IR-fourier spectroscopic study of homogeneous and heterophase melts and glasses in the K,Ca/NO<Subscript>3</Subscript> system

The infrared spectra of the homogeneous and heterophase melts and glasses of the K,Ca/NO₃ system were studied. The effects of finely disperse Al₂O₃ powder additions on the structural dynamic properties of K,Ca/NO₃ were revealed. The temperature dependence of the parameters of the vibration bands corresponding to the inner vibrations of NO ₃ ^? was studied. A model of structure and a mechanism of charge transfer in heterophase nitrate glasses were suggested.     

Pyroelectric properties of high-resistant KTiOPO4 crystals in the temperature range 4.2–300 K

The results of measuring the pyroelectric coefficient γ _s ^σ of nominally perfect KTiOPO₄ (KTP) crystals grown from solution in a melt with a potassium to phosphorus ratio of ～2 are presented. The γ _s ^σ (T) dependence is monotonic in the range from 4.2 to 250 K. Deviations from a linear dependence are observed beginning from 250 K, which is considered to be due to interstitial-potassium transport in the KTP crystal field. The spontaneous polarization of unclamped KTP samples is estimated from the results of the measurements. In terms of the crystal-physics approach, it is shown that the main contribution to a polar state of KTP is made by the dipole moments of two nonequivalent mesoscopic tetrahedra forming two sublattices that are polarized in opposite directions and bound by Ti(1) ions.     

Relaxation of vibrationally excited states in solid “nitrate–nitrite” binary systems

The processes of molecular relaxation in the solid NaNO₃–NaNO₂ and KNO₃–KNO₂ “nitrate–nitrite” binary systems have been investigated by Raman spectroscopy. The relaxation time of the vibration ν₁(A) of an NO^- ₃ anion in the binary system is found to be shorter than that in individual nitrate. The increase in the relaxation rate is explained by the existence of an additional mechanism of relaxation of vibrationally excited states of the nitrate ion in the system. This mechanism is related to the excitation of vibration of another anion (NO^- ₂) and generation of a lattice phonon. It has been established that this relaxation mechanism is implemented provided that the difference between the frequencies of the aforementioned vibrations correspond to the range of sufficiently high density of states in the phonon spectrum.     

Temperature-Phase Dependence of the Vibration Spectrum and Orientation Mobility of the Tetrafluoroborate Ion in n-Bu4NBF4 Organic Salt

Physics of the Solid State - The structural and dynamic properties of a tetrafluoroborate ion in n-Bu4NBF4 organic salt at different temperatures and phase states were studied by oscillation...     

Effect of heat treatment on the structure and properties of a BiFeO<Subscript>3</Subscript> nanopowder

This paper presents the results of an investigation of changes in the structure, magnetic, electrical, and thermal properties of a nanostructured bismuth ferrite powder prepared by the combustion of nitrateorganic precursors before and after heat treatment at temperatures of 500, 600, 700, and 800°C. It has been shown that there is a dependence of the magnetic properties on the dispersion of the particles. The specific features of the temperature and frequency dependences of the dielectric properties over wide ranges of frequencies and temperatures, as well as near the Néel temperature, have been considered.     

Transformation of the Structure of ZnO–C Powders during Mechanical Activation and Spark Plasma Sintering

The processes of grinding and transformation of the structure of the ZnO–C powder mixture at the mechanical activation by ball milling in an inert atmosphere have been investigated. The mechanical activation of the ZnO–C powder mixture is shown to lead to the formation of graphene oxide shells on the surface of crushed zinc oxide particles. The influence of the duration of activation of powder mixtures on the dynamics of their compaction during spark plasma sintering and structure of the ceramics obtained has been investigated. It is established that an increase in the activation duration to 100 h leads to a monotonic decrease in the density of sintered ceramics. The carbon shell formed during sintering at ZnO grain boundaries is shown to have the structure of reduced graphene oxide.

     

Temperature dependence of associative equilibria of DMSO according to raman scattering spectra

Raman scattering spectra of dimethyl sulfoxide (DMSO) are studied in the area of the line corresponding to symmetric CSC stretching vibrations of the molecule. It is established that this line is composed of a low-frequency component that corresponds to the vibrations of monomeric molecules and a high-frequency component that corresponds to the vibrations of DMSO dimers. Values of self-association equilibrium constants K _a varying in range from 0.20 (23°C) to 0.081 (100°C) are obtained. Since the intensities of the respective components of the line contour are proportional to the compound’s concentrations, the enthalpy of DMSO self-association (ΔH = ?11.7 ± 0.9 kJ/mol) is determined from the temperature dependences.