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Powder X-ray Diffraction Patterns (powder + x-ray_diffraction_pattern)
Selected AbstractsThe Structure of Yttrialite and Its Identification Using Laboratory and Synchrotron-Based Powder X-Ray DiffractionJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2009William J. Heward A highly crystalline sample of the impurity stabilized phase y -Y2Si2O7, generally known as yttrialite, has been formed from the melt of a glass with a nominal composition of 62(SiO2),10(Al2O3),28(Y2O3) mol%. Powder X-ray diffraction patterns were collected using in-house instrumentation and the 11-BM diffractometer at the Advanced Photon Source, Argonne National Laboratory, Argonne, IL. Rietveld refinements were carried out on the patterns using two structural models. On patterns collected using in-house instrumentation the correct structure assignment was difficult to determine; however, the extremely high-quality data afforded by the 11-BM instrument showed conclusively that the sample was found to crystallize in the monoclinic system (SG=P21/m) with lattice parameters a=5.03032(6), b=8.06892(6), c=7.33620(6) Å, and ,=108.673(1). Furthermore, simulations have shown that it is likely that this structure model can be used to describe natural yttrialite or yttrialite that is formed at low temperatures, though the possibility that such materials are paracrystalline is also discussed. [source] Ab initio structure determination of phase II of racemic ibuprofen by X-ray powder diffractionACTA CRYSTALLOGRAPHICA SECTION B, Issue 1 2010Patrick Derollez Annealing of the quenched ibuprofen at 258,K yielded a new crystalline form, called phase II. Powder X-ray diffraction patterns of this phase II were recorded with a laboratory diffractometer equipped with an INEL G3000 goniometer and a curved position-sensitive detector CPS120. The starting structural model was found by a Monte-Carlo simulated annealing method. The final structure was obtained through Rietveld refinements with rigid-body constraints for the phenyl group and soft restraints on the other interatomic bond lengths and bond angles. The cell volume is 5% larger than that of the conventional phase I at 258,K. It is also shown that the orientation of the propanoic acid group is drastically changed with respect to phase I, leading to strong modifications of the orientation of the O,H...O hydrogen bonds with respect to the chains of dimers. These structural considerations could explain the metastable character of this phase II. [source] Synthesis, crystal structure and characterization of new transition metal compounds of bromophenols: Bis(2,4,6-tribromophenolato) di(N-methylimidazole)M(II) (M=Co, Cu)CRYSTAL RESEARCH AND TECHNOLOGY, Issue 3 2005P. Camurlu Abstract Bis(2,4,6-tribromophenolato)di(N-methyl imidazole)M(II), where M stands for cobalt and copper metals, was synthesized via reaction of the corresponding metal sulphate and 2,4,6-tribromophenolate in aqueous media in the presence of N-methyl imidazole and sodium hydroxide. Although various crystallization procedures were applied only cobalt complex was obtained as single crystals. The Co(II) ion has a distorted octahedral enviroment involving two O atoms and two N atoms of the Bis(2,4,6-tribromophenolato)di(N-methyl imidazole) ligand. Powder x-ray diffraction pattern of copper compound was used for cooper complex. For characterizations of complexes carbon, hydrogen and nitrogen elemental analysis, FTIR and UV spectroscopy, DSC thermal analysis and magnetic susceptibility measurements at room temperature were performed. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Rational, Facile Synthesis and Characterization of the Neutral Mixed-Metal Organometallic Oxides Cp*2MoxW6,xO17 (Cp* = C5Me5, x = 0, 2, 4, 6)EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 34 2009Gülnur Taban-Çal Abstract The reaction of the bis(pentamethylcyclopentadienyl)pentaoxidodimetal complexes Cp*2M2O5 with four equivalents of Na2M,O4 (M, M, = Mo, W) in acidic aqueous medium constitutes a soft and selective entry into neutral Lindqvist-type organometallic mixed-metal oxides Cp*2MoxW6,xO17 [x = 6 (1), 4 (2), 2 (3), 0 (4)]. The identity of the complexes is demonstrated by elemental analyses, thermogravimetric analyses and infrared spectroscopy. Thermal degradation of 1,4 up to above 500 °C leads to Mox/6W1,x/6O3. The molecular identity and geometry of compound 2 is further confirmed by a fit of the powder X-ray diffraction pattern with a model obtained from previously reported single-crystal X-ray structures of 1 and 4, with which 2 is isomorphous. DFT calculations on models obtained by replacing Cp* with Cp (I,IV) validate the structural assignments and assist in the assignment of the M,M,,O vibrations. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Comparative analysis of triacylglycerol composition, melting properties and polymorphic behavior of palm oil and fractionsEUROPEAN JOURNAL OF LIPID SCIENCE AND TECHNOLOGY, Issue 4 2007Sabine Braipson-Danthine Abstract Palm oil is without doubt the most widely fractionated oil. Dry fractionation is based on differences in the melting points of triacylglycerols (TAG) which will crystallize selectively during the cooling process. Unfortunately, limitations due to intersolubility, closely linked to polymorphism, induce formation of co-crystals at each crystallization step. For this reason, only restricted TAG enrichments are observed. In this work, a series of samples (24) of palm oil, solid and liquid fractions (stearins, mid fractions, oleins and superoleins) have been selected and examined in terms of TAG composition (by HPLC), differential scanning calorimetry (DSC) melting profile and variable temperature powder X-ray diffraction pattern. Three major endotherms [low-melting, high-melting and very high-melting peaks (LMP, HMP and VHMP)] are detected in the DSC melting profiles (5,°C/min). The VHMP is only recorded for palm stearin which contains more SSS components. The HMP contribution is weak for palm olein and even not observed for palm super oleins. The LMP is usually made up of UUU, SUU and SUS components; SUS components are observed in both LMP and HMP; the HMP is also made up of some SSS, except for palm oleins and super oleins. Sub-,2, sub-,1, ,, ,'2, ,'1 and , polymorphic forms are recorded; the LMP components preferentially crystallize in sub-,2, sub-,1 and ,,forms; the HMP components generally crystallize in ,'2 and ,'1, with a tendency to exhibit ,,crystals, depending on the SSS content. Components of the VHMP have an increased tendency to stabilize in the ,,form; in view of the results, we can assume that there is a clear relationship between TAG composition, melting properties and polymorphic behavior and of palm oil and fractions. [source] Effect of Pb on the properties of Sr2YRu1-xCuxO6 crystals grown from PbO-PbF2 solutions at high temperaturesCRYSTAL RESEARCH AND TECHNOLOGY, Issue 6 2007S. M. Rao Abstract Single crystals of Sr2YRu1-xCuxO6 with x=0 and x=0.1 were grown using PbO-PbF2 based solutions at different temperatures in the range 1150,1350°C. The influence of Pb from the solutions and the Cu from the solid solutions of Sr2YRu1-xCuxO6 on the resulting crystals was studied using microstructure and magnetic property measurements. The peaks in the powder X-ray diffraction patterns and Raman spectra do not change in the case of x=0 crystals but shift in the presence of Cu. A diamagnetic transition indicative of superconductivity was observed in the presence of Cu and an antiferromagnetic behavior with x=0. Based on these results it is concluded that Pb may not be incorporated in the crystals and even if it does the influence is not observed. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Self-Assembled Nanostructures: Role of Water in Directing Diphenylalanine Assembly into Nanotubes and Nanowires (Adv. Mater.ADVANCED MATERIALS, Issue 5 20105/2010) The controllable assembly behavior of diphenylalanine molecules to form nanowires (NWs) and nanotubes (NTs) and their structural details are presented. Hyotcherl Ihee, Sang Ouk Kim and co-workers show on p. 583 that the nanoscale morphologies are closely related to molecular arrangements of diphenylalanine as revealed by Rietveld refinement of powder X-ray diffraction patterns and electron-density distributions in NTs and NWs via the maximum entropy method analysis. [source] Role of Water in Directing Diphenylalanine Assembly into Nanotubes and NanowiresADVANCED MATERIALS, Issue 5 2010Jangbae Kim The controllable assembly behavior of diphenylalanine molecules to form nanowires (NWs) and nanotubes (NTs) and their structural details are presented (see figure). The nanoscale morphologies are closely related to molecular arrangements of diphenylalanine as revealed by Rietveld refinement of powder X-ray diffraction patterns and electron-density distributions in NTs and NWs via the maximum entropy method analysis. [source] Crystal structure prediction for eniluracilJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 8 2001Mark Sacchetti Abstract State-of-the-art molecular modeling tools were used to predict the crystal structure of eniluracil, a compound for which it has not been possible to grow a single crystal. Two methods were used, one that incorporates molecular structure and powder X-ray diffraction data and another that employs molecular structure and lattice energy calculations into the search algorithm. Two structures were identified, one with P21/c and the other with P21 symmetry, both of which are consistent with the infrared and Raman spectra. A detailed analysis of the simulated and experimental powder X-ray diffraction patterns indicates that the P21/c structure is the best representation of the crystal structure. © 2001 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 90:1049,1055, 2001 [source] Dry Grinding of Mefenamic Acid Particles for Enhancement of its Water Dissolution RatePARTICLE & PARTICLE SYSTEMS CHARACTERIZATION, Issue 3 2007Tomohiro Iwasaki Abstract This paper details an investigation into the enhancement of the water dissolution rate of mefenamic acid (MA) by means of a dry grinding treatment. The physico-chemical properties of the ground MA particles were analyzed by measurements of specific surface area, powder X-ray diffraction patterns, differential scanning calorimetry thermograms and infrared spectra, and the effects of the change in the physico-chemical properties (especially, crystalline structure) on the dissolution rate were studied. The polymorphic transition from Form I (original) to II and the change of the molecular structure of MA did not occur in the grinding treatments. However, the specific surface area of the MA particles increased, and the crystallinity decreased (i.e., the amorphization level increased) as the grinding progressed. Hydrogen bonds formed between the carboxyl groups of the opposed asymmetric MA molecules were broken gradually after the grinding limit was attained in the grinding system, resulting in an effective improvement of the initial dissolution rate. [source] A symmetrical indexing scheme for decagonal quasicrystals analogous to Miller,Bravais indexing of hexagonal crystalsACTA CRYSTALLOGRAPHICA SECTION A, Issue 1 2007S. Ranganathan The problems of redundancy and superfluous indices in indexing the planes and axes in a decagonal quasicrystal are considered, using a scheme of five coplanar vectors in the quasiperiodic plane and one perpendicular vector. Of all the indexing schemes in use, this scheme offers the maximum advantage. An analogy is drawn to the hexagonal system using Miller,Bravais indices. Based on this, a symmetry-based indexing system for decagonal phases is devised that follows a simplified approximate zone law analogous to the exact zone law for the hexagonal case. The indices based on this scheme will be designated as `Frank indices'. High-symmetry electron diffraction zone-axis patterns as well as powder X-ray diffraction patterns are indexed using Frank indices and compared with those of other indexing schemes. [source] | |||||||||||||