Type Of Diffractometer Research Articles

Energy-Dispersive Residual Stress Analysis under Laboratory Conditions: Concept for a New Type of Diffractometer

In the past decade energy-dispersive (ED) synchrotron diffraction has evolved into a powerful tool for materials analysis. Recording complete diffraction patterns in rather few different measuring directions allows for depth-resolved analysis not only of the near-surface residual stress state, but also of composition and even texture gradients. However, since the number of synchrotron beamlines dedicated to ED-diffraction is restricted to very few instruments, alternatives have to be found which allow for ED residual stress analysis even under low flux laboratory conditions. In this project we start to establish the scientific basis for a measuring and evaluation method to make the transfer of the ED method to the laboratory dimensions possible, which is adapted to the conditions of much lower photon flux and larger beam divergences of laboratory X-ray sources. In this paper, we present the concept of an ED-diffractometer which is equipped with two detectors to enable simultaneous data acquisition for two orientations of the diffraction vector with respect to the sample reference system. The first constructive and experimental steps are presented and furthermore the possibilities and limitations of the new laboratory method and the advantages of the ED diffraction method to realize short measurement times in order to realize a high resolution of information depth are discussed.

Angle calculations for a `4S+2D' six-circle diffractometer

Angle calculations are derived for the operation of a `4S+2D' six-circle X-ray or neutron diffractometer. The six degrees of freedom [four sample-orienting (`4S') and two detector-orienting (`2D')] of the diffractometer are used to control the scattering vector and a reference vector in the laboratory frame of reference. Several modes of operation unavailable in other types of diffractometer are presented.

New Class Of Diffractometer Speeds X-ray Crystal Structure Determinations

A new type of diffractometer is making it possible to obtain X-ray structures of organic, organometallic, and inorganic molecules in hours, rather than in the usual days or weeks. The instruments use charge-coupled device (CCD) chips to detect X-ray diffraction patterns of molecules. In X-ray diffractometry, the diffraction of X-rays from crystals produces interference patterns that can be interpreted to determine the three-dimensional arrangement of atoms in the crystal. The data collection process is usually slow and tedious, but CCDs are capable of speeding things up considerably. CCDs are electronic chips that can detect two-dimensional light patterns and digitize them. In a diffractometer, a phosphor screen is used to convert diffracted X-rays to light. A CCD chip behind the phosphor screen collects the light and transfers the data to a computer, which then interprets it to generate a crystal structure. CCD-based X-ray diffractometry is sometimes called crystallographic chemical analysis to ...

Crystalline-State Reaction of Cobaloxime Complexes. 18. Metastable Intermediate Structure Observed by a New X-Ray Diffractometer for Rapid Data Collection

Abstract A crystal of [(R)-1,2-bis(methoxycarbonyl)ethyl]bis(dimethylglyoximato)(diphenylmethylphosphine)cobalt(III) changes its cell dimensions with retention of the single crystal form on exposure to visible light. The change is so fast that a new type of diffractometer (IPD-WAS) was developed for rapid data collection. The structures were analyzed at four different stages of the change using the diffractometer, which enabled us to collect the three-dimensional intensity data within 2 h. The cell dimensions of the monoclinic crystal varied from a = 13.678(2), b = 24.880(6), c = 9.391(2) Å, β = 107.99(1)°, and V = 3040(1) Å3 to a = 13.56(1), b = 25.06(1), c = 9.381(6) Å, β = 107.35(6)°, and V = 3044(3) Å3. The space group was changed from P21 to P21/n. The structures at four stages showed that there are two crystallographically independent molecules, A and B, in an asymmetric unit of the crystal before irradiation and that the chiral 1,2-bis(methoxycarbonyl)ethyl (bmce) group of the B molecule is completely inverted to the opposite configuration while the chiral bmce group of the A molecule remains unaltered after irradiation. This brings about an inversion center between the two molecules. The reaction cavity for the B bmce group is significantly greater than that for the A bmce group. At the intermediate stages, the B bmce group takes complicated disordered structures, which indicates that there exists a metastable intermediate structure in the inversion process.

Neutron diffraction data on liquid D 2 from steady- and pulsed-source experiments

The way in which inelastic scattering affects the measured intensity in a neutron diffraction experiment on light molecules is very different on a reactor-based two-axis diffractometer and on a time-of-flight diffractometer at a pulsed source. Recent measurements of S( Q) in liquid D 2 close to the triple point have been carried out on both types of diffractometer. We compare here the results obtained with the two techniques for S( Q) and its partial derivatives with respect to density and temperature.

Angle Calculations for a `2+2' Surface X-ray Diffractometer

Angle calculations are presented for a new type of diffractometer, which has two degrees of freedom for the sample and two degrees of freedom for the detector. The sample and detector motions are mechanically uncoupled. This geometry is used to implement a surface diffractometer and the corrections necessary to extract integrated intensities in two of the most useful modes are presented. The relative merits of this geometry and further extensions to it are discussed. Experimental data, showing the existence of an interfacial microstructure at the Si/SiO2 interface, are also presented to illustrate the advantage of this geometry.

迅速Ｘ線構造解析の現状と展望

X-Ray crystal structure analysis has become very easy and an enormous number of crystal structures have been determined. Although such a development is partly brought about by the four-circle diffractometer, recent developments in technique of crystal structure analysis and computation require another diffractometer for quick data collection. Two methods are proposed; the synchrotron radiation to obtain more intense X-rays, and the Imaging-plate as a two-dimensional detector. Several types of diffractometer using the Imaging-plate have been made, for example, IPD-WAS, R-AXIS IIc, DIP-320 W and FIXD. The three-dimensional intensity data can be collected within 35 hours whereas about 23 days are necessary for the four-circle diffractometer. The data will be collected more quickly at photon Factory, using the synchrotron radiation.Recently an unstable intermediate structure has been observed by the step-wise structure analysis for the crystalline-state racemization of the cobaloxime complex crystal using the above IPD-WAS. A desolvation process has been observed for another cobaloxime complex crystal. Such a dynamical process observed in crystals should make clear the reaction mechanism more precisely.A new type of diffractometer is now designed to analyze the crystal structure within a submillisecond at SPring-8. Some structures at the excited states will be analyzed in near future.

Bragg-Brentano and Seeman-Bohlin Diffractometers for Thin Films

AbstractThe performances of Seeman-Bohlin (S-B) and Bragg-Brentano (B-B) diffractometers with flat thin film samples were compared on the basis of equal instrumental aberrations. It was found that the S-B arrangement has only a marginal advantage as regards diffracted intensity, and that both types of diffractometer may be successfully employed for characterization of thin films. Diffraction data obtained with very thin metallic films (down to 30 Å) are included for illustration. In order to eliminate reflections from the singlecrystal substrate in the B-B diffractometer, sample tilting was employed. Provided the tilting angle remains within 0.5°, sample tilting causes only moderate additional broadening of the thin film peaks.

Stress Measurement and Precision Diffraction Angles on Large Grained Specimens

This note describes a diffractometer technique that is successful on specimens that yield sharp diffraction peaks but that have grain sizes somewhat too large to give reliable results with the usual powder diffraction methods, owing to the peak profiles being distorted or displaced by having too few grains reflecting, Such specimens are not uncommon in stress analysis and the errors encountered are sometimes reduced by oscillating the specimen through an angle range, Δβ, of a degree or so about the diffractometer axis, thereby increasing the number of recorded reflections. The technique discussed here is basically a single crystal technique rather than a powder technique, and with a diffractometer capable of measuring reflections at high angles on both sides of the initial beam this technique would amount to W. L. Bond's precision method. For the usual diffractometer, however, high diffraction angles must be measured on one side only, even though some instruments permit the lower angle reflections to be measured on both sides for accurately locating the zero of the 2θ scale. We are discussing a technique as applied to these usual types of diffractometers.

International Union of Crystallography Commission on Crystallographic Apparatus. Single crystal intensity measurement project report. I. Inter-experimental agreement

Seventeen sets of measurements of structure factors of d(+)-tartaric acid, within the range (sin θ)/λ < 0.5 Å−1, were provided by the participants in the International Union of Crystallography Single Crystal Intensity Measurement Project. Each participant used a different crystal, all being derived from a single crystallization batch. The results in the Project are representative of those from a wide variety of currently used diffractometers and techniques. The instruments included four-circle, normal-beam and equi-inclination diffractometers. Cu and Mo radiations were used – unfiltered, with single and balanced filters, and with crystal monochromators. The aims of the project were twofold: (a) to provide an estimate of the spread of F values associated with the range of variables involved in the project and (b) to locate, if possible, the sources of error. A number of agreement indices were used to measure the spread of F values both for equivalent reflections within any one experiment and for comparisons between experiments. In an attempt to allocate errors to certain plausible sources, an analysis-of-variance was applied to the weighted deviations of individual values of F from the set of mean values. The variables specified were intensity I, a θ angle factor d* and the Miller indices h,k,1. From the values of the agreement indices and the interaction curves from the analysis-of-variance, it was possible to recognize outlier sets that differ considerably from the mean and to isolate these, where necessary, before arriving at an estimate of the error spread of the main group. In this project, there is no one simple figure of merit which provides a ready assessment of the accuracy of measurement of structure factors. Rather, there are several ways of indicating the probable accuracy. One way is to present the spread of values of Rij(Σ(|Fi| − |Fj|)/Σ ½(|Fi| + |Fj|). This shows that two scaled experimental sets of structure factors, measured under circumstances similar to those of the project, will most probably differ by 6%, agree no better than 3%, and usually no worse than 10% except in cases of extreme systematic error where it may rise to 50% or more. From the analysis-of-variance, inferences are drawn concerning the concordance of results derived from the different types of diffractometer, on features of technique associated with the diffractometers and on other aspects, including 2 dependence, monochromaticity, count rates and extinction in the crystals. It is concluded that other sources of error may be present and that future projects should be designed to reveal these.

On the design of single crystal diffractometers to measure a number of reflections simultaneously

Single-crystal diffractometers derived from inclination Weissenberg goniometers can be adapted to measure more than one reflection at a time. Two reflections can be measured simultaneously, one from each of any two levels that are symmetrically on either side of the flat-cone setting, or several reflections can be measured quasi-simultaneously, one from each level within about ±0.05 r.l.u. of the flat-cone setting. The modifications which permit these new modes of operation are described, together with corresponding changes in the design and use of four-circle diffractometers. The general relationships between the two types of diffractometer are also discussed.