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Research fields

New intermetallic compounds and single crystal growth

More than one hundred quasicrystalline phases have been discovered so far together with a large number of related periodic crystals.

The list is still growing and phase diagram studies continue to be a source of discovery largely unexploited.

Samples can be synthesized in our group using arc melting, induction melting, sintering or melt spinning and characterized by thermal differential analysis, X-ray diffraction or electron microscopies. In the best cases, it is possible to grow centimeter size single crystals by Czochralski or flux methods.

Structure and growth of complex metallic alloys.


Surfaces of complex metallic alloys

The determination of atomic and electronic structures is key to understand and optimize the surface properties of these compounds.

We have developed an internationally recognized expertise in this field by coupling both experimental surface science methods and ab initio calculations based on the density functional theory.

This allows us to precisely determine the surface structures and to study the mechanisms of surface formation like surface plane selection, the role of chemical bonding, possible surface segregation phenomena, etc.. which lead to a specific surface structure and reactivity.

Left: STM image of a clean quasicrystalline surface.
Right:  Isosurfaces of charge density differences for atomic hydrogen adsorbed at specific sites of the Al13Co4 (100) surface: Dρ > 0 in yellow andDρ < 0 in blue.

 

Thin films

Complex metallic alloy surfaces are used as templates to grow ultrathin metal films.

This allows to study how such complex materials make interfaces with more conventional ones. Interfaces are also important in wetting and friction experiments.

In some cases, it is possible to induce some of the symmetry elements of the substrate into the film structure and thus makes new materials which do not exist otherwise, like quasiperiodic Pb for example.

Left: STM image of a Bi thin film deposited on the Al13Co4 (100) surface.
Right: STM image of a quasiperiodic Pb thin film.

 

Surface alloys

Interdiffusion can occur at the interface between a film and the substrate, which can lead to the formation of intermetallic compounds in the near-surface region. The latter is called a surface alloy.

This phenomenon actually occurs in metal nanoparticles on oxide supports used in heterogeneous catalysis. The catalytic activity is usually ascribed, at least in part, to the formation of intermetallic phases by reduction of the powder catalyst under reaction conditions.

We reproduce such phenomenon under ultra-high vacuum conditions to determine the formation conditions and the structure of these surface alloys.

Left: STM image of a Bi thin film deposited on the Al13Co4 (100) surface.
Right: STM image of a quasiperiodic Pb thin film.

 

Molecules on surfaces

Surface functionalization with molecular films is an active field of research motivated by the possibility to make new devices for molecular electronics or organic photovoltaic.

The electronic and optical properties of the molecules are known to strongly depend on how these molecules are adsorbed on the surface.

We study the nucleation and growth of self-organized molecular films on metal surfaces and adsorption geometries using both surface science experiments and numerical simulations.

STM image (6x6 nm2) of a quasiperiodic molecular film.


Composite materials for 3D printing technologies

Additive manufacturing stands for a multitude of new methods that are used to produce functional parts very rapidly without any shape constraints starting from a CAD model.

The parts are produced in a layer-by-layer fashion, by fusing powders which can be polymers, metallic or ceramic particles or composites. In collaboration with a local industrial partner and the Additive Materials and Processes Skills Center of the Institut Jean Lamour, we have developed new composite materials which can be processed by 3D printing technologies.

The use of quasicrystalline particles leads to improved functional properties of the parts. The composite powders are commercialized under the trademark PAQ®.

Picture : intake manifold made of a polyamide composite reinforced by quasicrystalline particles and manufactured by selective laser sintering technology.


Wetting, friction and structural complexity

The remarkable wetting and friction properties of complex metallic alloys were evidenced quite early after their discoveries in our group and are at the heart of possible applications of these materials.

Results indicate unexpected correlations between these measured properties, the electron density of states at the Fermi level and complexity index characterizing complex metallic alloys that depends on the number of atoms contained in the unit cell.

 

 

 

Friction coefficient observed under vacuum between a 100C6 steel indenter and various Al-based compounds as a function of the number of valence electrons. The square symbol at the upper left part stands for Al metal while the two star symbols are for quasicrystalline phases. Other symbols represent different binaries and ternaries Al-based compounds.



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Matériaux composites pour l'impression 3D

La fabrication additive désigne un ensemble de techniques permettant de réaliser très rapidement des pièces fonctionnelles sans contrainte de forme à partir d’un modèle CAO.

Les pièces sont réalisées couche par couche, le plus souvent par fusion sélective de poudres qui peuvent être des polymères, des particules métalliques, céramiques ou bien encore des composites. En partenariat avec un industriel de la Région Lorraine et le Centre de Compétences matériaux et Procédés Additifs de l’Institut Jean Lamour, nous avons développé plusieurs types de matériaux composites adaptés à ces techniques d’impression 3D.

L’utilisation de particules quasicristallines permet d’obtenir de meilleures propriétés fonctionnelles. Cette application est commercialisée sous le nom de PAQ®

Photo : répartiteur d’admission d’air directement fonctionnel réalisé par frittage laser sélectif à partir d’un matériau composite polyamide renforcé par des particules quasicristallines.


Mouillage, frottement et complexité structurale

Les propriétés remarquables de mouillage et de frottement des alliages métalliques complexes ont été mises en évidence assez tôt après la découverte des quasicristaux par les travaux de l’équipe et sont au cœur de certaines applications de ces matériaux.

Les résultats mettent en évidence des corrélations inattendues entre ces propriétés mesurées, la densité d’états électroniques et un indice de complexité caractérisant les intermétalliques complexes dépendant du nombre d’atomes contenus dans la maille.

 

 

Figure : frottement observé sous vide secondaire entre un antagoniste en acier dur 100C6 et une série de composés à base d’aluminium en fonction du nombre d’électrons de valence du composé. Le carré le plus haut à gauche représente le métal aluminium alors que les deux étoiles au-dessous des valeurs de frottement proviennent de deux échantillons quasicristallins. Les autres symboles représentent divers composés binaires et ternaires à base d’aluminium.

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