Standard Diffractometer Research Articles

CoII4MoV12O28(OH)12(H2O)12]·12H2O: facilitating single-crystal growth by deuteration

The structure of the neutral heterometal oxide cluster dodecaaqua-di-μ(3)-hydroxido-deca-μ(2)-hydroxido-octacosaoxidotetracobalt(II)dodecamolybdenum(V) dodecahydrate, [Mo(12)O(28)(μ(2)-OH)(10)(μ(3)-OH)(2){Co(H(2)O)(3)}(4)], is virtually identical to the previously reported Ni(II) analogue [Mo(12)O(28)(μ(2)-OH)(10)(μ(3)-OH)(2){Ni(II)(H(2)O)(3)}(4)] [Müller, Beugholt, Kögerler, Bögge, Budko & Luban (2000). Inorg. Chem. 39, 5176-5177], the first molecular magnet to exhibit signs of magnetostriction. The formation kinetics of the neutral cluster species, which is insoluble in water, can be significantly slowed by the use of deuterated reactants in order to grow single crystals of sufficient size for single-crystal X-ray diffraction studies using standard diffractometers. One half of the main cluster and six solvent water molecules constitute the asymmetric unit. The main cluster is located on a mirror plane.

The interatomic vector’s method, algorithms, and programs for the solution of atomic structure of nanoclusters in crystal

A calculation technique and corresponding algorithms have been developed using the formalism of Fourier transform of finite functions. A software package for obtaining distributions of cluster interatomic vectors from diffuse X-ray scattering has been written and debugged. The programs were checked on a 30-atom cluster [CdTb3F26]. The attempts to obtain experimental data on a single crystal with nanoclusters using an Xcalibur S diffractometer (Oxford Diffraction) with a coordinate CCD detector were no success. The standard diffractometer software contains errors that lead to incorrect results upon the reconstruction of the distribution of diffuse scattering from different runs. These errors are of little importance when Bragg peaks are processed.

In situ X-ray diffraction investigations during high-energy oxygen ion implantation in transition metals

An in situ X-ray diffraction study was performed to characterize aspects of the kinetics of structural phase formations in transition metals during oxygen implantation. A specially designed high-temperature vacuum chamber for X-ray measurements was installed at the high-energy implantation beamline of the 3MV-Tandetron accelerator. Titanium and molybdenum sheets were implanted with oxygen ions with an energy of 1.5MeV up to a fluence of 1.6×1018O+-ions/cm2 without sample cooling. During implantation, the phase formation was continually investigated by in situ and real-time X-ray diffraction (XRD) with a position-sensitive proportional counter system. The phase formation was studied during annealing process by in situ XRD. The obtained results were compared with ex situ XRD measurements performed by different techniques at a standard diffractometer. The analysis of XRD patterns indicates the formation of a buried MoO2 layer in molybdenum. In the Ti samples no buried oxide is formed due to significant oxygen diffusion.

128-Channel Silicon Strip Detector Installed at a Powder Diffractometer

Silicon strip detectors represent a new class of one-dimensional position-sensitive single photon counting devices. They allow a reduction of measurement time at the powder diffractometers by a factor up to 100 compared to instruments with a single counter, while maintaining comparable count statistics. Present work describes a 128-channel detector working with a standard diffractometer. The detector is 12.8 mm long and covers the angular range of 3.2 deg. We discuss the diffraction geometry in real and reciprocal space, the FWHM of diffraction peaks, and the background level. Measurements were made on standard samples and on complex samples of industrial importance (e. g., portland clinker). Applications of the detector to diffraction measurements of single crystals and thin films are discussed briefly.

Relative merits of reflection and transmission techniques in laboratory powder diffraction

Data for the standard material NBS SRM 674, TiO2, were collected on two diffractometers: a) a Philips PW 1050/37 standard diffractometer of the Bragg-Brentano type equipped with a post diffraction curved Ge monochromator, b) a Stoe Stadi P diffractometer of transmission type equipped with a curved incident beam Ge monochromator. Both monochromators were set to select pure CuKα1 radiation. The reflection type instrument gives a much larger peak to background ratio than the transmission instrument, for which the background is much higher than with the reflection instrument. Rietveld refinements were carried out on both data sets with the programs DBWS-9807 and general structure analysis system (GSAS). The structural parameter of the oxygen atom of rutile depends neither on data set nor program, whereas, e.g., thermal displacement parameters seem to depend on both data set and program.

A portable ultrahigh vacuum organic molecular beam deposition system for in situ x-ray diffraction measurements

A portable UHV molecular beam deposition system has been developed for synthesis, in situ, and real-time x-ray diffraction measurements of organic thin films, multilayers, and superlattices. The system has been optimized for small size, while still incorporating full features necessary to achieve thin film growth under molecular beam epitaxy (MBE) conditions. It can be used independently for thin film growth, or it can be transported and mounted on standard diffractometers. Additionally, it can be docked to a stationary multipurpose MBE growth system for sample transfer, thus permitting more extensive growth and characterization. The design and performance of this system are reported, with emphasis on modifications required to deposit organic materials. To demonstrate the capabilities for real-time x-ray scattering experiments, some preliminary results of a study of epitaxial growth of 3,4,9,10-perylene-tetracarboxylic dianhydride on Ag(111) substrates are given.

The effect of profile step width on the determination of crystal structure parameters and estimated standard deviations by X-ray Rietveld analysis

Crystal-structure parameters and their associated estimated standard deviations (e.s.d.'s) have been determined for α-Al2O3 by Rietveld analysis of Cu Kα X-ray powder diffraction data collected on a standard diffractometer with profile step widths ranging from 0.01 to 0.32° 2θ. Estimates of the true precision of the parameters have been obtained by replication of the experiment five times. The degree of serial correlation between adjacent points in the profiles has been quantitatively determined by the use of the Durbin–Watson d statistic. Values of the conventional profile agreement indices, Rp, Rwp and goodness of fit, are not influenced by the scan-point density, but the Bragg R-factor decreases to a limiting value as the step width is decreased. The structural parameters obtained at all step widths are statistically indistinguishable at the 1σ level, although there is some loss of accuracy relative to single-crystal values at widths larger than 0.16°. The least-squares e.s.d.'s decrease linearly with the reciprocal square root of the number of steps in the pattern, as expected, but the e.s.d.'s of the unit-cell dimensions are the only ones that are significantly smaller than estimates of their true precision obtained from repetitions of the experiment. In the case of α-Al2O3, and possibly in general, the optimum step width for Rietveld analysis corresponds approximately to the minimum value of the full-width at half-maximum for well resolved peaks.

Application of a multichannel position-sensitive X-ray detector to protein crystallography

A multichannel X-ray diffractometer is described, comprising a position-sensitive detector (xenon-filled proportional chamber, number of channels: 64 × 64, channel size: 2 × 2 mm), an Arndt–Wonacott oscillation camera, a digital processor for determining photon coordinates, and a number of computers for accumulation and processing of diffraction data and for control of the detector. The design allows the detector to be moved in the direction of the primary beam and at right angles to it. For a protein with a lattice constant of ~60 Å, the detector may simultaneously record only {{1}\over{16}} of the 2.5 Å diffraction pattern and has to be moved to record the full data. The diffractometer including this detector was constructed mainly to perfect the whole system of data collection, elaborate a set of programs and evaluate the accuracy. However it can be used to investigate medium-sized proteins with lattice constants of ~60 Å, with a resolution of 4.5 to 5 Å and a two- or three-fold gain in time over a standard diffractometer. Data are collected by the rotation method. One diffraction pattern corresponds to a crystal rotation of 0.5 to 1°. A series of successive patterns is recorded on disk. The squares of the structure factors are computed after the series is completed. The R value (reproducibility of the results) is 4–7%.

Determination of the amorphous content of superconducting films by x-ray diffraction and its relation to transition temperature

A method has been developed for the determination of the amorphous content of superconducting films (niobium-germanium) based on x-ray analysis. Measurements are made in reflection using a standard diffractometer which includes a silicon semiconductor counter. The intensity of the diffraction line of the substrate was measured at an angle outside the amorphous halo region of the films to calibrate their surface density. The second angle of measurement was chosen to be within the region of the amorphous halo but away from the diffraction lines of the substrate or crystalline components of the films under investigation. Expression have been derived for calculation of the amorphous content. For the set of films investigated, a direct correlation of the amorphous concentration and the superconducting transition temperature has been observed.

A polythermal attachment for X-ray powder diffractometers

A new type of thermostatic attachment to standard diffractometers allowing operations both above and below room temperature (-150 to +900 degrees C) and under vacuum is described. It has proved to be very useful in studying chemical reactivity and phase transitions owing to its simple assembly and great flexibility. The thermal expansion of sodium chloride is reported to illustrate the obtainable accuracy.

A Position-Sensitive Proportinal Counter for Residual Stress Measurement by means of Microbeam X-Rays

AbstractA position-sensitive proportional counter (PSPC) with high counting efficiency has been made for stress analysis with low intensity X-rays such as microbeam X-rays.This PSPC system has made it possible to measure the residual stress in a small region such as a fatigue crack tip in very short time compared with the measurement by standard diffractometer or film methods.

Study on X-Ray Stress Analysis Using a New Position-Sensitive Proportional Counter

A position-sensitive proportional counter suitable for the X-ray stress measurement has been developed and residual stresses were measured with an apparatus that uses this PSD system. The counter was designed to have a good angular resolution over the counter length for the diffracted X-ray beam and high counting rates. The mean angular resolution measured was about 0.2° in 2θ (FWHM) at 200 mm, and the maximum allowable counting rate reached about 40,000 cps.The time required for the data accumulation was shown to be 1/10 to 1/30 of the time required with a standard diffractometer.

A xenon-filled multiwire arc detector for X-ray diffraction

A xenon-filled multiwire proportional chamber with high and uniform photon-detection efficiency has been built and incorporated into a high-speed data-collection system for protein crystallography. This system has been used to collect more than 200 000 reflection intensities from one parent and four heavy-atom derivative crystals of a complex of dihydrofolate reductase and methotrexate (a cancer drug). Its data collection rate is about 30 times faster than the rate of a standard diffractometer (1400 reflection intensities per hour versus 50 reflection intensities per hour). The precision of the chamber data is also better with an intensity reliability R of 5% as compared with 6.7% from the diffractometer data. The difference Patterson maps between parent and heavy-atom derivative data show very clearly the positions of the heavy atoms.

A multiwire proportional chamber as an area detector for protein crystallography

A multiwire proportional chamber (30 × 30 cm) together with its electronic readout into a large core memory (mass core) has been used successfully as a digital area detector for protein crystallography. The diffraction pattern stored in the mass core can be displayed on a TV monitor. An IBM 1800 computer has fast random access to the mass core and is used on line to estimate the integrated reflection intensities. To characterize this new area detector, the geometric linearity, the resolution and the quantum detection uniformity have been measured. Preliminary results show that with this new system one can collect intensity data from protein crystals about an order of magnitude faster than with the standard diffractometer.

Low-temperature, high-pressure X-ray cell

A beryllium high-pressure cell (0–4 kbar), suitable for single-crystal studies, has been constructed so that it can be mounted either on a standard diffractometer or on other X-ray instruments and can operate over the temperature range 80–300°K. This cell has been used to determine the linear compressibilities of various materials as well as to determine shifts in atomic position with pressure of simple materials. More recently, the symmetry of phases in the pressure-temperature phase diagram for (CH3)4NMnCl3 has been determined.

Rapid Recording of Powder Diffraction Patterns With Si(Li) X-Ray Energy Analysis System: W and Cu Targets and Error Analysis

X-ray diffraction patterns using continuous radiation from copper and tungsten target x-ray tubes and detected with a Si(Li) energy analysis system are presented. Errors caused by a misaligned diffractometer and x-ray penetration into the sample are shown to be more difficult to correct and larger in magnitude than errors arising from energy calibration. All these errors can be minimized by mixing a standard with the unknown sample.The energy resolution of the detector influences the breadth of the diffraction peaks more strongly than the standard slit systems available with commercial diffractometers. Thus, to reduce the recording time and maintain the same standard deviation for the data, one should increase the sizes of the front and receiving slits including the Soller slits. X-ray energy diffraction patterns can be recorded with standard deviations less than +0.001 Å in the d spacing with only 200 sec measurement time using the standard diffractometer slit system. Copper targets are probably as useful as tungsten even though the continuous intensity is about three times.less. Copper has fewer interfering characteristic lines, and its use permits convenient conversion to normal θ scanning diffractometer operation.

Experimental Study of Effect of Crystallite Size Statistics on X-Ray Diffractometer Intensities

The relative rms deviation σ of the intensity of a rapidly rotating polycrystallite specimen is σ=[6.5R sinθ]/[h(mNeff)½], where R=goniometer radius, θ=Bragg angle, h=(hf+hs)/2, hf=length of focal spot, hs=length of receiving slit, m=multiplicity factor, and Neff the effective number of irradiated crystallites. Experimental data on silicon powder specimens are presented to show the dependence of σ on crystallite sizes, choice of x-ray wavelengths and various other experimental parameters. Comparisons of data for rapidly rotating and stationary specimens having crystallite sizes in the 30–50 μ range show that rotation improves σ by a factor of 7 or 8 for peak intensities and 4 or 5 for integrated intensities, using a standard diffractometer.