In conventional multiphase Rietveld refinement, now being used for quantitative phase determination, the crystal structure of each phase needs to be known in order to generate a calculated standard pattern of the phase to be refined against the measured XRD pattern. This is a disadvantage when the structural data for a phase are imperfect or unknown and may prevent an analysis.

A method is given whereby a phase with an imperfectly known or unknown crystal structure can be included in a multiphase Rietveld refinement, with other well-characterised phases, by use of an empirical or “observed” hkl file for that phase, with the SIROQUANT software package. The amplitudes 1F(hkl)1 in the empirical hkl file of the phase generate a reference profile for it which agrees with a measured standard pattern of the phase. Methods are given for the creation and scaling of empirical or “observed” phase hkl datasets. The Rietveld variable parameters (preferred orientation, linewidth, lineshape and unit cell) are refinable in the usual way for a phase with an empirical hkl dataset.

The family of zeolitic imidazolate framework (ZIF) compounds is efficient sorbent materials that can be used for catalytic, ion exchange, gas storage, and gas separation applications. A high-resolution reference X-ray powder diffraction pattern for one of the ZIF members, bis(2-methylimidazolyl)-zinc, C8H10N4Zn (commonly known as ZIF-8), was determined using synchrotron diffraction data obtained at the Advanced Photon Source (APS) in Argonne, IL. The sample was confirmed to be cubic I-43m, with a = 17.01162(6) Å, V = 4932.08 Å3, and Z = 12. The reference X-ray powder diffraction pattern has been submitted for inclusion in the Powder Diffraction File (PDF).

Eighty specimens of cellulosic materials were analyzed over a period of several years to study the diffraction characteristics resulting from polymorphism, crystallinity, and chemical substitution. The aim of the study was to produce and verify the quality of reference data useful for the diffraction analyses of cellulosic materials. These reference data can be used for material identification, polymorphism, and crystallinity measurements. Overall 13 new references have been characterized for publication in the Powder Diffraction File (PDF) and several others are in the process of publication.

The structure of a high-pressure polymorph of glycine (the β′-polymorph formed reversibly at 0.8 GPa from the β-polymorph) was determined from high-resolution X-ray powder diffraction data collected in situ in a diamond anvil cell at nine pressure points up to 2.6 GPa. X-ray powder diffraction study gave a structural model of at least the same quality as that obtained from a single-crystal diffraction experiment. The difference between the powder-diffraction and the single-crystal models is related to the orientation of the NH3-tails and the structure of the hydrogen-bonds network. The phase transition between the β- and β′-polymorphs is reversible and preserves a single crystal intact. No transformations were observed between the β-, α-, and β′-polymorphs on compression and decompression, although the α- and β′-polymorphs belong to the same space group (P21/c). The instability of the β- and γ-forms with pressure can be predicted easily when considering the densities of their structures versus pressure. The direction of the transformation (i.e., which of the high-pressure polymorphs is formed) is determined by structural filiation between the parent and the high-pressure phases because of the kinetic control of the transformations.

Improved X-ray powder diffraction data for orthorhombic phosphorus, S.G. C mca (64) obtained in situ at synthesis conditions of 1.2 GPa and 1100 K, are described. Representative, as synthesized, data include 2.552X, 3.3204, 2.5953, 5.1912, 1.6302, for least-squares unit-cell a=3.3182(6) Å, b=10.3744(18) Å and c=4.3227(9) Å. As an illustration of the quality of the data, the structure was solved from powder XRD and Rietveld refined to give a=3.3199(2) Å, b= 10.3678(4) Å, c=4.3154(2)Å, and V=148.535(12) Å3 with the P atom on 8f (1/2, y,z) with y=0.1044(22) and z=0.9179(7).

The texture index introduced by Harris (1952) is reconsidered from the point of view of the orientation distribution of crystallites in a flat powder specimen. It is shown that the texture index can be used as an approximate measure of texture degree or as a texture correction factor in cases of a weak texture. Its failure in both these aspects for the strong textures is caused by an incorrect averaging of pole densities contained in the original definition of this quantity.

In recent years, grazing incidence angle attachments have been shown to be very useful in the phase identification of thin polycrystalline films. These devices are sold commercially as attachments to standard powder diffractometers. The attachment normally consists of a long soller slit assembly and a flat crystal monochromator. The soller slit with or without the monochromator is mounted on the diffracted beam side. In this paper we discuss the effects of different configurations from collimator to monochromator on diffraction data. An understanding of these effects is essential in order to obtain more reliable information on phase transformations, crystallite size, microstrain, and residual stress studies.

Single-phase samples of La1−xCaxMnO3 compounds have been synthesized by solid-state reaction. Detailed Rietveld analysis of powder X-ray diffraction data showed that La1−xCaxMnO3 undergoes a structural phase transformation from R-3c to Pnma at X=0.05–0.075. There is a linear variation of lattice parameters as a function of calcium concentration. The slope of this linear variation changes at X=0.6. A correlation between observed Mn-O bond lengths, corresponding to different compositions, and possible magnetic phases is discussed.

XRF is generally considered a nondestructive analytical method in the sense that a specimen is not altered by the analytical procedure. This study is related to paintings and illuminated manuscripts, where the analytes are often inorganic pigments embedded into organic matrices such as fabrics (canvases), paper or parchment, binders, and varnish. We found that a typical measurement cycle with conventional tubes and energy dispersive systems (e.g., 100 s, 100 W tube-power) causes no visible harm. However, 3 kW radiative power for several minutes and more (as often required for wide angle scans as well as for the analysis of light elements or traces in a wavelength dispersive spectrometer) can leave visible traces of permanent yellowing, brittleness, and even mechanical decomposition. In such cases scanning electron microscopy-images indicate permanent alteration of the cellulose fibers and, in paper, of the binder. Employment of modern X-ray optical devices which focus the photons of a wide beam onto a small spot may also leave visible (and invisible) traces of destruction.

Highly uniform fine powder sample layers may be prepared for X-ray diffractometry by aerosol suspension and collection on glass fiber filter substrates. A tubular aerosol suspension chamber (TASC) has been fabricated for this purpose. Essential components include a 500 ml gas buret, 4.7-cm filter cassette, rotameter, and rotary pump. Aerosol particles are generated within the TASC buret by convection within a fluidized bed of glass beads mixed with the sample. Exceptional uniformity of load and randomness of particle orientation has been demonstrated for samples prepared with this system. For quantitative analytical work accurate intensities may be obtained using corrections to raw intensities based on fundamental sample and filter properties.

Palmierite (K2Pb(SO4)2) has been prepared via a chemical synthesis method. Intensity differences were observed when X-ray powder data from the newly synthesized compound were compared to the published powder diffraction card (PDF) 29-1015 for Palmierite. Investigation of these differences indicated the possibility of preferred orientation and/or chemical inhomogeneity affecting intensities, particularly those of the basal (00l) reflections. Annealing of the Palmierite was found to reduce the effects of preferred orientation. Electron microprobe analysis confirmed K:Pb:S as 2:1:2 for the for the annealed Palmierite powder. Subsequent least-squares refinement and Rietveld analysis of the annealed powder showed peak intensities very close to that of a calculated Palmierite pattern (based on single crystal data), yet substantially higher than many of the PDF 29-1015 published intensities. Further investigation of peak intensity variation via calculated patterns suggested that the intensity discrepancies between the annealed sample and those found in PDF 29-1015 were potentially due to chemical variation in the K2Pb(SO4)2 composition. X-ray powder diffraction and crystal data for Palmierite are reported for the annealed sample. Palmierite is trigonal/hexagonal with unit cell parameters a=5.497(1) Å, c=20.864(2) Å, space group R-3m(166), and Z=3.

Selected hydrides (TiH2, ZrH2), chlorides (VCl3, ScCl3) or oxides (V2O5) utilized as additives facilitating hydrogen release and uptake for magnesium hydride were investigated using mechano-chemical treatment and in-situ synchrotron radiation powder X-ray diffraction studies. The fastest hydrogen desorption and absorption kinetics for MgH2 was observed for a sample with 5 mol% V2O5 at 320 °C. Additional activation of the system (2 cycles, vacuum/p(H2) ~150 bar, 450 °C) leads to significant improvement of the kinetics even at lower temperatures, 270 °C. The observed prolific effect is achieved through the full reduction of vanadium oxides and formation of an efficient vanadium catalyst as nanoparticles and possibly interfacial effects in the MgO/Mg/MgH2/V system introduced during cycling hydrogen release and uptake in hydrogen/dynamic vacuum at 450 °C. Nanostructuring as well as hydrogen permeability via vanadium nanoparticles may improve kinetics and reduce the apparent activation energy for hydrogen release. Thus, the enhancement of hydrogen release/uptake in the MgH2 owe to “in situ” formation of vanadium nanoparticles by reduction of V2O5.

The crystal structure of several compounds of Ca1−xSrxZr4(PO4)6 ceramics has been investigated by X-ray powder diffraction at room temperature. All compounds form a solid solution with a unique unit cell. While the lattice parameter a of the hexagonal unit cell decreases of about 0.9% with increasing Sr content only slightly, it considerably elongates in c direction (2.8%). No structural transformation has been observed by high-temperature X-ray diffraction up to 1000 °C.

A series of BaO:RxOy:CuO materials has been prepared where R=Y, La, Ce, Pr, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. They have been characterized by X-ray powder diffraction methods. All BaR2CuO5 phases, commonly referred to as the “green phases”, are orthorhombic with space group Pbnm(62) and are isostructural. These single phase materials could be prepared with most lanthanides, except for La, Ce, Pr, Nd and Tb. Possible reasons for the exceptions are discussed. Both La and Nd tend to form a brown solid solution of Ba2+2xR4-2xCu2-xO10-2x with a tetragonal space group of P4/mbm(127). The major phases found in the Ce, Pr and Tb compositions are the perovskite-related structures BaRO3, and in the Pr case, Ba2PrCu3O6+x as well. The cell parameters of the green phase materials increase progressively from the Lu compound to the Sm compound: a ranges from 7.0506(6) to 7.2754(4) Å, b from 12. 0534(8) to 12. 4029(7) Å, c from 5.6099(5) to 5. 7602(3) Å, and the cell volume from 476.75(6) to 519.78(4) Å3. A correlation of the crystallographic data with the size of the R elements is given.

The crystal structure of four cyanometallates has been determined from X-ray powder diffraction data using the Rietveld method. The variously hydrated compounds Cu3[Co(CN)6]2, Mn3[Co(CN)6]2 and KNi[Fe(CN)6] crystallize at cubic symmetry (Fm3m) with lattice parameters 10.032(2), 10.413(3) and 10.234(5) Å, respectively. The crystal of KMn[Fe(CN)6]·2H2O shows a monoclinic structure (P21/c) with the lattice parameters a=10.108(2) Å, b=10.104(3) Å, c=10.114(3) Å, β=92°, 93°. The starting model was based on an isomorphic Mn3[Co(CN)6]2 single crystal structure, where Co and Mn ions are octahedrally coordinated by C and N atoms, respectively, forming three-dimensional bimetallic networks with the C≡N groups as bridging ligands.

To establish standard working practices and further understanding of the application of X-ray fluorescence (XRF) spectroscopy to works of art and cultural heritage materials, a series of round-robin tests have been conducted biannually since 2002. In 2008 the round-robin explored the application of XRF to the study of paintings on canvas. Thirteen samples, consisting of both modern and traditional pigments on canvas, were distributed to 25 participating institutions for analysis. The samples were designed to explore common challenges encountered in the XRF analysis of painted works including peak overlaps, sum peaks, layering/shielding effects, detection of low-Z pigments, and modern pigments. The results from representative samples highlighting each topic are discussed.

A system enabling X-ray diffraction patterns under controlled conditions of relative humidity and temperature has been devised and combined with an X-ray powder diffractometer. Relative humidity in the sample space is controlled by mixing dry N2 gas with saturated water vapor. Temperatures of the sample and inner wall of the sample chamber are monitored by two attached thermocouples and the information was fed back to the control unit. Relative humidity between 0% and the 95%, and temperature between room temperature and 60 °C can be controlled. All parameters including those for XRD are programmable and the system runs automatically. The function of the system was checked by recording the XRD patterns of montmorillonite (a clay mineral) and NaCl under increasing and decreasing relative humidity.

X-ray diffraction (XRD) line-broadening analysis has been used to determine dislocation densities in zirconium alloys with hexagonal closepacked (hep) crystal structures and a complex distribution of dislocations reflecting the plastic, anisotropy of the material. The validity of the technique has been assessed by comparison with direct measurements of dislocation densities in deformed polycrystalline and neutron-irradiated single crystal material using transmission electron microscopy (TEM). The results show that-there is good agreement between the XRD and TEM for measurements on the deformed material whereas there is a large discrepancy for measurements on the irradiated single crystal; the XRD measurements significantly underestimating the TEM observations.