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Consecutive stochastic 90° polarization switching events, clearly resolved in recent experiments, are described by a new nucleation and growth multi-step model. It extends the classical Kolmogorov-Avrami-Ishibashi approach and includes possible consecutive 90°-and parallel 180°-switching events. The model predicts the results of simultaneous time-resolved macroscopic measurements of polarization and strain, performed on a tetragonal Pb(Zr,Ti)O3 ceramic in a wide range of electric fields over a time domain of five orders of the magnitude. It allows the determination of the fractions of individual switching processes, their characteristic switching times, activation fields, and respective Avrami indices.

A stochastic model for polarization switching in tetragonal ferroelectric ceramics is introduced, which includes sequential 90 • -and parallel 180 • -switching processes and accounts for the dispersion of characteristic switching times due to a nonuniform spatial distribution of the applied field. It presents merging of the recent multistep stochastic mechanism (MSM) with the earlier nucleation limited switching (NLS) and inhomogeneous field mechanism (IFM) models. The new model provides a much better description of simultaneous polarization and strain responses over a wide time window and a deeper insight into the microscopic switching mechanisms, as is exemplarily shown by comparison with measurements on lead zirconate titanate. a) Electronic address:

Domain walls and phase boundaries are fundamental ingredients of ferroelectrics and strongly influence their functional properties. Although both interfaces have been studied for decades, often only a phenomenological macroscopic understanding has been established. The recent developments in experiments and theory allow to address the relevant time and length scales and revisit nucleation, phase propagation and the coupling of domains and phase transitions. This review attempts to specify regularities of domain formation and evolution at ferroelectric transitions and give an overview on unusual polar topological structures that appear as transient states and at the nanoscale. We survey the benefits, validity, and limitations of experimental tools as well as simulation methods to study phase and domain interfaces. We focus on the recent success of these tools in joint scale-bridging studies to solve long lasting puzzles in the field and give an outlook on recent trends in superlattices.

Abstract⎯Carbon microspheres with a mean diameter of 3-3.5 µm were prepared by solid-phase pyrolysis of polyethylene and metal-free phthalocyanine. Morphology, structure and magnetic properties of the samples were investigated by electron microscopy, Raman spectroscopy, magnetometry and electron paramagnetic resonance. Carbon microspheres are composed of graphitic nanocrystallites with longitudinal sizes of 10-15 nm. The samples reveal strong paramagnetism, which in the case of metal-free phthalocyanine pyrolysis is 3 times higher (~5×10 19 spin/g) due to the unpaired spins of impurity nitrogen atoms.