Phase states and dielectric properties of sodium-potassium niobate solid solutions

The temperature dependence of dielectric constant ? for single crystals of Na_1?xK_xNbO₃ (0.04?x?0.15) is studied for the first time. From the shape of the ?(T) anomalies corresponding to rotational phase transitions, the type of interaction between the order parameters and the polarization is determined. A phenomenological model is developed which adequately describes the experimentally observed sequence of high-temperature (T>300°C) phase transitions, the dielectric anomalies associated with these transitions, and the changes in the phase states under the action of external factors (pressure, electric field).     

Distribution of the density of electron states in TiC-VC and TiC-TiN solid solutions

The published results of a calculation of the energy band structure of TiC, VC, and TiN are utilized in histograms of the density of states in TiC_xN_1–x and Ti_xV_1–xC solid solutions. It is shown that the density of states at the Fermi level varies in different ways with the composition of TiC-VC and TiC-TiN solid solutions and it is shown that the rigid band model is inapplicable to the physical properties of these solid solutions.Translated from Izvestiya Uchebnykh Zavedenii, Fizika, No. 6, pp. 15–19, June, 1980.     

Fluctuation states and optical spectra of solid solutions with a strong isoelectronic perturbation

We propose an approach to describing the density of fluctuation states in a disordered solid solution with a strong perturbation introduced by isoelectronic substitution in the range of attraction-center concentrations below the threshold of percolation along the sites of a disordered sublattice. To estimate the number of localized states we use the results of lattice percolation theory. We describe a method for distinguishing, within the continuum percolation theory, among the various “radiating” states of the fluctuation-induced tail, states that form the luminescence band at weak excitation. We also establish the position of the band of radiating states in relation to the absorption band of the excitonic ground state and the mobility edge of the system. The approach is used to describe the optical spectra of the solid solution ZnSe_1−c Te_c, which at low Te concentrations can be interpreted as a system with strong scattering. We take into account the exciton-phonon interaction and show that the calculated and observed luminescence spectra of localized excitons are in good agreement with each other. Zh. éksp. Teor. Fiz. 115, 1039–1062 (March 1999)     

Volume effects in the theory of equilibrium and quasiequilibrium states of multicomponent solid solutions

A phenomenological theory of equilibrium and quasiequilibrium states of multicomponent solid solutions is constructed taking account of volume effects. Quasiequilibrium states are characterized by the fact that only some of the conditions for thermal dynamic equilibrium of the system are satisfied. The short-range parts of the interatomic interactions are taken into account by introducing the proper volumes of the atoms based on a generalized lattice model. The long-range parts of the potentials are taken into account in the effective-field approximation. The equations for the quasiequilibrium components in the solutions are introduced taking account of the nonuniformity in the distributions of the less mobile nonequilibrium components. The conditions for spinodal decomposition of a solid solution with an arbitrary number of components in the equilibrium and quasiequilibrium cases are obtained. An equation for equilibrium spinodal decomposition of a three-component microheterogeneous solid solution is found. Fiz. Tverd. Tela (St. Petersburg) 41, 1609–1613 (September 1999)     

Cholesteric states of micellar solutions

The effects of optically active compounds on amphiphilic nematics are reported. The following systems have been studied : (1) caesium decylsulphate, decanol, water plus tartaric acid ; (2) ammonium decylsulphate, ammonium sulphate, decanol, water plus brucine sulphate ; and (3) decylammonium chloride, water plus cholesterol. Phase transitions to cholesteric states are induced by the optically active compounds in all systems. Brucine sulphate has the highest twisting power ; tartaric acid the lowest. The results are analysed on the basis of intermolecular interactions and an explanation is proposed for the observed differences in twisting power.     

Phase states in solid solutions based on BiFeO<Subscript>3</Subscript>

Concentration and temperature regions of the existence of different phases (R3c, Pbnm, P4mm, Amm2, Pbcm, and Pm3m) in solid solutions of BiFeO₃-BiMnO₃, BiFeO₃-KNbO₃, and BiFeO₃-NaNbO₃ are determined.     

Thermodynamics of nitrogen-molybdenum solid solutions

The equilibrium between N₂ gas at atmospheric pressure and molybdenum-nitrogen solid solutions has been measured in the temperature range 1618–1883 K. The solvent metal was in the form of single crystals of MARZ-grade Mo. Deviations in the thermodynamic behavior consistent with a dual site occupancy mechanism, suggested by previous data, were not found.The data have been discussed in terms of the effects of hydrostatic pressure on the metal lattice and the presence of trapping sites in the solvent lattice.     

Decomposition of solid NaCl-AgCl solutions

The dependence of the microhardness on the aging time for NaCl-AgCl solid solutions was found at room temperature for solutions of between 10 and 30 mole% AgCl in NaCl. During decomposition under these conditions the microhardness passes through a maximum. The relationship between the change in the microhardness and the changes in the intensity distribution of x radiation scattered by the decomposing solid solution has been established.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 11, pp. 18–22, November, 1970.     

Fast solute diffusion in solid and supersaturated solid solutions

In this paper, we review the experimental data concerning fast diffusion of solute in Pb matrix and Pb (solute) solid solutions. Using both calorimetric and radiotracer techniques the temperature dependence of solute diffusion coefficients in Pb (solute) supersaturated solid solutions is determined. On the basis of experimental results it is shown that these coefficients can only be understood by assuming different defect states for solutes in solid and supersaturated solid solutions.     

Exciton luminescence of quasi-two-dimensional solid solutions

Absorption and luminescence of the quantum wells formed by the (Zn-Cd)Se and (Ga-In)As solid solutions are studied in the range of exciton size-quantization ground state. The spectra observed are described by a model assuming the two-dimensional character of fluctuation states in quantum wells and the presence of a percolation threshold within the absorption contour.     

Thermodynamics of molybdenum-niobium-hydrogen ternary solid solutions

The enthalpy of solution of hydrogen has been measured in a series of Mo-Nb solid solutions in the composition range 0–77 at.% Nb. In the solid solutions of Mo and Nb there is good evidence that the enthalpy of solution of H will not be influenced by strain energy factors or by a change in the electronic work function of the metal surface with composition. No correlation between the measured enthalpies and the density of electron states at the Fermi surface was found. The binary Mo-Nb system was chosen because the density of states varies drastically across the system, exhibiting an extremum.