Thesis

“Perovzalates” are a new family of hybrid perovskites based on oxalate, with around ten examples listed since 2019 (AILi3MII(C2O4)3, with A = K+, Rb+, Cs+, NH4+; M = Fe2+, Co2+, Ni2+). Just like conventional perovskites, they are potentially interesting for countless applications (catalysis, optics, solar etc.), presenting additional advantages linked to the oxalate anion, which allows the incorporation of larger cations than in other hybrid pervovskites, while preserving a crystal structure similar to oxide perovskites.

However, this class of new materials is still barely explored, and the syntheses far from being mastered: the few reports to date systematically produce mixtures of phases, and relate to single crystals taken from heterogeneous solutions. In this context, the major problem is to synthesize an extended class of pure perovzalates.

This thesis addresses this challenge by exploiting a property discovered in the laboratory: the crystallization of metal oxalates by co-precipitation in water passes through transient “mineral emulsions”, that is to say nano-droplets rich in reagents which separate from water. The originality of this thesis is to exploit the nanostructuring provided by these mineral emulsions, and to test in particular using nanotomographic techniques accessible in synchrotron if they make it possible to confine the cations until crystallization.