CNRS Laboratory of Condensed Matter Chemistry, Bordeaux

Bordeaux, France

CNRS Laboratory of Condensed Matter Chemistry, Bordeaux

Bordeaux, France
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Gonidec M.,CNRS Laboratory of Condensed Matter Chemistry, Bordeaux
Optical Materials Express | Year: 2017

We describe a theoretical study of gradient metasurfaces that - unlike most theoretical designs requiring advanced fabrication techniques - could easily be produced by a simple patterning method, templated microlens lithography (TEMPL). We show here that positional gradients of identical microstructures can lead to a gradient of phase lag across the metasurface. Using a radial gradient in the pitch of a hexagonal array of identical microfabricated resonators, one could thus produce gradient metasurfaces with the ability to focus infrared light. We provide illustrative examples of devices and compare their theoretical capabilities. © 2017 Optical Society of America.

Masquelier C.,CNRS Laboratory of Chemistry and Reactivity of Solids | Masquelier C.,French National Center for Scientific Research | Masquelier C.,CNRS RS2E | Croguennec L.,CNRS Laboratory of Condensed Matter Chemistry, Bordeaux | And 2 more authors.
Chemical Reviews | Year: 2013

The concept of investigating three-dimensional frameworks based on the NASICON structure as hosts for reversible insertion/extraction of alkali cations (electrodes) arose in the mid 1980s mostly from concerns about possible stability or reactivity versus metallic Na (or Li) when used as solid electrolytes. The NASICON framework was used by Goodenough in the late 1980s as a very demonstrative example of the possibility for the chemist to elaborate electrode materials functioning at controlled operating voltages. Noticeably, these structures have been recently investigated by three independent groups as model compounds for the understanding of complex Li NMR signals in paramagnetic compounds, and useful insights into the activation energies for hopping between the lithium sites were provided.

Matar S.F.,CNRS Laboratory of Condensed Matter Chemistry, Bordeaux
Computational Materials Science | Year: 2013

The overall large ionic character of MgH2 is reduced by inserting light elements from the first period, B and C, using a trirutile host superstructure. From DFT computations, both elements are found destabilizing to the structure with largely positive cohesive energy with interstitial B and slightly negative cohesive energy with interstitial C. This trend is also observed for low amounts of insertion down to (B,C)0.167MgH 2. From the Bader charge analysis the largely ionic character of hydrogen is decreased to an average H-0.37 in the neighborhood of C and H-0.75 for the other hydrogen atoms (resp. H-0.64 and H-0.76 for B insertion). This peculiar behavior should enable enhancing the kinetics of H release for potential applications. © 2012 Elsevier B.V. All rights reserved.

Leblanc M.,CNRS Le Mans Institute of Molecules and Materials | Maisonneuve V.,CNRS Le Mans Institute of Molecules and Materials | Tressaud A.,CNRS Laboratory of Condensed Matter Chemistry, Bordeaux
Chemical Reviews | Year: 2015

Most important structural types of transition metal fluorocompounds and fluoride salts are reviewed. Besides solid-state or conventional reactions, several new processes are presented for a controlled elaboration of fluorides, such as subcritical solvothermal conditions, gaseous fluorination, reaction in ionic liquids, and low-temperature fluorine insertion. Because of the importance of inorganic metal fluorides in many innovating processes, the knowledge of their structural characteristics appears to be a decisive tool for getting a better understanding of the relevant parameters controlling their physical chemical properties.

Guionneau P.,CNRS Laboratory of Condensed Matter Chemistry, Bordeaux
Dalton Transactions | Year: 2014

The spin-crossover phenomenon (SCO) is a fascinating field that potentially concerns any material containing a (d4-d7) transition metal complex finding therefore an echo in as diverse research fields as chemistry, physics, biology and geology. Particularly, molecular and coordination-polymers SCO solids are thoroughly investigated since their bistability promises new routes towards a large panel of potential applications including smart pigments, optical switches or memory devices. Notwithstanding these motivating applicative targets, numerous fundamental aspects of SCO are still debated. Among them, the investigation of the structure-property relationships is unfailingly at the heart of the SCO research field. All the facets of the richness of the structural behaviors shown by SCO compounds are only revealed when exploring the whole sample scales-from atomic to macroscopic-all the external stimuli-temperature, pressure, light and any combinations and derived perturbations-and the various forms of the SCO compounds in the solid state-crystalline powders, single-crystals, poorly crystalline or nano-sized particles. Crystallography allows investigating all these aspects of SCO solids. In the past few years, crystallography has certainly been in a significant phase of development pushing the frontiers of investigations, in particular thanks to the progress in X-ray diffraction techniques. The encounter between SCO materials and crystallography is captivating, taking advantages from each other. In this paper, a personal account mainly based on our recent results provides perspectives and new approaches that should be developed in the investigation of SCO materials. © 2014 The Royal Society of Chemistry.

Marre S.,CNRS Laboratory of Condensed Matter Chemistry, Bordeaux | Jensen K.F.,Massachusetts Institute of Technology
Chemical Society Reviews | Year: 2010

In this critical review, we present an overview of the current progress in synthesis of micro and nanostructures by using microfluidics techniques. Emphasis is placed on processes that can be realized on chip, such as polymerization, precipitation, sol-gel, thermolysis and multistep processes. Continuous flow, microfluidic systems show particular promise in controlling size, shape and size distribution of synthesized micro and nanoparticles. Moreover, the use of microfluidics expands the synthesis space (e.g., temperature, pressure, reagents) to conditions not easily accessed in conventional batch procedures and thus, opens new methods for the realization of complex engineered nanostructures and new materials systems. (187 references) © 2010 The Royal Society of Chemistry.

Matar S.F.,CNRS Laboratory of Condensed Matter Chemistry, Bordeaux
Progress in Solid State Chemistry | Year: 2012

A coherent overview of the physical and chemical properties of the family of transition metal hydrido complexes is addressed from ab initio through an exhaustive treatment from the solid state at different levels to the molecular state, taking a promising class of compounds for potential applications, the non-ahydrido complexes as an illustrative case study. A new chemical vision is presented, pertaining to structure-property relationships such as the different chemical behaviors of the tricapped trigonal prismatic {TH9} (T = Tc, Re) complex anions at the two distinct lattice sites. From energy differences different stability and binding of the Tc versus Re based compounds are underlined whereby the latter is found more tightly bonded. Such solid state results are also supported by calculations at the molecular level with larger infra-red frequencies within the ReH9 complex anion versus TcH9 corresponding to both bending and stretching T-H modes in agreement with experiment. Electronic density of states show both compounds to be insulating with large band gaps and narrow valence bands which are differentiated for the two sites of the transition element (T1 and T2): T1H9 sub-motifs at the corners and T2H9 ones forming a honeycomb arrangement as it is illustrated from the electron localization function (ELF) plots and chemical bonding. ELF maps are also significant of largely ionic 2K +(TH9) 2- compound within which covalent-like (TH9) 2- show electron localization on hydrogen and free electron behavior within the tricapped trigonal prism. © 2012 Elsevier Ltd.

Matar S.F.,CNRS Laboratory of Condensed Matter Chemistry, Bordeaux
Progress in Solid State Chemistry | Year: 2010

The review aims to provide a coverage of different classes of intermetallic systems, which have the ability of absorbing hydrogen in different amounts, like binary and ternary Laves phases and Haucke-type intermetallics. Such intermetallic hydrides are attractive for applied research as potential candidates for on-board vehicular use (engines, batteries, etc.). Focus is made here on the fundamental features regarding the physical and chemical properties obtained from the first-principles - ab initio, for a better understanding of the role played by inserted hydrogen. Beside establishing the equation of state, the binding energetics, the electronic band structure, the magneto-volume effects, the hyperfine field etc., we endeavor answering the relevant question raised by solid state chemistry: "where are the electrons?". This is approached through different schemes calling for a description of the chemical bonding, of the electron localization as well as the charge density mappings and the numerical Bader charge analysis scaling the iono-covalence of hydrogen within the lattice. For the sake of a complete scope we extend the studies to characteristics regarding the valence state changes in cerium based hydrided phases and the magnetism (spin-only, spin-orbit coupling, magnetic order of the ground state) in hydrogen modified ternary uranium intermetallics. © 2010 Elsevier Ltd. All rights reserved.

Matar S.F.,CNRS Laboratory of Condensed Matter Chemistry, Bordeaux
Progress in Solid State Chemistry | Year: 2013

Cerium based intermetallic compounds exhibit a wealth of physical properties originating from the electronic states of Ce, i.e. diamagnetic Ce4+ ([Xe] 4f0), paramagnetic Ce3+ ([Xe] 4f1). Switching between the electronic states can be induced either chemically such as by inserting hydrogen, by substitutions (size effects) or physically by applying external pressure. The review exposes different classes of Ce intermetallic compounds whose properties are interpreted and/or predicted thanks to quantum computations in the framework of the density functional theoretical (DFT). Focus is broadly made on the family of the equiatomic cerium intermetallic compounds, namely ternary CeTX where T is a transition metal and X a p-element where the hydrogenation effects take a considerable place in changing the electronic configuration of Ce. Other stoichiometries of cerium intermetallic compounds with their physical properties are discussed subsequently in the later part of the review. Rather than presenting an exhaustive enumeration of stoichiometries, illustrative case studies are selected for each class of materials to provide, after presenting the experimental context, insights into original outcome from methods targeted at selective physical and chemical properties. © 2013 Elsevier Ltd. All rights reserved.

Guignard M.,CNRS Laboratory of Condensed Matter Chemistry, Bordeaux | Didier C.,CNRS Laboratory of Condensed Matter Chemistry, Bordeaux | Darriet J.,CNRS Laboratory of Condensed Matter Chemistry, Bordeaux | Bordet P.,CNRS Neel Institute | And 2 more authors.
Nature Materials | Year: 2013

Layered oxides are the subject of intense studies either for their properties as electrode materials for high-energy batteries or for their original physical properties due to the strong electronic correlations resulting from their unique structure. Here we present the detailed phase diagram of the layered P2-Na x VO 2 system determined from electrochemical intercalation/ deintercalation in sodium batteries and insitu X-ray diffraction experiments. It shows that four main single-phase domains exist within the 0.5≤x≤0.9 range. During the sodium deintercalation (intercalation), they differ from one another in the sodium/vacancy ordering between the VO 2 slabs, which leads to commensurable or incommensurable superstructures. The electrochemical curve reveals that three peculiar compositions exhibit special structures for x = 1/2, 5/8 and 2/3. The detailed structural characterization of the P2-Na 1/2 VO 2 phase shows that the Na + ions are perfectly ordered to minimize Na + /Na + electrostatic repulsions. Within the VO 2 layers, the vanadium ions form pseudo-trimers with very short V-V distances (two at 2.581Åand one at 2.687Å). This original distribution leads to a peculiar magnetic behaviour with a low magnetic susceptibility and an unexpected low Curie constant. This phase also presents a first-order structural transition above room temperature accompanied by magnetic and electronic transitions. This work opens up a new research domain in the field of strongly electron-correlated materials. From the electrochemical point of view this system may be at the origin of an entire material family optimized by cationic substitutions.

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