Paul G. Evans, Materials Science and Engineering, University of Wisconsin-Madison
The atomic-scale periodicity of ferroelectric/dielectric superlattices leads to an exciting variety of structural and dynamic effects in applied electric fields. The richness of these phenomena arises in part from the interaction between from crystallographic symmetry, including various distortions of the unit cells of the component materials, and longer-range effects associated with ferroelectric remnant polarization. The relative importance of local and long-range phenomena can be tuned via the choice of component layers and the stacking sequence of the superlattice. We illustrate these points using results from two systems with different ferroelectric and dielectric components: a BaTiO3/CaTiO3 (BTO/CTO) superlattice in which the polarization is strongly coupled between layers and PbTiO3/SrTiO3 (PTO/STO) in which weaker polarization coupling leads to the spontaneous formation of nanoscale polarization domains. The time and spatial scales of these phenomena are an excellent match for emerging synchrotron x-ray scattering techniques, particularly via a combination of nanobeam techniques and time-resolved diffraction. We will discuss the x-ray nanobeam techniques we have developed to address these problems, surprising domain dynamics in the STO/PTO system, and the scaling of these phenomena to sub nanosecond timescales.
