concerning the nature and the extent of freezing-rate dependent perturbations of the original organizations. In order to obtain this information, we have developed a method based on the comparison of x-ray diffraction patterns of samples before and after freezing, prior to fracturing and replication.Our experimental set-up is shown in Fig. 1. The sample to be quenched is placed on its holder which is then mounted on a small metal holder (O) fixed on a glass capillary (p), whose position is controlled by a micromanipulator.

Examination of Rabbit Fc Crystals

1968 ◽  
Vol 26 ◽  
pp. 140-141
Author(s):  
J. P. Robinson ◽  
P. G. Lenhert
Keyword(s):  
Molecular Weight ◽  
Flat Plate ◽  
Phosphate Buffer ◽  
Asymmetric Unit ◽  
X Ray Diffraction ◽  
X Ray ◽  
Neutral Ph ◽  
Small Crystals ◽  
Carbon Coated ◽  
Diffraction Patterns

Crystallographic studies of rabbit Fc using X-ray diffraction patterns were recently reported. The unit cell constants were reported to be a = 69. 2 A°, b = 73. 1 A°, c = 60. 6 A°, B = 104° 30', space group P21, monoclinic, volume of asymmetric unit V = 148, 000 A°3. The molecular weight of the fragment was determined to be 55, 000 ± 2000 which is in agreement with earlier determinations by other methods.Fc crystals were formed in water or dilute phosphate buffer at neutral pH. The resulting crystal was a flat plate as previously described. Preparations of small crystals were negatively stained by mixing the suspension with equal volumes of 2% silicotungstate at neutral pH. A drop of the mixture was placed on a carbon coated grid and allowed to stand for a few minutes. The excess liquid was removed and the grid was immediately put in the microscope.

Control of the phase composition of advanced calcium phosphates using an x-ray diffractometer with a curved position-sensitive detector

2020 ◽  
Vol 86 (6) ◽  
pp. 29-35
Author(s):  
V. P. Sirotinkin ◽  
O. V. Baranov ◽  
A. Yu. Fedotov ◽  
S. M. Barinov
Keyword(s):  
Phase Composition ◽  
Calcium Phosphates ◽  
Position Sensitive Detector ◽  
Sensitive Detector ◽  
X Ray Diffraction ◽  
X Ray ◽  
Impurity Phases ◽  
Position Sensitive ◽  
Diffraction Peaks ◽  
Diffraction Patterns

The results of studying the phase composition of advanced calcium phosphates Ca10(PO4)6(OH)2, β-Ca3(PO4)2, α-Ca3(PO4)2, CaHPO4 · 2H2O, Ca8(HPO4)2(PO4)4 · 5H2O using an x-ray diffractometer with a curved position-sensitive detector are presented. Optimal experimental conditions (angular positions of the x-ray tube and detector, size of the slits, exposure time) were determined with allowance for possible formation of the impurity phases during synthesis. The construction features of diffractometers with a position-sensitive detector affecting the profile characteristics of x-ray diffraction peaks are considered. The composition for calibration of the diffractometer (a mixture of sodium acetate and yttrium oxide) was determined. Theoretical x-ray diffraction patterns for corresponding calcium phosphates are constructed on the basis of the literature data. These x-ray diffraction patterns were used to determine the phase composition of the advanced calcium phosphates. The features of advanced calcium phosphates, which should be taken into account during the phase analysis, are indicated. The powder of high-temperature form of tricalcium phosphate strongly adsorbs water from the environment. A strong texture is observed on the x-ray diffraction spectra of dicalcium phosphate dihydrate. A rather specific x-ray diffraction pattern of octacalcium phosphate pentahydrate revealed the only one strong peak at small angles. In all cases, significant deviations are observed for the recorded angular positions and relative intensity of the diffraction peaks. The results of the study of experimentally obtained mixtures of calcium phosphate are presented. It is shown that the graphic comparison of experimental x-ray diffraction spectra and pre-recorded spectra of the reference calcium phosphates and possible impurity phases is the most effective method. In this case, there is no need for calibration. When using this method, the total time for analysis of one sample is no more than 10 min.

Infrared spectroscopic study of the YPO4-YCrO4 system

1985 ◽  
Vol 50 (10) ◽  
pp. 2139-2145
Author(s):  
Alexander Muck ◽  
Eva Šantavá ◽  
Bohumil Hájek
Keyword(s):  
Spectroscopic Study ◽  
Infrared Spectra ◽  
Point Of View ◽  
Mixed Crystals ◽  
Crystal Symmetry ◽  
Infrared Spectroscopic Study ◽  
X Ray Diffraction ◽  
X Ray ◽  
Infrared Spectroscopic ◽  
Diffraction Patterns

The infrared spectra and powder X-ray diffraction patterns of polycrystalline YPO4-YCrO4 samples are studied from the point of view of their crystal symmetry. Mixed crystals of the D4h19 symmetry are formed over the region of 0-30 mol.% YPO4 in YCrO4. The Td → D2d → D2 or C2v(GS eff) correlation is appropriate for both PO43- and CrO43- anions.

scholarly journals Deep learning for visualization and novelty detection in large X-ray diffraction datasets

2021 ◽  
Vol 7 (1) ◽  
Author(s):  
Lars Banko ◽  
Phillip M. Maffettone ◽  
Dennis Naujoks ◽  
Daniel Olds ◽  
Alfred Ludwig
Keyword(s):  
Thin Film ◽  
Crystal Structure ◽  
Artificial Intelligence ◽  
Deep Learning ◽  
Novelty Detection ◽  
Structural Similarity ◽  
X Ray Diffraction ◽  
X Ray ◽  
Diffraction Patterns ◽  
Post Hoc

AbstractWe apply variational autoencoders (VAE) to X-ray diffraction (XRD) data analysis on both simulated and experimental thin-film data. We show that crystal structure representations learned by a VAE reveal latent information, such as the structural similarity of textured diffraction patterns. While other artificial intelligence (AI) agents are effective at classifying XRD data into known phases, a similarly conditioned VAE is uniquely effective at knowing what it doesn’t know: it can rapidly identify data outside the distribution it was trained on, such as novel phases and mixtures. These capabilities demonstrate that a VAE is a valuable AI agent for aiding materials discovery and understanding XRD measurements both ‘on-the-fly’ and during post hoc analysis.

scholarly journals Simultaneous Multi-Bragg Peak Coherent X-ray Diffraction Imaging

Crystals ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 312
Author(s):  
Florian Lauraux ◽  
Stéphane Labat ◽  
Sarah Yehya ◽  
Marie-Ingrid Richard ◽  
Steven J. Leake ◽  
...  
Keyword(s):  
Bragg Reflection ◽  
Volume Ratio ◽  
X Ray Diffraction ◽  
X Ray ◽  
Crystal Substrate ◽  
In Series ◽  
Diffraction Imaging ◽  
Diffraction Patterns ◽  
Lattice Planes ◽  
Oriented Parallel

The simultaneous measurement of two Bragg reflections by Bragg coherent X-ray diffraction is demonstrated on a twinned Au crystal, which was prepared by the solid-state dewetting of a 30 nm thin gold film on a sapphire substrate. The crystal was oriented on a goniometer so that two lattice planes fulfill the Bragg condition at the same time. The Au 111 and Au 200 Bragg peaks were measured simultaneously by scanning the energy of the incident X-ray beam and recording the diffraction patterns with two two-dimensional detectors. While the former Bragg reflection is not sensitive to the twin boundary, which is oriented parallel to the crystal–substrate interface, the latter reflection is only sensitive to one part of the crystal. The volume ratio between the two parts of the twinned crystal is about 1:9, which is also confirmed by Laue microdiffraction of the same crystal. The parallel measurement of multiple Bragg reflections is essential for future in situ and operando studies, which are so far limited to either a single Bragg reflection or several in series, to facilitate the precise monitoring of both the strain field and defects during the application of external stimuli.

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