Growth of dendrite domains and superfast domain shape transformation in ferroelectrics

12.11.2019 13:00 – 14:00

The experimental study of formation of the dendrite domains in uniaxial ferroelectric and superfast transformation of the concave polygonal domain appeared after merging to the convex one will be presented and described. The obtained effects will be considered using unified kinetic approach based on the analogy between kinetics of ferroelectric domains and phase growth during first-order phase transformation (such as crystal growth).
The evolution of the shapes of isolated domains during polarization reversal in uniform electric field in lithium niobate LiNbO3 (CLN) and potassium titanyl-phosphate (КТР) single crystals by in situ optical imaging with high temporal resolution. The static domains at the surface were imaged by scanning electron microscopy and in the bulk – by confocal Raman microscopy and Cherenkov-type second harmonic generation.
It was demonstrated that the stochastic nucleation at the elevated temperatures in CLN leads to topological instability and dendrite domain shapes [1,2]. The growth of dendrite domains (snowflakes) has been observed at the elevated temperature in the plates covered by artificial dielectric layer [3]. The field dependence of the shape of dendrite envelope was revealed. The obtained results have been confirmed by phase field modeling.
The kinetic approach to domain growth based on step generation and kink motion along the wall has been used for explanation of the shape variety [4]. The nucleation probabilities are determined by the excess over the threshold value of the local value of the sum of external field and partially screened (residual) depolarization field depending on the domain shape.
The domain shape change due to ineffective screening and formation of the trail of residual charges was demonstrated experimentally and by computer simulation [4]. It was shown that the determined step nucleation at the vertices and anisotropic kink motion dominated at low temperatures (< 200oC), whereas the stochastic nucleation with equiprobable nucleation sites is observed at the elevated temperatures (> 200oC). The convex hexagon domain shapes determined by symmetry have been observed for effective screening of depolarization field. Screening retardation leads to the irregular and concave polygons.
The first experimental study of the transformation of the concave polygonal domain appeared after merging to the convex (shape stability effect) [5] one has been realized. The convex growth of isolated hexagonal domains was governed by the slowest domain walls, while the concave growth after domain merging – by superfast walls with several orders of magnitude higher velocity [6]. We reconstructed experimentally the v-plot (kinetic Wulff plot) for domain wall motion by analysis of both convex and concave domain growth [6,7].

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Bâtiment: Ecole de Physique

Auditoire Stueckelberg

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