Anion Blended Materials Conception – ANION-CO

Besides conventional chemical methods based on the optimization of existing materials (a large part being oxide-compounds) onward reaching their limits, alternative strategies are necessary to pursue or generate a substantial improvement of existing materials necessary to bring them into the market or to create new phases associated with new phenomena. In this project, we develop the idea of a rationalized approach based on the controlled diversification of the anionic array of inorganic compounds as an alternative method to modify or target new phases. Indeed, it is a general statement that the solid-state chemistry/physics community intuitively classifies the materials within separate classes of compounds on the basis of the concerned anion (oxides, sulfides, halides, pictnides, intermetallics …) while clearly this aspect greatly limits the physical potentialities. We propose a project in rupture with this state of the art: the elaboration of novel compounds and materials with mixed anion and chemical bonding types. On the basis of the limited examples of such compounds in the litterature, which most of the times show unpredicted behaviors (e.g. superconducting LaOFeAs), we bet on a number of original compounds, each of them at the potential origin of broad future fields of prospection.
A meticulous choice of anionic interplay guided by theoretical approaches and based on competition between anions will be applied to achieve specific features and properties. This project will be developed following several aspects:
- The validation of an efficient original oxygen mobility mechanism recently generated in our group thanks to fluorine incorporation into hexagonal perovskites oxides and its extension to other polytypes of this family with the aim to exacerbate these features for potential applications as electrodes.
- Nitrogen incorporation will be developed to generate new oxy-nitrides outside the beaten tracks of cubic perovskites containing early transition metals, i.e. well chosen hexagonal perovskites with adapted cationic environment around N3-. As oxy-nitrides from complex oxides based on other transition metals (Mn, Co, Fe, Co…) assume particular difficulties, mainly related to the nitrogen high cationic avidity, we propose to overcome these barriers by an appropriate choice of parent oxides. In particular, we also target versatile 2D parent-structures exhibiting layers with cations forming triangular or honeycomb lattices potentially stable to accommodate nitrogen. As an example, the NaxCoO2 exhibits rich cationic cages capable to accommodate nitrogen and to oxidize further upon a simple N3-/O2- substitution. The development of new phases within the structure types and metal transitions that we propose should allow the merging of new phases. Besides the breakthrough that would constitute of their elaboration, the expected alteration of the properties of the parent compounds will be of great academic interest but may also for specific applications (for instance the case of some hexagonal perovskites developed in the project with interesting microwave dielectric characteristics).
- Finally, we aim to target original systems based on mixed anions (for instance O-S, S-F, S-Cl, F-P…) and mixed cations to favor segregation obeying to anion-cation affinities. A complete segregation will lead to new intergrowth structures (such as the superconductor LaOFeAs). The resulting 2D structural units would subsequently exhibit different chemical natures and hold their proper properties as shown from DFT calculations. The properties decoupling into independent blocks is an advantage in taking control of the properties that will be exploited in this project. A predictive approach should help in targeting interesting compositions. In that purpose, the chemical nature of the anions in a chosen system should be substantially different to enable strong cation-anion preferences.