Electronic ferroelectrics remain up to now largely overlooked and deserve more attention, both on the solid state chemistry side, to find new suitable candidates, and on a fundamental one, to establish the origin and parameters necessary to this type of multiferroicity.
Based on the discovery of a giant magnetoelectric effect in charge-ordered Fe2BO4, the aim of BORA-BORA is to synthesize and characterize in details compounds belonging to two systems of borates, namely the warwickite and the ludwigite. In the search for new ferroelectrics, both structures provide two key features : mixed valence, and low dimensional network, of transition metal atoms, two known ingredients for electronic multiferroicity. The ludwigite structure offers in addition the possibility to play both on the nature of the substituting transition metal cation and on the site on which it will be substituted preferentially.
Synthesis of new compounds and combination of local and larger scale structural characterization techniques with physical properties measurements will be at the core of the project, whose aim is not only to identify new electronic ferroelectrics, but also to shed light on the mechanisms at play in these materials, an issue that is still open up to now. The partnership involves researchers from the Léon Brillouin and the CRISMAT laboratory, as well as the SOLEIL synchrotron. With regards to structural characterizations, X-ray, electron and neutron diffraction techniques will be used to study crystal structures, charge-ordering superstructures phenomena, and non-centrosymmetry issues that are essential in ferroelectrics. XAFS and XANES spectroscopies will give additional information on the valence states of the different cations, their surrounding crystal fields, and if relevant, their spin states. Dielectric constant and pyroelectric polarization measurements will be an important part of the physical characterizations, and will be complemented with neutron diffraction experiments, the knowledge of magnetic structures being necessary to identify the possible magnetoelectric coupling mechanisms. Magnetic circular dichroism experiments will be performed to correlate valence and the local magnetic moment.
Madame Françoise DAMAY (Laboratoire Léon Brillouin)
The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.
LLB Laboratoire Léon Brillouin
SOLEIL Synchrotron SOLEIL
Help of the ANR 400,895 euros
Beginning and duration of the scientific project: September 2016 - 36 Months