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Lock N.,Center for Materials Crystallography | Lock N.,University of Gottingen | Jensen E.M.L.,Center for Materials Crystallography | Mi J.,Center for Materials Crystallography | And 4 more authors.
Dalton Transactions | Year: 2013

Metal functionalized nanoparticles potentially have improved properties e.g. in catalytic applications, but their precise structures are often very challenging to determine. Here we report a structural benchmark study based on tetragonal anatase TiO2 nanoparticles containing 0-2 wt% copper. The particles were synthesized by continuous flow synthesis under supercritical water-isopropanol conditions. Size determination using synchrotron PXRD, TEM, and X-ray total scattering reveals 5-7 nm monodisperse particles. The precise dopant structure and thermal stability of the highly crystalline powders were characterized by X-ray absorption spectroscopy and multi-temperature synchrotron PXRD (300-1000 K). The combined evidence reveals that copper is present as a dopant on the particle surfaces, most likely in an amorphous oxide or hydroxide shell. UV-VIS spectroscopy shows that copper presence at concentrations higher than 0.3 wt% lowers the band gap energy. The particles are unaffected by heating to 600 K, while growth and partial transformation to rutile TiO2 occur at higher temperatures. Anisotropic unit cell behavior of anatase is observed as a consequence of the particle growth (a decreases and c increases). This journal is © The Royal Society of Chemistry 2013.


Eikeland E.,Center for Materials Crystallography | Lock N.,University of Aarhus | Filso M.,Center for Materials Crystallography | Stingaciu M.,Center for Materials Crystallography | And 4 more authors.
Inorganic Chemistry | Year: 2014

Four transition metal formate coordination polymers with anionic frameworks, namely, Na[Mn(HCOO)3], K[Mn(HCOO)3], Na2[Cu3(HCOO)8], and K2[Cu5(HCOO)12], were synthesized using a mild solution chemistry approach. Multitemperature single-crystal (100-300 K) and powder X-ray diffraction studies of the compounds reveal structures of large diversity ranging from cubic chiral Na-Mn formate to triclinic Na-Cu formate. The structural variety is caused by the nature of the transition metals, the alkali metal ion templation, and the versatility of the formate group, which offers metal-metal coordination through three different O-C-O bridging modes (syn-syn, syn-anti, anti-anti) in addition to metal-metal bridging via a single oxygen atom. The two manganese(II) compounds contain mononuclear, octahedrally coordinated moieties, but the three-dimensional connectivity between the manganese octahedra is very different in the two structures. The two copper frameworks, in contrast, consist of binuclear and mononuclear moieties (Na-Cu formate) and trinuclear and mononuclear moieties (K-Cu formate), respectively. Procrystal electron density analysis of the compounds indicates one-dimensional K+-ion conductivity in K-Mn and K-Cu, and the nature of the proposed potassium ion migration is compared with results from similar analysis on known Na+ and K+ ion conductors. K-Mn and Na-Mn were tested as cathode materials, but this resulted in poor reversibility due to low conductivity or structural collapse. The magnetic properties of the compounds were studied by vibrating sample magnetometric measurements, and their thermal stabilities were determined by thermogravimetric analysis and differential thermal analysis. Despite structural differences, the metal formates that contain the same transition metal have similar magnetic properties and thermal decomposition pathways, that is, the nature of the transition metal controls the compound properties. © 2014 American Chemical Society.


Bindzus N.,Center for Materials Crystallography | Straaso T.,Niels Bohr Institute | Wahlberg N.,Center for Materials Crystallography | Becker J.,Center for Materials Crystallography | And 4 more authors.
Acta Crystallographica Section A: Foundations and Advances | Year: 2014

Synchrotron powder X-ray diffraction data are used to determine the core electron deformation of diamond. Core shell contraction inherently linked to covalent bond formation is observed in close correspondence with theoretical predictions. Accordingly, a precise and physically sound reconstruction of the electron density in diamond necessitates the use of an extended multipolar model, which abandons the assumption of an inert core. The present investigation is facilitated by negligible model bias in the extraction of structure factors, which is accomplished by simultaneous multipolar and Rietveld refinement accurately determining an atomic displacement parameter (ADP) of 0.00181 (1)°2. The deconvolution of thermal motion is a critical step in experimental core electron polarization studies, and for diamond it is imperative to exploit the monatomic crystal structure by implementing Wilson plots in determination of the ADP. This empowers the electron-density analysis to precisely administer both the deconvolution of thermal motion and the employment of the extended multipolar model on an experimental basis. © 2014 International Union of Crystallography.


Straaso T.,Copenhagen University | Dippel A.-C.,German Electron Synchrotron | Becker J.,Center for Materials Crystallography | Als-Nielsen J.,Copenhagen University
Journal of Synchrotron Radiation | Year: 2014

Under the experimental condition that all Bragg peaks in a powder X-ray diffraction (PXRD) pattern have the same shape, one can readily obtain the Bragg intensities without fitting any parameters. This condition is fulfilled at the P02.1 beamline at PETRA III using the seventh harmonic from a 23 mm-period undulator (60 keV) at a distance of 65 m. For grain sizes of the order of 1 μm, the Bragg peak shape in the PXRD is entirely determined by the diameter of the capillary containing the powder sample and the pixel size of the image plate detector, and consequently it is independent of the scattering angle. As an example, a diamond powder has been chosen and structure factors derived which are in accordance with those calculated from density functional theory methods of the WIEN2k package to within an accuracy that allows a detailed electron density analysis.© 2014 International Union of Crystallography.


Andersen H.L.,Center for Materials Crystallography | Jensen K.M.O.,Center for Materials Crystallography | Tyrsted C.,Center for Materials Crystallography | Bojesen E.D.,Center for Materials Crystallography | Christensen M.,Center for Materials Crystallography
Crystal Growth and Design | Year: 2014

The formation and growth of maghemite (γ-Fe2O3) nanocrystals during the hydrothermal synthesis from aqueous solutions of ammonium iron(III) citrate (C6H8O7· xFe(III)·yNH3) have been studied by in situ powder X-ray diffraction (PXRD). Data analysis by Rietveld refinement and whole powder pattern modeling (WPPM) reveals that the crystallite size and size distribution can be precisely tuned through simple adjustments of the reaction temperature and time. Increasing the reaction temperature causes faster growth and results in larger crystallites while the size distribution broaden as reaction times increase, regardless of temperature. The crystallization kinetics were investigated by fitting the Johnson-Mehl-Avrami-Kolmogorov (JMAK) kinetic model to the growth curves. The activation energy was found to be 67(15) kJ/mol, and the limiting mechanisms of crystallite formation were determined. The growth was studied with various precursor compositions of ammonium iron(III) citrate and Fe(NO3)3·9H2O or FeCl 3·6H2O. Increasing the fraction of Fe(NO 3)3·9H2O in the precursor results in larger maghemite nanocrystallites. The addition of Fe(NO3) 3·9H2O also results in the formation of the thermodynamically more stable hematite (α-Fe2O3) phase as a byproduct. © 2014 American Chemical Society.


Norby P.,Center for Materials Crystallography | Roelsgaard M.,Center for Materials Crystallography | Sondergaard M.,Center for Materials Crystallography | Iversen B.B.,Center for Materials Crystallography
Crystal Growth and Design | Year: 2016

MSb2O4 constitutes a relatively unexplored class of multinary oxides that is traditionally synthesized by high-temperature solid-state methods. Here, we report a facile synthesis of CoSb2O4 under hydrothermal conditions (T = 135-300 °C, 256 bar). Using in situ synchrotron powder X-ray diffraction (PXRD), the formation and growth of CoSb2O4 nanoparticles are followed in real time using different precursor stoichiometries. Phase-pure CoSb2O4 can be formed at 135 °C, although the formation mechanism changes with precursor stoichiometry. The crystallite size can be fine-tuned between 14 and 17.5 nm under nonstoichiometric conditions, but crystallites twice as large are found in the stoichiometric case. An activation energy of 65(12) kJ/mol is obtained for the crystallization from a nonstoichiometric precursor. Modeling of atomic displacement parameters obtained from Rietveld refinement of multi-temperature high-resolution synchrotron PXRD data gives a Debye temperature of 331(11) K. The thermal expansion coefficients for the material was found to be αa = 6.2(1) × 10-6 K-1 and αc = 3.1(4) × 10-6 K-1. Electrochemical measurement shows that CoSb2O4 displays a large irreversible capacity (1131 mAh/g) on the first cycle in Li-ion half-cells and that the capacity decreases significantly in the following cycles. © 2016 American Chemical Society.


Straas T.,Niels Bohr Institute | Becker J.,Center for Materials Crystallography | Iversen B.B.,Center for Materials Crystallography | Als-Nielsen J.,Niels Bohr Institute
Journal of Synchrotron Radiation | Year: 2013

In a powder diffraction pattern one measures the intensity of Miller-indexed Bragg peaks versus the wavevector transfer sin/. With increasing wavevector transfer the density of occurrence of Bragg peaks increases while their intensity decreases until they vanish into the background level. The lowest possible background level is that due to Compton scattering from the powder. A powder diffraction instrument has been designed and tested that yields this ideal low-background level, obtainable by having the space between sample and detector all in vacuum with the entrance window so far upstream that scattering from it is negligible. To minimize overlap of Bragg peaks the combination of fine collimation of synchrotron radiation, a thin cylindrical sample and a high-resolution imaging plate detector is taken advantage of. © 2013 International Union of Crystallography Printed in Singapore-all rights reserved.


Madsen S.R.,Center for Materials Crystallography | Moggach S.A.,University of Edinburgh | Overgaard J.,Center for Materials Crystallography | Brummerstedt Iversen B.,Center for Materials Crystallography
Acta Crystallographica Section B: Structural Science, Crystal Engineering and Materials | Year: 2016

The effect of pressure on the crystal structure of a coordination polymer, emim[MnII(btc)] (emim = 1-ethyl,3-methyl imidazolium cation, btc = 1,3,5-benzene-tricarboxylate), was investigated with single-crystal X-ray diffraction. At 4.3 GPa the unit-cell volume had decreased by 14% compared with ambient conditions. The unit-cell contraction is highly anisotropic, with the a- and b-axes decreasing by 5.5 and 9.5%, respectively, and the c-axis compressing a mere 0.25% up to 1.7 GPa followed by a 0.2% expansion between 1.7 and 4.3 GPa. The 0.2% increase in length of the c-axis in this interval happens above the quasi-hydrostatic limit of the pressure-transmitting medium and therefore it might be a consequence of strain gradients. Under ambient conditions, two MnO6 units are connected by two carboxylate ligands to form dimeric units. On increasing pressure, a non-bonded O atom from a bridging carboxylate group approaches the Mn atom, with the Mn - O distance decreasing from 2.866 (1) Å at 0.3 GPa to 2.482 (6) Å at 4.3 GPa, increasing the coordination environment of the Mn ion from six- to seven-coordinated. © 2016.


Andersen H.L.,Center for Materials Crystallography | Christensen M.,Center for Materials Crystallography
Nanoscale | Year: 2015

The evolution of size and size distribution during hydrothermal synthesis of nanocrystalline CoFe2O4 has been studied by in situ synchrotron powder X-ray diffraction (PXRD). Varying synthesis temperature or [OH-] concentration in the precursor proves to have no significant effect on the final volume-weighted nanocrystallite sizes (∼12 nm) of CoFe2O4. However, analysis by whole powder pattern modeling of the [OH-] concentration series reveals a substantial difference in the number-weighted size distributions when varying the amount of base used. Furthermore, changing the metal ion concentration prior to NaOH addition in the precursor preparation gives a handle to control the nanoparticle sizes (∼5-15 nm). All in situ experiments show almost instantaneous formation of the CoFe2O4 nanocrystallites, without significant growth or broadening of the size distribution after 60 s. Magnetic hysteresis curve measurements illustrate, how this facilitates the tailoring of materials with specific magnetic properties, as larger particles (∼15 nm) exhibit hard magnetic properties while the smaller particles (∼6-7 nm) are superparamagnetic. This journal is © The Royal Society of Chemistry.


PubMed | University of Edinburgh and Center for Materials Crystallography
Type: Journal Article | Journal: Acta crystallographica Section B, Structural science, crystal engineering and materials | Year: 2016

The effect of pressure on the crystal structure of a coordination polymer, emim[Mn(II)(btc)] (emim = 1-ethyl,3-methyl imidazolium cation, btc = 1,3,5-benzene-tricarboxylate), was investigated with single-crystal X-ray diffraction. At 4.3GPa the unit-cell volume had decreased by 14% compared with ambient conditions. The unit-cell contraction is highly anisotropic, with the a- and b-axes decreasing by 5.5 and 9.5%, respectively, and the c-axis compressing a mere 0.25% up to 1.7GPa followed by a 0.2% expansion between 1.7 and 4.3GPa. The 0.2% increase in length of the c-axis in this interval happens above the quasi-hydrostatic limit of the pressure-transmitting medium and therefore it might be a consequence of strain gradients. Under ambient conditions, two MnO6 units are connected by two carboxylate ligands to form dimeric units. On increasing pressure, a non-bonded O atom from a bridging carboxylate group approaches the Mn atom, with the Mn-O distance decreasing from 2.866(1) at 0.3GPa to 2.482(6) at 4.3GPa, increasing the coordination environment of the Mn ion from six- to seven-coordinated.

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