Release 2003 of the Powder Diffraction File (PDF) contains ∼280 000 unique entries organized in a series of tables in a relational database format. The PDF is available in two products, PDF-4/Full File and PDF-4/Organics, which allow users to access and query over 150 million filled entry fields. An editorial database is used to generate the commercial products that contain tables of experimental details and statistical evaluation criteria used by the editors to evaluate quality and determine quality marks for each entry in the PDF. This editorial database has nearly doubled the searchable entry fields. This database was mined to evaluate experimental methods in X-ray diffraction. Both experimental powder diffraction data and data calculated from predominantly single crystal X-ray structural analyses were assigned statistical quality criteria. For experimental powder data, the average delta two theta values for all d-spacings in the entry set were used. Calculated data were evaluated using R factor values as the primary quality criteria. A Quality Index, which measures the errors in refined unit cell parameters divided by the magnitude of the cell parameter, can be used to compare all types of data. Experimental variables were then analyzed versus these criteria. Variables include optic configuration, (i.e., Seeman–Bohlin, Guinier, Debye–Scherrer), use of internal and external standards, use of monochromators, wavelength divergence, wavelength selection, equipment radius, specimen transparency, and specimen absorption. This study significantly differs from prior round robin analyses in that the use of the database allows us to study very large population sets for every variable analyzed.

A Monte Carlo code for indexing powder diffraction patterns is presented. Cell parameters are generated randomly and tested against an idealized powder profile generated from the extracted d’s and I’s. Limits with this program in solving problems associated with zeropoint errors and impurity lines are examined. Most problems (V<2000 Å3, cell parameters <20 Å) are solved in less than 1–15 min if the symmetry is as low as monoclinic (with a >2 GHz processor); more time is needed for triclinic cases. Attempts are shown to be successful for the indexation of two-phase samples in simple cases (combining orthorhombic or higher symmetries). © 2004 International Centre for Diffraction Data.

Key words: powder diffraction, indexing, Monte Carlo

The crystal structure of the common expectorant guaifenesin, 3-(2-methoxyphenoxy)-1, 2-propanediol (C10H14O4) was solved by applying Monte Carlo simulated annealing techniques to synchrotron powder data, and refined using the Rietveld method. Initial structure solutions yielded an unreasonable conformation, and an unacceptable refinement. Quantum chemical geometry optimizations were used to identify the correct conformation. Guaifenesin crystallizes in the orthorhombic space group P212121 (#19), with a=7.657 05(7), b=25.670 20(24), c=4.979 66(4) Å, V=978.79(2) Å3, and Z=4. Both hydroxyl groups act as hydrogen bond donors and acceptors, resulting in the formation of a two-dimensional network of strong hydrogen bonds in the ac plane. The solid state conformation is ∼4 kcal/mol higher in energy than the minimum-energy conformation of an isolated molecule, but the formation of the hydrogen bonds results in an energy gain of ∼100 kcal/mol. Knowledge of the crystal structure permits quantitative phase analysis of guaifenesin-containing pharmaceuticals (such as Duratuss GP 120-1200) by the Rietveld method.

A qualitative phase identification system for crystalline mixtures is presented. The system provides up to five-phase qualitative identification using up to nine-peak filtration, and additive full peak matching based on the powder diffraction file of ICDD. It was implemented using Microsoft Visual C++, and runs under most common Windows systems. Screenshots and examples are included.

Ge–Si inverted huts, which formed at the Si∕Ge interface of Si∕Ge superlattice grown at low temperatures, have been measured by X-ray diffraction, grazing incidence X-ray specular and off-specular reflectivities, and transmission electron microscopy (TEM). The surface of the Si∕Ge superlattice is smooth, and there are no Ge–Si huts appearing on the surface. The roughness of the surfaces is less than 3 Å. Large lattice strain induced by lattice mismatch between Si and Ge is found to be relaxed because of the intermixing of Ge and Si at the Si∕Ge interface.

Direct methods and Rietveld analysis were applied to high-resolution synchrotron X-ray powder diffraction data to solve the crystal structure of dicalcium chromate hydrate (Ca2CrO5⋅3H2O). The compound crystallizes in monoclinic symmetry (space group Cm, Z=2), with a=8.23575(5) Å, b=7.90302(4) Å, c=5.20331(3) Å, and β=98.0137(3)°. The structure is built from double-layers of CrO4 tetrahedra and CaO8 polyhedra that run parallel to the (001) plane.

Mn2+ and Cd2+ form a family of isostructural hexacyanoferrates(II,III). Their crystal structures, including those of mixed compositions containing K+ and Cs+ as charge balance cations, were resolved and refined from XRD powder patterns. The crystal structures of M3[Fe(CN)6]2⋅xH2O and MCs2[Fe(CN)6] (where M=Mn, Cd) were refined in the space group Fm3m. The mixed salts, MK2[Fe(CN)6]⋅2H2O, were found to be orthorhombic (space group Pmn21). The orthorhombic structure results from a local distortion due to monohydrated potassium ions located in interstitial sites. On ionic exchange in an aqueous solution containing Cs+, the orthorhombic distortion disappears and the cubic cell is obtained. Cs+ is a large ion, which practically fills the available interstitial voids stabilizing the cubic structure. In solutions of K+ and Cs+ the single salts, M2[Fe(CN)6]⋅8H2O (monoclinic P21/n) also transform, in this case liberating M2+ ions and forming the corresponding mixed salts. An analogous but slow structural transformation was also observed in the anhydrous forms of these single salts. These structural transformations could be relevant to the use of these compounds as ion exchangers and particularly for the sorption of 137Cs+ from radioactive waste solutions. The XRD data were complemented with structural information from infrared (IR), Mössbauer and water vapor adsorption techniques. © 2004 International Centre for Diffraction Data.

In an attempt to fill a gap between fully automatic search/match programs and purely manual methods based on paper products, a relational database plug-in has been developed that functions as a PC-based Search/Index program for extracting information from PDF-4 powder diffraction databases. The plug-in provides an adjustable search window and match window to account for experimental errors. Both Hanawalt and Fink search methods are incorporated. In this paper, we report search-indexing results obtained with the new PDF-4 plug-in applied to a new relational database, the PDF-4/Organics 2003. This database has 24 385 experimental entries and 122 816 calculated patterns derived from the Cambridge Crystallographic Database. We introduce a goodness of match (GOM) parameter to describe the relative agreement between the experimental input data and selected reference patterns from the PDF-4/Organics 2003. The relevance of the GOM is illustrated in several example problems. Multiphase samples can be treated on a phase-by-phase basis.

(Pr0.55Ca0.45)(Mn1−yCry)O3 (with y=0.00, 0.03, and 0.06) have been prepared by means of a solid state reaction from stoichiometric powder mixtures of binary oxides. X-ray powder diffraction analysis reveals the formation of the perovskite-type compound for the whole considered compositions; no evidence for secondary phases may be detected. The structural refinements have been carried out using X-ray powder diffraction data applying the Rietveld method; the lattice parameters of the orthorhombic cell faintly change with composition. On the contrary the tilting of the octahedra results are strongly dependent on the concentration of Cr in the 4b site. Bond valence sum method has been applied in order to evaluate the possible presence of lattice-induced strains and the amount of Mn4+. Structural data are also reported.

The compound Er2BaF8 is prepared by heating appropriate amounts of BaF2 and ErF3 at 900 °C for 18 h in a dry argon filled quartz ampoule. The polycrystalline sample obtained was characterized by a Rietveld refinement of the observed powder diffraction data. This compound crystallizes in a monoclinic lattice with unit cell parameters: a=6.9620(2), b=10.4960(3), c=4.2541(1) Å and β=99.685(1)°, V=306.14(1) Å3, Z=2, (space group C 2/m, No. 12). The structure analysis reveals the presence of one kind of Ba and Er atoms in the unit cell. There are three different kinds of fluorine atoms, namely F1, F2, and F3 in the ratio of 8:4:4. The Er atoms form a square-antiprism polyhedron with eight fluorine atoms, which share three of its edges to form a ring of six ErF8 polyhedra. The rings of ErF8 polyhedra are connected via two opposite corners along the c-axis of the unit cell. The voids formed within the rings are occupied by Ba atoms, which maintain a twelve-coordination polyhedron with the fluorine atoms. As per the Rietveld analysis, the F3 site may exist as a disordered state by shifting the fluorine atom from the two-fold axes. © 2004 International Centre for Diffraction Data.

An instrument for the simultaneous measurement of X-ray powder diffraction (XRD) data and differential scanning calorimetry (DSC) data under a controlled humidity condition has been developed in order to achieve a design concept of reliable and simple in operation. Examples of the application to studies on hydration, dehydration, and rehydration processes of pharmaceutical compounds under various humidity conditions are presented. The usefulness of the present XRD-DSC system will be demonstrated.

Fe–N thin films were deposited on glass substrates by dc magnetron sputtering under various Ar∕N2 discharge conditions. Crystal structures and elemental compositions of the films were characterized by X-ray diffraction and X-ray photoelectron spectroscopy. Magnetic properties of the films were measured using a superconducting quantum interference device magnetometer. Films deposited at different N2∕(Ar+N2) flow ratios were found to have different crystal structures and different nitrogen contents. When the flow ratios were 60%, 50%, and 30%, a nonmagnetic single-phase FeN was formed in the films. At the flow ratio of 10%, two crystal phases of γ′-Fe4N and ε-Fe3N were detected. When the flow ratio reduced to 5%, a mixture of α-Fe, ε-Fe3N, FeN0.056, and α″-Fe16N2 phases was obtained. The value of saturation magnetization for the mixture was found to be larger than that of pure Fe.

X-ray powder diffraction (XRD) is utilized for the determination of polymorphism in crystalline organic materials. Though convenient to use in a laboratory setting, XRD is not easily adapted to in situ monitoring of synthetic chemical production applications or thin film depositions. Near-infrared spectroscopy (NIR) can be adapted to in situ manufacturing schemes by use of a source/detector probe. Conversely, NIR is unable to conclusively define the existence of polymorphism in crystalline materials. By combining the two techniques, a novel simultaneous NIR/XRD instrument has been developed. During material’s analysis, results from XRD allowed for the determination of the existence of polymorphic phases, and NIR data were collected as a fingerprint for each of the observed polymorphs. These NIR fingerprints allowed for the development of a library, which can be referenced during the use of a NIR probe in manufacturing settings. The NIR/XRD instrument was also used to monitor materials during exposure to ambient air. XRD can detect crystalline phase changes and NIR can monitor solvent loss and/or water uptake.

A Mg-stabilized triclinic tricalcium silicate form of type Ca3−xMgxSiO5, T3, was synthesized. Rietveld analysis using synchrotron X-ray powder diffraction data suggested that unlike the T1 form, the T3 structure was unmodulated. This refinement illustrated that the only existing model for a triclinic form of tricalcium silicate (T1) can be used to describe the nonmodulated T3 form.

Powder X-ray diffraction data for a new palladium(II) amino acid complex, of composition PdC12H20N2O4S2, are presented in this paper. Orthorhombic cell parameters are: a=10.740 Å, b=19.999 Å, and c=5.2470 Å. © 2004 International Centre for Diffraction Data.

Synthetic diamonds are an important class of industrial material. During synthesis impurities may get introduced into diamond. Identification and quantification of impurities is important as they affect the properties and suitability of the diamonds for their application. Impurities in an industrial synthetic diamond powder sample were analyzed by X-ray diffraction (XRD) and also by chemical methods. X-ray diffraction pattern showed diamond as the major phase and α-iron as a minor phase. Quantitative analysis of crystalline phases was done by performing Rietveld refinement of the XRD profile. Chemical analysis showed the presence of several other impurities as well, though in small amounts. It was considered that the impurities other than iron were in amorphous form and an estimate of the amorphous content was made on this basis. Relative phase composition of diamond and iron as estimated by XRD were corrected for the amorphous content to obtain absolute phase composition.

The structures of SmAlSi and SmAlGe were determined by the powder diffraction method. These compounds have a tetragonal structure of LaPtSi type, which is a ternary substitutional variant of α-ThSi2. Both prototype structures have the same extinction rules, and as a result, the choice of the structural type must be based on very careful examination of the peak intensities. This was done with the aid of a Rietveld refinement, which indicates a better fit of the LaPtSi structure.

The crystal structures of ASnFe(PO4)3 (A=Na2, Ca, Cd) phases, obtained by conventional solid state reaction techniques at (950–1000 °C), were determined at room temperature from X-ray powder diffraction (XRD) using Rietveld analysis. The three materials exhibit the Nasicon-type structure (R3c space group, Z=6) with a random distribution of Sn(Fe) within the framework. Hexagonal cell parameters when A=Na2, Ca and Cd are: a=8.628(1) Å, c=22.151(2) Å; a=8.569(1) Å, c=22.037(2) Å and a=8.587(1) Å, c=21.653(2) Å, respectively. Structural refinements show a partial occupancy of M1 (Na(1)) and M2 (Na(2)) sites in Na2SnFe(PO4)3 leading to the cationic distribution [Na1.22□1.78]M2[Na0.78□0.22]M1SnFe(PO4)3. Ca2+ ions are distributed only in the M1 site of [□3]M2[Ca]M1SnFe(PO4)3. From XRD data, it is difficult to unambiguously distinguish between Cd2+ and Sn4+ ions in CdSnFe(PO4)3. Nevertheless the overall set of cation–anion distances within the Nasicon framework clearly shows that the cationic distribution can be illustrated by the [□3]M2[Cd]M1SnFe(PO4)3 crystallographic formula. Distortion within the [Sn(Fe)(PO4)3] frameworks, in ASnFe(PO4)3 (A=Na2,Ca,Cd) phases, is shown to be related to the M1 site size. © 2004 International Centre for Diffraction Data.

Ten fragments of bronze age frescoes from the Greek group of volcanic islands known as Santorini have been examined by powder X-ray diffraction. A qualitative phase analysis based on line positions only was supplemented by the Rietveld method which uses complete diffraction profiles to increase the credibility of the phase analysis.

The Rietveld method allows a precise quantitative phase analysis of building materials. Thanks to the development of stable-functioning software and the use of high-performance detectors, a quantitative phase analysis by X-ray, including sample preparation, and measurement and evaluation, can be performed in fewer than ten minutes. This has made it possible to integrate the method into existing laboratory automation systems for process and quality control to provide a means of online monitoring. Due to the completely automated operating principle of the Rietveld software, no additional staff is required and the results are user-independent. The Rietveld method is now being employed in industrial laboratories and also in various cement plants owned by the Lafarge Group as the standard method of quantitative analysis of Portland Cement clinkers and Portland Cements (CEM I, CEM II A-L).