Arsenic molybdate, As4Mo3015, has been investigated by means of X-ray powder diffraction. The diffraction data were collected with a focussing (Guinier-type) transmission diffractometer equipped with a primary-beam monochromator (Ge 111) for CuKα radiation and a scanning position-sensitive detection system. A monoclinic unit cell was determined using an indexing program.

The crystal structure of Cr2[Ni(CN)4]3·10H2O has been determined on X-ray diffraction powder data by means of the Rietveld method. The starting model was based on the isomorphic, disordered structure of Mn3[Co(CN)6]2·12H2O. At room temperature the crystal is cubic, F4¯3m, a=10.097(6) Å, V=1029.4(5) Å3. The structure is disordered and contains 1.33 formula weights per unit cell. The Ni and Cr ions are coordinated by N and C atoms, respectively, forming octahedra linked by CN groups. The water molecules replace partly the chromium, carbon, and nitrogen positions in the crystal. The final R values are: Rwp=0.032 (Rexp=0.023), RB=0.088, and DW-Stat.=1.31 (DWexp=1.8).

Measurements of X-ray diffraction patterns of high-Tc superconductor and tungsten–carbide powder samples using a Bragg–Brentano diffractometer showed systematic variations of the intensities for different preparation conditions. For specimens with high surface roughness, an angle-dependent decrease of the intensities is observed which is caused by the microabsorption of the X-rays due to the microstructure of the powder sample. In Rietveld analysis, the thermal parameters are strongly influenced by this effect and may tend to negative values. A realistic description of the surface structure of flat powder samples is proposed. Using an analytical approximation for the microabsorption effect and its dependence on the microstructural parameters the Rietveld refinement yields reasonable values for the thermal parameters.

High quality powder diffraction data were obtained from a specimen containing inseparable impurities, by using single crystal precession photographs to explore all possible reflections for the mineral being studied. In this manner it is acceptable to ignore weak reflections that do not index on the unit cell and that are not observed on the single crystal photographs. Triphylite is given as an example.

A commercially available photoconductor material, p-diethylaminobenzaldehyde diphenylamine hydrazone, C23H25N3, has been purified and recrystallized from an absolute alcohol solution. The triclinic compound has been characterized by X-ray powder diffraction. Experimental 2θ values corrected for systematic errors, relative peak intensities, values of d, and the Miller indices of 74 observed reflections with 2θ up to 30.5° are reported. The powder diffraction data have been evaluated, and figures of merit are reported. Unit-cell parameters least-squares refined from the 74 observed reflections of the triclinic compound are in good agreement with those obtained from the single-crystal structure analysis.

New powder X-ray data for cancrinite [ideally Na8Si6Al6O24 (CO3)2·2 H2O] are reported along with in-situ real-time thermal processes recorded using energy dispersive X-ray diffractometry (EDXD). A completely anhydrous phase is obtained after heating the sample up to 600 °C and quickly cooling it to room temperature, as shown by means of both Rietveld analysis and IR spectroscopy. The anhydrous phase does not show any tendency to re-acquire molecular water. During the heating process, at around 450 °C, a peak splitting is observed, possibly due to a reversible phase transition.

An Excel command macro has been developed which directly transforms X-ray powder diffraction data to a spreadsheet format. This spreadsheet format offers a number of data reduction and plotting capabilities not available in a diffractometer's software. The conventional approach uses computer programs to transform the data outside a spreadsheet. The development of these programs is not a simple process, and requires the user to be familiar with computer programming and the software of a diffractometer. Furthermore, these programs are diffractometer-specific. A different approach is followed in which an Excel macro transforms the data within a spreadsheet. This macro, with minor modifications, can be applied generally to treat data from any diffractometer. A copy of the macro and an example illustrating its working principle are included.

A Siemens D500 powder diffractometer has been modified to accommodate data collection and storage by an IBM microcomputer. The interface mechanism, described in detail, is simple, versatile and relatively low cost. The system performance is evaluated and further enhancements suggested.

The correct formulas for geometrical factors for correction of diffracted intensities in Seemann-Bohlin diffractometry were tested. A Huber 653 goniometer, gold and titanium nitride layers, white tin, and rutile as specimens were used in the reflection mode. A Huber 642 goniometer and olivine as a specimen were used in the transmission mode. It was found that, due to a variable specimen-detector distance during 2θ scan, the variable efficiency of the Soller slits in the diffracted beam must be taken into account. The model describing this effect analytically is presented. As a final test the structures of white tin, rutile, and olivine were refined from the measured data corrected for different factors.

The crystal structure of the Aurivillius compound Bi2BaTa2O9 prepared via the chemical route was determined by direct methods using EXPO97, and refined using the Rietveld method with conventional X-ray diffraction data. The structure was found to be tetragonal (space group I4/mmm, number 139) and Z=2, isomorphic of the Bi2BaNb2O9 reported by Blake and co-workers in the literature (1997). Two refinements were performed using the two asymmetry functions of DBWS-9807 (release 20/May/99). The unit cell for each case are: a=3.932 22(6) Å, c=25.5053(6) Å (RA) and a=3.932 50(7) Å, c=25.5069(6) Å (RCF). The differences for atom positions, interatomic distances and angles are in the range of one standard deviation. Final agreements factors are: Rwp=7.97%, S=1.84, RBragg=4.28%(RA), Rwp=7.98%, S=1.84, RBragg=4.30%(RCF). The occupancies of Ba and Bi in site 2b were refined but constrained to have their summation equal to 1.00. The same constraints were applied to the Ba and Bi of the 4e site. The results show that on site 2b there are 70% of Ba and 30% of Bi and on the site 4e there are 82% of Bi and 18% of Ba. The charge equilibrium is maintained for one standard deviation of the site occupancies.© 2000 International Centre for Diffraction Data.

Simple relationships exist between the individual phase scale factors derived from Rietveld analysis of multiphase mixtures and (i) the ‘reference intensity ratio’ used in traditional methods of discrete-peak phase analysis, (ii) the phase abundance itself and (iii) the relative pattern intensities in simulated powder patterns. These relationships are shown to follow naturally from the fundamental integrated-intensity phase-analysis equations provided in standard texts. In the event that preferred orientation, crystallinity, extinction and/or microabsorption cannot be adequately incorporated into the Rietveld models for individual phases, it is demonstrated that the Rietveld ab initio ‘pattern intensity constants’ can be scaled/calibrated experimentally, as in other whole-pattern methods of analysis, while retaining all the advantages of the Rietveld method.

Surface roughness of planar samples causes an additional attenuation of X-ray diffraction intensity measured in Bragg–Brentano geometry. The decrease of intensity becomes stronger with decreasing scattering angle. This is part of the microabsorption effect. Two quantitative expressions describing the microabsorption effect are incorporated into the DBWS 9006-PC Rietveid program [D. B. Wiles and R. A. Young, J. Appl. Crystallogr. 15, 149–151 (1981)]. The procedure is applied to scattering data obtained from YBa2Cu3O7-powder samples with different degree of surface roughness but approximately identical bulk structure. The procedure is proved to work well. However, the values obtained for the parameters of the temperature factors and the microabsorption effect are correlated, and careful discussion is necessary to interpret the results.

X-ray powder patterns for the phases in the CaO-SrO-CuO ternary system, along with the corresponding crystal structures, were obtained from the literature and from the Powder Diffraction File. Available XRD patterns were compared with each other and with a calculated pattern for each phase, yielding a recommended reference pattern. The simulated powder patterns presented here deal with the phases found within the (Ca,Sr)O, (Ca,Sr)2CuO3, (Ca,Sr)14Cu24O41, (Ca,Sr)CuO2, (Ca,Sr)Cu2O3, and (Ca,Sr)Cu2O2 solid solution series and are recommended for the Powder Diffraction File (PDF).