Disorder and Diffuse Scattering in non-stoichiometric oxides

Proper description of the oxygen diffusion in Ruddlesden-Popper (RP) frameworks at low temperatures is critical for the development of a variety of technological devices. Order/disorder phase transitions have been shown to have a huge influence on the diffusion rate, essentially dynamically enhanced in the disordered phase. We are interested here to better describe oxygen diffusion in Pr$_{2}$NiO$_{4.25}$, which shows oxygen ordering of the interstitial oxygen atoms up to the mesoscale, while the disordered phase shows strong diffuse scattering around the former satellite positions caused by the average perturbation of this long-range order. By utilizing a superspace approach, the modeling of incommensurate modulations embedded within the crystal structure in a higher-dimensional space is possible, and we aim to access information on both, periodic and aperiodic components including dynamical aspects, not only to understand atomic arrangements and discriminate between different diffusion mechanisms but also describe phase transitions. The modeling of disorder struc- tures from reciprocal space with superspace for single-crystal diffuse scattering allows the simplification of the analysis to comprehensibly understand the relationships between the crystal structure and the functional properties with further interpretation of the structural dynamics that are difficult to access with other techniques.