Synthesis of multi-cationic dawsonite, towards a versatile high-entropy oxide synthesis route

High entropy materials are known in metallurgy for a long time but only since 2015, they have emerged in the ceramic community gathering more and more interest due to their interesting properties. These promising materials are composed of no less than five cations that could lead to surprising catalytic properties and more. The interesting properties arise thanks to a single-phase stabilization due to the configurational entropy; furthermore, the combination of different anions and cations opens a large field of possible applications. They are now at the centre of a growing field considering the global energetic crisis, and the lack of precious metals for catalytic activities. The goal of this thesis is to start with a short description of high-entropy ceramics and the origin of their behaviour, after that moving to the synthesis of a new type of high-entropy oxide and its characterization. The centre of the work is the synthesis of a five-cations high entropy ceramic, a new precursor of a high-entropy oxide, called Dawsonite and its changes after calcination. In addition, another path through this material is described following a solid-state synthesis for achieving the same high entropy mixture. On the side, there is the development of a new type of segmented flow reactor completely automatized for synthesizing new high entropy ceramics. The importance of this device is related to the capacity of changing the proportions between the constituents. These areas are the two main topics of the work and starting point for the next developments in research concerning the catalytic activities of these particular ceramics.