13 results on '"Brunelli, Michela"'
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2. Rhombic-shaped nanodomains in columbite driven by contrasting cation order.
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TARANTINO, SERENA C., ZEMA, MICHELE, CAPITANI, GIANCARLO, SCAVINI, MARCO, GHIGNA, PAOLO, BRUNELLI, MICHELA, and CARPENTER, MICHAEL A.
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MICROSTRUCTURE ,CRYSTALS ,PHASE transitions ,X-ray diffraction ,SYNCHROTRONS ,CATIONS - Abstract
Transient (non-equilibrium) microstructures in crystals may arise in an order-disorder phase transition that generates lattice strain. A two-phase field can develop if fluctuations of the order parameter lead to nucleation of an ordered phase in a disordered matrix, as we describe here for columbite. Synchrotron X-ray diffraction and transmission electron microscopy show that ordering in columbite involves two discrete phases with different degree of order but the same composition. A highly unusual distribution of ordered rhombic-shaped domains within a disordered matrix establishes on a nanometer scale and remains relatively stable over a prolonged period of annealing. Progressive ordering takes place within the ordered domains and the disordered matrix but the domains maintain more or less constant shape and distribution. We speculate that a new family of such microstructures could develop in other oxide phases with cation ordering transitions that are strongly first order in character. Long-term stability of such microstructures and their dependence on strain could open up the possibility of engineering the properties of crystals containing a percolating disordered matrix with ordered nanodomains of controlled dimensions. [ABSTRACT FROM AUTHOR]
- Published
- 2011
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3. Temperature phase changes in solid bicyclo[3.3.1]nonane-2,6-dione and bicyclo[3.3.1]nonane-3,7-dione from powder X-ray diffraction data.
- Author
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Brunelli, Michela, Neumann, Marcus A., Fitch, Andrew N., and Mora, Asiloé J.
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SIMULATED annealing , *X-ray diffraction , *SYNCHROTRONS , *MOLECULAR structure , *PHASE transitions , *ALGORITHMS - Abstract
The crystal structures of bicyclo[3.3.1]nonane-2,6-dione and bicyclo[3.3.1]nonane-3,7-dione have been solved by direct methods and by direct-space simulated annealing, respectively, from powder synchrotron X-ray diffraction data. Both compounds have a transition to a face-centred-cubic orientationally disordered phase (phase I) near 363 K, as shown by differential scanning calorimetry and powder diffraction measurements. Phase II of bicyclo[3.3.1]nonane-2,6-dione, which occurs below 363 K, is monoclinic, space group C2/ c, with a = 7.38042 (4), b = 10.38220 (5), c = 9.75092 (5) Å and β = 95.359 (1)° at 80 K. Phase II of bicyclo[3.3.1]nonane-3,7-dione, which occurs below 365 K, is tetragonal, space group P41212, with a = 6.8558 (1) and c = 16.9375 (1) Å at 100 K. This phase coexists in a biphasic mixture with a minor monoclinic phase II′ [ a = 11.450 (6), b = 20.583 (1), c = 6.3779 (3) Å, β = 94.7555 (5)°, at 100 K] detected in the sample, which impeded indexing with standard programs. The crystal structures of phases II were solved by direct methods and by direct-space simulated annealing, employing powder synchrotron X-ray diffraction data of increased instrumental intensity and resolution from the ID31 beamline at the ESRF, and novel indexing algorithms. Ab initio molecular orbital calculations on the two systems are reported. In the solid state, the molecules pack in chair–chair conformation; molecular structures and packing are discussed. [ABSTRACT FROM AUTHOR]
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- 2007
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4. Temperature effects on the hydrogen-bond patterns in 4-piperidinecarboxylic acid.
- Author
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Mora, Asiloé J., Avila, Edward E., Delgado, Gerzon E., Fitch, Andrew N., and Brunelli, Michela
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PIPERIDINE ,CARBOXYLIC acids ,TEMPERATURE effect ,HYDROGEN bonding ,COMPLEX compounds ,X-ray diffraction ,MOLECULAR structure - Abstract
A temperature-controlled X-ray powder diffraction experiment, complemented with TGA and DSC analysis, allowed us to follow changes in the molecular conformation and hydrogen-bond patterns of 4-piperidinecarboxylic acid. The presence of three phases is confirmed. Phase 1 represents the monohydrated form of 4-piperidinecarboxylic acid, which exists from room temperature to 359 K, where dehydration occurs. Phase 2 measured at 363 K corresponds to an anhydrous form of the acid. At ca 458 K the onset of a second, more gradual transition is observed, which ends at around 543 K. Phase 3 measured at 543 K is a hightemperature anhydrous form of the acid. The structures of phases 2 and 3 were solved from synchrotron powder diffraction data by simulated annealing using the DASH program and refined by the Rietveld method. The phase changes are accompanied by modification of the hydrogenbond patterns and of the torsional orientation of the terminal carboxylate group. This group makes a 49° rotation about the C1-C2 bond during the first transition. [ABSTRACT FROM AUTHOR]
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- 2005
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5. Low-Temperature Crystal Structure of S-camphor Solved from Powder Synchrotron X-ray Diffraction Data by Simulated Annealing
- Author
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Brunelli, Michela, Fitchci, Andrew N., and Mora, Asiloé J.
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CAMPHOR , *CRYSTALLOGRAPHY , *PHASE transitions , *X-ray diffraction - Abstract
The ordered, low-temperature crystal structure of the pure enantiomer of camphor (C10H16O) has been solved from high-resolution powder synchrotron X-ray diffraction data. The structure is orthorhombic, space group P212121, Z=8, with a=8.9277(2) A˚, b=27.0359(5) A˚, and c=7.3814(1) A˚ at 100 K. The structure was solved by autoindexing of the pattern, space group determination, and then optimization of the positions and orientations of the two independent molecules in the unit cell by simulated annealing. The molecular structure obtained from the restrained Rietveld refinement shows reasonable agreement with that optimized from ab initio molecular orbital calculations. In the crystal structure, the molecules are aligned antiferroelectrically and weak C–H…O hydrogen bonds link together the independent molecules. [Copyright &y& Elsevier]
- Published
- 2002
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6. trans-Decahydronaphthalene (decalin) from powder diffraction data.
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Eibl, Stefan, Fitch, Andrew, Brunelli, Michela, Evans, Alexander Dominic, Pattison, Philip, Plazanet, Marie, Johnson, Mark Robert, Alba-Simionesco, Christiane, and Schober, Helmut
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DECAHYDRONAPHTHALENE ,ORGANIC compounds ,CRYSTALLOGRAPHY ,X-ray diffraction ,SOLVENTS ,HYDROGEN bonding - Abstract
The article focuses on the crystal structure of the organic compound trans-Decahydronaphthalene or decalin which has been solved and refined using X-ray powder diffraction data. According to the authors, the organic compound has a variety of applications in research and industry, from multipurpose solvent to a hydrogen-storage medium for fuel cells. It notes that the location of the trans-decalin molecule is on an inversion centre with both rings in a chair conformation. Also cited is that the organic compound crystallizes easily without hydrogen bonds.
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- 2009
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7. A glass capillary cell for in situ powderX-ray diffraction of condensed volatile compounds. Solid HCFC-123a and HCFC-124.
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Brunelli, Michela and Fitch, Andrew N.
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X-ray diffraction , *CONDENSATION - Abstract
Describes a rotating glass capillary cell with a gas handling system built to allow in situ studies by powder X-ray diffraction. Condensation of volatile compounds; Disordered hexagonal structures; Hydrochlorofluorocarbons.
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- 2003
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8. Structural Description of Pressure-Induced Amorphization in ZrW{sub 2}O{sub 8}
- Author
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Brunelli, Michela [ESRF, BP220, F-38043 Grenoble Cedex (France)]
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- 2007
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9. Defect Structure of Y-Doped Ceria on DifferentLength Scales.
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Coduri, Mauro, Scavini, Marco, Allieta, Mattia, Brunelli, Michela, and Ferrero, Claudio
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CRYSTAL defects , *DOPED semiconductors , *CERIUM oxides , *CRYSTAL structure , *X-ray diffraction , *YTTRIUM , *CRYSTALLOGRAPHY - Abstract
Anexhaustive structural investigation of a Y-doped ceria (Ce1–xYxO2–x/2) system over different lengthscales was performed by combining Rietveld and Pair Distribution Functionanalyses of X-ray and neutron powder diffraction data. For low dopingamounts, which are the most interesting for application, the localstructure of Y-doped ceria can be envisaged as a set of distortedCeO2- and Y2O3-like droplets. Byconsidering interatomic distances on a larger scale, the above dropletsaverage out into domains resembling the crystallographic structureof Y2O3. The increasing spread and amount ofthe domains with doping forces them to interact with each other, leadingto the formation of antiphase boundaries. Single phase systems areobserved at the average ensemble level. [ABSTRACT FROM AUTHOR]
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- 2013
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10. Diffraction study of pressure-amorphized ZrW2O8 using in situ and recovered samples.
- Author
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Keen, David A., Goodwin, Andrew L., Tucker, Matthew G., Hriljac, Joseph A., Bennett, Thomas D., Dove, Martin T., Kleppe, Annette K., Jephcoat, Andrew P., and Brunelli, Michela
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X-ray diffraction , *CRYSTALLINE electric field , *AMORPHOUS substances , *STRUCTURAL frame models , *TOPOLOGY - Abstract
High-energy x-ray diffraction data from a series of amorphous ZrW2O8 samples, recovered from a number of different pressures, have been measured and compared with similar data collected from a sample contained within a diamond anvil cell and measured in situ at high pressure. Samples at lower pressures are a mix of crystalline and amorphous phases, whereas those above 7 GPa (both recovered and in situ) appear to be completely amorphous. Although there are only very small changes in the diffraction data from the pure phase samples recovered from different pressures, larger changes are observed in situ as a function of pressure. However, the same structural model can be used to describe all data, albeit using different densities. This strongly suggests that the amorphous phase is undergoing nonreconstructive compression in this pressure range, without fundamental modification of the underlying topology. [ABSTRACT FROM AUTHOR]
- Published
- 2011
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11. Aluminium substitution in iron(II–III)-layered double hydroxides: Formation and cationic order
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Ruby, Christian, Abdelmoula, Mustapha, Aissa, Rabha, Medjahdi, Ghouti, Brunelli, Michela, and François, Michel
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ALUMINUM , *METAL toxicology , *LIGHT metals , *MERCURY - Abstract
Abstract: The formation and the modifications of the structural properties of an aluminium-substituted iron(II–III)-layered double hydroxide (LDH) of formula (OH)12 SO4, 8H2O are followed by pH titration curves, Mössbauer spectroscopy and high-resolution X-ray powder diffraction using synchrotron radiation. Rietveld refinements allow to build a structural model for hydroxysulphate green rust, GR(SO4 2−), i.e. y=0, in which a bilayer of sulphate anions points to the Fe3+ species. A cationic order is proposed to occur in both GR(SO4 2−) and aluminium-substituted hydroxysulphate green rust when y<0.08. Variation of the cell parameters and a sharp decrease in average crystal size and anisotropy are detected for an aluminium content as low as y=0.01. The formation of Al-GR(SO4 2−) is preceded by the successive precipitation of FeIII and AlIII (oxy)hydroxides. Adsorption of more soluble AlIII species onto the initially formed ferric oxyhydroxide may be responsible for this slowdown of crystal growth. Therefore, the insertion of low aluminium amount (y∼0.01) could be an interesting way for increasing the surface reactivity of iron(II–III) LDH that maintains constant the quantity of the reactive FeII species of the material. [Copyright &y& Elsevier]
- Published
- 2008
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12. Hierarchically structured scleractinian coral biocrystals
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Przeniosło, Radosław, Stolarski, Jarosław, Mazur, Maciej, and Brunelli, Michela
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CORALS , *FIBERS , *BIOMINERALIZATION , *ARAGONITE - Abstract
Abstract: Microscopic (AFM and FESEM) observations show that scleractinian coral biomineral fibers in extant Desmophyllum and Favia, and fossil Jurassic Isastrea are composed of nanocrystalline grains of about 30–100nm in size. In contrast to these findings, SR diffraction data on the same coral materials exhibit narrow Bragg peaks suggesting much larger crystallite size. These seemingly contradicting results of microscopic and diffraction studies are reconciled within a new, minute-scale model of scleractinian biomineral fibers. In this model, nanocrystalline aragonite units are interconnected by mineral bridges and form aggregates usually larger than 200nm. Most likely, the size of the aggregates is resulting from physiological biomineralization cycles that control cellular secretion of ions and biopolymeric species. Intercalation of biopolymers into crystal lattice may influence consistently several structural parameters of the scleractinian coral bio-aragonite in all studied samples: (i) the lattice parameters and internal strains of the bio-aragonite are larger than in mineral aragonite, (ii) lattice parameter elongations and internal strains reveal directional anisotropy with respect to crystallographic axes. [Copyright &y& Elsevier]
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- 2008
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13. X-ray Illumination Induced Fe(II) Spin Crossover in the Prussian Blue Analogue Cesium Iron Hexacyanochromate.
- Author
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Papanikolaou, Dionisis, Margadonna, Serena, Kosaka, Wataru, Ohkoshi, Shin-ichi, Brunelli, Michela, and Prassides, Kosmas
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METAL ions , *X-ray diffraction , *PHASE transitions , *FRANCK-Condon principle , *ENERGY levels (Quantum mechanics) , *OXIDATION-reduction reaction , *CHEMICAL reactions - Abstract
The effect of X-ray illumination on the structural properties of the mixed valence Prussian blue analogue CsFeII[CrIII(CN)6] has been studied by time-dependent high-resolution synchrotron X-ray diffraction. Abrupt isosymmetric phase transitions, accompanied by dramatic volume collapse, were found in the temperature range 245–265 K, induced by sudden FeII spin transitions from the high spin (HS) (4t2g²eg, S = 2) to the low spin (LS) (6t2g0eg, S = 0) configuration. Absorption of X-ray photons generates photoexcited FeII(LS) domains whose size rapidly grows with time until the percolation threshold is reached and the structure collapse is triggered. The persistent character of the optically excited spin crossover states derives from the strong electron-phonon coupling, associated with the large lattice relaxations, which accompany the internal spin rearrangements. It is thus possible to use X-ray light in a controllable and efficient way to induce photoswitching between the ground and hidden or inaccessible excited states in suitably selected multistable materials in the bulk. [ABSTRACT FROM AUTHOR]
- Published
- 2006
- Full Text
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