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La chimie est une activité qui concerne une quarantaine de permanents, répartis dans différentes équipes de recherche et de pôles technologiques sur l’ensemble de l’Institut Néel. Les interactions permanentes entre chimistes et physiciens du laboratoire permettent le développement d’une science des matériaux forte et originale. L’activité est également tournée vers la valorisation des résultats comme le dépôt de plusieurs brevets portant sur le développement de nouveaux matériaux par différentes voies chimiques et la création d’une entreprise. L’activité chimie est structurée par des actions transversales qui visent à favoriser les collaborations inter-équipes et les synergies entre chimistes afin de développer une animation scientifique propre à faire émerger de nouvelles thématiques.
Les méthodes de la chimie utilisées et développées au sein de l’Institut sont nombreuses. On citera la chimie en solution, la réactivité de surface, la chimie de l’état solide ainsi que les réactions solide – gaz, les synthèses métallurgiques, la croissance de cristaux (bains fondus, solutions, transport dans l’état gazeux) et enfin les méthodes d’élaboration et de caractérisation physicochimiques sous conditions extrêmes, hautes pressions – hautes températures, fluides supercritiques. La maîtrise de ces méthodes permet de fabriquer des matériaux fonctionnels, micro et/ou nano structurés, sous forme de poudres ou de monocristaux, nanofils et films minces. Les propriétés visées sont variées et s’inscrivent dans les enjeux de l’Institut : magnétisme, optique, supraconductivité, stockage et conversion de l’énergie, capteurs biologiques… etc.
Hydrothermal/solvothermal methods are used by several groups, who develop and share specific autoclaves. The hydrothermal method is used for crystal engineering of metal iodates, that are promising materials for the realization of optical parametric amplifiers and oscillators in the IR range until 12 µm. This method leads to original phases and allows to control the rate of insertion of rare earths in many phases as La(IO3)3, AgGd(IO3)4 or Y(IO3)3 (MatONLP – MCMF group).
RE-doped Metal Iodate (left) and Single crystal of In(IO3)3 (right)
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The hydrothermal technique is also used to grow hydroxyhalides, especially of the atacamite family Cu3M(OH)6Cl2, a rare example of perfectly planar Kagome network of Cu2+ for frustrated magnetism studies of S = ½ systems (SPMCE – MCMF group). Single crystals of atacamite Cu3Zn(OH)6Cl2 |
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The chemical reactivity of aqueous solutions under hydrothermal conditions is studied through in situ synchrotron X-ray and optical Raman spectroscopies. The physico-chemistry properties of supercritical fluids (hydrogen bonding, solvation properties, nature of radicals), mostly H2O and CO2, and the speciation of dissolved metal in hydrothermal conditions have important implications for metal transport and petrology, fluid-rock interactions and CO2 storage. All these experiments are based on the development of high pressure-high temperature set-ups (strong expertise in high pressure within the MCMF department). A recent application of this technology is the study of the fate of organic molecules in hydrothermal conditions, in relation with the chemistry of oceanic hydrothermal vents (black smokers) (SPMCE – PLUM group)
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| X-ray Absorption Spectroscopy (CRG-FAME, ESRF) and use of a high-pressure autoclave. | Monitoring of Fe solubility and Short range order, both derived from the analysis of X-ray absorption spectra. |
In the Micro-Nano-Magnétisme group – Nano Department, nanoporous alumina membranes with honeycomb pore network are synthesized electrochemically under specific anodizing conditions with acidic electrolytes. The resulting membranes are used as templates for the electrochemical growth of soft magnetic (Ni or Co) and thermoelectric nanowires (BiSbTe and BiTeSe) arrays. Magnetic nanowires are studied for magnetic domain wall motion upon application of an external magnetic field or a spin-polarized current. The influence of pore diameter reduction on the magnetostatic interactions has been determined. Thermoelectric nanowire arrays are developed for optimizing their properties in view of power generation applications (collab. Schneider Electric).
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[bleu marine]Nanoporous alumina templates (honeycomb network) obtained by two-step anodizing in acidic aqueous media[/bleu marine]
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Oxides for cathodes of lithium secondary batteries are investigated in the SPMCE – MCMF group. Electrochemical intercalation of lithium has been recently studied in nanometric MnOx obtained by low-temperature chimie douce routes, as well as in high-potential spinel-type oxides such as LiNi0.5Mn1.5O4 and its derivatives. The associated redox reactions are followed electrochemically, and by various techniques such as XRD, EXAFS-XANES and Raman Spectroscopy. The electrochemical intercalation system is also used for studies of the effect on superconductivity of incorporation/extraction of alkali elements in iron pnictides and chalcogenides.
Sol-gel chemistry, molecular precursor methods and metal-organic decomposition (MOD) techniques have been selected for their flexibility, scalability and low cost. These wet chemical routes are coupled with various shaping techniques : spin-coating, dip-coating, spray-drying, spray-pyrolysis for the preparation of thin films or nanoparticles.
The Supraconducteurs-MCBT group makes textured YBa2Cu3O7 superconductors, that are produced by epitaxy, grain by grain, with an appropriate stacking of oxide films, themselves epitaxied on a textured metal substrate. Each step, deposition, nucleation and growth, is controlled separately. The resulting flat tapes are able to carry high superconducting currents (1 MA/cm2 at 77 K under self-field). This method will be adapted to a continuous process that will make possible to manufacture longer samples involving a new tube shaping (coll. with Nexans France and ArcelorMittal Stainless & Nickel Alloys).
Dip-coating : La2Zr2O7 (LZO) or CeO2 buffer layer epitaxied on textured Ni substrates before the final deposition of YBa2Cu3O7 (YBCO) superconducting coating.
The MatONLP – PLUM group develops an original process for confined nucleation and growth of molecular nanocrystals in silicate sol-gel matrices. This allows to prepare, through simple and generic one-step processes, bulk hybrid organic-inorganic nanocomposites and corresponding thin films and nanoparticles, for the development of highly sensitive fluorescent biosensors, filters or tracers for medical imaging.
Nanocrystals Ø = 60-80 nm emerging from silicate films after controlled surface dissolution. CNRS Patent PCT/FR2008/050490
Inorganic nanocrystals, oxides and borates, are also prepared by the sol-gel and polymeric precursor (modified Pechini) methods for the development of new fluorophores for lighting or ceramics for optics (MatONLP – PLUM and Supraconducteurs – MCBT).
Inorganic nanopowders for lighting (white luminescence)
Several chimie douce reactions are also investigated in lamellar cobaltates (SPMCE – MCMF) :
Chimie douce reaction schemes in lamellar cobaltates
A 2×1000 W Cyberstar image furnace (Cristaux massifs-MCMF tech group) allows to grow various compounds for physical studies. Recently studied systems are Sr-Ru-O oxides, langasites with a frustrated rare-earth network (Pr3Ga5SiO14 and Ba3NbFe3Si2O14) (Collaboration with the teams SPMCE-MCMF, MatONLP-PLUM and SFCE-MCBT).
Langasites Nd3Ga5SiO14 elaborated from zone melting growth to study frustrated magnetism and magnéto – optical properties
Technology transfer : partnership with the Cyberstar company
High-quality single crystals of heavy fermion materials, based on the ternary system: RareEarth – d transition element – p elements such as URu2Si2, CeRh3B2 or CeNi2B2C are grown from the melt for high-resolution angle-resolved photoemission spectroscopy (ARPES). The crystal growth of other exotic magnetic and heavy fermions materials are developed by the Cristaux Massifs – MCMF Tech group in collaboration with SFCE – MCBT and SPMCE – PLUM (new iron pnictide superconducting materials)
The Cristaux Massifs – MCMF Tech group is studying the growth of large periodically-poled KTiOPO4 (PPKTP) crystals from high temperature solutions. We first demonstrated domain growth from a microstructured substrate by liquid phase epitaxy, and aim then to grow large periodically-poled KTiOPO4 crystals. The optimization of physico-chemical conditions and growth kinetics of these domains will be realized by a pulling process from the growth solution: top seeded solution growth method. The growth of non-linear optics crystals doped with luminescent ions will also be carried for the self-converter RbTiOPO4:Er/Yb crystal with ionic charge compensation (Ba2+) on the alkaline site (collaboration MatONLP – MCMF).
Periodically poled bulk crystal of PPKTP obtained from an epitaxial growth on a PPKTP thin slab previously obtained by applying reverse electric fields
The flux technique with slow cooling is used in SPMCE – MCMF group to grow single crystals of various complex oxides with interesting magnetic or multiferroic properties (lamellar nickel or cobalt oxides, pyrochlores, spinels). The flux technique is now tentatively extended to high-pressure conditions in order to obtain compounds that are difficult to stabilize without pressure and not available so far in single-crystal form (BiMnO3, GeCu2O4 …)
GeCo2O4 grown by flux technique
BiMnO4 grown under High Pressure High Temperature
An original rapid growth reactor working in stationary conditions is developed in MatONLP-PLUM group. It can accommodate almost any chemical system combining the circulation and in-line treatment (over-heating, ultra-filtration and ultrasounds) of the growth solution to avoid spurious nucleation at high supersaturation applied to reach high growth rates. This method is highly suited to compounds studied in the MatONLP-PLUM group, such as low-solubility metal iodates (NaI3O8) for non-linear optical properties, and DKDP phosphate solid solutions [K(D(1-x)Hx)2PO4] for the “Laser MégaJoule” facility (collaboration with CEA).
DKDP crystal on a specific growth platform elaborated in less than 3 days under rapid growth conditions (left); Examples of high quality KDP and DKDP crystal (several cm3) obtained through different seed orientations and shaping (right).
Peptide grafting on hybrid core-shell nanoparticles for in vivo imaging (angiography)
Core-shell hybrid organic-inorganic nanoparticles are prepared through a one step spray-drying process for in vivo two-photon fluorescence imaging (OPTIMA- PLUM group). Through the nature of sol-gel precursors, coupled to their hydrolysis and condensation conditions, we favour the preparation of hydrophilic and non-porous silicate shells to improve their in vivo furtivity and their chemical stability. Finally, the silicate shells allow a convenient functionalization by grafting biomolecules as PEG groups or peptides (typically RGD peptides) at their surfaces for targeting in vivo tumor vascular endothelial cells (main collaborations with Grenoble Institut Neuroscience, ENS-Lyon, Lab. Spectrométrie Physique-UJF).
Diamond nanocrystals, exhibiting fluorescent nitrogen-vacancy centers, are also involved in the functionalization of optical tips. The aim is to develop high-resolution nano-source of photons for near-field optical microscope by grafting on the tip apex small diamond nanocrystals, 20nm in diameter, yielding to very stable and efficient fluorescence (OPTIMA – PLUM and Champ proche – Nano groups).
Biophysical studies of living cells require biofunctionalisation of the growth substrate, since cells need to interact specifically with proteins from the extracellular matrix to function properly. Methods for protein immobilization and patterning have been developed in the Thermodynamique des Petits Systèmes – MCBT group. The biophysical studies concern the auto-organisation of subcellular macromolecular scaffold such as stress fibers in fibroblasts. The extracellular protein fibronectin is used as the adhesion protein since it triggers all the biochemical regulation of interest.
Cell adhesion limitation by involving a biopolymer (polyethylenglycol /silanisation) Cell adhesion enhancement through protein plots (fibronectin)
Living cell adhesion control on Physical sensors (Temperature Conductivity)
To develop diamond-based biosensensors, the Semiconducteurs grand gap group – QUEST is optimizing wet chemical routes for localized electrochemical and chemical surface functionnalization with biomolecules (proteins, enzymes, ADN) on boron-doped diamond and carbon nanotubes. This novel chemical process for biofunctionnalization as localized chemical spots on a diamond surface opens the way to easier grafting of monomolecular layers of proteins, enzymes, ADN and other organic molecules in one step very close to the diamond surface.
Boron doped metallic diamond (AFM image)
Diamond/Carbon Nanotubes composites
In the framework of studies of electronic transport through single molecules, new mesoscopic phenomena, and quantum effects at the single-molecule level to develop molecular spintronics, the Nanospin group – QUEST is developing carbon nanotube (CNT)-based quantum devices for molecular spin detection in a nanoSQUID configuration. This requires surface functionalization by aminosilanes in order to deposit the nanotubes in a controllable way, and is carried out in specific nanochemistry equipment and reactors, such as CVD growth facilities for CNTs and a vapour phase silanization apparatus.
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(1) CNT individualization by surfactant (SDS), (2) CNT grafting with aminosilane (AFM), (3) Selective grafting of molecular magnets on CNT
In the field of hydrides (IICE – PLUM group), alkali borohydrides are of particular interest for hydrogen storage due to their high hydrogen storage capacity (ex. LiBH4 contains 18.4 wt% H2). The main drawback is their stability which prevents reversibility in moderate temperature and pressure conditions. Thermodynamical destabilization can be achieved through reactive hydride composites which consist on an intimate mixture of alkali borohydride and a metal hydride. The formation of an intermediate phase lowers the formation enthalpy in comparison with pure borohydride. We focus our study on the system LiBH4– MgH2, and in particular on the role of activators on the reversibility and kinetics of the reaction : 2 LiBH4 + MgH2 ↔ 2 LiH + MgB2 + 4 H2
In situ synchrotron X Ray thermodiffractogram of 2 LiBH4-MgH2 during dehydrogenation
On the other hand, to produce performing alloys for H storage, reactive ball milling is used to prepare metallic materials with metastable phases while severe plastic deformation techniques (ECAP, cold rolling) allow to control the microstructure required to improve H-sorption kinetics at low temperatures and structural stability of Mg-based hydrides.
ECAP (Equal Channel Angular Pressing) set-up
Finally, extrinsic properties of magneto-caloric materials can be improved by nano-structuring In the case of La(Fe,Si)13 compounds it can be achieved by the use of techniques such as powder atomization or melt spinning.
TEM observation of vacancy coalescence in the dislocation-rich region (pore size=50nm)
Gas-solid reactions are also used as a crystal growth technique via chemical transport. This method is well suited for binary or ternary oxides of transition metal elements without strongly basic components; it is used to prepare crystals of spinels such as M2GeO4 using HCl or Cl2 as transporting agent (SPMCE – PLUM group).
Crystal growth technique via chemical transport
Institut Néel High Pressure High Temperature Devices (max 8GPa, 1500°C)
Institut Néel also possesses two hydraulic presses for high pressure-high temperature (HP-HT) syntheses up to 8 GPa. (Instrumentation -PLUM Tech group). These are used to stabilize strongly distorted oxides as perovskites with multiferroic properties, and to search for new compounds by exploring phase diagrams of oxides with unusual valence states or coordination, leading to interesting physical/structural properties. SPMCE – PLUM group focuses on solid solutions between 3d metals on the B-site of Bi, Pb or rare-earth containing distorted perovskites. HP-HT chemistry is also applied to the preparation of new superconducting compounds as (Ba, K)Fe2As2.
Studies of effect on powder BiCrO3 perovskite under High Pressure High Temperature
Defect-hydride structures may be stabilized using high pressure hydrogenation which activates metal atoms diffusion. Subsequent heat treatment gives way to vacancy coalescence resulting in nanoporous materials. This technique of generating vacancies in a hydride phase and subsequent degassing provides a method to introduce pores in metals from which novel properties can be expected. Metallurgy is mainly developed at high pressures on new Mg-based ternary hydrides or for ordered metal-vacancy-systems but also powder metallurgy is performed at ambient pressure on low temperature hydrides, magnesium-based hydrides or magneto-caloric materials (IICE- PLUM). By reacting magnesium or magnesium hydride with the first row transition metals new ternary hydrides based on transition metal-hydrido complexes are synthesized. The parent corresponding binary alloys do not exist, whereas the new metal framework held together by hydrogen does exist. This opens up possibilities to reduce the stability with respect to desorption. We anticipate to produce such phases by the use of high H pressure.
Crystallographic structure of Mg7TiH14
Institut Néel is equipped with a large range of resistive and induction furnaces, that allows an important synthetic solid state chemistry activity including under controlled atmosphere. The studies of solid solutions in magnetic, magneto-optic, multiferroics compounds elaborated in various conditions allows to determine the relations between chemical composition, structure and properties. Recent studies deal with langasites system that show the effect of substitution on several cationic crystallographic sites AInstitut Néel is equipped with a large range of resistive and induction furnaces, that allows an important synthetic solid state chemistry activity including under controlled atmosphere. The studies of solid solutions in magnetic, magneto-optic, multiferroics compounds elaborated in various conditions allows to determine the relations between chemical composition, structure and properties. Recent studies deal with langasites system that show the effect of substitution on several cationic crystallographic sites A3BC2D2O14 (SPMCE – PLUM group). An other work developed by the Cristaux massifs – PLUM tech group with the SFCE – MCBT group show the possibility to induce ferromagnetism in semiconductors by non-magnetic impurities (SnO2 reacted with K2CO3 at low temperature).
