Determination of point defects using Dark-Field X-ray Microscopy

Oxygen vacancies are one of the most common such defects in metallic oxides, and have been reported to play a crucial role in the physical functionalities. Despite of the enormous relevance of oxygen vacancies in ferroelectric materials, we still have no means to directly visualize populations and their dynamics within bulk materials.

Therefore, we propose to study their nature, distribution and concentration by using Dark-Field X-ray microscopy (DF-XRM), which overcomes the surface-scale and indirect limitations usually found in advanced spectroscopy and microscopy methods and classical chemical characterization by probing directly the elastic deformation caused by buried point defects in oxide materials.

We carried out several experiments under electric field and studied the effects within the material. On the other hand, we are developing a 3D multiscale model in order to complement the analysis of the experimental results. This method consists of a combination of atomistic simulations from DFT and finite elemental analysis in COMSOL Multiphysics. This approach allows us to recreate 3D maps of the local strain produced by the oxygen vacancies. We then use the obtained strain field to simulate Dark-Field X-ray microscopy images pixel by pixel.

This is the first time that DF-XRM is used to study point defect and more importantly that a multiscale method is developed in order to support the experimental data.