Pyroelectric and elastic properties of lead magnesium niobate-and barium titanate-based solid solutions near a phase transition

The pyroelectric, elastic, and electrostrictive properties of lead magnesium niobate-and barium titanate-based solid solutions were studied under a dc electric field near a phase transition. The results obtained for a relaxor transition (in a lead magnesium scandium niobate solid solution) are compared with those derived for a conventional ferroelectric transition (in a barium strontium titanate solid solution). The dielectric and electromechanical contributions to the induced pyroelectric effect are discussed.     

Size effect in the theory of ordered solid solutions

The method of calculating the energy of elastic deformation of crystalline lattice, proposed by Pines, is modified by taking into account the dependence of the size of atoms on their specific neighborhood in the first coordination sphere, in order to apply it to the theory of ordered solid solutions with superstructures B2 (CuZn alloy), and L1₂ (AuCu₃ alloy). The calculations were made of the dependences of atomic radiuses of the alloys' components, of mean interatomic spacing, and of energy of elastic deformation of the crystalline lattice, on the degree of the long-distance order. That dependence agrees quite well with the known experimental data. The calculation indicates that the energy of elastic deformation of the crystalline lattice facilitates the establishment of the long-distance order in the CuZn and AuCu₃ alloys.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 79–87, 1972.     

Crystallographic patterns of the shape memory effect in non-ordered solid solutions

A method is proposed to estimate the possibility of achieving shape memory effects in martensite alloys with disordered lattices. The analysis of orientational relationships between the lattices of austenite and martensite allows one to detect those which are able to form self-accommodation complexes, an important part of the memory effect mechanism. This method has been applied to the Ti₄₈Zr₄₈Nb₄ alloy in which two martensite phases are formed: hexagonal α′ and orthorhombic α″ martensites.     

Pyroelectric effect in composites produced through electric-discharge plasma-assisted crystallization

The effect of the electric discharge-enhanced thermal crystallization of the polymer phase on the structure and pyroelectric properties of a polymer-pyroelectric composite is considered. It is shown that the changes in the polymer-phase structure during the electric discharge-enhanced thermal crystallization cause the number of charge carriers localized at the interface due to electrothermal polarization and the pyroelectric coefficient of the polymer-ceramics composite to increase noticeably.     

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.     

Hydrogen-vacancy interactions in Ni-H solid solutions

The data for the solubility of hydrogen in nickel in equilibrium with H₂-gas at atmospheric pressure have been analyzed in terms of a model which considers H-vacancy interactions. This model has been shown to be compatible with both the thermodynamic and kinetic data for Ni-H system.     

Electric dipole echo in solid solutions

A theory of microwave electric dipole echo in solid solutions is formulated in the example of (KBr)_1–x(KCN)_x. The behavior of the echo is attributed to tunneling CN^– molecules, which are treated as analogs of two-level systems in glasses. A concentration-dependent density of states of the two-level system is used in the calculations. The difference between the behavior of the echo signal in solid solutions and the behavior of the echo in glasses and spin systems is indicated. New echo signals associated with asymmetry of the double-well potential are found.Branch of the Institute of Solid-State and Semiconductor Physics, Academy of Sciences of Belarus, Vitebsk. Physicotechnical Institute, Kazan Science Center, Russian Academy of Sciences, Kazan. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 49–58, July, 1993.     

Short-range order in Fe-Rh solid solutions

We have used diffuse scattering of x-rays (DSX) and a model potential to show short-range order exists in iron-rhodium alloys. After the alloy Fe-25 at. % Rh was quenched following annealing at 900°C for 1 h, a clearly visible diffuse maximum (characteristic of short-range order) appeared in the diffraction pattern, in addition to reflections from the α- and γ-phases. For the single-phase, dilute solid solution Fe-2.5 at. % Rh, starting with the effects of static displacements, we have calculated the short-range order parameters (α₁ = −0.02, α₂ = −0.09, α₃ = 0.02, α₄ = 0.05). The elastic constants of Fe-2.5 at. % Rh needed to compute the short-range order parameters from the DSX data were calculated using a model potential. Theoretical calculations of the order energy and the short-range order parameters, performed using a model potential for these alloys, agree with the experimental data. M. V. Lomonosov Moscow State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 71–77, March, 1998.     

Chemical diffusion in interstitial solid solutions

A model has been set up to account for the variation of diffusivity with composition in the case of interstitial chemical diffusion in the presence of a solute atom gradient. It is shown that the magnitude of the gradient does not affect the diffusivity, provided that it is not very steep. The differential effect of the gradient of specific volume resulting from the species gradient on the jump frequency is taken into account. The predictions of the model are compared with kinetic data for carbon in f.c.c. iron measured both with and without a chemical concentration gradient.     

Segregation surface in binary solid solutions

Analytic equations describing the concentration profile, surface energy, and adsorption for a binary solid solution with the emergence of one of the components to the surface (surface segregation) were obtained using a unique approach, a modified van der Waals approximation. The calculation results were compared with the experimental secondary ion mass spectrometry data on Cu-Ge and Cu-Al metallic binary solutions; agreement was satisfactory.     

Atomic transport in ionic solid solutions

Summary This paper examines certain aspects of the relation of tracer diffusion coefficients to the corresponding so-called intrinsic diffusion coefficients arising in chemical interdiffusion in binary solid solutions. Although no exact general relation between these quantities is to be expected, the existence of such a relation for the solute species is to be anticipated in dilute solid solutions. In metallic alloys they become equal in the dilute limit, but in solid solutions of ionic conductors the ratio depends on details of the system (in particular on the solute and solvent ion charges and the degree of association between solute ions and charge compensating defects). Both the macroscopic and microscopic theories of these ionic solutions are described. A rather clear conflict exists between the theoretical predictions and some existing experimental results on the system Cr₂O₃ in MgO. In honour of Prof. Fausto Fumi on the occasion of his retirement from teaching.     

Spin-dependent recombination in GaAsN solid solutions

Room-temperature spin-dependent recombination in a series of GaAs_1?xN_x solid solutions (x = 2.1, 2.7, 3.4%) has been observed as manifested by a more than threefold decrease in intensity of the edge photoluminescence upon switching from circular to linear polarization of the exciting light or upon the application of a transverse magnetic field (～300 G). The interband absorption of the circularly polarized light is accompanied by the spin polarization of conduction electrons, which reaches 35% with an increase in the pumping level. The observed effects are explained in terms of the dynamic polarization of deep paramagnetic centers and the spin-dependent trapping of conduction electrons on these centers. The electron spin relaxation time, as estimated from the dependence of the edge photoluminescence depolarization in the transverse magnetic field (the Hanle effect) on the pumping intensity, is on the order of 1 ns. According to the adopted theory, the electron spin relaxation time in the presence of spin-dependent recombination is determined by a slow spin relaxation of localized electrons. The sign (positive) of the g factor of localized electrons has been experimentally determined from the direction of the magnetic-field-induced rotation of their average spin observed in the three GaAsN crystals studied.     

Compositional fluctuations in isotopic solid solutions

The effect of compositional fluctuations in isotopic solid solutions on the frequency shift and broadening of Raman lines is investigated. The broadening of the optical phonon line depends on the composition throughout the concentration range of the binary solid solution. It is shown that the line broadening is caused by elastic phonon scattering from compositional fluctuations. The type, size, and number of fluctuations responsible for the scattering are determined, and the dependences of these quantities on the concentration of solid solution components are established.     

Quasiequilibrium states of solid solutions

A phenomenological theory of quasiequilibrium states of solid solutions with at least three components is constructed under the assumption that the atomic mobilities of the components differ in order of magnitude. The short-range parts of the interatomic interactions are taken into account by introducing atomic self-volumes. 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 derived neglecting the mobility of the least mobile component. It is shown that, for a nonuniform distribution of this component, the nonequilibrium critical temperature ceases being unique within the sample and acquires a local character. In consequence, opposing processes occur in the system in the temperature interval between T _c ^min and T _c ^max — homogenization in some sections and formation of interphase boundaries in others. Fiz. Tverd. Tela (St. Petersburg) 41, 60–63 (January 1999)