Diffraction Photographs Research Articles

X-Ray Diffraction and Electron Optical Studies on Smectite and α -Cristobalite Associations

AbstractAlteration products of volcanic materials from various localities in Wyoming, U.S.A., Italy, Yugoslavia and Mozambique are mainly smectites and cristobalites with small amounts of kaolinite.Smectite and cristobalite form separate and intergrown aggregates of microcristallinity. X-ray diffraction studies show that the silica is α-cristobalite with a noticeable stacking disorder. Small aggregates of optically pure α-cristobalite, which were separated by an appropriate mixture of bromo-form and carbon tetrachloride, are shown to contain a noticeable amount of smectite on Debye-Scherrer diffraction photographs for the samples from Italy and Wyoming, U.S.A.Transmission electron micrographs and selected area electron diffraction photographs show, in addition to smectite and α-cristobalite aggregates, the presence of idiomorph single crystals of kaolinite.

A computer controlled film scanner for X-ray crystallography

A description is given of a computer controlled rotating drum film scanner suitable for the measurement of X-ray diffraction photographs. The advantages of such a densitometer for protein crystallography are discussed. By measuring integrated densities 'on line' and taking advantage of the high positional accuracy of the scanner, a very satisfactory combination of speed, accuracy and flexibility can be achieved. It is found that commonly used X-ray films are significantly nonlinear even at optical densities less than 1.2 but by using a parabolic modification of the integrated densities the usable density range can be extended to optical densities of at least 2.5.

Crystal and molecular structure of the 2 : 1 adduct of bis(pentafluorophenyl)mercury(II) and bis(diphenylarsino)methane

The title compound crystallizes in the monoclinic system with a= 14·07, b= 17·34, c= 19·33 A, β= 91° 3′, Z= 4, and space-group C2/c. The structure was solved by conventional Patterson and Fourier methods and refined by least-squares techniques to R 0·9 for 1218 independent reflections. The compound has a two-fold axis about the methylene carbon atom of the diarsine moiety. Each mercury atom has one arsenic atom within the sum of van der Waals radii from it, and there is a T-shaped distribution of two C6F5 groups and the arsenic atom about mercury with a Hg ⋯ As distance of 3·40 ± 0·02 A and C–Hg–C angle of 173 ± 4°. X-Ray powder diffraction photographs indicate that the compound [(C6F5)2Hg]2Ph2P·CH2·PPh2 has the same structure.

The streaking of X-ray diffraction spots in platelet-shaped polytypic crystals

The c-axis oscillation X-ray diffraction photographs of platelet-shaped polytypic crystals exhibit 10.l, 20l, etc. rows which are sharply divided into two zones, one having streaked diffraction spots and the other having sharp spots. Evidence and arguments have been advanced to show that this behaviour is due to shape-effect on the diffraction, and the observed streaking is not representative of any real disorder in the stacking of the layers in the crystal.

Growth of barite group crystals by the flux evaporation method

Single crystals of BaSO 4, SrSO 4 and PbSO 4 have been grown by the flux evaporation method by employing NaCl as flux for BaSO 4 and SrSO 4, and Na 2SO 4 for PbSO 4. The crystals grown by this method are identified with the help of X-ray diffraction photographs. The effect of cooling rate on the morphology of the crystals has been studied in the case of SrSO 4 and BaSO 4. By employing etching techniques, the dislocation densities of BaSO 4 and SrSO 4 have been evaluated and found to be very low as compared to that of natural crystals. A plausible mechanism of growth of the crystals grown by the chemically reacted flux method by Patel et al. has been suggested.

A preliminary X-ray crystallographic investigation of yeast phosphoglycerate mutase

X-ray diffraction photographs of yeast phosphoglycerate mutase show that the molecule of 110,700 daltons has one true 2-fold axis of symmetry. The X-ray intensity distribution also indicates the presence of further 2-fold axes suggesting that the enzyme is a tetramer with 222 symmetry.

Data correlation and error analysis in electron diffraction studies of gases

The autocorrelation function was used to determine the average correlation coefficients in the electron diffraction intensities from the Cornell apparatus. Weight matrices with off-diagonal elements were used in least squares refinements of one average intensity curve obtained from several diffraction photographs in each of three experimental configurations, of three average intensity curves, each of one experimental configuration, and of fifteen intensity curves. The standard deviations are 2.2 to 4.0 times greater than those obtained using diagonal weight matrices. The autocorrelation function gives the same estimate of data correlation as the method of Seip, Strand, and Stølevik. Standard deviations calculated by the method of Murata and Morino are 70–80% of those obtained from the autocorrelation function and the Norwegian method. The correlation in the Cornell, Oslo and Manchester electron diffraction data is approximately equal and considerably greater than that reported by the Tokyo group.

Influence of heat-treatment on the average structure of Mg[Al2Si3O10], a stuffed derivative of the high-quartz structure *

AbstractThe quartz-like average structure of single crystals of the composition MgO · Al2O3· 3SiO2was investigated. The crystals showed in x-ray diffraction photographs diffuse superstructure reflections. These diffuse reflections were generated by heat treatment at about 1000°C and subsequent quenching of crystals showing well developed superstructure reflections in form of satellites before heating.The Mg atoms are located within the main structure channels running parallelc. Eighty percent of the Mg atoms occupy the sites coordinated by six O atoms, the remaining Mg atoms the sites surrounded by four O atoms. This distribution of Mg atoms over all possible sites does not agree with the distribution in not heat-treated crystals, in which there was evidence that Mg atoms were only in the sixfold O coordination. The parameters of the framework atoms [(Si,Al) and O] of heat-treated and not heat-treated crystals do not show significant differences.

Multiple Borrmann Diffraction

High-resolution, divergent-beam x-ray diffraction photographs reveal previously unreported detail in multiple Borrmann (000), (111), (111) reflections undergoing anomalous transmission through perfect germanium crystals. These have been accounted for satisfactorily using the plane-wave formulation of the dynamical theory of x-ray diffraction.

Use of Digital Voltmeter for Selected Area Diffraction Calibration

In the interpretation of selected area electron diffraction patterns, the crystal interplanar spacing value d is generally obtained from the formula(1)where D is the measured diameter of the diffraction photograph and F is an instrument factor. The value of F is defined as(2)where λ is the deBroglie wavelength of the high voltage electron and Le is the effective length of the diffraction camera. The error is d then is(3)The error in λ for most modern instruments is quite small, 0.01% or less. The diameter of the ring D can, in general, be read to 0.1 mm which for most patterns is about 0.1%-0.2%. The major source of error in disdue to error in F in general and Le in particular.

The infrared spectra and polymorphism of long chain esters: IV. Some esters from tetradecanol, hexadecanol, octadecanol, eicosanol, docosanol and dodecanoic, tetradecanoic, hexadecanoic, octadecanoic and eicosanoic acid

AbstractInfrared spectra and x‐ray diffraction photographs have been recorded for some normal‐chain esters of long chain acids and long chain alcohols. The substances show no polymorphism but two different structure types exist, one with the chains tilting towards the end group planes and one with vertical chains. The IR spectra permit determination of the chain length of the acid methylene chain. The length of the alcohol chain cannot be deduced.

Spinodal Decomposition in the System CoFe2O4‐Co3O4

A miscibility gap exists in the spinel‐structured region of the pseudobinary CoFe2O4‐CO3O4 system in air. Phase decomposition inside the miscibility gap was investigated by transmission electron microscopy and by X‐ray diffraction. In samples containing 35 and 50 cation % Fe, the first observable changes on aging at 500°C were appearance of side bands on X‐ray diffraction photographs of powder samples and of a periodic structure under the electron microscope. When specimens which contained 50 cation % Fe were aged at 700°C, the first observed change was another set of diffraction lines; homogeneously distributed fine particles were also observed. The former behavior was attributed to spinodal decomposition and the latter to classical nucleation and growth.

Direct demonstration of the helical nature of paramyosin filaments

A method is described by which the front and rear sides of a paramyosin filament can both be shadowed with a platinum-palladium alloy. An electron micrograph of such a filament shows the structure on both sides. A symmetrical cross, indicative of a helical arrangement is seen in the optical diffraction photograph made from the micrograph.

Solution of electron diffraction photographs of vapors allowing for vibrations of the nuclei in the molecule

Solution of electron diffraction photographs of vapors allowing for vibrations of the nuclei in the molecule

Orientation of microcrystals for X-ray diffraction studies

A method is described for obtaining X-ray diffraction photographs, equivalent to those obtained under single-crystal rotation conditions, from materials available only in the form of fine microcrystalline powders of acicular or platy habit. The technique involves dispersing the crystalline powder in an appropriate thermoplastic polymer followed by streaming orientation of the particles in an extrusion process. The particles are held in their new positions by solidification of the polymer melt. With acicular powders, and using a polyethylene matrix, the orientation is improved by cold drawing. The oriented composite is immediately ready for X-ray studies.

High-speed X-ray diffraction photography

The speed of the conventional process of X-ray diffraction photography can be greatly improved by the use of a new industrial X-ray film and a fluorescent screen. This process produces a transparent film with about a tenfold decrease in exposure time and at a cost less than that of standard nonscreen film.

Phase Transitions in Perovskitelike Compounds of the Rare Earths

High-temperature powder x-ray diffraction photography and differential thermal analysis give 1643 K for the rhombohedral-to-cubic transition temperature of PrAl${\mathrm{O}}_{3}$; for NdAl${\mathrm{O}}_{3}$, this transition temperature is estimated to be 2020 K. The 800 K transition temperature of LaAl${\mathrm{O}}_{3}$ is further confirmed. A rhombohedral-to-cubic transition temperature of 1230 K is predicted for CeAl${\mathrm{O}}_{3}$. The orthorhombic-to-rhombohedral transition temperatures of LaFe${\mathrm{O}}_{3}$, LaGa${\mathrm{O}}_{3}$, and SmAl${\mathrm{O}}_{3}$ have been corroborated; these are 1260, 1150, and 1075 K, respectively. Ruiz et al. have reported an orthorhombic-to-rhombohedral transition in LaCr${\mathrm{O}}_{3}$ at 550 K, and the rhombohedral-to-cubic transition near 1300 K. The former occurs actually at 533\ifmmode\pm\else\textpm\fi{}3 K, the latter above 1873 K and probably near 2000 K.

Sulfate-binding protein from Salmonella typhimurium: physical properties.

This protein binds sulfate strongly and is implicated in sulfate transport in Salmonella typhimurium. It has a molecular weight of 32,000 and an axial ratio of 4:1. Crystals are elongate prisms up to 0.5 millimeter. X-ray diffraction photographs give discrete crystalline reflections to a spacing of at least 2 angstroms. The unit cell is orthorhombic P2(1)2(1)2(1), with four molecules per unit cell of 40.8 by 47.5 by 136 angstroms. This is consistent with a highly asymmetric molecule such as the prolate ellipsoid suggested by the other physical measurements. Addition of sulfate had minimum effects on the physical properties as measured by light absorption, optical rotary dispersion, circular dichroism, fluorescence and its depolarization, nuclear magnetic resonance, and sedimentation velocity.

The effect of temperature on the arrangement of dislocations in CdI2crystals

X-ray a-axis diffraction photographs of solution-grown single crystals of cadmium iodide frequently show streaking, arcing and polytypism. When the crystals are treated below the melting point the streaking is reduced, the arcing increased and higher polytypes transform into the most common type 4H. These changes in streaking and polytypism are possibly due to the regular diffusion of partial and unit edge-dislocations formed during the crystal growth. An increase in the arcing may result from the creation of fresh dislocations which move into the existing tilt boundaries or form their own boundaries.

Crystal Structures of the Three Modifications of Nitrogen 14 and Nitrogen 15 at High Pressure

We have determined from x-ray diffraction photographs that high-pressure γ N2 is tetragonal with two molecules per unit cell in special position f of space group P42 / mnm. At an average pressure and temperature of 4015 atm and 20.5°K, respectively, the unit cell dimensions are a = 3.957 Å and c = 5.109 Å, giving a molar volume in good agreement with that from p–V–T measurements. The β N2 solid modification, which is contiguous with the melting curve, remains hexagonal up to at least 4125 atm and 49°K where the unit cell constants are a = 3.861 Å and c = 6.265 Å. Over the pressure range investigated, the c / a ratio is very close to the ideal value for closest packing of hard spheres. The atomic positions in hexagonal (β) N2, which are known to be highly disordered at low pressure, show no evidence of ordering at the highest pressures studied. The third allotrope, α N2, is cubic at 3785 atm and 19.6°K with four molecules in a unit cell 5.433 Å on a side. Both the Pa3 and P213 space groups, which have been reported at zero pressure, appear to be spatially possible at limiting high pressures for α N2. However, from our diffraction measurements on the cubic solid at all pressures, we were unable to prove the existence of the P213 structure. The measurements on pure 30N2 show that this isotope also exists in the same three solid modifications as 28N2 with cell dimensions that are similar for both isotopes. However, the transition to γ N2 at 20°K for the mass-15 isotope occurs 400 atm lower than that for the mass-14 isotope.