Description du sujet de thèse

Structure and dynamics in oxygen deficient perovskite type oxides
This thesis focuses on the synthesis (solid state and crystal growth), structural and microstructural characterization by X-ray (laboratory/synchrotron) and neutron scattering techniques, completed by theoretical simulations of structure and dynamics as well as magnetic properties, to better understand ion diffusion mechanisms in solid oxides, especially at moderate temperatures.

Contexte de travail

Perovskite and Ruddlesden-Popper type oxides are a fascinating class of materials, which possess diverse technological applications as ion conductors for energy storage and transformation, (electro)catalysts, devices in solar cells, magnetism, and many others. The electronic properties of perovskites can be tailored through cation substitution and oxygen stoichiometry adjustment, leading to complex local structures with microtwinning and oxygen vacancy ordering.
Structure refinement based on total scattering methods up to high q-values (neutron and X-ray PDF-analysis) have revealed hidden features like 1D vacancy channels and Brownmillerite nano-domains within the Perovskite phase.
These results are consistent with the analysis of 17O magic-angle spinning NMR spectra which also focus on the local environments. Together with the fact that defined annealing at elevated temperatures allows to vary and control the domain size, such phases show a very particular domain structure with mesoscopic periodicities, consisting of Brownmillerite building blocks (BBB), interconnected by an interface zone. These structures exhibit mesoscopic periodicities and interface zones facilitating catalytic reactions and ion diffusion pathways.
The polarizing character of such interface structure becomes especially interesting to promote catalytic reactions, e.g. at the gas-solid interface, wherever molecules showing a dipole moment are involved.

Contraintes et risques

NO