In the absence of single crystals, silver(I) 3,5-dimethylpyrazolate, [Ag(dmpz)]3, has been structurally characterized by ab initio X-ray powder diffraction, using conventional laboratory data. Its crystals are triclinic, P1¯, with a=8.0876(10), b=11.1204(13), c=11.6136(16) Å, α=68.293(6), β=78.350(7), and γ=81.243(6)°. The structure has been solved by Patterson, difference Fourier, and geometrical modeling, and ultimately refined by the Rietveld method down to Rp=0.068, Rwp=0.085, and RF=0.055, for 4300 observations in the 17<2θ<103° range. Each molecule consists of a cyclic, trimeric assembly of Ag(dmpz) fragments, with the dmpz ligand bridging, in the exo-bidentate mode, nonbonded Ag…Ag edges.

Stress in the early stages of growth has been measured in α-Al2O3 (alumina) scales formed on FeCrAl- and NiAl-based alloys during heating in air at 1000 °C to 1200 °C. Scale thickness ranges from 0.5 to 5 μm, times from 5 to 720 min. Stress was measured using the multiple-tilt method. In order to measure the thinnest scales at the earliest times, focused, monochromatic synchrotron radiation was used for high intensity, and a fixed, small angle of incidence was used along with an appropriate wavelength to maximize scattering from the film relative to the background from the substrate. Depending on the composition, transient tensile stresses of up to 1.2 GPa were observed, with maximum stress at times ranging from >10 h at 1000 °C to <10 min at 1200 °C. Thermal stresses induced by an abrupt temperature change were found to relax much more quickly, suggesting that the kinetics observed during isothermal growth reflect a dynamic competition between stress generation and stress relaxation. These results challenge commonly accepted models of growth stress in scales that predict that a compressive stress will be generated as the metal converts to a larger-volume oxide in a constrained location such as an interface. The observed tensile stress may be due to another mechanism altogether (e.g., grain coalescence), or to the conversion of a transitional Al2O3 to the equilibrium α-Al2O3 phase. For one composition, transitional Al2O3 is observed during the period of tensile stress

The crystal structure of cobalt(II) acetate tetrahydrate, Co(C2H3O2)·4H2O, has been refined using single-crystal, laboratory powder, and synchrotron powder diffraction data, both individually and in various combinations. The compound crystallizes in the monoclinic space group P21/c, with a=4.80688(3), b=11.92012(7), c=8.45992(5) Å, β=94.3416(4)° at 27 °C, and Z=2. The crystal structure consists of discrete centrosymmetric trans-Co(C2H3O2)(H2O)4 complexes, linked by a three-dimensional network of hydrogen bonds. Each complex participates in 14 hydrogen bonds, 12 intermolecular, and 2 intramolecular. Compared to the single-crystal refinement, refinement of laboratory powder data yielded an average difference in bond distances of 0.02 Å, in bond angles of 3°, and in root mean square atomic displacements of 0.07 Å. The standard uncertainties of the bond distances were 0.01 Å, compared to the 0.001–0.002 Å in the single-crystal refinement. Refinement of the synchrotron powder data yielded improved accuracy and precision. It proved impossible to locate or refine hydrogen positions using a single-powder dataset, but the hydrogens could be refined using rigid groups in a joint refinement of the two powder datasets. Even from powder refinements, it is possible to obtain suitable accuracy and precision to distinguish C–O and C=O bonds, and to examine details of chemical bonding.

In this study, the application of (an)isotropic size determination using a recently proposed model for the double-Voigt approach is demonstrated and validated against line profile simulations using the Whole Powder Pattern Modelling approach. The fitting of simulated line profiles demonstrates that the attained crystallite sizes and morphologies are in very reasonable agreement with the simulated values and thus demonstrate that even in routine application scenarios credible size and morphology information can be obtained using the double-Voigt approximation. The aim of this contribution is to provide a comprehensive introduction to the problem, address the practical application of the developed model, and discuss the accuracy of the double-Voigt approach and derived size parameters. Mathematical formulations for the visualization of modeled morphologies, supporting the application of the recently developed macros, are additionally provided.

μPDSM, a powder diffraction search/match system, is derived from the original interactive time-sharing system written for the NIH/EPA Chemical Information System. Transformed and essentially rewritten, it still searches the entire JCPDS database, but on an inexpensive IBM PC microcomputer. In the transition from mainframe to micro, μPDSM has lost none of its speed or performance. Indeed, the basic discriminating power of the search/match algorithms had to be improved, since the Powder Diffraction File is some 50% larger than it was when The CIS version was in operation. While μPDSM will solve typical problems on a “push-button” mode, it provides an environment that promotes optimization of search parameters by the diffractionist, and provides all of the subfile and chemistry functions associated with larger systems.

We have calculated X-ray powder-diffraction data for schoepite, [(UO2)8O2(OH)12](H2O)12, using unit-cell and atomic parameters from the crystal structure (a 14.337, b 16.813, c 14.781, Z=4, Dx=4.87 gcm−3). Schoepite crystallizes in space group P21ca but is strongly pseudo- centrosymmetric, and observed reflections (Irel>0.1%) conform to space group Pbca. The six strongest reflections for schoepite are [d(Å), hkl (relative intensity)] 7.365, 002 (100), 3.253, 242 (55), 3.626, 240 (36), 3.223, 402 (25), 3.683, 004 (20), 2.584, 244 (18). The calculated intensities of reflections that distinguish space group Pbca from space group Pbna (the space group of metaschoepite), i.e., h0l with h odd and l even, are weak, and may not be evident in experimental powder patterns. The a axis of schoepite (14.34 Å) is significantly longer than that of synthetic metaschoepite (13.98 Å), and the two phases can best be distinguished by their unit-cell parameters. However, potential overlap of the strongest reflections can make identification and unit-cell determination difficult, especially for fine-grained material. Natural samples commonly contain intergrowths of schoepite, metaschoepite, and dehydrated schoepite. The calculated powder pattern for schoepite agrees well with data reported for natural schoepite (PDF 13-241) but shows discrepancies with the data from synthesis products. Data for “synthetic schoepite” indicate that this product was a mixture. Powder data labeled “paraschoepite” in the Powder Diffraction File do not correspond to the mineral of that name.

The new compound, KCr3(SO4)2(OH)6, was prepared by low-hydrothermal synthesis. The structure was refined by the Rietveld technique in space group (Z = 3), a =7.2416(3) Å, c = 17.0788(9) Å, V = 775.63 Å3, Rp = 7.7, Rwp =10.1, RB = 6.8. The compound is isotypic with alunite, KAl3(SO4)2(OH)6. The temperature of decomposition under nitrogen atmosphere to a hitherto unknown form is about 550 K. The water content of alunite-type compounds is discussed.

Improved powder XRD patterns for the titanium suboxides, TinO2n−1 (4≤n≤9), have been calculated from published single-crystal structures. To provide the best match with experimental data, the entire diffraction traces were simulated, and d-spacings and intensities extracted in the same manner as from experimental traces. The accuracy of the new patterns has been verified by comparison with measured powder patterns, particularly in the case of the n=4 and n=5 compounds where single-phase powders can be prepared relatively easily. Difficulties experienced preparing higher homologues have been related to the thermodynamic properties of this system.

Representative compounds of the new family of magnetic materials Gd5−xNdxSi4 were analyzed by X-ray diffraction at the XRD1 beamline at Laboratório Nacional de Luz Síncrotron. To reduce X-ray absorption, thin layers of the powder samples were mounted outside the capillaries and measured in Debye–Scherrer geometry as usual. The XRD analyses and the magnetometry results indicate that the behavior of the magnetic transition temperature as a function of Nd content may be directly related to the average of the four smallest interatomic distances between different rare earth sites of the majority phase of each compound. The quality and consistency of the results show that the XRD1 beamline is able to perform satisfactory XRD experiments on high-absorption materials even off the best conditions.

An increasingly frequent used sample holder, the zero-background holder (ZBH), is evaluated for use in external standard calibration of powder patterns. The effectiveness of the ZBH calibration method is determined by comparison to the conventional internal- and external-standard calibration techniques. The three calibration methods are compared using the results of lattice parameter refinements of test powders, using Si as the standard. Several test materials were used in the evaluation which cover a wide range of absorption coefficients so sample transparency effects can be distinguished from sample displacement effects. Results of the calibrations clearly indicate that the ZBH method gives precision and accuracy comparable to the internal-standard method, and significantly better than the external-standard technique. In addition, the ZBH method yields substantially better results than the internal-standard method for materials with low absorption coefficients. Low-angle calibrations are also made on a ZBH using a proposed standard, silver behenate, which has peaks from 1.5° to 20° 2θ. These calibrations have shown that if care is not taken to establish a monolayer of powder on the ZBH crystal, significant errors in refined lattice parameters will result.

Based on high purity constituents ternary AlFeSi intermetallic phases were prepared and annealed at 600°C for a month with compositions close to that of αH-AlFeSi (Al8Fe2Si) phase (∼8 wt.% Si, ∼32 wt.% Fe). The powder diffraction patterns and the chemical compositions of the different αH-AlFeSi intermetallic compounds formed as major components in the samples were investigated by X-ray powder diffraction and electron microprobe analysis, respectively.

A complete powder diffraction pattern is presented for the αH-AlFeSi intermetallic phase with 8 wt.% silicon and 33.5 wt.% iron content formed almost congruently. The refined cell parameters are given as

a = 12.4056 (7) Å

c = 26.236 (2) Å

Comparing the observed intensities with intensities calculated from single crystal data, gave very good agreement.

The lattice parameters of αH-AlFeSi phases with different silicon content were refined by the least-squares method. A contraction of the unit cell caused by the increase of the silicon content in the phase can be observed. Relative changes of the cell dimensions for 1 wt. % increase in silicon are −0.06%, −0.09 % and −0.21 % for the parameters a and c and for the unit cell volume, V, respectively.

Ongoing software developments for creating three-dimensional (3D) printed crystallographic models seamlessly from Crystallographic Information Framework (CIF) data (*.cif files) are reported. Color versus monochrome printing is briefly discussed. Recommendations are made on the basis of our preliminary printing efforts. A brief outlook on new materials for 3D printing is given.

Powders of Al and Ti were blended and compacted, the compact then melted in an attempt to produce single phase Al3Ti. Optical microscopy of the cast and homogenized specimen revealed an almost single phase microstructure with minor amounts of a second phase. The composition of the matrix was measured using fully quantitative energy dispersive X-ray analysis. By use of X-ray diffractometry, the interplanar spacings and the associated integrated peak intensities were experimentally measured for the binary DO22 compound, Al3Ti. Using standard structure factor equations, the intensities were calculated for the various reflections. Good agreement was obtained between calculated and observed intensities.

The structures of orthorhombic (a=5.5686(2)Å, b=9.8946 (2)Å, c=3.19369(12Å) and cubic (a=9.177(3)Å) Cd2SnO4were refined by Rietveld analysis of X-ray powder diffraction patterns. Both of these polymorphs were chemically treated with hydrogen gas mixtures at 400°C, resulting in a colour change from yellow to green. Small structural changes were observed for the orthorhombic material, which underwent a uniform contraction (≈0.02%) of cell size and movement of some oxygen atoms towards the tin atoms. Evidence for loss of structural oxygen was sought, but could not be found above the detection limit of 0.3%. Cubic Cd2SnO4possesses the spinel structure with a large (at least 65%) degree of inversion. Samples prepared with a smaller cell have so far proved unsuitable for Reitveld analysis.

An analysis of the microstructure of nanocrystalline cerium oxide produced by thermal decomposition of cerium (IV) oxide nitrate at temperatures in the range 230° to 960 °C is described. Parameters describing the breadths and shape of X-ray diffraction line profiles were obtained by means of pattern decomposition and a method based on the Voigt function was used to obtain information on the temperature dependence of the microstructure. No marked anisotropy in size and strain broadening was observed. It was found that the crystallites are on average spherical, the dimensions increasing significantly with formation temperature, while microstrains decrease with annealing temperature. The results of size determinations were compared with SEM measurements. They suggest a competition between the crystallite growth and “particle” growth processes in the initial sintering of the loosely packed cerium oxide powder.

Neutron diffraction provides a direct probe for the ordering of spins from unpaired electrons in materials with magnetic properties. The ordering of the spins can be modeled in many cases by adding spin directions to standard crystallographic models. This requires, however, that crystallographic space groups be extended by addition of a “color” attribute to symmetry operations, which determines if the operation maintains or flips the direction of a magnetic spin. Rietveld analysis provides a mechanism for fitting magnetic structure models to powder diffraction data. The general structure and analysis system (GSAS) software suite is commonly used for Rietveld analysis and includes the ability to compute magnetic scattering. Different approaches are commonly used within GSAS to create models that include magnetism. Three equivalent but different approaches are presented to provide a tutorial on how magnetic scattering data may be modeled using differing treatment of symmetry. Also discussed is how magnetic models may be visualized. The commands used to run the GSAS programs are summarized within, but are shown in great detail in supplementary web pages.

The compressive stress distribution below the specimen surface of severely surface deformed steels by shot peening was investigated by using laboratory X-rays and high-energy X-rays from a synchrotron radiation source, SPring-8 in the Japan Synchrotron Radiation Research Institute. Medium carbon steel plates were heat treated in two different conditions. The Vickers hardness of materials A and B after heat treatment is 408 and 617 HV, respectively. The specimens were shot peened with fine cast iron particles of the size of 50 μm. The coverage was selected to be 5000%. For the synchrotron radiation, by using the monochromatic X-ray beam with several energy levels, the stress values at the arbitrary penetration depth were measured by the constant penetration depth method. The shot-peened specimens were fatigued under four-point bending. The improvement of fatigue strength of material A was not so large because of large surface roughness. On the other hand, for material B, the surface roughness was smaller and the fatigue strength was higher than that of ground specimens.

Standard Reference Materials (SRM) are stable materials which have one or more properties certified by the National Bureau of Standards. A general introduction is given to the types of SRM's and their certification. SRM's for X-ray diffraction are described in detail, including their intended use and their certified and other properties. New SRM's are under consideration as quantitative standards, intensity and line shape standards, and materials properties standards.

Pearson VII functions, some of the most useful descriptions of the intensity distribution within the X-ray powder reflection, have been used to study distortion in the perovskite-type structure of KMnF3. Separate full-widths, Δ, at half-maximum intensity, and Pearson exponents, m, were taken for the low- and high-angle sides of the profiles. The background was assumed to be linear. For the distorted structure, summation was made over all overlapping lines that might possibly contribute to the observed profile. Measurements were performed using a powder diffractometer with a specially adapted electronic system consisting of an automatic data recorder and a method, developed at this laboratory, for transferring data to an IBM PC/AT computer. By these means it could be shown that at 10° K the crystal structure of KMnF3distorts from cubic to monoclinic.