The project "Influence of temperature and high pressure on the structural and physical properties in Fe‐based Charge Order systems" (acronym: COFein) is one of the eight projects selected as part of the 2012 edition of "l'Appel Blanc International ANR - ANCS/UEFISCDI", a collaboration protocol between the research financing bodies from France and Romania respectively.
This project deals with the preparation and the study of iron based oxides (in form of poly‐ and single‐crystals) presenting charge ordering, combining the +2 and +3 iron oxidation states. Indeed, charge ordering in transition metal oxides is a fundamental parameter for obtaining original magnetic and/or electric properties. That was largely shown within the framework of the studies on colossal magneto‐resistance in manganese perovskites and it again seems at the origin of the ferroelectricity in CaMn7O12 or LuFe2O4.
Our project breaks up into several sections:
‐ We chose to revisit the systems of “iron borates and phosphates” presenting iron mixed valences on the basis of literature and of our experience of solid state chemists in this field, to highlight unusual properties (of which multiferroicity).
‐ The second research orientation is more creative and relates to the exploration of new systems, always on a “Fe, P, B, O” basis, to obtain new compounds of which we will characterize the structures and the properties.
‐ The (structural and the properties) evolution of materials will be followed versus temperature, magnetic field and also high pressures. Not only this last factor allows obtaining new phase diagrams, but it can lead to the stabilization of new crystalline “buildings”, and thus to new properties. This effect was already illustrated in a convincing way in the case of charge order compounds, with the appearance of an irreversible structural transition in LuFe2O4. A broad panel of techniques of laboratory and large‐scale facilities will be implemented for the most detailed and complete possible description of the structural, micro structural and properties of our materials.
‐ The purpose of this crystallo‐chemistry work of is to establish relationships between the structures and the (magnetic and electric) properties of our compounds. This has as much interest from the fundamental point of view as for the optimization of the properties for potential applications.