Experimental Powder X-ray Diffraction Data Research Articles

Synthesis and luminescence studies of Dy3+ doped Li3Sc(BO3)2 polycrystalline powder for warm white light

Li3Sc(BO3)2, an orthoborate polycrystalline compound, was synthesised using the solid-state synthesis method as a pure and Dy2O3-doped material. Dy3+ ions were used in various concentrations (from 1 to 6 mol. %). The experimental powder X-ray diffraction data and calculated Rietveld refined data are found to be in good agreement, verifying the effectiveness of the synthesis procedure. The luminescence studies were performed under the excitations of X-ray, proton beam, and UV light. The success of radioluminescence studies verifies the prospects of the Dy3+-doped compound for its application as a radiation scintillator in imaging. The experimental study of cross-relaxation processes confirms the lack of potential evidence of the quenching of the emission peak at 765 nm through the absorption via 6H15/2 → 6F3/2 electronic transition cross-relaxation channel −1. The CIE 1931 colour coordinates and correlated colour temperatures were determined for all doped samples under X-ray, proton beam, and photoluminescence excitations. The obtained combined emission colour appeared in the warm white region, unlike many other Dy3+-doped phosphors that suffer suppression of luminescence through the cross-relaxation process.

Low Temperature Transitional Aluminas: Structure Specifics and Related X-ray Diffraction Features

Despite the fact that metastable aluminum oxides are actively used in industry, there is a discrepancy in the literature regarding their crystal structure. All this leads to difficulties in data interpretation and, as a consequence, classification problems. This work is aimed at solving these tasks. The main features of powder X-ray diffraction of typical samples of three Al2O3 polymorphs (γ-, χ-, η-) are analyzed. Specifics and fundamental differences in X-ray scattering and their relationship with the structural organization at the nanostructure level are clearly shown. The work demonstrates the possibilities of analyzing experimental powder X-ray diffraction data using a modern approach based on the Debye Scattering Equation for studying the organization of such complex systems.

X-ray diffraction data-assisted structure searches

X-ray diffraction (XRD) is an important technique for structure determination. However, in traditional methods, estimated structural information (e.g., unit cell parameters and space group) is required to determine the precise structure from XRD data. We propose a versatile global search method for determining crystal structures from experimental powder XRD data without guessed structural information. Unlike in traditional structure prediction, which uses total energy as the fitness function, the fitness in our method is the degree of dissimilarity between the simulated and the experimental XRD patterns. To improve the efficiency of structure searching using powder XRD data, several techniques are implemented, including background subtraction, profile parameter optimization by simulated annealing, and structure evolution using CALYPSO. The efficiency and robustness of our method is demonstrated here using predictions of previous known structures (hexagonal ZnO and anatase TiO2). The method is also used to explore the high-pressure phases of binary compounds CaLi2 and Ca3C2; it uncovers candidate structures (C2221 for CaLi2 at 54 GPa and Cm2m for Ca3C2 at 12.5 GPa) whose simulated XRD patterns agree with their experimental patterns.

Combining the Advantages of Powder X-ray Diffraction and NMR Crystallography in Structure Determination of the Pharmaceutical Material Cimetidine Hydrochloride

We report the crystal structure of the anhydrous phase of cimetidine hydrochloride, determined directly from powder X-ray diffraction data. The material was prepared by dehydration of the readily obtained monohydrate form of cimetidine hydrochloride, the only form for which a crystal structure has previously been reported. As such, solid-state dehydration processes typically yield the product phase as a microcrystalline powder, and structure determination was carried out directly from powder X-ray diffraction data, using the direct-space genetic algorithm technique for structure solution followed by Rietveld refinement. The structure determined from powder X-ray diffraction was further validated by calculating solid-state 13C NMR data for the crystal structure (using first-principles periodic DFT techniques within the GIPAW approach) and assessing the quality of agreement with the corresponding experimental solid-state 13C CPMAS NMR data. This strategy provides a robust vindication of the correctness of the crystal structure by assessing the quality of agreement of the structure both with experimental powder X-ray diffraction data and with experimental solid-state 13C NMR data.

Exploiting the Synergy of Powder X-ray Diffraction and Solid-State NMR Spectroscopy in Structure Determination of Organic Molecular Solids

We report a strategy for structure determination of organic materials in which complete solid-state nuclear magnetic resonance (NMR) spectral data is utilized within the context of structure determination from powder X-ray diffraction (XRD) data. Following determination of the crystal structure from powder XRD data, first-principles density functional theory-based techniques within the GIPAW approach are exploited to calculate the solid-state NMR data for the structure, followed by careful scrutiny of the agreement with experimental solid-state NMR data. The successful application of this approach is demonstrated by structure determination of the 1:1 cocrystal of indomethacin and nicotinamide. The 1H and 13C chemical shifts calculated for the crystal structure determined from the powder XRD data are in excellent agreement with those measured experimentally, notably including the two-dimensional correlation of 1H and 13C chemical shifts for directly bonded 13C–1H moieties. The key feature of this combined approach is that the quality of the structure determined is assessed both against experimental powder XRD data and against experimental solid-state NMR data, thus providing a very robust validation of the veracity of the structure.

Local distortion in Co-doped LSMO from entropy-maximized charge density distribution

Perovskite structure manganites La 0.67Sr 0.22Mn 1.11− x Co x O 3 were prepared by the solid state reaction method. An X-ray analysis of the structure was undertaken using the Rietveld technique on the experimental powder X-ray diffraction data and, then, a charge density distribution study was undertaken, using the maximum entropy method (MEM). The charge density in the unit cell was reconstructed and the effect of Co 3+ doping in the Mn–O matrix was studied. Local distortions due to Co doping were analyzed and the results are now discussed.

A structure refinement strategy for NMR crystallography: An improved crystal structure of silica-ZSM-12 zeolite from 29Si chemical shift tensors

A strategy for performing crystal structure refinements with NMR chemical shift tensors is described in detail and implemented for the zeolite silica-ZSM-12 (framework type code MTW). The 29Si chemical shift tensors were determined from a slow magic-angle spinning spectrum obtained at an ultrahigh magnetic field of 21.1 T. The Si and O atomic coordinate parameters were optimized to give the best agreement between experimentally measured and ab initio calculated principal components of the 29Si chemical shift tensors, with the closest Si–O, O–O, and Si–Si distances restrained to correspond with the distributions of the distances found in a set of single-crystal X-ray diffraction (XRD) structures of high-silica zeolites. An improved structure for the silica-ZSM-12 zeolite, compared to a prior structure derived from powder XRD data, is obtained in which the agreement between the experimental and calculated 29Si chemical shift tensors is dramatically improved, the Si–O, O–O, and Si–Si distances correspond to the expected distributions, while the calculated powder XRD pattern remains in good agreement with the experimental powder XRD data. It is anticipated that this “NMR crystallography” structure refinement strategy will be an important tool for the accurate structure determination of materials that are difficult to fully characterize by traditional diffraction methods.

Theoretical Prediction of Crystal Structure of <i>N</i>-(1-naphthyl) Succinimide Compound

The indexing for experimental X-ray diffraction powder patterns of polycrystalline sample was performed on N-(1-naphthyl)-succinimide compound by using Materials Studio software, and the important information on crystal system, space group, and crystal lattice parameters was provided via the powder refinement and space searching processes. The simulated X-ray diffraction pattern of the calculated crystal unit cell agrees with the experimental XRD powder data. The theoretical crystal prediction of structure using the minimum energy conformation obtained by density-functional theory calculation as the input molecular structure, can afford a series of the hypothetical crystal structures in P2(subscript 1)2(subscript 1)2(subscript 1) space group. It can be found that the parameters of the crystal unit cell, agreeing with both the result from powder indexing calculation and the single-crystal data, have been obtained by the refinement against experimental powder X-ray diffraction data of the polycrystalline sample of N-(1-naphthyl)-succinimide.

Powder Diffraction Indexing as a Pattern Recognition Problem: A New Approach for Unit Cell Determination Based on an Artificial Neural Network

An artificial neural network, in combination with local optimization, is shown to be an effective approach for determining unit cell parameters directly from powder diffraction data. The viability of this new approach is initially demonstrated using simulated powder diffraction data. Subsequently, the successful application of the method to determine unit cell parameters is illustrated for two materials using experimental powder X-ray diffraction data recorded on a standard laboratory diffractometer.

Synthesis, Structure Determination, and Aqueous Durability of Cs2ZrSi3O9

The structure of Cs2ZrSi3O9 synthesized using a sol–gel method was determined from the Rietveld refinement of experimental powder X-ray diffraction data. The refinement confirmed that this compound was isostructural with wadeite: its structure was hexagonal (space group P63/m), and its lattice parameters were a= 7.2303(2) A and c= 10.2682(4) A. The aqueous durability of Cs2ZrSi3O9 varied, depending on the solution conditions. In modified leach tests with buffered (pH 7) and unbuffered solutions, the 7-d cesium release rates were <1.2 × 10−4 g·(m2·day)−1, which indicated high aqueous durability. However, in unsaturated, unbuffered solutions with a pH of 9–10, the durability was much lower, with 7-d cesium release rates of 2.2 × 10−3 g·(m2·day)−1. The ability of this material to retain cesium in aqueous environments can be explained by its condensed ring structure, in which the size of the channel openings is smaller than the diameter of a Cs+ ion. However, dissolution of the network silicate occurred at high pH, which resulted in the release of cesium.