Alexander Stepanovich Sidorkin

The dielectric properties of ferroelectric composites and the specific features of the phase transitions occurring in them are discussed in comparison with the homogeneous ferroelectrics incorporated in the composites studied. The components incorporated into the dielectric matrix of ferroelectrics are considered to be triglycine sulfate, single crystals of potassium dihydrogen phosphate group, sodium nitrite, and perovskite-type materials. The factors changing the temperature range of polar phase existence in the ferroelectric composites under consideration are revealed and discussed. The results of the studies performed in this field are briefly reviewed. The work with the ferroelectric components incorporated into the aforementioned composites was performed in cooperation and under the guidance of L.A. Shuvalov.

The dielectric properties of ferroelectric composites and the specific features of the phase transitions occurring in them are discussed in comparison with the homogeneous ferroelectrics incorporated in the composites studied. The components incorporated into the dielectric matrix of ferroelectrics are considered to be triglycine sulfate, single crystals of potassium dihydrogen phosphate group, sodium nitrite, and perovskite-type materials. The factors changing the temperature range of polar phase existence in the ferroelectric composites under consideration are revealed and discussed. The results of the studies performed in this field are briefly reviewed. The work with the ferroelectric components incorporated into the aforementioned composites was performed in cooperation and under the guidance of L.A. Shuvalov.

The influence of electrical interactions between layers on phase transformations in ferroelectric superlattices with alternating layers of isotropic dielectric-ferroelectric is studied theoretically. The change in the temperature of the phase transition to the ferroelectric phase, spontaneous polarization, and dielectric response in these structures are estimated depending on the ratio between the thicknesses of different layers of the lattice. It is shown that the effect of the depolarizing field on the behavior of ferroactive particles in an external field in the ferroelectric component leads to an increase in the dielectric constant of the material.

We review dielectric properties of BaZrO3/BaTiO3 (BZ/BT) superlattices deposited on a single-crystal MgO substrate, and having a period of 13.32 nm. These superlattices have specific properties distinguishing them from BZ or BT bulk materials, and from thin films, with a ferroelectric phase transition around 393-395 °?, significantly higher than in bulk samples and thin films of BT, and appearing of second order. The polarization switching occurs in two stages and the precise analysis of experimental data demonstrates that the motion of the domain walls causes the switching processes. We conclude that the mobility of the domain walls decreases on heating. The presence of an internal bias field has been demonstrated and shown to be directed from the superlattice to the substrate, in agreement with an analysis based on the flexoelectric effect. The switching current has been shown to vary in weak fields as 1/E? with the exponent ? much smaller than in thin ferroelectric films. The appearance of the power index ?, which is significantly different from unity, may be due to a decrease in the average value of the switched polarization due to the boundaries between layers of different materials.

The mechanisms of increasing the dielectric response of the BaTiO₃/BaZrO₃ ferroelectric superlattices in comparison with the characteristics of the bulk materials of the lattice are discussed. It is assumed that changes in the dielectric response in superlattices are caused by mechanical stresses arising in layers of the superlattice due to the mismatch of the sizes of the unit cells that make up the lattice of single-crystal layers. These stresses lead to the formation of longitudinal polarization in the layers of barium titanate and to the related contribution of the transverse component of the dielectric tensor to the effective permeability of the superlattice in the direction normal to the plane of the layers. The misfit stresses cause the appearance of a ferroelectric phase transition in the barium zirconate the lattice layers with an increase in the dielectric constant of these layers in the direction normal to the plane of the lattice layers. Highlights: Mismatch stresses in ferroelectric superlattices Graphical Abstract

The dielectric properties of the bipolar SrTiO₃/BaTiO₃/SrTiO₃ structures synthesized by pulsed laser sputtering on a single-crystal SrTiO₃ substrate doped with Nb with a buffer conducting oxide sublayer of LaSrCoO₃ are studied. It is shown that the structure has a transition temperature to the ferroelectric state approximately equal to 320°С. The transition into the polar phase has all the features of a second-order phase transition. The indicated structures are characterized by the presence of an internal field entirely associated with the presence of a substrate.

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.

The dielectric properties of composite materials prepared by the embedding of ferroelectrics potassium dihydrogen phosphate (KDP), cesium dihydrophosphate (CDP), as well as antiferroelectric ammonium dihydrogen phosphate (ADP) into porous glass matrices with an average size of through pores of 7, 46, and 320 nm have been studied. It was found that an increase occurred in the phase transitions temperature (T_C) for embedded particles in comparison with corresponding bulk materials. Some possible mechanisms of influence of “restricted geometry” on the Curie temperature are discussed. Estimates of T_C shifting as a result of the “pressure effect” caused by elastic stresses in embedded particles as well as the result of bias electric field influence arising due to the piezoelectric effect are made. The possibility of using the tunneling Ising model to explain the experimental results is discussed.

Structural, dielectric and switching properties of epitaxial ferroelectric superlattices (SL) of barium zirconate BaZrO₃/barium titanate BaTiO₃ are investigated. In SL there is a ferroelectric phase transition at a temperature of 393°C close to the second type. The study of switching of SL in rectangular pulse fields showed that the dependence of the maximum switching current on the applied field is characterized by “activation” and “linear” regimes separated by a threshold field, which decreases when approaching the Curie point.