Michela Brunelli

University of Milan, Milano, Lombardy, Italy

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Publications (133)384.63 Total impact

  • Michela Brunelli · Mauro Coduri · Monica Ceretti · Werner Paulus

    No preview · Article · Dec 2015 · Journal of Physics D Applied Physics
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    ABSTRACT: A new hierarchical approach is presented for elucidating the structural disorder in Ce1−xGdxO2−x/2 solid solutions on different scale lengths. The primary goal of this investigation is to shed light on the relations between the short-range and the average structure of these materials via an analysis of disorder on the mesocopic scale. Real-space (pair distribution function) and reciprocal-space (Rietveld refinement and microstructure probing) analysis of X-ray powder diffraction data and electron spin resonance (ESR) investigations were carried out following this approach. On the local scale, Gd- and Ce-rich droplets (i.e. small regions a few ångströms wide) form, exhibiting either a distorted fluorite (CeO2) or a C-type (Gd2O3) structure in the whole compositional range. These droplets can then form C-type nanodomains which, for Gd concentrations x Gd ≤ 0.25, are embedded in the fluorite matrix. At the site percolation threshold p C for a cubic lattice (x Gd = p C ≃ 0.311), C-type nanodomains percolate inside each crystallite and a structural phase transformation is observed. When this occurs, the peak-to-peak ESR line width ΔH pp shows a step-like behaviour, which can be associated with the increase in Gd–Gd dipolar interactions. A general crystallographic rationale is presented to explain the fluorite-to-C-type phase transformation. The approach shown here could be adopted more generally in the analysis of disorder in other highly doped materials.
    Full-text · Article · Sep 2015
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    Lee Brooks · Michela Brunelli · Philip Pattison · Graeme R Jones · Andrew Fitch
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    ABSTRACT: The crystal structures of eight mono-methyl alkanes have been determined from single-crystal or high-resolution powder X-ray diffraction using synchrotron radiation. Mono-methyl alkanes can be found on the cuticles of insects and are believed to act as recognition pheromones in some social species, e.g. ants, wasps etc. The molecules were synthesized as pure S enantiomers and are (S)-9-methylpentacosane, C26H54; (S)-9-methylheptacosane and (S)-11-methylheptacosane, C28H58; (S)-7-methylnonacosane, (S)-9-methylnonacosane, (S)-11-methylnonacosane and (S)-13-methylnonacosane, C30H62; and (S)-9-methylhentriacontane, C32H66. All crystallize in space group P21. Depending on the position of the methyl group on the carbon chain, two packing schemes are observed, in which the molecules pack together hexagonally as linear rods with terminal and side methyl groups clustering to form distinct motifs. Carbon-chain torsion angles deviate by less than 10° from the fully extended conformation, but with one packing form showing greater curvature than the other near the position of the methyl side group. The crystal structures are optimized by dispersion-corrected DFT calculations, because of the difficulties in refining accurate structural parameters from powder diffraction data from relatively poorly crystalline materials.
    Full-text · Article · Sep 2015
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    Full-text · Article · Aug 2015 · Acta Crystallographica Section A: Foundations and Advances
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    Preview · Article · Aug 2015 · Acta Crystallographica Section A: Foundations and Advances
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    ABSTRACT: The size of dopant-rich nanodomains was assessed in four samples of Ce1−μ Y μ O2−μ/2 through systematic pair distribution function (PDF) refinements. Experimental G(r) curves were fitted by different structural models with the aim of finding a description which balanced precise structure parameterization and reasonable number of parameters. The most reliable model was a single Y2O3-like phase, which best accommodated to the close relationship between the fluorite (CeO2-like) and C-type (Y2O3-like) structures. In this model, a refined cation coordinate, x(M2), measured the relative occurrence in the G(r) of the chemical environment of Y and Ce at any value of r. The r-value at which x(M2) vanished, i.e. at which the refined C-type cell becomes a redundant, low-symmetry description of a fluorite cell, was assumed as the size of a C-type domain. Subtle features in G(r) could be attributed to the fluorite or C-type phase up to ~500 Å thanks to the narrow instrumental resolution function of the ID31 beamline (now ID22) at the ESRF, which allows us to get high resolution PDF data.
    Full-text · Article · Jun 2015 · Powder Diffraction
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    ABSTRACT: LiBH4 has gained much attention as a potential hydrogen storage material due to its high hydrogen storage capacity of 18.5 wt%. However, LiBH4 only releases its full hydrogen capacity at temperatures greater than 600 °C and requires hydrogen pressures of at least 350 bar to rehydrogenate the end products. The dehydrogenation temperature can be altered by thermodynamic tuning through the addition of a reactive agent resulting in a lower enthalpy of dehydrogenation. Most multicomponent hydride systems display dehydrogenation temperatures above 300 °C, making them less desirable for automotive applications. In this work we report the solid-state decomposition of LiBH4 in the 2LiBH4:CaNi5 system below the LiBH4 melting temperature of 270 °C. In situ neutron diffraction measurements confirmed the decomposition took place in the solid state at 200 °C, forming LiD, CaD2, Ni3B and Ni2B phases as end products. The solid-state decomposition was further supported by SEM and TEM measurements showing the presence of nano-crystalline particles.
    No preview · Article · Feb 2015 · International Journal of Hydrogen Energy
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    ABSTRACT: Neutron diffraction studies performed on the solid solution of (BiFeO3)1−x(PbTiO3)x reveal a mixture of two nanoscale phases with different crystal structures: a rhombohedral BiFeO3-based phase and a tetragonal PbTiO3-based phase. The ratio of Fe3+ and Ti4+ ions in the two phases is practically constant; only the proportion of the phases changes. The magnetic moments in the BiFeO3-based phase, in contrast to BiFeO3, deviate from the basal plane. The temperature evolutions of the spin components along the hexagonal axis and within the perpendicular plane are different, leading to a spin re-orientation transition. The antiferromagnetic order in the PbTiO3-based phase corresponds to a simple structure with the propagation vector (1/2, 1/2, 1/2). The temperature dependence of the antiferromagnetic moment in the tetragonal phase at x = 0.5 indicates a canted antiferromagnetic order and a net ferromagnetic moment. A strong magnetic coupling between the two constituting phases due to the nanoscale character of the phases and well-developed interface between nanoparticles has been observed. The system of (BiFeO3)1−x(PbTiO3)x demonstrates an interesting scenario, where the proximity effects in the unstable system play a crucial role in the appearance of the unusual magnetic properties.
    Full-text · Article · Jan 2015 · Journal of Physics Condensed Matter
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    Michela Brunelli · Monica Ceretti

    Preview · Article · Jan 2015 · The European Physical Journal Conferences
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    ABSTRACT: The crystallographic structure of Tb- and Pr-doped ceria is investigated through X-ray and neutron powder diffraction, combining pair distribution function and UV–vis spectroscopy. Compared to trivalent dopants, Tb and Pr show peculiar optical and crystallographic properties: whilst Tb have a mixed +3/+4 valence state, Pr is stable mostly in the +4 valence state up to ~50% dopant concentration. For larger Pr amounts, doping promotes a fluorite to monoclinic phase transformation. A straightforward method for extracting the dopant oxidation state by the cell parameter dependence on the ionic radius is also proposed.
    No preview · Article · Dec 2014 · Solid State Ionics
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    ABSTRACT: Inelastic neutron scattering experiments and ab-initio calculations have been used to investigate the vibrational modes, in a wide energy region between 0 and 200 meV, of hydrogenated graphene produced by chemical method. The results show the presence of atomic hydrogen chemisorbed at the graphene surface. At 10 K, the measured high energy density of states is remarkably similar to that of hydrogenated ball-milled graphite, in which hydrogen is most likely bonded to C atoms at the edges. In fact, in both hydrogenated graphene and hydrogenated ball-milled graphite, the high frequency modes (100-200 meV) show strong similarities with the C-H bending modes of the coronene molecule, in which hydrogen is bonded at the edges. This hypothesis has been supported by ab-initio calculations.
    Full-text · Article · Nov 2014 · Journal of Physics Conference Series
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    ABSTRACT: Cyclic alpha-peptoids hold the attention of both synthetic and supramolecular chemists for their biostability and potential diversity but also for their elegant and intriguing architectures.[1] Peptoids differ from peptides in the side chains, which are shifted by one position along the peptide backbone to the nitrogen atom to give N-substituted oligoglycine. The lack of the amide proton prevents the formation of NH···OC hydrogen bonds and weaker interactions, as CH···OC hydrogen bonds and CH-pi interactions, play a key role. Inter-annular CH···OC hydrogen bonds can provide face to face or side by side arrangement of macrocycles mimicking beta-sheet secondary structure in proteins.[2] In particular, the role of side chains in the solid state assembly of peptoid macrocycles will be discussed to show how they can promote the formation of a peptoid nanotube by acting as pillars, extending vertically with respect to the macrocycle planes. [3] Examples of the solid state assembly of free and metallated cyclic peptoids will be reported to show their extreme versatility as building blocks for designing new materials, with novel chemical properties and defined biological activities. In particular the first crystal structure of a recently synthesized novel cyclic alpha-peptoid, containing open channels with a radius of approximately 7 Å, will be discussed as a case of the successful engineering of cyclopeptoid crystals. In figure it is shown the channel void surface as seen along the a axis (0.0003 au, CrystalExplorer 3.1). The results of recent variable temperature high resolution XRPD measurements performed at ESRF beamline ID31 will be also reported to highlight the unusual thermal stability of this class of compounds and how the mobility of the side chains may be exploited to prepare new functional materials. EU FP7-People- IRSES grant number 319011 is gratefully acknowledged.
    No preview · Article · Aug 2014 · Acta Crystallographica Section A: Foundations and Advances
  • Andrew Fitch · Lee Brooks · Philip Pattison · Michela Brunelli · Graeme Jones
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    ABSTRACT: Eight chiral monomethyl alkanes have been synthesized and their crystal structures solved from high resolution powder diffraction patterns collected using synchrotron radiation. Such compounds have been seen to act as recognition pheromones in social insects. Carbon chain lengths varied from C 2 5 to C 3 1 with the methyl group at various positions along the chain. One compound, (S)-7-methylnonacosane, also formed a low quality single crystal from which its structure was solved and refined. Although the powder diffraction patterns were good enough to solve the crystal structures, using the standard technique of real-space simulated annealing, with near-linear molecules, chemically unreasonable distortions occurred during Rietveld refinement unless many distance, angle and torsion restraints were imposed. From the results of the single-crystal structure it is evident that there is a gentle bend in the molecule close to the position of the methyl side chain. Thus imposing a near-linear molecule is incorrect, and giving sufficient freedom in the Rietveld refinement to allow the molecule to bend leads to an inaccurate structure. In short, the correct structure must be known to judge the strength of the restraints to apply, and this must vary at different parts of the chain. As an alternative to refining the structure from the powder diffraction data, the structures have been optimized via dispersion-corrected DFT calculations (Van der Streek and Neumann, 2010) starting from the powder structures. Agreement between the single-crystal and DFT-minimized structures is satisfactory, with an rms distance of 0.054 Å and a maximum distance of 0.132 Å when comparing carbon atoms positions. With this approach, a well defined structure optimization strategy is used for all the crystal structures. The molecules studied fall into two packing types, (both with monoclinic symmetry), depending on the position of the methyl group on the main carbon chain relative to the overall chain length.
    No preview · Article · Aug 2014 · Acta Crystallographica Section A: Foundations and Advances
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    ABSTRACT: We report the structural analysis of the highly-doped lithium fulleride Li12C60, performed using low-temperature neutron powder diffraction. Although the main reflections could be initially indexed with a fcc cell, Monte Carlo Simulated Annealing suggests an unusual monoclinic arrangement for the fullerene molecules. In this structure, C-60 units with the same orientation are alternatively stacked to form layers, thus maximising their sterical crowding. Rietveld refinement allowed to localise Li ions, which are organised in clusters belonging to the pseudo-tetrahedral voids with a non-complete charge transfer as confirmed by Raman spectroscopy.
    Full-text · Article · Aug 2014 · Chemical Physics Letters
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    ABSTRACT: An exhaustive structural investigation of a Y-doped ceria (Ce1–xYxO2–x/2) system over different length scales was performed by combining Rietveld and Pair Distribution Function analyses of X-ray and neutron powder diffraction data. For low doping amounts, which are the most interesting for application, the local structure of Y-doped ceria can be envisaged as a set of distorted CeO2- and Y2O3-like droplets. By considering interatomic distances on a larger scale, the above droplets average out into domains resembling the crystallographic structure of Y2O3. The increasing spread and amount of the domains with doping forces them to interact with each other, leading to the formation of antiphase boundaries. Single phase systems are observed at the average ensemble level.
    No preview · Article · Oct 2013 · Chemistry of Materials
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    Michela Brunelli · Pierre Bordet · Paolo Scardi

    Full-text · Article · Sep 2013
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    ABSTRACT: LiH is a highly stable light metal hydride with a hydrogen capacity of 12.5 wt%. However, having a dehydrogenation enthalpy, ΔHdehy, of 181.2 kJ mol(-1)(H2) and a resultant T(1 bar) of 944 °C, it is not a practical hydride for most hydrogen storage applications. In the work presented here, germanium has been found to dramatically reduce the dehydrogenation temperature for LiH down to just 270 °C. The enthalpy of dehydrogenation was reduced through the formation of lithium germanides. The reaction pathway was identified in this study using in situ powder neutron diffraction, showing the successive formation of more Li-rich germanides, following the series: LiGe, Li4Ge2H, Li9Ge4, and Li7Ge2. The enthalpy of formation for these germanides provides the thermodynamic tuning to reduce the ΔHdehy for the system. The 3LiH-Ge system investigated is found to be reversible with a maximum capacity of 3.0 ± 0.1 wt%.
    No preview · Article · May 2013 · Physical Chemistry Chemical Physics
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    ABSTRACT: MOF zipper: Thermal removal of axial pyridine ligands from the non-covalently pillared metal-organic framework [Zn (camph) (py) ]⋅2EtOH prompts migration of alternate camphorate ligands to zip Zn centers from adjacent layers into continuous chains within the nonporous material [Zn (camph) ]. Unzipping to generate new pillared, layered MOFs occurs on exposure to new axial ligands.
    No preview · Article · Mar 2013 · Chemistry - A European Journal
  • Mauro Coduri · Marco Scavini · Michela Brunelli · Paolo Masala
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    ABSTRACT: Doped ceria materials are widely studied for their application in solid oxide fuel cell devices. In this work we report on the average and local structure evolution of La-doped ceria (Ce(1-x)La(x)O(2-x/2), x = 0.25) under fuel cells' operating conditions. The effect of doping on the average structure is investigated using conventional Rietveld analysis of neutron powder diffraction data. The extent of disorder as well as the local structure evolution at high temperature are investigated by employing very hard X-rays under both air and reducing atmosphere.
    No preview · Article · Feb 2013 · Physical Chemistry Chemical Physics
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    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 hemi-hydrate I and dehydrate II forms 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 R 2 2 (16), and ribbons, graph symbol R 2 2 (16)R 3 4 (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.
    Full-text · Article · Feb 2013 · Crystal Growth & Design

Publication Stats

2k Citations
384.63 Total Impact Points

Institutions

  • 2014-2015
    • University of Milan
      • Department of Chemistry, Biochemistry and Biotechnologies for Medical Sciences
      Milano, Lombardy, Italy
  • 2009-2015
    • Institut Laue-Langevin
      Grenoble, Rhône-Alpes, France
  • 2003-2012
    • European Synchrotron Radiation Facility
      • Division of Experiments
      Grenoble, Rhône-Alpes, France
  • 2010
    • University of Reading
      • School of Pharmacy
      Reading, England, United Kingdom
    • Università degli studi di Parma
      Parma, Emilia-Romagna, Italy
  • 2007-2009
    • French National Centre for Scientific Research
      Lutetia Parisorum, Île-de-France, France
  • 2006
    • Durham University
      • Department of Chemistry
      Durham, England, United Kingdom
  • 2004
    • University of Ferrara
      Ferrare, Emilia-Romagna, Italy
  • 1997-1998
    • Sapienza University of Rome
      • Department of Physics
      Roma, Latium, Italy
    • Università degli Studi di Roma "Tor Vergata"
      • Dipartimento di Fisica
      Roma, Latium, Italy