Multidimensional crystals and nanostructures with multiple functionalities

 

Our research activity is centered on the chemistry of oxide and intermetallic compounds and lies at the interfaces between solid state chemistry, materials physical chemistry, divided solids, solution chemistry and theory. The synthesis and the study of the structures and properties of materials are developed based on the relationships between theory and experiment. In particular, the dimensionality of materials and the use of confinement will be used to optimize their physical properties. Multi-scale structural and spectroscopic investigations of these materials in situ as functions of pressure and temperature are performed in the laboratory and at large-scale facilities (synchrotrons, neutron sources). This approach gives us direct access to dynamic phenomena which govern the properties of confinement of the studied materials. In addition, an overall understanding of their behavior is obtained with theoretical calculations.
 
The members of the group have international recognition in the areas of synthesis of oxide and intermetallic type inorganic materials, hydrothermal and Bridgman techniques of crystal growth, mecanosynthesis, thin film growth by cathodic pulverization, in situ crystallography as functions of pressure and temperature, high pressure techniques, multiscale structural and physical characterization and theoretical calculations. The original approaches of the group are in particular :
 
  • The use of the parameter pressure from 1 MPa in autoclaves up to 50 GPa in diamond anvil cells for the synthesis and in situ investigations of functional materials. The control of different pressure-temperature conditions to crystallize materials at different scales and to develop chemical treatment methods for sustainable development
  • The use of synthesis techniques which allow metastable materials to be produced under non-equilibrium conditions. The development of experimental and theoretical techniques for the study of the thermal properties of multidimensional materials
The materials prepared by the group have a wide range of applications in the areas of energy (electrical, optical, piezoelectric, thermoelectric, thermal, photonic, magnetic, ionic conductors…) and sustainable development (recycling of industrial silicates, wasted energy harvesting, low consumption lighting…).
 
 

Organizational chart

 

Research activities / fields

 
 

Theory-modeling-experiments relations

 

The object of this work axis is the development of theoretical models and computing programs with the aims to reach a better understanding of the chemical and physical properties of the materials of interest for our team and on the other hand to predict new structures optimized for electronic in full synergy with the experimentalists who synthesize them. Within this framework/background/context, we are using from the so-called ab initio method  to lighter but parametrized methods such as tight binding or molecular dynamics methods. 

Our savoir faire/know-how is broad and extends from vibrational (IR, Raman, INS) and thermoelectric response functions to the non-linear response functions (Pockels, SHG, Kerr effect) including the electro-mechanical and magneto-electrical mechanisms.
 
 
Stability and diffusion barriers 
 

With the help of DFT calculations, we are studying the stability of materials under various conditions: atmosphere, pressure, temperature. Thanks to these studies, we are able to select new materials with some of which could be metastable. In the latter case, several techniques ofsynthesis are used permitting to work under out-of-equilibrium conditions, such as mechanical alloying and magnetron sputtering or under high-pressure/high-temperature conditions. 

Among our other interests are the aspects related to the stability at the interfaces and to diffusion mechanisms by studying the diffusion barriers under thin film form. These studies are especially important for the applications at high temperatures because of the phenomena of oxidation and interdiffusion of the materials.

 

 
Multi-functional single crystals grown by hydro(solvo)thermal and Bridgman methods 
 
Single crystals of AO2 (A=Si, Ge) and ABO4 (A= Al, Ga et B= P, As) quartz isotype are the historical materials of this activity. Mixed solid solutions with other chemical elements (transition metals, actinides or lanthanides) will be investigated in order to enhance the physical properties of the materials. The growth of these crystals require the use of different hydrothermal conditions (150°C<T<500°C and 1MPa<P<300MPa), figure a.
 

The Bridgman method is used for intermetallic/oxide-type single crystals synthesis over a wide range of temperature (up tp 1600°C and potentially 2000°C). Suitable synthesis conditions can be adapted by controlling the atmosphere (Ar, O2) for centimetric-size single crystal synthesis.

Synthesis of new high performance materials is the main goal of this activity. As an example the study of the effect of chemical substitution in multiple fonction materials can permit to optimize the intrinsic physical properties (piezoelectricity, non linear optics, thermoelectricity, photoelectricity…) or create new ones (multiferroïcity and new coupling, figure b.

 

FerrOïcs = f(P,T,E,B)
 
 
This research activity is devoted to the « in-situ » study of structure-physical properties relationship of ferroïc materials at the micro-meso-macro-scopic scale as a function of pressure, temperature, electric and magnetic fields. The physical properties of materials by i) chemical substitution, 2i) defect creation or 3) external perturbation like pressure or magnetic field  will be investigated. Multiferroïc coupling in intermetallic/oxide materials based on transition metals and particularly on iron (oxides) will be mainly studied giving rise to a large range of physical properties. Additionally, high pressure-high temperature interactions in Fe-O will be investigated in order to synthesize  new materials.
 
 
Thermal properties and Materials with complex structures
 
The main families of semiconducting or metallic materials we are currently studying are compounds with cage type, incommensurate ot low symmetry structures. Several synthesis routes are and will be used depending to the stability of the studied materials: mechanical alloying, hydro-thermal, or under high-pressure/high-temperature conditions.
 
 
 
We are interesting by the lattice dynamics of materials with cage type structure. The mechanisms driving the thermal properties are studied by combining DFT calculations, vibrational spectroscopy and macroscopic experiments on the thermal properties. One of the aims is to understand the conditions in which the vibrations of the guest atoms become strongly anharmonic and what the impact on the physical properties is. We are also developing measurement techniques and experimental devices for the characterization of the thermal conductivity and heat capacity adapted to several various geometries (bulk, thin films, nanowires) and various conditions (temperature, pressure). 
 
 
 
 
Nanomaterials and nanocomposites 
 
Intermetallic and oxide materials, for which the low dimensionality affects their electronic transport, thermal, mechanical and photonic properties, are of particular interest. Different dimensions will be investigated :
 
  • Based on our know-how in sol-gel synthesis followed by hydrothermal treatment of SiO2 and AlPO4 materials and in high pressure techniques, the goal is to prepare new zeolite/polymer nanocomposites. The monomers are inserted and then polymerized under high pressure and, if needed, high temperature. This enables the sub-nanometer scale to be reached with strongly confined, isolated chains of organic of inorganic polymers with novel electronic, mechanical and optical properties. A similar approach will be used to prepare zeolite/nanowire composites by inserting metal atoms in the pores at high pressure and high temperature.
  •  

  • Our field of investigation extends to the study of intermetallic and oxide materials under various forms: nanometric powder, nanowires, thin films. One of our main aims is to study the effect of dimensionality on the electronic, thermal and photonic properties.  Thanks to the low-dimensionality, the thermal conductivity of the materials can be reduced without significant degradation of the electronic properties. The critical size below which there is electronic confinement would permit to increase the thermoelectric power, improving the potential of the studied  material for thermoelectric applications. For photovoltaic applications, the reduced dimensionality will permit to get higher amounts of light energy than from a conventional photovoltaic cell. The obtained nano-object will then introduced, after functionalization, in an organic matrix so that one can have benefits from both the remarkable properties of nano-object and the easier shaping of the polymer.
 
 
 
 
Sustainable development 
 
Several aspects will be studied :
 
  • With regard to the increasing problems concerning sustainable development and environmental protection, it is necessary to develop processes of destruction of the industrial waste and if possible to value them. In the case of waste containing asbestos, the use of hydrothermal conditions to destroy cement waste and their transformation towards other materials reduces energy consumption. Thus, the purpose is to define the greenest possible process of waste elimination and to valorize the products of the treatment either by isolating each of the chemical elements or by synthesizing another material for other applications.
  • Clathrates and zeolites have cage/channel type structures which have large potential for applications such as sequestration of polluting elements. The geometry and dimension of cages and channels will determine, which type of guest atoms can be intercalated. One of the aims of these studies will be to understand the diffusion mechanisms intra- and inter-cage/channel in order to optimize the sequestration of the studied chemical elements.
 
 
 
 
 
  • AIME, AM2N, CMOS, IMNO, MACS
  • IEM, L2C, IES, Géosciences Montpellier
  • CRISMAT, CRISTAL INNOV, FEMTO, ICMCB, ICN, ILM, SIMaP, ICMMO, ICMPE, LNCMI, ILL
  • CNR (Italie), INCEMC (Roumanie), Univ. Meknès, Univ. Turin, DQMP (Genève), EPFL (Lausanne)
  • C-THERM
  • ANR COFeIn 2013-2016
  • ANR MASCOTH 2014-2017
  • Thèse LABEX CheMISyst + accompagnement 2013-2016
  • PICS CNR/CNRS 2013-2016
  • Sous-traitant projet ANR ASTRID ECLATEMPS 2013-2016
  • Thèse Nîmes Métropole (collaboration SOMEZ – ICN)  2015-2018
  • Projet industriel (St Gobain – CREE): purification du SiC par traitement hydrothermal
  • Order and disorder in zeolites across different length scales du LABEX CheMISyst 2016-2019
  • PRIN (PROGETTI DI RICERCA DI RILEVANTE INTERESSE NAZIONALE) ZAPPING (High-pressure nano-confinement in Zeolites: the mineral science know-how APPlied to engineerING of innovative materials for technological and environmental applications) 2017-2019
  • IONANO «  Inorganique Organique NANO-composite pour applications thermoélectriques » co-financement Labex CheMISyst - Université de Montpellier
  • 6 ANR, 1 INSU et 2 projets H2020 FET en cours d’expertise

Institut Charles Gerhardt Montpellier - Direction

UMR 5253 - CNRS/UM/ENSCM
  • Université de Montpellier
  • Place Eugène Bataillon
  • CC 1700 - Bâtiment 17 -1er étage
  • Tel: +33 (0)4 67 14 93 50
  • Email: direction@icgm.fr
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