Projet ANR-11-BS04-0004 – ODACE : Ordre et désordre dans les édifices cristallins apériodiques.
Programme : Blanc - SIMI 4 - Physique (Blanc SIMI 4) 2011
Année de financement : 2011
Coordinateur du projet : Monsieur Marc DE BOISSIEU (CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE - DELEGATION REGIONALE RHONE-ALPES SECTEUR ALPES)
Partenaires : Centre national de la recherche scientifique; Centre national de la recherche scientifique; Centre national de la recherche scientifique
Montant : 715000.0 euros
Date de début : 2012
Durée : 48 mois
Résumé : Aperiodic crystals are long range ordered materials which lack the translational invariance found in periodic crystal and as such present a new paradigm for solid state physics and material science. Aperiodic crystals encompass incommensurately modulated structure, incommensurate composite compounds and quasicrystals. They are found in a large variety of systems such as simple element under pressure, mineral, oxides, high Tc superconductors, ferroelectrics, charge density waves compounds, organic molecular compounds, complex metallic alloys… 
Their atomic structure is now better understood, using the unifying framework of the superspace or high-dimensional description of aperiodic crystals. Whereas the influence of the long range aperiodic order on physical properties remain a challenging question, one of the most fascinating issue in this field remains the nature of the driving force responsible for the formation of aperiodic long range-order. Whereas for periodic crystals the propagation of long range order can be understood with a simple model of stacking of unit cells, this concept breaks down for aperiodic crystals. How is the aperiodic long range order propagated when the crystal forms, what are the stabilizing mechanisms of aperiodic order, is the electronic structure a decisive factor, what is the balance between energy and entropy in the stabilization?
To contribute to these questions we propose to carry out a joint study of four different phases. They span the three different classes of aperiodic crystals (incommensuratly modulated structure, composite and quasicrystals). They involve three different class of materials: inorganic oxide compounds, organic molecular compounds and complex metallic alloys. This allows to have quite different interactions in play with covalent bonding, hydrogen like bonds and metallic like bonds.
We will carry out a simultaneous study of the four phases. Their structure will be determined accurately, in order to pin-point the two or more competing length scales or geometrical frustration motifs. The phase transitions, frequently observed as a function of temperature or pressure, will also be studied in details, since they are related to the interactions in play. The disorder and diffuse scattering, observed as pre-transitional fluctuations or as equilibrium fluctuations will be studied by different techniques. In particular their dynamical aspect when present should give clues on the nature of the long wavelength fluctuations particular to the aperiodic order and named phasons.
This overall experimental study will be complemented by simulation at the atomic scale using DFT calculations or adapted Hamiltonian allowing to tackle large systems.
This comparative study should shed some light on the universal mechanisms leading to aperiodic order.