The article presents the results of studies of theBaMg(1/3)Ta(2/3)O(3) (BMT) complex perovskite crystal using Raman spectroscopy and density functional theory (DFT) calculation. The polarized Raman spectra of a cubic BMT single crystal are obtained in two different geometries in a broad temperature range (5-580 K). The density functional theory calculations of the lattice dynamics and vibrational spectra of the BMT crystal in the & Gcy; point of the trigonal phase are carried out. The simulated Raman spectra are analyzed in comparison with the experimental spectra of cubic single crystals and those of ceramics in the trigonal phase. The Raman spectra peculiarities are observed and explained.

BaMg1/3Ta2/3O3 (BMT) crystals belong to the family of complex perovskites and are well known for their excellent microwave dielectric properties. In this work, structural optimization of the lattice parameters was performed. Electron density functional theory calculations of the electronic band structure of BMT crystal of the trigonal phase were carried out along & Gcy;-A-K-M-L directions of the Brillouin zone. The calculated band gap energy was 3.554 eV. The partial density of states of BMT crystal in P-3 m1 phase was simulated. Top of the valence band was formed by 2p-states of O and bottom of the conduction band - by 5d-states of Ta.

The structure of the relaxor ferroelectrics PbNi1/3Ta2/3O3 (PNT) was studied by powder X-ray diffraction. The measurements were performed at 313.5 ± 1 K using a powder, which was prepared by grinding PNT single crystals grown by the spontaneous crystallization. The structure refinement and the fitting of the simulated diffraction pattern to the experimental data were performed by the Rietveld method. It was demonstrated that the grown crystals of PNT have a perovskite structure (sp. gr. Pm3m (221), a = 4.02679(2) Å). Polarized Raman spectra of PNT were recorded at room temperature. The main modes of the light scattering spectra were assigned to the Е1 and А1 components of the transverse optical phonon (ТО1) and the А1 component of the longitudinal optical phonon (LO3). The temperature dependence of the dielectric susceptibility shows a broad frequency-dependent anomaly with a maximum at 89 К at a frequency of 1 kHz.

The structure of the relaxor ferroelectrics PbNi 1/3 Ta 2/3 O 3 (PNT) was studied by powder X-ray diffraction. The measurements were performed at 313.5 ± 1 K using a powder, which was prepared by grinding PNT single crystals grown by the spontaneous crystallization. The structure refinement and the fitting of the simulated diffraction pattern to the experimental data were performed by the Rietveld method. It was demonstrated that the grown crystals of PNT have a perovskite structure (sp. gr. Pm 3̅ m (221), a = 4.02679(2) Å). Polarized Raman spectra of PNT were recorded at room temperature. The main modes of the light scattering spectra were assigned to the Е 1 and А 1 components of the transverse optical phonon (ТО1) and the А 1 component of the longitudinal optical phonon (LO3). The temperature dependence of the dielectric susceptibility shows a broad frequency-dependent anomaly with a maximum at 89 К at a frequency of 1 kHz.

Stillwellite, ideally CeBSiO5, is a rare mineral, however, its discovery stimulated the intense studies of a new class of stillwellite-like materials with remarkable electrical and optical properties. With the use of the modern non–ambient single crystal X-ray diffraction, this work sheds some light on the evolution of stillwellite crystal structure during the process of high-temperature transformations noted for the most of these practically important compounds. Here a sample of natural stillwellite [stillwellite-(Ce)] from the Darai-Pioz alkaline massif (Tadjikistan) has been studied by means of electron microscopy, IR spectroscopy, single crystal and powder X-ray diffraction (XRD) in a wide temperature range from -180 up to 1200 °C. The dielectric properties are also measured in the range from -180 up to 500 °C. The low (LT) and the high temperature (HT) structure deformation and transformation are described from single XRD data including the detail analysis of deformation of cationic polyhedra on heating. Both LT (disordered) and HT (ordered) stillwellite phases are characterized as relatively low expansion materials. The high-temperature transformation of stillwellite involves some negative thermal expansion caused by order-disorder process and presumably by the partial oxidation of Ce3+ to Ce4+. The dielectric properties show a maximum in this region as well, but the study of dielectric hysteresis loops did not confirm the ferroelectric order of stillwellite structure at room temperature. The high-temperature behavior and the decomposition process of stillwellite are dictated by the partial oxidation of cerium.

A new type of remote red quantum-dot (QD) component was designed and fabricated to improve the color-rendering properties of conventional white LED (light-emitting diode) lightings. Based on an optical simulation, the rectangular cavity-type QD cap was designed with an opening window on the top surface. Red QD caps were fabricated using a typical injection molding technique and CdSe/ZnS QDs with a core/shell structure whose average size was ~6 nm. Red QD caps were applied to conventional 6-inch, 15-W white LED downlighting consisting of 72 LEDs arrayed concentrically. The red QD caps placed over white LEDs enhanced the red components in the long-wavelength range resulting in the increase of the color rendering index (CRI) from 82.9 to 94.5. The correlated color temperature was tuned easily in a wide range by adopting various configurations consisting of different QD caps. The spatial and angular homogeneities were secured on the emitting area because QD caps placed over the white LEDs did not exhibit any substantial optical path length difference. The present study demonstrates that adopting QD caps in conventional LED lightings provides a flexible and efficient method to realize a high color-rendering property and to adjust correlated color temperature appropriately for a specific application.

The effect of the rare-earth ion Er3+, which has a large orbital contribution to the magnetic moment, were studied to phase transitions and phase transformations of 2D nanoregions of phase separation in the ErMn2O5 multiferroic. These nanoregions are the semiconductor heterostructures (superlattices) and are formed due to self-organization processes in the ErMn2O5 matrix. Significant effect of Er3+ ions, the moments of which are rigidly oriented along the c axis of the crystal, on the magnetic dynamics, heat capacity and multiferroic properties of layers superlattises was found at a wide temperature range 5-300 K in ErMn2O5 multiferroics. Keywords: multiferroic, 2D phase separation nanoregions, semiconductor-heterostructures, superlattices, phase transitions, phase transformations.

The effect of rare-earth ions Er3+, which has a large orbital contribution to the magnetic moment, on the phase transitions and states of the phase separation nanoregions has been studied in multiferroic ErMn2O5. These nanoregions are semiconductor heterostructures formed due to self-organization processes in the ErMn2O5 matrix. A significant effect of Er3+ ions, the moments of which are rigidly oriented along the c axis of the crystal, on the magnetic dynamics, heat capacity, and multiferroic properties of superlattices layers in a wide temperature range of 5 divided by 300 K has been revealed.

In this paper, the behavior of quasielastic light scattering (QELS) in a PbMg1/3Nb2/3O3 (PMN) crystal under broadband Brillouin light scattering in a temperature range from 750 K to 80 K was studied. It was shown that QELS consists of two components: narrow (0.9 GHz to 11 GHz) and wide (80 GHz to 600 GHz). The dependencies of the intensity, I, of these components on the frequency, ν, are well described by the power law I ~ eνα, with different α, and are determined by the distribution of the relaxation times. The analysis of the Brillouin spectra showed that the behavior of the relaxation time of both the components of QELS with temperature change is well described by the Arrhenius law. Additionally, in the vicinity of the intermediate temperature T* ≈ 380 K, a critical relaxation time behavior for the narrow component of QELS was detected. In the vicinity of the same temperature, a maximum in the integral intensity of both the components of QELS was observed, which is adjacent to another maximum in the region of the Vogel–Fulcher temperature TVF ≈ 250 K corresponding to the transformation of the crystal to a nonergodic state.

Results of studies of dielectric response and polarization in PbCo1/3Ta2/3O3 (PCT) single crystals grown by spontaneous crystallization are presented. Anomalies in the temperature dependence of the complex dielectric permittivity at 350, 270, 183, and 105 K have been observed. Using the thermally stimulated depolarization method, the temperature region of remnant polarization existence has been revealed below 270 K. It is assumed that in PCT, as well as in PbCo1/3Nb2/3O3 (PCN), in low-temperature region the phase separation caused by continuous switching of charge (valence) of Co2+/Co3+ and Ta4+/Ta5+ ions is realized.

This paper presents results of a study of temperature dependences of dielectric response and DC and AC - conductivity in single crystals of the relaxor ferroelectric PbNi1/3Nb2/3O3 (PNN) in a wide range of frequencies (10 Hz - 100 kHz) and temperatures (80 - 750 K). Anomalies in the dielectric response in the form of broad frequency-dependent maxima in the vicinity of 153 and 730 K are observed. The thermal activation character of DC conductivity has been obtained, and activation energies determined as Ea = 770 meV (T > 310 K) and Ea = 23 meV (T <310 K). The analysis of conductivity gives reason to assume the existence of local conductivity in the low-temperature region. It is shown that the conductivity character changes above 350 K from the local to the bulk one. Measurement by thermally stimulated depolarization has shown the presence of a residual polarization below 130 K.

This paper presents the results of studies of a low-frequency vibration spectrum of PbCo1/3Nb2/3O3(PCN) relaxor ferroelectric crystal using the Brillouin and Raman light scattering in the temperature range from 80 to 750 K. The analysis of the temperature behaviour of the longitudinal acoustic phonon in Brillouin scattering spectra showed no anomalies in the vicinity of 'diffuse phase transition' (T-m= 250 K) in PCN. Polarized Raman light scattering spectra were obtained in PCN over the entire temperature range studied. Analysis of low-frequency optical mode behaviour in PCN during temperature change also revealed no correlations with dielectric permeability anomaly in the vicinity ofT(m): softening of optical phonon at 43 cm(-1)frequency in VV polarization is observed at 170 K. In the same temperature range, there are anomalies (a 'narrow' and weak component) in quasi-elastic light scattering (QELS) obtained in temperature behaviour with VH polarization in Raman spectra in PCN. A 'wide' and intense QELS component, obtained in Raman spectra with VV polarization, shows anomalies in the vicinity ofT(m). We associate the anomalies of optical phonons and QELS with structure distortions in the formation of phase stratification and the dynamics of polar nano-regions.

Experiments on non-steady-state photoelectromotive force (photo-EMF) excitation are implemented with a P b N i 1 / 3 N b 2 / 3 O 3 crystal at wavelength λ = 660 n m . We study the paraelectric phase of the crystal, which belongs to a very peculiar class of materials—relaxor ferroelectrics. The dependencies of the signal amplitude on the frequency of phase modulation, light intensity, and spatial frequency are measured, and photoelectric parameters such as photoconductivity, diffusion, and Debye screening lengths are estimated from them. The signal characteristics demonstrate nonlinear dependencies on light intensity, which is explained by the laser heating of the medium. An unusual difference in the behavior of the photoconductivity response and non-steady-state photo-EMF is revealed.

The effect of the rare-earth ion Er3+, which has a large orbital contribution to the magnetic moment, were studied to phase transitions and phase transformations of 2D nanoregions of phase separation in the ErMn2O5 multiferroic. These nanoregions are the semiconductor heterostructures (superlattices) and are formed due to self-organization processes in the ErMn2O5 matrix. Significant effect of Er3+ ions, the moments of which are rigidly oriented along the c axis of the crystal, on the magnetic dynamics, heat capacity and multiferroic properties of layers superlattises was found at a wide temperature range 5 K - 300 K in ErMn2O5 multiferroics.

In this paper, the results of a study of the temperature dependences of dielectric response and conductivity at direct and alternating current in single crystals of PbNi1/3Nb2/3O3 (PNN) relaxor ferroelectric in a wide frequency range (from 10 Hz to 100 kHz) and temperature range (80–750 K) are presented. Dielectric response anomalies in the form of broad frequency-dependent maxima are observed near 153 and 730 K. The ther-moactive type of conductivity is found under the direct current and activation energies Ea = 770 meV for T > 310 K and Ea = 23 meV for T < 310 K are determined. The results of the conductivity analysis give grounds to assume the existence of local conductivity in the low temperature range. It is shown that the conductivity behavior changes from local to bulk conductivity with the increase in temperature starting from 350 K. The temperature range of existence of residual polarization (observed at T < 130 K) is determined by measuring the thermostimulated depolarization current.

Phase transformations of bovine serum albumin (BSA) are investigated using the Brilluoin light scattering in the temperature range from 300 to 380 K in solutions with concentrations of 50 and 5 mg/mL. As the reference sequence, the sequence of phase transformations in a concentrated (100 mg/mL) BSA solution are used for analyzing the results. It is shown that the sequence of BSA phase transformations is modified upon a decrease in the concentration. For example, in the vicinity of denaturation, the region with fibrilform protein aggregates disappears, and the properties of gel-type high-temperature phase change.

Results of Brillouin light scattering studies of phase transformations in bovine serum albumin (BSA) in the temperature range 300 – 380 K in the protein solution with concentration 50 and 5 mg/ml are presented. In the analysis of the results, the sequence of phase transformations in a concentrated BSA solution (100 mg/ml) was used as a reference. It was shown that sequence of BSA phase transformations modified with a decrease in concentration. For instance, in the vicinity of denaturation, the region with fibril-like aggregate disappears, and the properties of the gel-like high temperature phase change.

The temperature dependences of the veloсity of hypersound ( V ( T )) in solutions with various concentrations of guanidine hydrochloride (GndHCl) are studied by Brillouin–Mandelstam light scattering spectroscopy in the temperature range from 263 to 353 K. It is shown that the temperature dependence of the sound velocity has a pronounced maximum at low concentrations of GndHCl. An increase in the concentration of GndHCl in a solution is accompanied by a shift of the maximum to the low-temperature region and an increase in the absolute values of the sound velocity, which means a decrease in the adiabatic compressibility over the entire range of studied temperatures. The temperature dependence of the adiabatic compressibility is constructed at low concentrations of GndHCl. The contribution of relaxation processes to the temperature behavior of the attenuation of hypersound in solutions of GndHCl is determined. It is shown that their behavior is activated thermally and described by the Arrhenius law. The values of the activation energy of relaxation processes are calculated. Possible mechanisms that underlie the observed phenomena are discussed.

Temperature dependences of hypersound velocity V(T) in solutions with different guanidine hydrochloride (GdnHCl) concentrations have been studied by Brillouin light scattering at temperatures from 263 to 353 K. It has been shown that for low GdnHCl concentrations the V(T) dependence has a pronounced maximum. An increase in the GdnHCl concentration in the solution is accompanied by a shift of the maximum towards lower temperatures and also an increase in the absolute value of hypersound velocity and, hence, a decrease in the adiabatic compressibility in the entire temperature range studied. The temperature dependence of adiabatic compressibility at low concentrations of GndHCl is ploted. The contribution of relaxation processes to the temperature behavior of hypersound attenuation in GndHCl solutions is determined. It is shown that their behavior is thermally activated and described by Arrhenius ' law. The values of activation energy of relaxation processes are calculated. Possible mechanisms underlying the effects observed are considered.