A Synchrotron X-ray Diffraction from Perovskite Thin Films: Probing the Effects of Microscopic Structure on Macroscopic Properties
Perovskite oxides are a fascinating class of materials - they exhibit a huge range of properties such as magnetic ordering, ferroelectricity, metal to insulator transitions, piezoelectricity, just to name a few. These properties are extremely sensitive to the position, bonding, and electronic state of the central atom. As a result, small strains or structural changes can have large effects on the functional properties. The perovskites present an exciting opportunity to gain insight into these phenomena by pairing structural characterization with measurements of the macroscopic properties. In this talk, I will discuss how synchrotron x-ray diffraction can be used to study ferroelectricity, piezoelectricity, and charge disproportionation in perovskite thin films.
Ferroelectric domains in (Pb,Zr)TiO3 thin films were written using PFM. X-ray nanodiffraction was used to simultaneously image the domains and probe the structure. By comparing our results with PFM imaging, we find that the strain induced by the writing process is responsible for certain polarizations being less stable than others. In piezoelectric thin films, the film is macroscopically attached (clamped) to its substrate and the average piezoelectric distortion along the film-substrate interface must be zero. We observe very different results at the microscopic level. Using time-resolved x-ray microdiffraction, we find that the piezoelectric response of individual domains in BiFeO3 thin films is not zero and varies on a domain-by-domain basis. Finally, we combine electronic transport measurements with x-ray diffraction from charge disproportionation in La1/3Sr2/3FeO3 thin films. The temperature dependence of the resistivity and intensity and correlation lengths of the charge disproportionation reflections give insight into the nature of this phase transition.