X-ray Rietveld refinements were conducted on a series of eleven lanthanide phases, Sr2RGaCu2Oy (2112 phase, R = Pr, Nd, Sm, Eu, Gd, Dy, Ho, Y, Er, Tm, and Yb) that are structurally related to the ...high Tc superconductor Ba2YCu3O7 (213). In the 2112 structure, instead of square planar Cu-O chains, tetrahedral GaO4 chains were found to run in a zig-zag fashion along the diagonal of the basal 213 ab-direction. Reference powder patterns for these compounds were prepared by using the Rietveld decomposition technique. The unit cell volume of these compounds follows the expected trend of the lanthanide contraction. The lattice parameters range from a = 2.2969 nm, b = 0.5559 nm and c = 0.54474 nm for R = Pr, to a = 2.2806 nm, b = 0.5460 nm and c = 0.53777 nm for R = Yb. An electron diffraction study of the Sm- and Er-analogues showed characteristic diffuse streaks along the b-axis, suggesting some disorder within the GaO4 chains. 13 refs.
The nuclear magnetic resonance (NMR) powder patterns observed for the
31P spin pair in Lawesson's reagent (
1) were analyzed. Using an efficient procedure, wide ranges of the spin parameters were ...examined to determine whether they might reproduce the experimental one-dimensional (1D) spectrum of the present A
2 spin system. It was demonstrated that the parameters were not uniquely determined from the 1D powder pattern only, but a significant reduction of their uncertainties was realized using the two-dimensional (2D) powder pattern. The molecular structure of
1 was discussed in terms of the refined spin parameters.
The nuclear magnetic resonance (NMR) spectra of disordered materials are often interpreted by assuming distributions of the interaction parameters and fitting the spectra under these assumptions. ...Here we illustrate methods to extract the distributions directly from the spectra, making no such prior assumptions. The inhomogeneously broadened powder pattern observed in the NMR spectrum of a disordered solid is expressed as an integral over the powder patterns for individual sites weighted by the population distribution of the different sites. The resulting integral equation is solved for the underlying probability distribution of sites, both by singular value decomposition and by a regularization method. Results are shown for model and real one-dimensional and two-dimensional NMR experiments, with and without noise.
Crystallographic modelling Driessen, R A; Loopstra, B O; de Bruijn, D P ...
Journal of computer-aided molecular design
2, Issue:
3
Journal Article
Peer reviewed
The project on crystallographic modelling aims at extending the application of interactive graphics to inorganic structures. Starting from the available expertise in organic and protein modelling, ...the symmetry of the crystal structure is used not only to draw fixed models of many unit cells of the structure, which as an entity can be interactively manipulated, but also to change details of the structures interactively with retention of the original symmetry. Real-time shifts of atom positions are automatically applied to all symmetry-equivalent atoms given the symmetry constraints. This also applies to translations and rotations of groups of atoms. In order to get feedback about these structural changes one can simulate powder diffraction patterns in real-time mode and compare them with the experimental powder patterns. These features are crucial in truly crystallographic modelling, but have not been implemented before in other programs. The program can be used in combination with standard molecular modelling programs and is also interfaced to the Inorganic Crystal Structure Database. Before describing the realization of these features on state-of-the-art hardware, we will review the expertise in molecular modelling and discuss an MS-DOS program to study inorganic crystal structures.
The Lower Miocene Macelj-sandstones, from the western part of Hrvatsko Zagorje, are green in colour with variable amounts of glauconitic grains. This paper presents the results of mineralogical and ...some petrological analysis of three characteristic samples of these sandstones.
The natural sandstone samples were analysed by polarising microscope and by X-ray powder diffraction (XRD). After separation, the pure or almost pure glauconitic materials were analysed by XRD, chemical analysis and thermal analysis (TG, DTA and DTG). The results show variation, not only in the glauconitic material of the sandstone samples, but also within individual samples. The amount of smectite layers varies from <5% to approximately 40% depending on the degree of order and the stage of glauconite evolution. This is indicated by the contents of K, Al, Fe, adsorbed water and cation exchange capacity as well as XRD powder patterns.
Theoretical X-ray powder patterns for (1) illite/air dried montmorillonite interstratification, and (2) illite/ethylene glycol treated montmorillonite one are presented. The mean number of layers and ...its standard deviation are fixed at N=10 and σ=2.0 respectively. Their basal spacings expected are collected in the table.
•Co0.7Zn0.3TmxFe2−xO4 (0.0 ≤ x ≤ 0.04) NPs were fabricated by sonochemical method.•IT exhibited superparamagnetic (SP) at RT and ferromagnetic property at 10 K.•An increasing trend in the Ms, Mr, Hc, ...and nB values was noticed for lower Tm3+ substitution content.
This study expressed the influence of Tm substitution on the structural, optical and magnetic properties of Co-Zn spinel ferrites (Co0.7Zn0.3TmxFe2−xO4 (0.0 ≤ x ≤ 0.04)). The different compositions were synthesized by sonochemical method using Qsonica ultrasonic homogenizer, frequency: 20 kHz and power: 70 W for 60 min. XRD patterns proved the presence of single-phase spinel ferrites with crystallites size in the 8–10 nm range. Cation distribution approved the occupancy of octahedral (B) site by Tm. The morphology and the elements stoichiometry are obtainable through FE-SEM, EDX and elemental mapping. Optical band gap (Eg) values were estimated via DR % (percent diffuse reflectance) investigations and Kubelka-Munk theory. Tauc plots revealed that direct Eg values are ranging between 1.49 and 1.68 eV. The analyses of magnetization versus magnetic field, M(H), were performed. The following magnetic parameters like saturation magnetization Ms, squareness ratio (SQR = Mr/Ms), magnetic moment nB, coercivity Hc and remanence Mr have been evaluated. M(H) curves revealed the superparamagnetic (SP) at RT and ferromagnetic property at 10 K. It was showed that the Tm3+ substitutions significantly affect the magnetic properties of host spinel ferrites. An increasing trend in the Ms, Mr, Hc, and nB values was noticed for lower Tm3+ substitution content.
The direct‐derivation (DD) method is a new technique for quantitative phase analysis (QPA) Toraya (2016). J. Appl. Cryst. 49, 1508–1516. A simple equation, called the intensity–composition (IC) ...formula, is used to derive weight fractions of individual components (wk; k = 1–K) in a mixture. Two kinds of parameters are required as input data of the formula. One is the parameter Sk, which is the sum of observed powder diffraction intensities for each component, measured in a wide 2gθ range and corrected for the Lorentz–polarization factor. The other is the parameter ak−1, defined by ak−1 = Mk−1∑nik2, where Mk is the chemical formula weight and nik is the number of electrons belonging to the ith atom in the chemical formula unit. The parameter ak−1 was originally derived by using the relationship between the peak height and the integrated value of the peak at the origin of the Patterson function, implicitly assuming the presence of periodic structures like crystals. In this study, the formula has been derived theoretically from a general assemblage of atoms resembling amorphous material, and the same expression as the original formula has been obtained. The physical meaning of ak−1, which represents `the total scattering power per chemical formula weight', has been reconfirmed in the present formulation. The IC formula has been tested experimentally by using two‐, three‐ and four‐component mixtures containing SiO2 or GeO2 glass powder. In the whole‐powder‐pattern fitting (WPPF) procedure, incorporated into the DD method, a background‐subtracted halo pattern is directly fitted as one of the components in the mixture, together with profile models for crystalline components. In the WPPF, an interaction was observed between the parameters of the background function (BGF) and the parameter for scaling the halo pattern, and this resulted in systematic deviations of wk from weighed values. The deviations were ≤0.7% in the case of binary mixtures when the BGF was fixed at the correct background height, supporting the hypothesis that the DD method is applicable to the QPA of amorphous components.
The direct‐derivation method has been applied to the quantitative phase analysis of mixtures containing amorphous components. A theoretical basis has been given to the formula for deriving individual weight fractions from observed intensity data. The formula has been experimentally tested by whole‐powder‐pattern fitting to the observed patterns of mixtures containing amorphous components.
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