Abstract
With the use of the modified Sawyer-Tower scheme and Merz technique, studies were conducted on the repolarization characteristics of ferroelectric (BaZrO3/BaTiO3) superlattices on monocrystalline MgO substrate. Studies of temperature changes in the dielectric hysteresis loops indicated a sufficiently smooth decrease in spontaneous polarization compared with homogeneous barium titanate near the phase transition temperature of the superlattice. Experimental studies of switched currents have shown that the switching processes in the synthesized superlattices are implemented in two stages: activation motion (“creep” mode) and non-activation motion (slip mode). The presence of the activation switching stage and the numerical estimates show that with high probability, the movement of domain boundaries accomplishes the processes of switching in the studied superlattice. The threshold field separating the stated stages decreases with increasing temperature up to the Curie point of the superlattice, similar to the coercive field. Detection of the non-strictly exponential dependence of the switching current on the reverse field strength in the activation stage was modulated by the dependence with the power-law exponent for the applied electric field. Both techniques indicate that the studied superlattices have a small internal displacement field directed from the superlattice to the substrate.
Highlights
Artificially created layered materials, such as ferroelectric superlattices, are actively studied both in the fundamental physics of solid-state nanostructures and in applied physical materials science
The basic theoretical representations of the change in polarization of ferroelectric superlattices are based on the Landau - Khalatnikov model[10,11,12,13,14,15,16,17], in which the kinetics of repolarization is determined by the degree of deviation from the equilibrium state and the relaxation time of the order parameter or by the viscosity coefficients for changing the polarization in different layers of the superlattice
Indicated changes in the temperature behavior of the polarization can be interpreted as a change in the phase transition from the first type to the second in the ferroelectric superlattices versus bulk barium titanate
Summary
Artificially created layered materials, such as ferroelectric superlattices, are actively studied both in the fundamental physics of solid-state nanostructures and in applied physical materials science. The possibility of obtaining the required switching characteristics of these materials for their use in ferroelectric memory devices has attracted particular attention to the switching processes of ferroelectric thin-film structures and superlattices[5,6,7]. The presence of a domain structure in ferroelectric superlattices and thin films was observed in experiments using X-ray diffraction[8,9]. The polarization vector changes due to its correlation with deformation This change leads to shifting of atomic planes consisting of the same atoms in domains with opposite sign, and it was registered using Wulff-Bragg’s condition. The purpose of this work is a more detailed study of the polarization switching in ferroelectric superlattices using the Sawyer-Tower and the Merz methods
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