As we celebrate the 75th anniversary of the Powder Diffraction File, the PDF® is still a method for chemical and material analyses. The database and embedded software are designed to solve a range of solid-state material analysis problems that includes phase identification, quantitative analysis, crystallinity, and crystallite size measurements. A versatile platform allows users to interpret X-ray, electron, neutron, or synchrotron diffraction patterns for their analyses. Over several decades as diffraction hardware and software continued to improve, the International Centre for Diffraction Data continues to improve the methods and the PDF database, offering unprecedented analysis capabilities to the modern user.

The aim of this work was to design, construct, install, and commission an on-line, X-ray diffraction (XRD) analyzer capable of continuously monitoring phase abundances for use in process plant control. This has been achieved through a joint project between CSIRO Minerals and Fuel & Combustion Technology Pty. Ltd. with an instrument designed for use in a Portland cement manufacturing plant. Key factors in tailoring such an instrument to the cement industry were (i) the handling and presentation of a dry sample and (ii) the development of an analytical method suitable for the complex suite of phases contained within Portland cement. The instrument incorporates continuous flow of sample through the diffractometer using a purpose-built sample presentation stage. The XRD data are collected simultaneously using a wide range (120° 2θ) position sensitive detector, thus enabling rapid collection of the full diffraction pattern. The data are then analyzed using a Rietveld analysis method to obtain a quantitative estimate of each of the phases present. The instrument is controlled by a PC linked to the diffractometer through a purpose built interface. The phase abundance information is then transmitted to the central computer in the cement plant where it can be used for the control of mill parameters such as temperature and retention times as well as gypsum feed rate.

The crystal structures of (NH4)H2C6H5O7 and (NH4)3C6H5O7 have been determined using a combination of powder and single crystal techniques. The structure of (NH4)2HC6H5O7 has been determined previously by single crystal diffraction. All three structures were optimized using density functional techniques. The crystal structures are dominated by N-H⋅⋅⋅O hydrogen bonds, though O-H⋅⋅⋅O hydrogen bonds are also important. In (NH4)H2C6H5O7 very strong centrosymmetric charge-assisted O-H-O hydrogen bonds link one end of the citrate into chains along the b-axis. A more-normal O-H⋅⋅⋅O hydrogen bond links the other end of the citrate to the central ionized carboxyl group. In (NH4)2HC6H5O7, the very strong centrosymmetric O-H-O hydrogen bonds link the citrates into zig-zag chains along the b-axis. The citrates occupy layers parallel to the bc plane, and the ammonium ions link the layers through N-H⋅⋅⋅O hydrogen bonds. In (NH4)3C6H5O7, the hydroxyl group forms a hydrogen bond to a terminal carboxylate, and there is an extensive array of N-H⋅⋅⋅O hydrogen bonds. The energies of the density functional theory-optimized structures lead to a correlation between the energy of an N-H⋅⋅⋅O hydrogen bond and the Mulliken overlap population: E(N-H⋅⋅⋅O) (kcal/mole) = 23.1(overlap)½. Powder patterns of (NH4)H2C6H5O7 and (NH4)3C6H5O7 have been submitted to International Centre for Diffraction Data for inclusion in the powder diffraction file.

Polycapillary optics are utilized in a wide variety of applications and are integral components in many state of the art instruments. Polycapillary optics operate by collecting X-rays and efficiently propagating them by total external reflection to form focused and parallel beams. We discuss the general parameters for designing these optics and provide specific examples on balancing the interrelations of beam flux, source size, focal spot-size, and beam divergence. The development of compact X-ray sources with characteristics tailored to match the requirements of polycapillary optics allows substantial reduction in size, weight, and power of complete X-ray systems. These compact systems have enabled the development of portable, remote, and in-line sensors for applications in industry, science and medicine. We present examples of the utility and potential of these optics for enhancing a wide variety of X-ray analyses.

The calculated XRD profiles of alite (impure Ca3SiO5, the major phase in Portland cement) derived from seven postulated crystal structures for alite were compared with a measured alite profile, extracted from the XRD pattern of a standard Portland cement. Only two of these profiles were found suitable for multiphase Rietveld phase quantification, namely those given by the monoclinic superlattice and triclinic models. These, however, gave very slow computing times because the large low-symmetry structures generated many X-ray reflections over the pattern. Also tested was an “observed” standard profile for alite, derived from experimental alite profiles, and generated using the (hkl) file feature of the SIROQUANT P.C. quantitative analysis system. This file was based on rhombohedral pseudosymmetry and contained very few (hkl) reflections, compared to the low-symmetry models (64 reflections instead of 951 for the monoclinic and 1691 for the triclinic models, respectively). The latter standard profile gave the best fit to the known phase concentrations and gave computing times which were shorter by factors of 2.5 and 4.9 than those for the monoclinic and triclinic standard profiles, respectively.

Two different approaches for studying sample’s contributions to diffraction-line broadening are analyzed by applying them to several nickel hydroxide samples. Both are based in the refinement of powder diffraction data but differ in the microstructural model used. The first one consists in the refinement of the powder diffraction pattern using the FAULTS program, a modification of DIFFaX, which assigns peak broadening mainly to the presence of stacking faults and treats finite size effects by convolution with a Voigt function. The second method makes use of the program FULLPROF, which allows the use of linear combinations of spherical harmonics to model peak broadening coming from anisotropic size effects. The complementary use of transmission electron microscopy has allowed us to evaluate the best approach for the Ni(OH)2 case. In addition, peak shifts, corresponding to reflections 10l (l≠0) were observed in defective nickel hydroxide samples that can be directly correlated with the degree of faulting.

CheMin is a miniature X-ray diffraction/X-ray fluorescence instrument that is included in the payload of the Mars 2009 Mars Science Laboratory mission. A portable CheMin prototype was built to test the capability of the instrument for remote in situ mineralogical characterization of geological materials. The instrument was successfully deployed at a variety of Mars analog sites in Death Valley, CA, in May 2004.

In the Rietveld method for the analysis of powder diffraction data the entire pattern is calculated using a model for the positions of the peaks (the unit cell parameters), their intensities (dependent on the atomic positional and thermal parameters, preferred orientation, etc.) and their widths and shapes, together with a description of the background. The calculated pattern is then compared with the observed step profile, point by point, and the model parameters are adjusted by least-squares methods.

In order to ensure the best possible outcome of the refinement, a number of critical decisions must be made prior to the collection of the step intensities. For constant wavelength diffractometers, these decisions relate to the wavelength, beam collimation, range of diffraction angles, angular distance between steps, and counting time (X-rays) or monitor setting (neutrons) at each step. The effect of the first three of these factors is well known, but the selection of appropriate values for the counting time T (in effect, the intensity) and for the step interval (which, for a given scan range, determines the number of steps, N) is not straightforward. In fact, N and T are usually chosen more by tradition or by pressure of instrument time than by a consideration of their possible effect on the results of the analysis.

Since each measured step intensity is used in the Rietveld method, the number of ‘observations’, N, in a scan can be made arbitrarily large (independent of the number of Bragg reflections) by decreasing the step interval. It is, however, the intensities of the Bragg peaks that are the fundamental quantities in any structure analysis, not the step intensities themselves. Thus, although the precision of the peak intensity measurement is improved by increasing N or T, this only occurs up to the point where counting variance becomes negligible in relation to other sources of error; further increases provide no additional structural information.

Systematic studies of the effect of variations in T indicate that the optimum value of the maximum step intensity is only a few thousand counts. If significantly larger numbers of counts are accumulated, the accuracy of the structural parameters is not improved, time is wasted, and the usual weighting scheme based on counting variance becomes inappropriate (i.e., the parameter esd's reflect their precision rather than their accuracy). In the case of step width, the optimum value is between one-fifth and one-half the minimum full-width at half-maximum (FWHM) of well-resolved peaks, the exact value depending on T and the complexity of the diffraction pattern. Smaller steps provide little or no improvement in parameter accuracy (especially when step intensities are large) and, at the same time, introduce serial correlation between adjacent residuals in the profile, again leading to wasted time and corruption of the esd's.

In practice, it is the combination of N and T chosen for the experiment that is of greatest importance in determining the efficiency of the data collection strategy. If the pattern has many overlapping peaks, N should be large, corresponding to a step interval of about FWHM/5, to provide adequate peak resolution, and T should be correspondingly small to minimize serial correlation. For a fixed total data collection time, a given level of Rietveld precision can be achieved more efficiently by the use of large N and small T than by combinations of small N and large T. The implications of these restrictions for ‘real-time’ data collection are noteworthy.

Due to the extraordinary beam characteristics of the new PETRA III synchrotron, i.e., the high brilliance, the extremely low emittance of 1 nm rad, and the high fraction of coherent photons even in the hard X-ray range, the imaging beamline (IBL) at PETRA III will provide state of the art imaging and tomography capabilities with resolution well into the nanometer range. Novel applications of tomographic techniques allow for high speed in situ measurements as well as highest spatial and density resolutions. Additionally, the highly coherent beam enables the application of phase contrast methods in an exceptional way. Since the focus is on the energy range between 5 and 50 keV, the IBL will among others be ideally suited for microtomography and nanotomography on small engineering materials science samples as well as for studying soft matter, bones, medical implants, and biomatter.

The possibilities of modelling the diffraction profiles from bimodal microstructure in computer program MSTRUCT are demonstrated on two examples. A special “Double Component” profile effect can be utilized for such problems. At first it was applied to an analysis of a mixture of two nanocrystalline anatase powders with different crystallite sizes and the relative ratio of both components was determined from X-ray diffraction data. In the second case study, diffraction peaks from a pure polycrystalline copper sample treated by equal channel angular pressing were fitted using a two-phase model of large recrystallized defect-free grains and ultrafine crystallites with high dislocation density. The method is shown to be suitable for determination of the relative fraction of the microstructural components as well as other parameters (e.g. dislocation density).

X-ray diffraction (XRD) and X-ray fluorescence (XRF) are widely used analytical techniques for materials characterization; the information they provide can be considered complementary, as the former is mostly used to obtain crystallographic information and analyze phase content, whereas the latter is sensitive to elemental composition. Many researchers and technologists working in a variety of application fields already use them together in some sort of a “combined” approach, by separately performing XRD and XRF data collection and analysis on the same sample and then comparing the analytical results obtained to integrate and complement the respective analytical information. In this work, we propose a true combined approach to merge both XRD and XRF data acquisition and analysis. Custom analytical X-ray instrumentation has been developed to perform the simultaneous data acquisition, by using a single X-ray source and dedicated detectors to collect the diffracted and fluorescent X-ray photons from the same sample volume. Additionally, a combined XRD/XRF data analysis methodology has been implemented by extending Rietveld based code to incorporate the full pattern fitting of XRF spectra starting from the phases instead of a simple matrix elemental composition. We report two analytical examples from different application fields to better illustrate the capabilities of the proposed approach.

Investigation into the early hydration of Portland cement was performed by in situ X-ray diffraction (XRD). Technical white cement was used for the XRD analysis on a D5000 diffractometer (Siemens). All diffraction patterns of the in situ measurement which were recorded up to 22 h of hydration at defined temperatures were analyzed by Rietveld refinement. The resulting phase composition was transformed with respect to free water and C-S-H leading to the total composition of the cement paste. The hydration reactions can be observed by dissolution of clinker phases as well as by the formation of the hydrate phases ettringite and portlandite. With increasing temperatures the reactions proceed faster. The formation of ettringite is directly influenced by the rate of dissolution of anhydrite and tricalcium aluminate (C3A). The beginning of the main period of hydration is marked by the start of portlandite formation. The experiments point out that a quantitative phase analysis of the cement hydration is feasible with standard laboratory diffractometers.

The crystal structure of La1−xSrxCoO3−δ (0≤x≤0.6) has been studied, using powder X-Ray diffraction. The crystal structure shows a transition from rhombohedral distorted perovskite for LaCoO3−δ into cubic perovskite for La0.4Sr0.6CoO3−δ. The cubic unit cell parameter is ac=3.8342(1) Å for La0.4Sr0.6CoO3−δ, the space group probably being Pm3m. Using a hexagonal setting, the cell parameters for La0.5Sr0.5CoO3−δ, are a=5.4300(3) Å, c=13.2516(10) Å; a=5.4375(1) Å, c=13.2313(4) Å for La0.6Sr0.4CoO3−δ; a=5.4437(1) Å, c=13.2085(5) Å for La0.7Sr0.3CoO3−δ; a=5.4497(2) Å, c=13.1781(6) Å for La0.8Sr0.2CoO3−δ and a=5.4445(2) Å, c=13.0936(6) Å for LaCoO3−δ with the space group probably being R3c.

The first object was to develop an X-ray diffractometric method for the detection and quantification of crystalline sucrose when it occurs as a mixture with amorphous sucrose. Standards consisting of amorphous sucrose physically mixed with 1 to 5 weight percent crystalline sucrose were prepared. The sum of the background subtracted integrated intensities of the 12.7°2θ (6.94 Å) and 13.1°2θ (6.73 Å) sucrose diffraction peaks were linearly related to the weight percent crystalline sucrose. The limits of detection and quantitation of crystalline sucrose were 0.9% and 1.8% w/w, respectively. The second object was to study the kinetics of crystallization of sucrose as a function of temperature (at 102, 105 and 110 °C under a water vapor pressure of 0 Torr) and water vapor pressure (17.4, 19.8 and 21.4 Torr at 27 °C). In all cases, the crystallization kinetics was best described by the Avrami-Erofe’ev model (three-dimensional nucleation).

The crystal structure of the two isostructural rare earth tungstates Ln6WO12 (Ln=Y, Ho) has been refined by the Rietveld method from X-ray powder diffraction data. They crystallize with a three-dimensional rhombohedral structure (S.G. R3¯ and Z=3 for the R-centered setting) closely related to that of the binary oxides Ln7O12 and deriving from the ideal fluorite structure. Final refinements, with isotropic thermal motion for each atom, resulted in profile and structure factors Rwp=0.166, RF=0.037 with Ln=Y and Rwp=0.121, RF=0.040 with Ln=Ho. The rare earth element is sevenfold coordinated with Ln–O bond lengths ranging from 2.19 to 2.70 Å for Y6WO12 and from 2.18 to 2.68 Å for Ho6WO12; the coordination polyhedron may be described as a monocapped trigonal prism. The tungsten atom is located at the center of a WO6 octahedron with a unique W–O distance of 1.98 and 1.92 Å for Y6WO12 and Ho6WO12, respectively.

A new method for the quantification of montmorillonite by full-profile Rietveld analysis of the XRD profile is presented. A measured standard XRD pattern of Algerian bentonite was used to construct a universally applicable montmorillonite (hkl) file for use with a P.C. based Rietveld XRD quantitative analysis system, SIROQUANT. “Universal” means that the standard file can be used for montmorillonites from other localities. The validity of the montmorillonite standard profile was tested with weighed mixtures of quartz and different standard montmorillonites. The results show the montmorillonite observed (hkl) file is generally applicable (i.e., universal), and can be used to quantify montmorillonite in any mineral without modification or chemical treatment of the sample. Two halfwidth functions were used for the montmorillonite, corresponding to the sharp (hk0) and broad (hkl) classes of reflections. A March preferred orientation parameter for montmorillonite was also refined.

External standard and internal standard calibrations are important procedures for achieving high accuracy in X-ray powder diffraction studies. The theoretical basis as well as procedures for obtaining calibration curves are given. Methods and examples of selecting Standard Reference Materials (SRMs) which are produced and issued by the National Bureau of Standards (NBS), and procedures of sample preparation with these standards are also described. Three examples are presented to indicate the value of using SRMs.

CaMnO3 is a parent compound for numerous multicomponent manganese perovskite oxides. Its crystallographic data are of primary importance in the science and technology of functional CaMnO3-based materials. In the present study, data were collected for a CaMnO3 sample at 302 K. The crystal structure refinement yields accurate absolute values of lattice parameters, a=5.281 59(4) Å, b=7.457 30(4) Å, and c=5.267 48(4) Å, leading to orthorhombic distortion of (c/a, √2c/b)=(0.997 33,0.998 95). The orthorhombic distortion of the CaMnO3 structure is discussed on the basis of comparison of our unit-cell size with data already published. At a graphical representation of the distortion, it is observed that there is a considerable scatter of the distortion values among the literature data but, interestingly, a considerable fraction of experimental results (including the present one) for stoichiometric samples are grouped around the distortion (c/a, √2c/b)=(0.9973,0.9990), which lies close to a maximum in the extent of orthorhombicity. The influence of off-stoichiometry on the orthorhombic distortion is discussed on the basis of available experimental data. Simulations, employing a mean-field approach for low temperatures, predict an increase in cell volume and structural distortions with the concentration of oxygen vacancies when the additional electrons are localized on the manganese. A simple model of delocalization produced the opposite effect, which is expected to combine with lattice vibrations to recover the cubic phase at high temperatures.

Because of their potential to induce a number of pathological diseases and their widespread industrial usage in the past, the fibrous minerals forming asbestos have been the subject of a number of studies in the past. Although quantification of asbestos minerals by optical and electron microscopy (SEM, TEM) is a routine technique in the case of dispersed airborn fibers, the detection and the quantification of small amount of fibrous minerals like chrysotile in bulk materials such as building materials is exceedingly difficult. A method for the detection and evaluation of asbestos minerals in massive samples is described, based on a combination of Rietveld and RIR (Reference Intensity Ratio) methods. Lower detection limits are about 0.5-1.0 wt % for chrysotile, depending on powder pattern, counting statistics, and matrix absorption. The chrysotile wt % determined on powder diffraction profiles collected on a conventional instrument is precise to about 1.0 wt % absolute (relative error in the range 0-10%). The technique is of straightforward application. If compared with the commonly used microscopic or spectroscopic techniques, it is of much advantage from the point of view of time, and the results are more accurate and statistically significant of the bulk material. A model for the cylindrically disordered structure of fibrous chrysotile is especially developed for the simulation of the X-ray powder patterns, and it is proposed here.

New ternary compounds of Ca14Al10Zn6O35 and Ca3Al4ZnO10 compositions have been synthesized in the CaO–Al2O3–ZnO system. Single crystals of the new compounds have been grown, and crystal structures and crystallochemical properties were established. The phenomenon of heterovalence isomorphous statistical substitution of aluminium for zinc in alumino-oxygen tetrahedra has been established. It is now possible to synthesize a large group of new ternary compounds, the compositions of which are similar to that of spinels. The structure and properties of the new phases are presented.© 1997 International Center for Diffraction Data.