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  • 1
    ISSN: 1063-7834
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The nucleation and growth of islands of a new phase on the surface of solids has been studied both experimentally and theoretically for the particular case of the transition from the pyrochlore to perovskite phase in a thin film of a lead zirconate-titanate ferroelectric. This transformation was chosen because the new-phase islands have a stable circular shape in this case, a relatively large size (10−5–10−4 m) permitting their observation with an optical microscope, and a low growth rate (10−8–10−9 m/s). A theoretical analysis of the process, based on the kinetic theory of first-order phase transitions proposed earlier, has been carried out and the behavior in time of all main characteristics of a phase transformation, namely, nucleation rate, concentration of the new-phase islands, their size distribution, and relative overheating, has been calculated. The same characteristics have been measured experimentally, thus permitting one for the first time to make a thorough comparison of the theoretical with experimental data on the kinetics of first-order phase transitions. They have been found to be in a good agreement.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1063-7834
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The process of new-phase nucleation in the YBa2Cu3O7−x system deposited by magnetron sputtering has been studied. The first experimental observation of the phenomenon of temporal self-organization in the course of new-phase formation, which was predicted theoretically,1–3 is reported. Auto-oscillations in the number of nuclei of various chemical compounds 20–60 nm in size were observed to occur within the 15 to 300-s time interval, the total number of nuclei varying aperiodically from 1013 m−2 to less than 1011 m−2.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Physics of the solid state 39 (1997), S. 1299-1304 
    ISSN: 1063-7834
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Kinetics of self-consistent growth of new-phase nuclei from eutectic melts have been studied. The growth kinetics of nuclei of eutectic composition are shown to depend on the sum of supersaturations over all components. It has been established that nuclei in a eutectic melt reach a common critical radius determined by supersaturation for both components. The concept of a diffusion dipole is introduced: a two-phase object in a eutectic melt or solid solution, in which two nuclei of different composition are related through a common diffusion field. The morphological stability of such dipoles is studied. It is found that a nucleus of eutectic composition is more stable with respect to small fluctuations in its shape than the corresponding one-component nucleus. It is shown that perturbations resulting in dipole-shape distortions develop perpendicular to the axis connecting the centers of the nuclei of different compositions (i.e. the dipole axis). This is consistent with the well-known experimental observation of the layered structure of eutectic compositions.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Physics of the solid state 40 (1998), S. 1147-1150 
    ISSN: 1063-7834
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A phenomenological model is proposed for the evolution of microcavities in materials under load based on a study of the kinetics of brittle fracture in a linearly elastic deformable medium containing a microcavity. The basic principle of the model is that, during deformation of a material containing a micropore, fluctuations of its shape occur. The surface tension at the micropore-medium interface stabilizes these fluctuations but if the load exceeds a critical value, these fluctuations may begin to evolve. In so doing, they distort the shape of the microcavity. These fluctuations are none other than cracks. This concept of crack growth and their nature has a close analogy with the evolution of dendrites formed in supercooled melts as a result of the loss of stable crystal shape. An analysis is made of the laws governing the evolution of a microcavity and local loss of shape stability under steady-state pressure for the case of a sphere containing a quasispherical cavity.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Physics of the solid state 40 (1998), S. 1467-1469 
    ISSN: 1063-7834
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A study is made of the dynamics of self-consistent motion and growth of spherical new-phase nuclei from a eutectic melt. The growth rate of nuclei is shown to be proportional to supersaturation in both components. Motion of a single nucleus in a concentration-gradient field and of a pair of nuclei in a self-consistent concentration field is investigated. The velocity of motion of the nucleus as a whole has been established to depend on the key parameters of the problem, namely, supersaturation, radii of the nuclei, and their separation. The force of mutual attraction between nuclei is estimated, and it is shown to be inversely proportional to the fifth power of their separation.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Physics of the solid state 42 (2000), S. 179-183 
    ISSN: 1063-7834
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A study is undertaken into the kinetics of phase transitions in solids under a load at a fixed temperature. The critical size of the micropores forming at a given load in the course of a phase transition in a material is found. The steady-state flux of pores in size space and the time required to reach this state, which depend at a given load on the surface energy of the solid and on an additional parameter characterizing the boundary kinetics of microdefects, are calculated. The parameters found in this work, which describe the onset of the latent stage in the fracture of a solid and the intensity of defect formation in the material in this stage, are new in the mechanics of fracture. This approach allows generalization to load-induced structural and martensitic transitions.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Technical physics letters 26 (2000), S. 609-611 
    ISSN: 1090-6533
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A model is suggested to describe the effect of tilt grain boundaries with partly random dislocation distribution on the critical current value in high-temperature superconductors. Within this model, the field of grain-boundary stresses σαβ acquires a much more pronounced long-range character than in the case of a periodic dislocation arrangement. At large distances x from a tilt grain boundary, σαβ ∝ x −3/2 (which corresponds to the quasi-equidistant dislocation walls), whereas at small x, we have σαβ ∝ x −1/2 (which corresponds to randomly arranged dislocation walls). A region with stresses exceeding a certain critical value is treated as the region of normal metal, and, therefore, the critical current passing through this region decreases exponentially. It is shown that the model suggested satisfactorily agrees with experimental data.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Physics of the solid state 42 (2000), S. 2314-2317 
    ISSN: 1063-7834
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A new mechanism of nanopore formation in carbon materials produced by the interaction of car-bides with chlorine is proposed. In essence, this method is the following. A series of nonlinear chemical reactions proceed in the course of a chemical interaction between chlorine and a carbide. If the external parameters, the component fluxes, and the diffusion rates satisfy certain relations, the self-organization process can occur. This process results in the creation of a periodic nanoporous structure in the carbon material formed. A mathematical model is proposed, the main characteristics of the process are calculated, and the restrictions on the parameters at which the formation of the porous structure becomes possible are found.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Journal of experimental and theoretical physics 86 (1998), S. 1201-1208 
    ISSN: 1090-6509
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We construct an asymptotic theory that describes the kinetics of first-order phase transitions. The theory is a considerable refinement of the well-known Lifshits-Slezov theory. The main difference between the two is that the Lifshits—Slezov theory uses for the first integral of the kinetic equation an approximate solution of the characteristic equation, which is valid in the entire range of sizes except for the blocking point, i.e., it uses a nonuniformly applicable approximation. At the same time, the behavior of the characteristic solution near the blocking point determines the asymptotic behavior of the size distribution function of the nuclei for the new phase. Our theory uses a uniformly applicable solution of the characteristic equation, a solution valid at long times over the entire range of sizes. This solution is used to find the asymptotic behavior of all basic properties of first-order phase transitions: the size distribution function, the average nucleus size, and the nucleus density.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 1370-1376 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A complete set of equations describing the evolution of phase composition of an island ensemble at the stage of the Ostwald ripening in the process of thin-film growth is derived and its solution is found. The size distribution function of islands in solid solutions is obtained for different types of growth mechanisms. The general approach to control phase composition and associated properties (electric, optical, mechanical, and others) in formed multicomponent systems is elaborated. It is shown that the most favorable conditions to control these properties occur at the Ostwald ripening stage and also during nonlinear phenomena, such as self-excited oscillations or self-organization. The relationship between size and composition of the new phase nuclei formed in the course of condensation of solid solution films is revealed. A set of equations describing the evolution of the size distribution function of the properties in island films of solid solutions during changes in external parameters of the system is derived and solved. We show that substantial dependence of composition on external parameters is revealed for the sizes of islands with radius R≤10−8 m, irrespective of the type of substance. For island-type films of stoichiometric composition, the diagram for coexistence of appropriate properties is plotted in the concentration-temperature coordinates that allows to us determine the conditions required to obtain the properties. Probable periodic changes in time and space of various properties on multicomponent systems undergoing the first order phase transition are predicted. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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