Structure and Dynamics in Ion Conducting Catalytic Ceramics – STUDYCEM

Oxides with Perovskite structure are a fascinating class of materials with a huge variety of technological applications, e.g. ion conductors for energy storage and transformation,
electrocatalyst, solar cells, magnetism. While the undistorted ABO3 structure shows a simple cubic structure, it turned out recently that many of these compounds present a more
complex structure on a local level, essentially based on micro-twinning and oxygen vacancy ordering. Such phases show a very particular domain structure with mesoscopic
periodicities, consisting of Brownmillerite Building Blocks interconnected by an interface zone. The latter also serves to switch domain orientations, forming anti-phase twin domains, thus promoting the creation of possible polar twin boundaries, even in case of a non-polar ferroelastic ground state of the underlying structure. The polarizing character of such interface structure becomes especially interesting to promote catalytic reactions at the gas-solid interface, wherever molecules showing a dipole moment are involved. In this regard we have evidenced recently, in Brownmillerite frameworks with the formula A2BB’O5, that octahedral B or tetrahedral B’ sites can be selectively substituted on either site. This is, e.g., the case for Sr2ScGaO5, where Sc and Ga are maintaining their respective octahedral and tetrahedral coordination while substituting one of these sites by 3d transition metal atoms, e.g. Mn, Fe or Co. We could further evidence, by combining neutron-pdf analysis and RIXS spectroscopy, that the local coordination for B and B’ is preserved both for the Brownmillerite and its cubic-Perovskite polymorph. Emphasis is put on the development of 17O/45Sc/71Ga/1H/2H solid-state NMR methodology for characterizing both the local structures and the dynamic aspects of mobile proton species, which will be correlated with the results from ab-initio molecular dynamics simulations.