The MnXTm1-XSe (0 <= & KHcy; <= 0.2) solid solutions have been first synthesized and their structural, magnetic, and transport properties have been studied in the temperature range of 80-1000 K and magnetic fields of up to 12 kOe. The surface morphology of the samples has been examined and the chemical analysis has been carried out. It is shown that the valence change with the increasing substitution concentration is accompanied by a change in the lattice parameter and a decrease in the magnetic moment of the samples. The Kondo temperatures caused by the manganese and thulium subsystem have been found in the low- and room-temperature regions. The temperature of localization of small-radius polarons has been determined. A drastic decrease in the relaxation time in the range of the manganese ion percolation through the lattice in the MnXTm1-XSe system has been established. The change of the current carrier type upon variation in the temperature and substitution concentration was determined from the Seebeck coefficient. A high-temperature extremum of thermopower was revealed, which is explained within the framework of the Anderson model.

A Bi2Fe4O9/BiFeO3 composite with a percentage ratio of 67/33 has been synthesized, its morphological analysis has been carried out. The average crystallite sizes for each phase have been determined. The magnetization hysteresis has been established and the temperature of its disappearance has been found. Using the infrared absorption spectra, temperatures of the magnetic phase transitions in each phase have been determined from the magnetic susceptibility, magnetostriction constant, ultrasound damping coefficient, and phonon mode softening. The change of magnetostriction constant sign observed in the vicinity of the spin reorientation transition and antiferromagnetic transition in mullite has been attributed to the change of the sign of the magnetoelastic constants. The interaction between the phases in the composite and the correlation of its structural and magnetic properties have been established.

Single crystals of Mn1.32Ni0.85Cu0.83BO5 with the ludwigite structure were obtained by the solution-melt method during spontaneous crystallization. The concentration of copper, manganese and nickel ions was determined by transmission microscopy. Manganese ions are included in compounds in the divalent and trivalent states. The study of temperature and field dependences showed that we have several magnetic transitions. The first transition, associated with the ferrimagnetic ordering of the magnetic moments of parts of the ions, observed in the region of 50 K. In the region of 25 K, a second magnetic transition is observed. Substitution of nickel ions for copper and divalent manganese of better disorder and competition of exchange interactions, which leads to the division of the magnetic system into several magnetic subsystems that are ordered at different temperatures.

A new bismuth pyrostannate-based composite Bi2(Sn0.7Fe0.3)2O7-x/Bi2Fe4O9 (BSFO/BFO) has been obtained by the solid-state synthesis. Temperature dependences of the magnetic hysteresis and remanent magnetization and the nonlinear field dependence of the magnetization for the Bi2Fe4O9 antiferromagnet have been established. A temperature of the formation of canted sublattices in the antiferromagnet with the occurrence of a spontaneous moment in mullite has been determined. The mechanism of the electric polarization hysteresis and the temperature dependence of the remanent polarization have been established. It has been shown, that, below the Ne & PRIME;el temperature, the dipole polarization is induced by a lone electron pair of bismuth ions. At T > TN, the migration polarization is caused by the charge carrier density at the chemical potential. A significant increase in the remanent magnetization of mullite in the bismuth pyrostannate matrix with oxygen vacancies over a value typical of polycrystalline mullite has been established. Remanent magnetization is explained in terms of ferron model.

The structural, transport, optical, and acoustic properties of a new TmXMn1-XSe (0 <= X <= 0.2) chalcogenide system have been studied in the temperature range of 80-500 K. The morphology and microstructure of the polycrystalline samples have been studied by scanning electron microscopy. Temperatures of maxima of the thermal expansion and sound attenuation coefficients related to the lattice strain and electronic transitions have been determined. The variation in the energy of activation of carriers near the percolation concentration caused by a change in the thulium valence has been revealed. The type of majority carriers has been established from the thermopower data. The temperature range of the anomalous compressibility associated with delocalization of electrons has been found from the temperature dependence of the thermal expansion coefficient. Jahn-Teller polarons have been found above the percolation concentration using the infrared spectroscopy data.

Magnetic microspheres with nonmagnetic acrylic glass core were fabricated using electroless deposition. There are favorable conditions for magnetic flux closure within each particle. As a result, the dipole-dipole interaction in the powder of such microspheres is reduced drastically. This is the key difference between powders of magnetic microspheres and powders of full magnetic spherical particles witch behavior is significantly affected by the dipole-dipole interaction. The magnetic hysteresis in the cobalt microspheres with nonmagnetic core is significantly large then in the full cobalt particles produced using the same technique.

Magnetic microspheres with nonmagnetic acrylic glass core were fabricated using electroless deposition. There are favorable conditions for magnetic flux closure within each particle. As a result, the dipole-dipole interaction in the powder of such microspheres is reduced drastically. This is the key difference between powders of magnetic microspheres and powders of full magnetic spherical particles witch behavior is significantly affected by the dipole-dipole interaction. The magnetic hysteresis in the cobalt microspheres with nonmagnetic core is significantly large then in the full cobalt particles produced using the same technique. Keywords: Magnetic microspheres, magnetic dipole-dipole interaction.

Light scattering and transmission by a monolayer polymer dispersed liquid crystal film containing liquid crystal droplets with inhomogeneous anchoring of liquid crystal molecules at the polymer-droplet interface is considered theoretically and experimentally. The developed optical model is based on the anomalous diffraction and interference approximations of the theory of scattering of waves. It is applied to describe the interference quenching effect for the coherently transmitted light and electrically controllable symmetry breaking effect in small-angle structure of light scattered by film containing droplets with inhomogeneous anchoring. The analysis of transmittance and reflectance of the one-dimensional photonic crystals composed of monolayers is carried out. The formation of the photonic band gaps is analyzed.

Single crystals of Mn1.32Ni0.85Cu0.83BO5 with the ludwigite structure were obtained by the solution-melt method during spontaneous crystallization. The concentration of copper, manganese and nickel ions was determined by transmission microscopy. Manganese ions are included in compounds in the divalent and trivalent states. The study of temperature and field dependences showed that we have several magnetic transitions. The first transition, associated with the ferrimagnetic ordering of the magnetic moments of parts of the ions, observed in the region of 50 K. In the region of 25 K, a second magnetic transition is observed. Substitution of nickel ions for copper and divalent manganese of better disorder and competition of exchange interactions, which leads to the division of the magnetic system into several magnetic subsystems that are ordered at different temperatures. Keywords: ludwigites, magnetic interface transition, indirect exchange interactions.

Composite films and nonwoven mats of the poly-3-hydroxybutyrate and chitosan natural polymers were prepared and investigated. DSC and FTIR techniques were used to confirm that P(3HB) blending with chitosan resulted in a decrease in P(3HB) crystallinity to 47% and 62% in the films and nonwoven mats, respectively. Scanning electron microscopy showed that addition of chitosan induced changes in the surface morphology of the composite films and a reduction in the diameter of ultrafine fibers in the nonwoven mats from 800 nm to 460 nm. The values of water contact angle for films (53°) and nonwoven mats (50.6°) suggested that chitosan enhanced hydrophilic properties and moisture absorption capacity of the composite materials. On the other hand, P(3HB) showed its reinforcing ability and improved the physical/mechanical properties of chitosan. The work included studies of in vitro biodegradation of the composite specimens and their ability to maintain cell growth and attachment in NIH 3T3 fibroblast culture.

A model to describe light scattering by polymer film containing of monolayer of liquid crystal droplets with inhomogeneous anchoring of liquid crystal molecules at the polymer-droplet interface is developed. It is based on the interference approximation of the wave scattering theory. The director field distribution in the droplet volume is determined by solving the free energy density minimization problem using the relaxation method. The spatial distribution of droplets in the layer is described by the hard disks model. The amplitude scattering matrices of individual droplets are found in the anomalous diffraction approximation. The algorithm for numerical analysis of the characteristics of light scattered in a polymer film containing droplets at homogeneous and inhomogeneous surface anchoring is described in terms of the partial filling factors of the monolayer film. Electrically controllable symmetry breaking effect of angular distribution of light scattered by films containing droplets with inhomogeneous anchoring at the polymer-droplet interface is described and experimentally confirmed. [GRAPHICS]

The specific heat, thermal expansion, permittivity, and electrocaloric effect in bulk of BaTiO3 (BT) samples in the form of nano- (nBT-500 nm) and micro- (mBT-1200 nm) ceramics fabricated using spark plasma sintering and solid-state plasma techniques have been investigated. The size effect has been reflected, to a great extent, in the suppression of the specific heat and thermal expansion anomalies and in the changes in the temperatures and entropies of phase transitions and permittivity, and a decrease in the maximum intensive electrocaloric effect: $$\Delta T_{{{\text{AD}}}}^{{\max }}$$ = 29 mK (E = 2.0 kV/cm) for nBT and $$\Delta T_{{{\text{AD}}}}^{{\max }}$$ = 70 mK (E = 2.5 kV/cm) for mBT. The conductivity growth at temperatures above 360 K leads to the significant irreversible heating of the samples due to the Joule heat release in the applied electric field, which dominates over the electrocaloric effect.

Calculations were performed using the transfer matrix of one-dimensional photonic crystals with low contrast and asymmetric structures of different periods. Such structures have been found in many plants. When joining two successively connected sublattices with different periods, an increase is observed in the amplitude of the electromagnetic field and the density of photon states inside the structure, and their change depends on the asymmetry of the thickness of the sublattices.

AbstractThe specific heat, thermal expansion, permittivity, and electrocaloric effect in bulk of BaTiO_3 (BT) samples in the form of nano- (nBT-500 nm) and micro- (mBT-1200 nm) ceramics fabricated using spark plasma sintering and solid-state plasma techniques have been investigated. The size effect has been reflected, to a great extent, in the suppression of the specific heat and thermal expansion anomalies and in the changes in the temperatures and entropies of phase transitions and permittivity, and a decrease in the maximum intensive electrocaloric effect: $$\Delta T_{{{\text{AD}}}}^{{\max }}$$ = 29 mK ( E = 2.0 kV/cm) for nBT and $$\Delta T_{{{\text{AD}}}}^{{\max }}$$ = 70 mK ( E = 2.5 kV/cm) for mBT. The conductivity growth at temperatures above 360 K leads to the significant irreversible heating of the samples due to the Joule heat release in the applied electric field, which dominates over the electrocaloric effect.

An optical-mechanical model has been developed to describe the transmittance, polarization and small-angle distribution of light scattered by an uniaxially-stretched polymer film containing the elongated ellipsoidal droplets of nematic liquid crystal. It is based on the approximations of Foldy-Twersky, anomalous diffraction, and single scattering. The spectral dependences of transmittances and polarizing abilities of the polymer dispersed liquid crystal films have been analyzed as well as the small-angle intensity distribution and the polarization degree of scattered light depending on the film thicknesses, refractive index of polymer matrix, sizes of droplets, their anisometry parameters, concentration, polydispersity, and optical axes orientation. The optical characteristics of films with homogeneous and inhomogeneous interfacial anchoring at the surface of liquid crystal droplets have been considered. The transmittance and polarizing ability of the films have been studied as functions of the angular aperture of the system recording scattered light. (C) 2019 Elsevier Ltd. All rights reserved.

A review of the state and analysis of works related to optical processes of photosynthesis are given. Particular attention is paid to the work on the investigation of these processes in iridoplasts and chloroplasts with photonic crystal structure. From a general point of view, a photonic crystal (PhC) is a superlattice with a characteristic scale of periodicity of permittivity (refractive indices) of the order of the wavelength of the light wave. In such structures, the forbidden bands occur in the spectrum of electromagnetic waves. This means that in a given spectral range the light of any polarization cannot enter the PhC or exit in any direction. An important property of PhC is high degree of localization of electromagnetic waves on the lattice defects. In this case, defective energy levels manifest themselves in the forbidden zones of the PhC. An atom or molecule emit a quantum with a frequency corresponding to a defective mode. Most of the works dealing with the study of optical processes of photosynthesis have not taken into account the features of light propagation in structures. Periodic structures have been found in the plant and animal world. This paper presents the effect of a long-period structure on the optical properties and local characteristics of light waves, including the transmission and reflection spectrum, as well as the distribution of the electromagnetic field in the layered structure. Based on modern mathematical apparatus, the main spectral and optical characteristics were calculated using the example of a begonia plant. In recent works describing the propagation of light, the long-period structure was not taken into account. However, for the interpretation of the results, concepts (antenna, reaction center, the presence of two photosystems) without a detailed description of the physical nature were introduced. In addition, we had to employ a resonance mechanism for the transfer of excitation energy from the donor molecule to the acceptor molecule and quantum coherence. The analysis of the data obtained within the framework of a unified approach made it possible to explain the mechanism of the effect on photosynthesis, namely, the appearance of two photosystems (division of the stop zone into two parts), the feature of the long-wavelength quantum yield, its amplification (Emerson effect), including the red boundary shift, the efficiency of photosynthesis with additional irradiation and the expansion of the absorption region.

The effect of thermal cycling and sintering temperature on the chemical and thermodynamic stability of the bulk multiferroic x La 0.7 Pb 0.3 MnO 3 –(1 – x )PbTiO 3 quasi-ceramic and ceramic composites has been experimentally investigated. It is shown that the limiting temperature of the long-term sample firing should not exceed 1070 K. It has been found that sintering at this temperature and/or short-term exposure of the samples at higher temperatures (up to 1220 K) significantly increase the sample compactness, stabilize the thermal expansion, and enhance the quality of the composites. It has been established that the component grain integrity is violated by shrinkage of the samples and a sharp change in their volume during the phase transition of a ferroelectric component.

Using data on the structure of plant leaves, specific features of light propagation in biophotoniccrystal structures have been established by the transfer matrix method. Splitting of the stopband in two bands has been found. The density of photonic states and the electromagnetic field value have been calculated. The occurrence of two photosystems (splitting of the stopband in two bands), the peculiarity of the long-wavelength quantum yield and its enhancement (Emerson effect), and water dissociation in the soft mode due to an increase in the electromagnetic field on the layers are explained.