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272 results on '"Brunelli, Michela"'

1. Verification of Anderson superexchange in MnO via magnetic pair distribution function analysis and \textit{ab initio} theory

Author

Frandsen, Benjamin A., Brunelli, Michela, Page, Katharine, Uemura, Yasutomo J., Staunton, Julie B., and Billinge, Simon J. L.

Subjects
Condensed Matter - Strongly Correlated Electrons, Condensed Matter - Materials Science
Abstract

We present temperature-dependent atomic and magnetic pair distribution function (PDF) analysis of neutron total scattering measurements of antiferromagnetic MnO, an archetypal strongly correlated transition-metal oxide. The known antiferromagnetic ground-state structure fits the low-temperature data closely with refined parameters that agree with conventional techniques, confirming the reliability of the newly developed magnetic PDF method. The measurements performed in the paramagnetic phase reveal significant short-range magnetic correlations on a $\sim$1~nm length scale that differ substantially from the low-temperature long-range spin arrangement. \textit{Ab initio} calculations using a self-interaction-corrected local spin density approximation of density functional theory predict magnetic interactions dominated by Anderson superexchange and reproduce the measured short-range magnetic correlations to a high degree of accuracy. Further calculations simulating an additional contribution from a direct exchange interaction show much worse agreement with the data. The Anderson superexchange model for MnO is thus verified by experiment and confirmed by \textit{ab initio} theory.

Published
2015
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2. Non-stoichiometry and the magnetic structure of Sr2CrO3FeAs

Author

Tegel, Marcus, Hummel, Franziska, Su, Yixi, Chatterji, Tapan, Brunelli, Michela, and Johrendt, Dirk

Subjects
Condensed Matter - Superconductivity, Condensed Matter - Strongly Correlated Electrons
Abstract

The iron arsenide Sr2CrO3FeAs with the tetragonal Sr2GaO3CuS-type structure was synthesized and its crystal structure re-determined by neutron powder diffraction. In contrast to previous X-ray crystallographic studies, a mixed occupancy of chromium and iron was found within the FeAs4/4 layer (93+/-1% Fe : 7+/-1% Cr). We suggest that the partial Cr-doping at the Fe site is the reason for the absence of a spin-density wave anomaly and superconductivity in this compound. Additional experiments via neutron polarization analysis revealed short-range spin correlations below ~100 K and long-range antiferromagnetic ordering below T_N = 36 K with a magnetic propagation vector of q = (1/2, 1/2, 0). The Cr3+ ions form a collinear magnetic structure of the C-type in the magnetic space group C_Pmma' (a' = a-b, b'=a+b, c'=c), where Cr3+-ions occupy the 4g (0, 1/4, z) Wyckoff position. The magnetic moments are aligned along the orthorhombic a'-axis. At 3.5 K, an ordered magnetic moment of 2.75+/-0.05 mu_B for the Cr3+-sublattice was refined., Comment: 6 pages, 6 figures

Published
2009
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3. Crystal structure and phase transitions across the metal-superconductor boundary in the SmFeAsO1-xFx (0 < x < 0.20) family

Author

Margadonna, Serena, Takabayashi, Yasuhiro, McDonald, Martin T., Brunelli, Michela, Wu, G., Liu, R. H., Chen, X. H., and Prassides, Kosmas

Subjects
Condensed Matter - Superconductivity
Abstract

The fluorine-doped rare-earth iron oxyarsenides, REFeAsO1-xFx (RE =rare earth) have recently emerged as a new family of high-temperature superconductors with transition temperatures (Tc) as high as 55 K (refs 1-4). Early work has provided compelling evidence that the undoped parent materials exhibit spin-density-wave (SDW) antiferromagnetic order and undergo a structural phase transition from tetragonal to orthorhombic crystal symmetry upon cooling.5 Both the magnetic and structural instabilities are suppressed upon doping with fluoride ions before the appearance of superconductivity.6,7 Here we use high-resolution synchrotron X-ray diffraction to study the structural properties of SmFeAsO1-xFx (0 < x < 0.20) in which superconductivity emerges near x ~ 0.07 and Tc increases monotonically with doping up to x ~ 0.20.8 We find that orthorhombic symmetry survives through the metal-superconductor boundary well into the superconducting regime 2 and the structural distortion is only suppressed at doping levels, x > 0.15 when the superconducting phase becomes metrically tetragonal. Remarkably this crystal symmetry crossover coincides with reported drastic anomalies in the resistivity and the Hall coefficient8 and a switch of the pressure coefficient of Tc from positive to negative,9 thereby implying that the low-temperature structure plays a key role in defining the electronic properties of these superconductors.

Published
2008
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9. A new Al-rich hydroxylian pseudorutile from Kalimantan, Indonesia

Author

Grey, Ian E., Bordet, Pierre, Wilson, Nicholas C., townend, Raimunda, Bastow, Timothy J., and Brunelli, Michela

Subjects
Diaspore -- Properties, Aluminum -- Properties, Crystals -- Structure, Crystals -- Observations, X-rays -- Diffraction, X-rays -- Methods, Earth sciences
Abstract

A new type of Al-rich hydroxylian pseudortuile (HPR), containing 64.6 wt% Ti[O.sub.2], 12.1 wt% [Al.sub.2][O.sub.3], 10.9 wt% [Fe.sub.2][O.sub.3], and 12.4 wt% [H.sub.2]O, has been identified in detrital heavy mineral concentrates from Central Kalimantan, Indonesia. The unusual translucent orange-colored grains have been characterized using electron microprobe analyses, thermal analyses, [sup.27]Al MAS NMR, and synchrotron XRD studies including the use of differential pair distribution function analysis, to determine how the Al is incorporated. The results support a model in which diaspore-form AIOOH is incorporated into nanopores in the solid hydrogel-like mineral. The HPR matrix structure comprises disordered unit-cell scale intergrowths of diaspore-type and rutile-type structure elements, which have a close dimensional match to the diaspore structure, thus providing a suitable template for epitactic nucleation and growth of the diaspore. The average composition of the grains is [Fe[Ti.sub.6][O.sub.10.8][(OH).sub.5.4]] x 1.8A1OOH x [H.sub.2]O, where the formula within the square brackets represents the HPR matrix, and the A1OOH and [H.sub.2]O occupy the intragrain pore volume. Keywords: Hydroxylian pseudorutile, Al-rich pseudorutile, synchrotron XRD study, diaspore-rutile intergrowth structure DOI: 10.2138/am.2010.3330

Published
2010
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10. Reversible gas uptake by a nonporous crystalline solid involving multiple changes in covalent bonding

Author

Espallargas, Guillermo Minguez, Hippler, Michael, Florence, Alastair J., Fernandes, Philippe, van de Streek, Jacco, Brunelli, Michela, David, William I.F., Shankland, Kenneth, and Brammer, Lee

Subjects
Coordination compounds -- Research, Coordination compounds -- Chemical properties, Crystal lattices -- Observations, Chemistry
Abstract

The molecular coordination compound trans-[Cu[Cl.sub.2][(3-Clpy).sub.2]] (3-Clpy = 3-chloropyridine), which is prepared as a microcrystalline powder, is reacted directly with gaseous HCl in the absence of water to yield the crystalline salt [(3-ClpyH).sub.2][Cu[Cl.sub.4]]. The reversible uptake of HCl molecules from the gas phase by a nonporous crystalline solid has proceeded in the absence of any solvent and with retention of crystallinity, despite many changes that are required by this process.

Published
2007

12. Exploring local disorder in fast oxygen ion conductors by atomic pair distribution function analysis

Author

Brunelli Michela and Ceretti Monica

Subjects
Physics, QC1-999
Abstract

A preliminary structural investigation of local disorder in fully oxidized La2NiO4+δ was performed by Pair Distribution Function (PDF) analyses of X-ray and neutron powder diffraction data. X-ray diffraction data were recorded in-situ on warming from room temperature up to 450 ∘C.

Published
2015
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16. Hydrogenation of ethylene over palladium: evolution of the catalyst structure by operando synchrotron-based techniques.

Author

Bugaev, Aram L., Usoltsev, Oleg A., Guda, Alexander A., Lomachenko, Kirill A., Brunelli, Michela, Groppo, Elena, Pellegrini, Riccardo, Soldatov, Alexander V., and van Bokhoven, Jeroen A.

Abstract

Palladium-based catalysts are exploited on an industrial scale for the selective hydrogenation of hydrocarbons. The formation of palladium carbide and hydride phases under reaction conditions changes the catalytic properties of the material, which points to the importance of operando characterization for determining the relation between the relative fractions of the two phases and the catalyst performance. We present a combined time-resolved characterization by X-ray absorption spectroscopy (in both near-edge and extended regions) and X-ray diffraction of a working palladium-based catalyst during the hydrogenation of ethylene in a wide range of partial pressures of ethylene and hydrogen. Synergistic coupling of multiple techniques allowed us to follow the structural evolution of the palladium lattice as well as the transitions between the metallic, hydride and carbide phases of palladium. The nanometric dimensions of the particles resulted in the considerable contribution of both surface and bulk carbides to the X-ray absorption spectra. During the reaction, palladium carbide is formed, which does not lead to a loss of activity. Unusual contraction of the unit cell parameter of the palladium lattice in the spent catalyst was observed upon increasing hydrogen partial pressure. [ABSTRACT FROM AUTHOR]

Published
2021
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22. Fullerenium salts: a new class of [C.sub.60]-based compounds

Author

Ricco, Mauro, Pontiroli, Daniele, Mazzani, Marcello, Gianferrari, Fabio, Pagliari, Massimo, Goffredi, Angelo, Brunelli, Michela, Zandomeneghi, Giorgia, Meier, Beat H., and Shiroka, Toni

Subjects
Arsenic -- Chemical properties, Oxidation-reduction reaction -- Analysis, Chemistry
Abstract

The preparation and characterization of a fullerenium salt in the solid state is described, where the fullerene is in the 2+ oxidized state. The oxidizing power of one of the strongest Lewis acids (As[F.sub.5]) is analyzed and the high-resolution structural analysis of the compound has shown that the highly reactive [C.sub.60.sup.2+] units are arranged according to a novel one dimensional 'zigzag' polymer structure.

Published
2010

23. From average to local structure: a Rietveld and an atomic pair distribution function (PDF) study of selenium clusters in zeolite-NdY

Author

Abeykoon, A.M. Milinda, Donner, Wolfgang, Brunelli, Michela, Castro-Colin, Miguel, Jacobson, Allan J., and Moss, Simon C.

Subjects
Organometallic compounds -- Structure, Organometallic compounds -- Chemical properties, Selenium -- Chemical properties, Zeolites -- Structure, Zeolites -- Chemical properties, Chemistry
Abstract

The structure of Se particles in the [alpha]-cages of zeolite NdY is determined by Rietveld refinement and pair distribution function (PDF) analysis of X-ray data. The intracluster correlations and the cluster-framework correlations giving rise to diffuse scattering are modeled by using PDF analysis.

Published
2009

26. Li4C60: A polymeric fulleride with a two-dimensional architecture and mixed interfullerence bonding motifs

Author

Margadonna, Serena, Pontiroli, Daniele, Belli, Matteo, Shiroka, Toni, Ricco, Mauro, and Brunelli, Michela

Subjects
Chemical bonds -- Research, Carbon -- Electric properties, Lithium compounds -- Electric properties, Chemistry
Abstract

It is shown that the Li4C60 fulleride adopts a 2D monoclinic polymer structure, comprising two types of differently bonded fullerence chains running perpendicular to each other in the ab basal plane. This structure is the first example of a fullerene polymer with a mixed mode of interfullerene bridging through both single C-C bonds and [2+2] cycloaddition.

Published
2004

27. Exploring local disorder in fast oxygen ion conductors by atomic pair distribution function analysis

Author

Brunelli, Michela, Ceretti, Monica, European Synchrotron Radiation Facility (ESRF), Institut Charles Gerhardt Montpellier - Institut de Chimie Moléculaire et des Matériaux de Montpellier (ICGM ICMMM), and Ecole Nationale Supérieure de Chimie de Montpellier (ENSCM)-Centre National de la Recherche Scientifique (CNRS)-Université de Montpellier (UM)-Université Montpellier 1 (UM1)-Université Montpellier 2 - Sciences et Techniques (UM2)-Institut de Chimie du CNRS (INC)

Subjects
[PHYS]Physics [physics], [CHIM.MATE]Chemical Sciences/Material chemistry, ComputingMilieux_MISCELLANEOUS
Abstract

International audience

Published
2015
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28. Local Structures of Oxygen-Deficient Perovskite Sr2ScGaO5Polymorphs Explored by Total Neutron Scattering and EXAFS Spectroscopy

Author

Ceretti, Monica, Agostini, Giovanni, Brunelli, Michela, Corallini, Serena, Perversi, Giuditta, Cuello, Gabriel, Marsicano, Anna, and Paulus, Werner

Abstract

Depending on the synthesis route, the oxygen ion electrolyte Sr2ScGaO5shows two polymorphs, a brownmillerite and a cubic perovskite framework. In order to better explore oxygen diffusion pathways and mechanisms, we report here on a multitechnical approach to characterize local structural changes for Sr2ScGaO5polymorphs as a function of temperature, using a neutron pair distribution function (PDF) analysis together with an extended X-ray absorption fine structure (EXAFS) analysis. While for the brownmillerite type structure PDF and Rietveld refinements yield identical structural descriptions, considerable differences are found for the cubic oxygen-deficient polymorph. On a local scale a brownmillerite type vacancy structure could be evidenced for the cubic phase, suggesting a complex short-range ordering and respective microstructure. Both PDF and EXAFS data confirm an octahedral and tetrahedral coordination for Sc and Ga, respectively, at a local scale for both polymorphs. Related changes in the bond distances and oxygen vacancy ordering are discussed.

Published
2020
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29. Magnesium Imide: Synthesis and Structure Determination of an Unconventional Alkaline Earth Imide from Decomposition of Magnesium Amide

Author

Dolci, Francesco, Napolitano, Emilio, Weidner, Eveline, Enzo, Stefano, Moretto, Pietro, Brunelli, Michela, Hansen, Thomas, Fichtner, Maximilian, and Lohstroh, Wiebke

Abstract

Magnesium imide (MgNH) was produced by monitoring the decomposition process of magnesium amide with in situ neutron diffraction. Significant changes in the structure of magnesium amide are detected during heat treatment and eventually result in the formation of crystalline MgNH. A model for the crystal structure of magnesium imide (MgNH) is presented for the first time. Remarkably, magnesium imide offers unique structural features similar to the cyclosilicate class and can be described as a porous solid formed by a sequence of linked chains of face sharing Mg6N6hexagonal prism clusters.

Published
2024
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30. Investigating the Stability of Double Head to Tail Dimers and Ribbons in Multicomponent Crystals of cis-4-Aminocyclohexanecarboxilic Acid with Water and Oxalic Acid

Author

Mora, Asiloé J., Belandria, Lusbely M., Ávila, Edward E., Seijas, Luis E., Delgado, Gerzon E., Miró, Aira, Almeida, Rafael, Brunelli, Michela, and Fitch, Andrew N.

Abstract

The current contribution aims to investigate the stability of commonly occurring motifs present in certain amino acid structures after introducing additional molecules to form multicomponent crystals. The crystal structures of the amino acid cis-4-aminocyclohexanecarboxylic acid hemihydrate Iand dehydrate IIforms and that of its oxalate salt cocrystallized with oxalic acid III, were investigated employing a combination of techniques. Both single-crystal and powder X-ray diffraction were used to solve the structures, while temperature-control powder X-ray diffraction was used to follow the dehydration of I. Regardless of the added molecules that induce modifications of the intermolecular interactions within the crystals, some recurring supramolecular structures were identified: double head to tail dimers, graph symbol R22(16), and ribbons, graph symbol R22(16)R34(10). Stabilities of these supramolecular motifs were investigated using theoretical modeling with DFT/B3LYP/6-31++G (d,p) and PM6-D2H calculations. The theoretical calculations reproduced the experimental findings, confirming the extraordinary stability of these motifs. The molecular recognition of amino acid pairs to form double head to tail-dimers is undoubtedly the initial driving force for the crystal formation in all the three crystals investigated.

Published
2024
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35. Proceedings of the Thirteenth European Powder Diffraction Conference

Author

Brunelli, Michela, Bordet, Pierre, Scardi, Paolo, Institut Laue-Langevin (ILL), ILL, Matériaux, Rayonnements, Structure (MRS), Institut Néel (NEEL), Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Centre National de la Recherche Scientifique (CNRS)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Centre National de la Recherche Scientifique (CNRS)-Université Joseph Fourier - Grenoble 1 (UJF), Dipartimento di Ingegneria dei Materiali e Tecnologie Industriali, Universita di Trento (DIMTI), and Università degli Studi di Trento (UNITN)

Subjects
Crystallography, EPDIC, [CHIM.CRIS]Chemical Sciences/Cristallography, Powder Diffraction
Abstract

International audience; Proceedings of the Thirteenth European Powder Diffraction Conference This special issueofPowder Diffraction offers a selection of contributions presented at theEuropean Powder Diffraction Conference (EPDIC) held in Grenoble, France on October 28-31,2012 (EPDIC- 13). EPDIC is the only European conference completely dedicated to all aspects of the analysis of polycrystalline materials by diffraction methods. Started in Munich , Germany in 1991, EPDICs have rapidly become reference poi nts for all researchers in the field and are now regarded to be ideal venues for the presentation and diffusion of new developments in powder diffraction instrumentation, analysis, and applications. The guest editors of this special issue of Powder Diffraction Michela Brunelli, ILL, Grenoble, France Pierre Bordet, CNRS, Grenoble, France Paolo Scardi, University of Trento, Trento, Italy

Published
2013
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46. Assembling nanotubes with cyclic peptoids

Author

Tedesco, Consiglia, primary, Izzo, Irene, additional, De Riccardis, Francesco, additional, Vaughan, Gavin, additional, Brunelli, Michela, additional, Fitch, Andrew, additional, and Barboour, Leonard, additional

Published
2014
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47. Phase Transformations in the CeO2–Sm2O3System: A Multiscale Powder Diffraction Investigation

Author

Coduri, Mauro, Masala, Paolo, Allieta, Mattia, Peral, Inma, Brunelli, Michela, Biffi, Carlo Alberto, and Scavini, Marco

Abstract

The structure evolution in the CeO2–Sm2O3system is revisited by combining high resolution synchrotron powder diffraction with pair distribution function (PDF) to inquire about local, mesoscopic, and average structure. The CeO2fluorite structure undergoes two phase transformations by Sm doping, first to a cubic (C-type) and then to a monoclinic (B-type) phase. Whereas the C to B-phase separation occurs completely and on a long-range scale, no miscibility gap is detected between fluorite and C-type phases. The transformation rather occurs by growth of C-type nanodomains embedded in the fluorite matrix, without any long-range phase separation. A side effect of this mechanism is the ordering of the oxygen vacancies, which is detrimental for the application of doped ceria as an electrolyte in fuel cells. The results are discussed in the framework of other Y and Gd dopants, and the relationship between nanostructuring and the above equilibria is also investigated.

Published
2018
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