The Cambridge Structural Database (CSD) is a database of small molecule organic and organometallic crystal structures elucidated using X-Ray and neutron crystallography. The CSD is distributed alongside a system of software (the Cambridge Structural Database System) to academic and industrial users. The system contains a number of applications (in particular DASH, ConQuest, and Mogul) that can be used to aid crystallographers in the solution and refinement of crystal structures from powder diffraction data, and in the interpretation of crystal structure models (in particular, Mercury). This publication uses a racemic form of ornidazole (Z′ = 3) to illustrate the efficacy of DASH in the crystal structure solution from powder diffraction data. Furthermore, numerous features in Mogul and Mercury that aid crystal structure solution and interpretation of crystallographic data are revised. Finally, a review of a new method for using database-derived geometric information directly in structural solution is presented.

The National Institute of Standards and Technology (NIST) certifies a suite of Standard Reference Materials (SRMs) to address specific aspects of the performance of X-ray powder diffraction instruments. This report describes SRM 1878b, the third generation of this powder diffraction SRM. SRM 1878b is intended for use in the preparation of calibration standards for the quantitative analyses of α-quartz by X-ray powder diffraction in accordance to National Institute for Occupational Safety and Health Analytical Method 7500, or equivalent. A unit of SRM 1878b consists of approximately 5 g of α-quartz powder bottled in an argon atmosphere. It is certified with respect to crystalline phase purity, or amorphous phase content, and lattice parameter. Neutron powder diffraction, both time of flight and constant wavelength, was used to certify the phase purity using SRM 676a as an internal standard. A NIST-built diffractometer, incorporating many advanced design features was used for certification measurements for lattice parameters.

Gemstones are pieces of materials that once cut and polished are used as jewels or adornments. Gemstones may be single crystal (such as diamonds), polycrystalline (such as lapis lazuli), or amorphous (such as amber). In any case, gems may have inclusions that may yield a variety of optic effects. It is also important to unravel the crystal structure of the inclusion(s) in order to determine the origin of the gem and to help to understand their formation mechanism. Here, we expand the use of powder diffraction to identify crystalline inclusions in bulk gemstones highlighting Mo Kα radiation to penetrate within compact gems. Initially, rock crystal quartz with rutile needles was investigated and rutile diffraction peaks were more conspicuous in the Mo pattern than in the Cu pattern. Next, rock crystal quartz with beetle legs was characterized and the red iron oxide inclusion was identified as hematite. The study of a fake gem, glass showing aventurine effect, gave the diffraction peaks of metallic copper. Later, polycrystalline gems, moss agate, and aventurine quartz were also studied. The powder patterns of these compact gemstones could be successfully fitted using the Rietveld method. Finally, we discuss opportunities for further improvements in laboratory powder diffraction to characterize inclusions in compact gems.

In this investigation, the ability of Rietveld refinement method was used to simultaneously refine the structure and microstructure and evaluate the linear defects of cubic crystals. To do this, the basis of Stephans theory, about the anisotropic strain broadening, was developed and the values of dislocation density as well as the fraction of dislocation types were estimated. The reliability of this procedure was checked by selecting four different nanocrystaslline samples and evaluating the microstructure of these materials. Finally, the results were compared with those extracted from the whole powder pattern modeling method. Good agreement was achieved between the results of two methods.

X-ray powder diffraction data for Bi2Mo3O12·nH2O (n = 4.75) were obtained. The crystal system was determined to be monoclinic with space group P21or P21/m. The unit cell parameters were refined to a = 6.334(2) Å, b = 11.593(2) Å, c = 5.777(2) Å, and β= 113.166(8)°.

X-ray powder diffraction data for a new potassium sodium silicate Na1.3K0.7Si2O5 are reported. The sample was prepared by calcining a mixture of NaOH, KOH, and sodium silicate (SiO2/Na2O=3.54, moisture content=60%) at 873 K for 2 h. The crystallographic data obtained by using the whole-powder-pattern decomposition method are Na1.3K0.7Si2O5, monoclinic, P21/c, a =4.8426(1) Å, b = 8.6892(2) Å, c = 11.9686(3) Å, β=90.373(2)°, V=503.60(2) Å3, Z=4, Dx = 2.51 g/cm3.

Observed and calculated X-ray powder diffraction data are reported for ZnGa2S4. After corrections to the observed data, refined tetragonal unit cell parameters ao= 5.2779(2), co= 10.4179(8) Å (λ = 1.54051 Å) were obtained. The powder pattern for ZnGa2S4was calculated in space group Iwith a stoichiometric amount of Zn and Ga randomly distributed amongst the two cation sites.

Phosphostrontium carbonate hydroxyapatites having the general formula Sr10(PO4)6(OH)(2-2x)(CO3)x were prepared by solid gas reaction at different temperatures in the range 0 ≤ x ≤ 1. Infrared spectroscopy investigation reveals a carbonate groups substituting hydroxyl ions. Intensity bands increasing with the carbonate amount introduced in the lattice, while the one corresponding to hydroxyl decreases until disappearance. The Rietveld refinement of the structural model using X-ray powder diffraction patterns is used to determine the substitution rate. It was quantified by the refinement of the occupancy sites affected by the substitution. The crystallographic study shows the evolution of the atomic coordinate in the apatite due to the carbonate incorporation. The variation of the main interatomic distances and the bond angles was also discussed.

It will be shown that there are different types of influence coefficients to correct for matrix effects in XRF analysis: the empirical coefficients calculated from regression analysis and valid for the standards on hand only; the theoretical binary coefficients that are essentially constant in a given concentration range; then the theoretical multi-element coefficients calculated from one given composition and valid for one specimen only.

With theoretical coefficients, however, a special calibration process is needed, because theory cannot take into account all the instrumental parameters. In the proposed calibration method it will be shown that the slope of the calibration curves is the link to correlate the theoretical formalism to the experimental reality; that the standards used do not have to be similar to the unknowns and that a few only are required; that the calibration curves can be extrapolated by a factor of two or three; that pure analytes are not required.

A systematic study of the production of characteristic X-rays by both light and heavy charged particles has been made. Using protons in the energy range 70-200 keV, data have been obtained for twenty-one X-ray lines encompassing a wavelength region from 1.44 to 44.00 Å from K-, L-, M-, and N-shells of elements with 6 ≤ Z ≤ 92. Additional X-ray production efficiencies have been measured in the K-, L-, M-, and N-shells using incident H2+, He++, N++, O++, and Ar++ ions in the energy range 90-400 keV. The ion beams were obtained from a 300 kV electrostatic accelerator, and beam analysis was obtained using a 7 kilogauss analysing magnet.

The data for proton excitation show that, for X-rays of a given wavelength, the X-ray production efficiency increases with the principal quantum number of the atomic shell being excited. These results contradict results reported by Sterk et al, but agree with results obtained earlier by Khan et al.

The results also show that the use of heavy ions (z > 5; obtains X-ray yields which are orders of magnitude higher than a repredicted by the direct scattering theory as used for protons and alpha particles.

Ion excitation of X-rays has been applied to the study of the oxidation kinetics of iron as part of a surface physics program. The wide range of target penetration depth as a function of both mass and energy of the ion has allowed us to study oxide film thickness as a function of oxidation temperature and impurity depth and concentration. Data are presented for protons and argon ions incident on high- purity ion with surface oxide films varying in thickness from 35 Å to 750 Å. Oxygen and carbon sensitivities to equivalents of fractional monolayers are routinely obtained using nondispersive analysis of the X-rays.

A versatile beam-scanning system has been developed for use with the Electron Microprobe X-ray Analyzer manufactured by Applied Research Laboratories, Inc. It provides for the display of X-ray intensities from any of three spectrometers, three nondispersive detectors (either counters or scintiallation counters), as well as the current collected by the target or the current backscattered by the target. The electrostatic deflection system does not interfere with the use of the optical-viewing system and provides a maximum scanning area of only slightly less than field of view of the optical-viewing system.

A stepping motor, controlled from the readout console, has also been developed which permits automatic point-by-point analysis of a specimen with minimum operator attention. In the use of this attachement, measurements may be made for fixed time, fixed charge, or fixed counts (integrated intensity) at each point. As a result, the step-scanning motor facilitates accurate measurement of one-dimensional concentration fluctuations and is particularly useful for phase identification and studies of diffusion and segregation.

Humidity sensitive mineral phases change their structure when humidity varies resulting in X-ray pattern changes in intensity, position, and shape of lines. These structural changes in hydrous minerals are induced by dehydration and rehydration, which can lead to phase transformations or to steady depletion which may result in a total structure collapse. By means of X-ray diffraction with a special attachment, such reactions can be followed. The controlled relative humidity is provided in situ, in a closed cell, by a flow of moistened helium gas which is flushed through the cell during the XRD analysis. Humidity diffractometry allows studies of reaction rates of dehydration-rehydration reactions and their reversibilities, as well as effects of additives and impurities on these reactions. Potential applications in basic research and in industry are demonstrated using montmorilionite, ettringites, sodium carbonates and calcium sulfates.

Our laboratory has been interested in the use of the X-ray spectragraph for routine rock analysis within limited rock types. This paper is meant as a progress report and to indicate the direction of our work on amphibolites to others interested ill the problem of rock analysis.

Even with the use of flow counters and pulse discriminators the intensities of the magnesium, aluminum and silicon peaks are quite low and most dilution techniques may not be used. The direct determination of major elements (except sodium) yields results directly comparable to the chemical results for potassium; manganese and titanium in the range from 0: 1 to 3% as the oxides. For iron (10-20%), calcium (8-12%) and silicon (45-52%) the accuracy is 2-3% but for each element occasional samples will be 5% from the chemical values. Aluminum and magnesium yield erratic results.

The use of ratios between elements occurring in. the samples yields slightly improved accuracies. The use of a strong absorber such as tungstic acid (40% by weight) greatly improves the ratios for aluminum and magnesium., without appreciably affecting their intensities. By a combination of the direct and tungstic acid techniques it is possible to attain accuracies of 2-3% with analysis time of two hours. At present we are attempting a combination with an internal standard method to yield greater accuracy.

Although widely recognized in the research community as one of the most accurate non-destructive methods for the determination of . residual stress in polycrystalline structural materials, x-ray diffraction has not been widely adopted in the field. This is partly due to the fact that such measurements require, most often, a well trained user with knowledge in both materials and mechanical sciences in addition to the specific know-how of the instrument. We believe that computer assistance could contribute to the promotion of this technique by increasing the productivity and accuracy of these measurements. We have developed a prototype expert system, using Nexpert Object's shell, to assist a non-trained operator in the validation and interpretation of X-ray diffraction residual stress data.

The present work describes this prototype which has been designed to confirm the feasibility of the concept. Its knowledge base contains relevant examples of the rules necessary for data validation. The prototype has also confirmed most of the concepts required for the implementation of a full-scale version by evaluating all of the major technical features such as graphics representation, external routines and database access.

In the measurement of residual stresses via diffraction (using x-rays or neutrons) it is strains that are actually determined, by employing the interplanar spacing (dhkl) of the ﹛hkl﹜ planes as an internal strain gauge. The change in this spacing is measured from the shift of diffraction peaks (and Bragg's law) at several orientations of the sample to the incident beam, and the resultant strains are converted to stresses with the “diffraction elastic constants”, S1 (hkl) and S2 (hkl)/2. While these take on the values (- v/E) and (1 + v )/E respectively for an isotropic solid, in anisotropic materials their values depend on marry factors: preferred orientation, shape and orientation of second phases, interaction between grains. In fact there are reports of variation these constants with plastic deformation and theory predicts variations with morphology. While it is possible to calculate approximate values for these constants from theory and the single crystal elastic constants , Si and S2/2 are really not elastic constants in the strictest sense because or these other factors, and it is best to measure them. One of us (I. C. Noyan) has recently examined this problem in some detail , and we summarize his results here.

Irregular backgrounds in time-of-flight neutron powder diffraction data and nonlinear backgrounds in angle dependent neutron powder diffraction data. were corrected by fitting fifth degree polynomials to those portions of the data most affected. The anomalous background intensities were in both cases due to non Bragg scattering. The polynomial fitting was carried out over a sufficiently widerange of the profile to avoid interfering with the Bragg peaks. The corrected data gave internally consistent results for the crystallographically nonequivalent (Si,Al) -0 (1) and(Si, Al) -0 (2) bond lengths in zeolite rho and compare favorably with previous refinements of this Zeolite in space group Im3m. Internal and external in consistencies of bond lengths are just as diagnostic of refinement difficulties as negative isotropic temperature factors or non positive definite an isotropic temperature factors are.

The performance of a room temperature mercuric iodide X-ray detector was investigated as a function of detector bias, amplifier time constant, and detector temperature. A Mn Kα line of 200 eV FWHM was obtained by using low noise electronics developed for Si(Li) detectors, including a cooled input PET. Measurements of the detector's resolution at various X-ray energies result in a Fano factor of 0.20.

X-ray, neutron or electron diffraction patterns of alloys with structural disorder (micro-crystalline, amorphous or liquid alloys) consist of few diffuserings or halos. The ratio Ia(K)/<f> 2, where Ia(K) is the elastically scattered intensity per atom, K = 4πsinθ/λ, and <f> is average scattering factor of the alloy, is the sum of the Laue monotonic scattering (<f2> - <f2>)/<f2>, the small angle scattering Is(K) and interference function I(K). For isotropic distribution of the atoms in the alloy, one can write:

and

where

ρ0 is the average atomic density, V(r) is the size factor , ci and fi are the atomic concentration and atomic scattering factor of element i, respectively. Iij(K) is called the partial interference function which is related to the number ρij(r) = cjρ0gij(r) of j-type atoms per unit volume at the distancer from an i-type atom.

By varying the scattering factors of the elements through application of different radiations (x-rays, neutrons and electrons) and/or isotope enrichment, one can measure several I(K) which allow the evaluation of Iij(K) for a particular alloy. Assuming that gij(r) is independent of the relative abundance of the elements in the alloy , Iij(K) can also be obtained from several I(K) of the alloys with different concentratiora measured with a single radiation. This procedure has been applied to liquid Ag-Sn, Au-Sn and Cu-Sn alloys. The interference functions I(K), and their Fourier transforms, of vapor-quenched Ag-Ge and Ag-Cu films indicate that these alloys are micro polycrystalline with particle sizes of 15A in the Ag-52 at.% Cu alloy, 20A in the Ag-83 at.% Ge alloy and 24A in the Ag-64 at.% Ge alloy.

The diffraction patterns of coarse grained materials are compared to specimens with crystallite sizes of less than 1 µm characterized by diffraction spots. Based on an analysis of spot intensities it is shown that for: (a) an at-random distribution of crystallite orientations and (b) under the assumption of specific crystallite shapes it becomes possible to evaluate the distribution N(l) of linear crystallite dimensions (0.1 µm < l < 20 µm) from measured spot intensity distributions z(i).

Powder X-ray diffraction data for cubic La0.3Sr0.7CoO3−δ, perovskite prepared by a combustion method, using metal-EDTA complexes are reported. The cubic cell parameter is: ac = 3.8323(9)Å.