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.

The analysis of crystalline organic phases by X-ray powder diffraction presents special problems, beyond those typically associated with inorganic materials. The large unit cells often associated with organic compounds, combined with the low symmetry of the structures, give rather complicated diffraction patterns that contain many low angle lines. The Bragg–Brentano geometric arrangement employed in most commercial diffractometers gives maximum (d-spacing error at low diffraction angles. This geometry, in turn, means that not only can the large (d-spacing data be of poor quality, but also that much of the low angle data required for the indexing of the pattern is subject to large errors.

Line profiles of a powder diffraction pattern and the aberrations which affect the centroid and the variances of the peaks have been analyzed using the visualization in scientific computing (ViSC) systems. The constrained optimization of those aberrations has been derived from the theory developed by Wilson (1963). It allows the determination of systematic instrumental effects and gives indication of other diffraction effects related to the samples. The CuKβ radiation was used to process the experimental data directly as it is comprised of only one single wavelength.

Improvements of standard X-ray powder diffractograms of two Y-type hexagonal ferrites (Ba2Co2Fe12O22, Ba2Zn2Fe12O22) are reported.

The effect of crystallite-size distribution on the shape of X-ray diffraction peaks from powder samples is investigated focusing the attention on the region within the top half of intensity. It is shown that, unlike profile tails, this central region can markedly depart from the Lorentzian shape for crystallite-size distributions that are quite acceptable from the physical point of view. Goal of this paper is to correlate the well-known m parameter in the Pearson VII function or the η weight in the pseudo-Voigt function with a number of different distributions of crystallite dimensions ranging from the δ function of all-equal-sized crystals to a very broad distribution. The suitably normalized curvature at the peak is a possible new parameter; its correlation with m and η is shown. Also, a procedure is suggested to derive the volume-average crystal thickness 〈Tw〉 from the FWHM and the knowledge of either m or η.

X-ray powder diffraction of Nitrofurantoin C8H6N4O5 reveals that the compound crystallizes in a monoclinic unit cell with the powder data unit cell parameters of a = 7.852(2), b= 6.497(1), c = 18.927(5) Å, β=93.15(2)°, V=964.1(2) Å3. The unit cell dimensions determined by single crystal agree very well with those of powder diffraction analysis. A comparison with the Powder Diffraction File (PDF) 34-1603 indicates that the present data provide a more precise match to the unit cell, include additional weak reflections, along with the indexing of the powder pattern.

Plastic crystals, such as neopentylglycol, 2, 2-dimethyl-1,3-propanediol, that exhibit polymorphic behavior are emerging materials for thermal energy storage. The energy is stored isothermally in the γ phase, FCC, during solid-state phase transformations. This γ phase of NPG has been determined as an orientational disordered phase. The low temperature α phase structure, which is of great significance in the evaluation of lattice expansions and other parameters, was first determined in 1961. However, the reported unit cell dimensions and the intensities of the reflections led to erroneous indexing of the powder patterns in binary systems. The α phase structure is redetermined here as monoclinic, M= 104.15 amu, space group P21/n (an alternate setting of , space group No. 14), a = 5.979(1)Å, b= 10.876(2)Å, c=10.099(2)Å, β=99.78(1)°, V=647.2(2)Å3 at 20°(± 1)C, Dx= 1.069 g cm s−3 for Z=4. In this paper the redetermined structure of the α phase of NPG is presented in projections of the atomic positions, in tables, and in calculated powder pattern and these results are compared with those reported by others. The powder patterns obtained from the Bragg–Brentano diffractometer are compared with our calculated pattern from the single crystal data. The structural parameters of the high temperature phase of NPG as determined by a Guinier diffraction system are also reported.

A new and improved sample holder suited for small samples has been developed for X-ray diffractometry. This holder is made from a commercial semiconductor grade of silicon wafer grown and cut along the [100]-axis, i.e., Si(100). This new holder not only meets almost all basic requirements of an ideal holder, namely, flat and damage free surface, low background noise, few interference peaks, and desired shape with different cavity sizes, but also provides additional advantages for measuring crystallite sizes and mass absorption coefficients. Furthermore, this holder is easy to clean and has good appearance because of its polished surface. A U.S. patent has been issued and a commercialization effort is underway.

A direct method is described for determining depth profiles (z-profiles) of diffraction data from experimentally determined τ-profiles, where z is the depth beneath the sample surface and τ is the 1/e penetration depth of the X-ray beam. With certain assumptions, the relation between these two profile functions can be expressed in the form of a Laplace transform. The criteria for fitting experimental τ-data to functions which can be utilized by the method are described. The method was applied to two τ-data sets taken from the literature: (1) of residual strain in an A1 thin film and (2) of residual stress in a surface ground A12O3/5vol% TiC composite. For each data set, it was found that the z-profiles obtained were of two types: oscillatory and nonoscillatory. The nonoscillatory profiles appeared to be qualitatively consistent for a given data set. The oscillatory profiles were considered to be not physically realistic. For the data sets considered, the nonoscillatory z-profiles were found to lie consistently above the corresponding τ-profiles, and to approach the τ-profiles at large z, as expected from the relation between the two.

CeO2 transforms to an orthorhombic PbCl2-type structure at a pressure of about 31 GPa. The phase transition is accompanied by a 9.8% volume contraction. The bulk modulus of the low-pressure fluorite-type structure is 236(4) GPa. Comparisons are made with the high-pressure behaviour of UO2 and ThO2.

A new compound [Mn(H2O)]0.25(VO)0.75PO4·2H2O was prepared by the reaction of V2O5 with the boiling aqueous solution of H3PO4 and KMnO4. The reaction product is a yellow-brown powder, stable in air. The tetragonal unit-cell parameters (298 K) are a = 6.2034(2)Å, c = 13.814(1)Å, V = 531.59Å3, Z = 4, Mr = 194.94, Dx = 2.493 g/cm3, Dexp = 2.52 g/cm3. X-ray (CoKα radiation) powder diffraction data (35 lines) are reported. The compound's structure is probably derived from the VOPO4·2H2O layered lattice by substitution of [Mn(H2O)]3+ ions for a quarter of the vanadyl groups VO3+. Practically the same powder data and unit-cell parameters were found for [Mn(H2O)]x(VO)1−xPO4·2H2O, where x ranges from 0.185 to 0.25.

The title compounds crystallize in the cubic space group Fd3m, Z = 8, with cell parameters of 8.2958(37) Å for NiFeGaO4 and 8.3921(24) Å for ZnFeGaO4. By comparison of experimental and calculated patterns with various site distribution models, ZnFeGaO4 has been determined to have the normal spinel structure and NiFeGaO4 a dominantly inverse spinel structure.