Ural State University, Lenin ave. 51, 620083 Ekaterinburg, Russia
In recent years enormous growth of interest in the polarization reversal in ferroelectric thin films is caused by exiting results in producing of integrated ferroelectric devices, first, nonvolatile dynamic memories. In present paper we will review the main experimental results concerning domains' evolution during switching and the theoretical description of this phenomenon taking into account the peculiarities of the process in thin films.
It is well-known that the polarization reversal in ferroelectrics is the complicated multi-stage evolution of the domain structure. The local and integral methods were used for its experimental investigation. By the local methods one can extract the detail information about the domain evolution, but it can be used only in limited number of model single crystals with optically distinguished domains. By studying lead germanate and gadolinium molybdate the correlation between symmetry of crystals and domains shape are demonstrated. It was shown that domain walls remote action due to peculiarities of electric field distribution in space and time (as a result of retardation effect) leads to correlated nucleation in superstrong field. We consider the evolution of domain structure as an example of phase transformation during the first-order phase transition. The local electric field is the driving force of switching process.
The integral registration of transient current is the only method appropriate for thin films. In such objects the reconstruction of domain structure goes independently in great number of grains of extremely small sizes. The experimental averaging favours the application of statistical theory. The description of domain's growth in finite sample in terms of geometrical catastrophes can be used. The mathematical treatment based on this approach allows to extract qualitatively new information about domain kinetic from integral experimental data. The method was tested by computer simulation and was used for thin films of PLT and PZT.
The proposed descriptions are of principal interest for the understanding of various experimental results in different ferroelectrics from unified physically clear point of view.
The work was supported in part by Russian Foundation of Fundamental Research under Grant No. 93-02-2451.