Publications by authors named "François Weill"

12 Publications

  • Page 1 of 1

Structural and Spectroscopic Studies of NaCuCr(PO): A Noncentrosymmetric Phosphate Belonging to the α-CrPO-Type Compounds.

Inorg Chem 2021 Jun 21;60(11):7803-7814. Epub 2021 May 21.

CNRS, Université de Bordeaux, ICMCB, 87 avenue du Dr. A. Schweitzer, Pessac F-33608, France.

An electron and joint neutron and X-ray diffraction study of the synthetic copper/chromium phosphate NaCuCr(PO) (NaCuP) is reported. A noncentrosymmetric 2 space group belonging to the well-known α-CrPO type is observed contrary to what is reported in NaMCr(PO) (M = Co and Ni) phosphates. The structural model is validated by bond valence sum analysis and charge-distribution (CHARDI) calculations and supported by complementary infrared and Raman spectroscopy investigations. Both Raman spectroscopy and theoretical study by deformation density approach further suggest the presence of Cu (3d) and Cr (3d) Jahn-Teller polaron effects as a key factor to the centro to noncentrosymmetric 2 phase change.
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http://dx.doi.org/10.1021/acs.inorgchem.1c00296DOI Listing
June 2021

Controlled Nanostructuration of Cobalt Oxyhydroxide Electrode Material for Hybrid Supercapacitors.

Materials (Basel) 2021 Apr 29;14(9). Epub 2021 Apr 29.

CNRS, University of Bordeaux, Bordeaux INP, ICMCB UMR CNRS #5026, F-33600 Pessac, France.

Nanostructuration is one of the most promising strategies to develop performant electrode materials for energy storage devices, such as hybrid supercapacitors. In this work, we studied the influence of precipitation medium and the use of a series of 1-alkyl-3-methylimidazolium bromide ionic liquids for the nanostructuration of β(III) cobalt oxyhydroxides. Then, the effect of the nanostructuration and the impact of the different ionic liquids used during synthesis were investigated in terms of energy storage performances. First, we demonstrated that forward precipitation, in a cobalt-rich medium, leads to smaller particles with higher specific surface areas (SSA) and an enhanced mesoporosity. Introduction of ionic liquids (ILs) in the precipitation medium further strongly increased the specific surface area and the mesoporosity to achieve well-nanostructured materials with a very high SSA of 265 m/g and porosity of 0.43 cm/g. Additionally, we showed that ILs used as surfactant and template also functionalize the nanomaterial surface, leading to a beneficial synergy between the highly ionic conductive IL and the cobalt oxyhydroxide, which lowers the resistance charge transfer and improves the specific capacity. The nature of the ionic liquid had an important influence on the final electrochemical properties and the best performances were reached with the ionic liquid containing the longest alkyl chain.
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http://dx.doi.org/10.3390/ma14092325DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8124577PMC
April 2021

Nanoparticles (NPs) of WO Compounds by Polyol Route with Enhanced Photochromic Properties.

Nanomaterials (Basel) 2019 Nov 1;9(11). Epub 2019 Nov 1.

CNRS, Univ. Bordeaux, Bordeaux INP, ICMCB, UMR5026, 87 Avenue du Dr. Albert Schweitzer, 33608 F-Pessac CEDEX, France.

Tungsten trioxide (WO) is well-known as one of the most promising chromogenic compounds. It has a drastic change of coloration induced from different external stimuli and so its applications are developed as gas sensors, electrochromic panels or photochromic sensors. This paper focuses on the photochromic properties of nanoWO, with tunable composition (with tunable oxygen sub-stoichiometry). Three reference samples with yellow, blue and black colors were prepared from polyol synthesis followed by post annealing under air, none post-annealing treatment, or a post-annealing under argon atmosphere. These three samples differ in terms of crystallographic structure (cubic system versus monoclinic system), oxygen vacancy concentration, electronic band diagram with occurrence of free or trapped electrons and their photochromic behavior. Constituting one main finding, it is shown that the photochromic behavior is highly dependent on the compound's composition/color. Rapid and important change of coloration under UV (ultraviolet) irradiation was evidenced especially on the blue compound, i.e., the photochromic coloring efficiency of this compound in terms of contrast between bleached and colored phase, as the kinetic aspect is high. The photochromism is reversible in a few hours. This hence opens a new window for the use of tungsten oxide as smart photochromic compounds.
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http://dx.doi.org/10.3390/nano9111555DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6915692PMC
November 2019

Hydrothermal Transformation of Titanate Scrolled Nanosheets to Anatase over a Wide pH Range and Contribution of Triethanolamine and Oleic Acid to Control the Morphology.

Inorg Chem 2019 Feb 1;58(4):2588-2598. Epub 2019 Feb 1.

ICMCB , CNRS, Université Bordeaux, UMR 5026 , 33608 Pessac , France.

Mild hydrothermal conditions used for the treatment of titanate scrolled nanosheets (SNSs) suspensions (140 °C, 72 h) resulted in a large variety of anatase TiO anisotropic nano-objects depending on the studied parameters: influence of the medium pH and the presence or not of structuring agents (SAs). The present work shows that such a hydrothermal treatment of the SNSs, whatever the pH, resulted in the formation of single-crystalline anatase nanoneedles (NNs) with a specific crystal-elongation direction and a pH-dependent morphological anisotropy with aspect ratios (ARs) from 1 to 8. The SNSs suspensions were prepared by the conventional ultrabasic treatment of TiO with NaOH, followed by washing with HNO to different pH values. The crystal size of the anatase TiO obtained from this hydrothermal treatment increased with the pH of the suspensions, from 15 nm nanoparticles (NPs; AR = 1) at pH 2.2 to 500 nm NNs (AR = 8) at a pH 10.8 with a long axis systematically along the anatase [001] direction. Triethanol amine and oleic acid were used as SAs. Their respective influence, when acting on their own, had little influence on the control of the size, shape, or polydispersity of the NNs. However, their concomitant use provided a much better control of not only the size and polydispersity, which was strongly reduced, but also on (i) the shape and morphology giving rise to a controlled access to well-defined nanorods as opposed to nanoneedles and (ii) the crystal phase purity eliminating the few percent brookite still visible in the X-ray diffraction patterns of samples prepared in SA-free conditions. This approach offers an on-demand control over the production of anatase morphologies with defined aspect ratios.
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http://dx.doi.org/10.1021/acs.inorgchem.8b03197DOI Listing
February 2019

Structural transformations of the LaPrNiO system probed by high-resolution synchrotron and neutron powder diffraction.

Dalton Trans 2018 Dec;48(1):266-277

CNRS, ICMCB, UMR 5026, F-33600 Pessac, France.

Compositions in the La2-xPrxNiO4+δ series offer an attractive balance of chemical stability and electrochemical performance for use as cathode materials in solid oxide fuel cells (SOFCs). A detailed crystallographic study of this system has been performed, combining both high resolution synchrotron and neutron powder diffraction data, in order to investigate structural details of the series as a function of composition, temperature and oxygen over-stoichiometry. The monoclinic structure (space group F2/m) of ambient temperature Pr-rich compositions for 1.0 < x ≤ 2.0 is discussed in terms of octahedra tilt arrangements and possible long-range structural modulations. In situ synchrotron diffraction experiments and TEM are employed to examine the role of temperature and interstitial oxygen on these structural distortions. With increasing La substitution, a region of mixed monoclinic and tetragonal phases is described for 0.5 ≤ x ≤ 1.0. La-Rich compositions are found to be single phase tetragonal (F4/mmm for 0 < x < 0.5) or orthorhombic (Fmmm for x = 0). Possible origins and electrochemical property consequences of the refined structural trends are considered.
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http://dx.doi.org/10.1039/c8dt03524eDOI Listing
December 2018

Tailoring the Composition of Eu-Doped YNbO Niobate: Structural Features and Luminescent Properties Induced by Spark Plasma Sintering.

Inorg Chem 2017 Apr 6;56(8):4496-4504. Epub 2017 Apr 6.

CNRS, ‡Univ. Bordeaux, and §Bordeaux INP, ICMCB, UPR9048 , F-33600 Pessac, France.

The defective fluorite-related YNbO host lattice was doped with Eu ions to understand the influence of spark plasma sintering (SPS) process on this host lattice. The intrinsic disorder due to the occurrence of oxygen vacancies results in amorphous-type responses of the luminescent cations, and the spectral distribution varies as a function of the niobium content. Two spectral fingerprints of europium emissions were clearly enhanced. The correlation between luminescence, X-ray diffraction, and electron diffraction characterizations shows the existence of local inhomogeneity. Indeed, the particular nonequilibrium sintering conditions allowed pointing out a lack of miscibility within the YNbO solid solution domain. Thus, the SPS pellet is a composite of two extreme compositions. This phase demixing is mainly induced by the pressure coupled with a current effect that makes possible ionic migration in this YNbO ionic conductive matrix.
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http://dx.doi.org/10.1021/acs.inorgchem.7b00088DOI Listing
April 2017

Tuning the Mn valence state in new Ca(0.66)Mn(2-x)Al(x)O4 (x≤ 0.4) oxides: impact on magnetic and redox properties.

Dalton Trans 2016 Mar 9;45(11):4647-58. Epub 2016 Feb 9.

CNRS, ICMCB, UPR 9048, F33600 Pessac, France.

New Ca(0.66)Mn(2-x)Al(x)O4 (x≤ 0.4) solid solutions crystallizing with the CaFe2O4-type structure (SG: Pnma) were synthesized for the first time by the glycine-nitrate process. The structures were determined on the basis of XRD Rietveld analysis and electron diffraction investigation. While the CaMn3O6 ('Ca(0.66)Mn2O4') oxide adopts a monoclinic unit cell, the Al substitution for Mn (x = 0.2, 0.4) leads to an orthorhombic cell with only two Mn atomic positions, with different valence states, and 33% of Ca sites empty. The Ca molar concentration decreases down to 0.6 in order to increase the Mn valence leading to a phase mixture, whereas a slight Ca content increase up to 0.7 leads to a decrease of Mn valence in the pure phase. The Al(3+) ions are located at a specific Mn site because their ionic radii are close to that of Mn(4+) and a more isotropic environment. The unit cell parameters and volume strongly decrease for a low Al content and tend to an asymptotic value of x = 0.33-0.4, around the limit of solubility. As the Al content increases, the Mn valence state in the same slightly distorted octahedral site increases up to 4+ whereas the other octahedral site is highly elongated and corresponds mainly to Jahn-Teller Mn(3+). At x = 0.33, these two Mn sites correspond to Mn(4+) and Mn(3+) respectively. Moreover, the aluminium content increase induces a weakening of the global antiferromagnetic long range interactions between the ferromagnetic chains. The Al substitution leads to the change of the Mn valence distribution as well as the unit cell symmetry of the CaMn3O6 phase. These 1D tunnel networks stabilizing the Mn(3+)/Mn(4+) valence states can be reduced under Ar/5%H2 between T = 300 °C and T = 600 °C (heating rate = 2 °C min(-1)) into pure Mn(2+) rocksalt solid solution despite the large difference in ionic radii. The re-oxidation leads to the same CaFe2O4-type structure and several redox cycles can be operated. The relationship between the two double chains of the edge-sharing octahedral sites and the rocksalt-type framework is clear and should appear as the driving force for the structural transformation during the reduction/oxidation processes. Finally, Al substitution allows an increasing of the Mn-O bond covalence and consequently the reduction in temperature.
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http://dx.doi.org/10.1039/c5dt02761fDOI Listing
March 2016

Thermal stability of Li2MnO3: from localized defects to the spinel phase.

Dalton Trans 2012 Feb 7;41(5):1574-81. Epub 2011 Dec 7.

CNRS, Université de Bordeaux, ICMCB site de l'ENSCBP, 87 avenue du Dr A. Schweitzer, Pessac, F-33608, France.

The thermal stability of Li(2)MnO(3) has been investigated by the means of coupled differential thermal analysis and thermogravimetric analysis associated with powder X ray diffraction. Various experiments performed in air and in argon allowed us to propose a mechanism of spinel-type defects formation in intergrowth with Li(2)MnO(3) when treated in air above 900 °C. The fidelity of the DIFFaX simulations performed led to the understanding of the influence of the existence of spinel type defects intergrowth on X ray and electron diffraction patterns. The formation of these defects occurs during cooling and is preceded by the formation of LiMnO(2) defects in heating. With sufficiently long thermal treatments, defects expand such that a spinel type phase can be observed after cooling.
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http://dx.doi.org/10.1039/c1dt11598gDOI Listing
February 2012

Investigation of the new P'3-Na0.60VO2 phase: structural and physical properties.

Inorg Chem 2009 Oct;48(19):9147-54

CNRS, Université de Bordeaux, ICMCB, 87 avenue du Dr. A. Schweitzer, 33608 Pessac Cedex, France.

A new layered phase Na(0.60)VO(2) was synthesized by chemical deintercalation of sodium from the pristine compound O3-NaVO(2). The Na(0.60)VO(2) compound exhibits a distorted P'3-type oxygen stacking (AABBCC) with an average monoclinic unit cell containing a = 4.9862(14) A, b = 2.8708(8) A, c = 5.917(2) A, and beta = 104.36(3) degrees. A modulated structure was observed by transmission electron microscopy and X-ray diffraction (XRD) measurements. Indexation of the XRD pattern was achieved by using the q vector equal to 0.44b*, and the 4D superspace group C2/m (0 beta 0) s0 was then deduced. The specific heat measurement showed a strong correlated system with a gamma value of around 20 mJ x mol(-1) x K(-2). The electrical conductivity shows a semiconductor-like behavior with an activation energy of 0.52 eV. A paramagnetic behavior of the susceptibility is observed below room temperature with a Curie constant equal to C = 0.076 emu x K(-1) x mol(-1) x Oe(-1). To explain this small value, a model of pseudotriangular clusters of vanadium with a random distribution of V(3+) and V(4+) was considered.
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http://dx.doi.org/10.1021/ic9008653DOI Listing
October 2009

On the strongly correlated electron hydride Ce2Ni2MgH7.7.

Inorg Chem 2008 Nov 22;47(22):10419-24. Epub 2008 Oct 22.

CNRS, Université de Bordeaux, ICMCB, 87 avenue du Docteur Albert Schweitzer, 33608 Pessac Cedex, France.

The intermediate valence compound Ce 2Ni 2Mg absorbs irreversibly hydrogen when exposed under 1 MPa of H 2 pressure at room temperature. The resulting hydride Ce 2Ni 2MgH 7.7 is stable in air and crystallizes as the deuteride La 2Ni 2MgD 8 in a monoclinic structure (space group P2 1 /c) with the unit cell parameters a = 11.7620(2), b = 7.7687(2), and c = 11.8969(2) A and beta = 92.75 degrees . The H-insertion in Ce 2Ni 2Mg induces a structural transition from a tetragonal to a monoclinic symmetry with an unit cell volume expansion Delta V m/ V m approximately 24.9%. The investigation of the hydride by magnetization, electrical resistivity, and specific heat measurements indicates a change from an intermediate valence behavior to a non-magnetic strongly correlated electron system. This transition results from a change of the coupling constant J cf between 4f(Ce) and conduction electrons induced by the hydrogenation.
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http://dx.doi.org/10.1021/ic801076bDOI Listing
November 2008

Supercritical fluid technology of nanoparticle coating for new ceramic materials.

J Nanosci Nanotechnol 2005 Jun;5(6):980-3

Institut de Chimie de la Matière Condensée de Bordeaux 87, Avenue du Dr A. Schweitzer, 33608 Pessac, Cedex, France.

This work highlights, for the first time, the coating of ferroelectric nanoparticles with a chemical fluid deposition process in supercritical fluids. BaTiO3 nanoparticles of about 50 nm are coated with a shell of a few nanometers of amorphous alumina and can be recovered as a dry powder for processing. The sintering of these core-shell nanoparticles gives access to a ceramic material with very interesting ferroelectric properties, in particular, dielectric losses below 1%.
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http://dx.doi.org/10.1166/jnn.2005.147DOI Listing
June 2005

Skin colonization by Malassezia species in neonates: a prospective study and relationship with neonatal cephalic pustulosis.

Arch Dermatol 2002 Feb;138(2):215-8

Service de Dermatologie, Hôpital Saint André, 1 rue Jean Burguet, 33075 Bordeaux, France.

Objectives: To assess skin colonization by Malassezia species in full-term healthy newborns, to investigate factors associated with colonization, and to look at acnelike cephalic pustulosis associated with this carriage.

Design: Samples were obtained from neonates and their mothers 0 to 5 days after birth and again 3 weeks later. Clinical patterns of common acnelike pustulosis were reported as mild (<10 papulopustules), moderate (> or =10 papulopustules), or absent. Direct examination and culture of sample. Identification of yeasts was based on microscopic and physiologic criteria.

Setting: A maternity hospital and the pediatric dermatology unit of a university hospital.

Participants: Consecutive series of 102 neonates and their mothers.

Main Outcome Measures: Incidence of skin colonization and type of Malassezia species found in neonates and correlation with neonatal cephalic pustulosis (neonatal acne).

Results: At the first visit, 11 neonates and 36 mothers had cultures positive for Malassezia. Malassezia sympodialis and Malassezia globosa were preferentially cultured. At 3 weeks, 29 (52%) of 56 neonates and 18 (32%) of 56 mothers had cultures positive for only M sympodialis and M globosa. Breastfeeding was not associated with a higher prevalence of Malassezia carriage in neonates. Malassezia colonization was higher when pustulosis was more severe and M sympodialis was found in pustules.

Conclusions: Malassezia colonization begins at birth and increases in the first weeks of life. A high prevalence of M sympodialis in neonates is noted from birth. Its association with neonatal acne is confirmed. Further investigation is needed to study the role of sebum secretion rate and quality in the neonatal period.
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http://dx.doi.org/10.1001/archderm.138.2.215DOI Listing
February 2002