General principles of the crystallization of nanostructured disperse systems

Regularities of the self-organization of ensembles of nanoparticles into crystalline structures in metal lyosols are studied by the Brownian dynamics. Van der Waals, elastic, and electrostatic interparticle interactions, as well as the action of dissipative and fluctuation forces are taken into account in the model. Pair interaction potentials for the polydisperse ensembles of particles are analyzed and the correlations between the pattern of potential curves and the type of formed structures (from crystalline to fractal) are revealed. The effect of interparticle tangential friction on the degree of ordering of formed structures is studied. It is demonstrated that this factor can determine the degree of ordering of nanoparticle aggregates. An essentially new approach to describing elastic interactions of nanoparticles of polymer-containing sols is implemented.     

On a Classical Limit of <Emphasis Type="Italic">q</Emphasis>-Deformed Whittaker Functions

Previously, we derive a representation of q-deformed \({\mathfrak{gl}_{\ell+1}}\) -Whittaker function as a sum over Gelfand–Zetlin patterns. This representation provides an analog of the Shintani–Casselman–Shalika formula for q-deformed \({\mathfrak{gl}_{\ell+1}}\) -Whittaker functions. In this note, we provide a derivation of the Givental integral representation of the classical \({\mathfrak{gl}_{\ell+1}}\) -Whittaker function as a limit q → 1 of the sum over the Gelfand–Zetlin patterns representation of the q-deformed \({\mathfrak{gl}_{\ell+1}}\) -Whittaker function. Thus, Givental representation provides an analog the Shintani–Casselman–Shalika formula for classical Whittaker functions.     

Effect of double annealing on the critical parameters of highly textured YBa2Cu3O6.9

The effect of low-temperature treatment (200°C) and subsequent annealing at 930°C on the critical parameters of highly textured YBa₂Cu₃O_6.9 is studied. The structural defects that are formed during the low-temperature decomposition of this compound into phases with different oxygen contents and during interaction with atmospheric moisture are shown to deteriorate the superconducting properties. After annealing at T = 930°C and subsequent oxidation, superconductivity is restored and the formed defects are partly retained and serve as effective pinning centers, including the case of high magnetic fields. The stresses induced by the low-temperature treatment lead to primary recrystallization at T = 930°C, which results in the disappearance of texture and an isotropic state of the material in high fields.     

Propagation of acoustic waves in a medium with the Rayleigh energy release mechanism

This research continues theoretical studies of propagation of acoustic waves in a plasma considering it in the context of a Rayleigh medium. For the first time, the solution to the problem with the boundary and not the initial conditions is examined. It is shown that for small values of the parameter characterizing the energy input in the plasma, the amplification coefficients of a harmonic acoustic wave in the problem of propagation of the initial perturbation and in the problem with the boundary conditions are close. However, if the energy input increases, the amplification of the wave propagating from the source is larger than in the problem of the initial perturbation propagation. The same concerns the amplification of waves with different frequencies for fixed parameters of the plasma; i.e., the difference between the amplification coefficients is larger, the lower the wave frequency. The resultant analytic dependences make it possible to determine exactly which of the problems (with the initial or boundary conditions) should be solved to compute the amplification coefficient of acoustic waves under specific experimental conditions.     

On the incorporation mechanism and distribution mode of impurities in potassium acid phthalate crystals grown from aqueous solutions

Mechanism of impurity structure formation in crystals grown from aqueous solutions has been studied on the example of potassium acid phtalate (abbreviated hereafter as KAP) single crystals. Gold decoration technique at an electronmicroscopic scale has been applied to the study of the distribution of uncontrolled impurities on KAP cleavage face (010) after 10, 20 and 30 days of growth, taking into consideration different growth rates in 〈001〉 and 〈001 〈 directions. A technique for visualization of impurities in water, based on the adsorption of these impurities by the surface of amorphous film of nitrocellulose (parlodion) and the vacuum decoration with gold of these impurities, has been developed. Differences in the impurity structure of KAP regions located in 〈001〉 and 〈001〉 directions from the seed have been established. In 〈001〉 direction after 20 days of growth impurity assemblies 0.1—0.4 μm in size are revealed, and in 〈001〉 direction heterogeneous impurity structure is revealed only after 30 days of growth. The real (impurity) structure of KAP outside impurity assemblies is quite homogeneous and is the same throughout the whole crystal volume, the impurities incorporating mainly into complex active centres. From comparison of the changes in time of the impurity structure of water used for crystallization solutions and the impurity structure of KAP crystals a conclusion is made that the impurity structure of crystals is “programmed” in the impurity structure of crystallization solutions which regularly changes with time, i. e. impurities from different kinds of assemblies which are selectively adsorbed by the growing crystal faces. The role of the adjacent to the growing face interfacial layers which control the growth rate and have a complex impurity structure is stressed.     

Electrical Processes Occurring at the Moment of Cleaving NaCl Crystals

The electrical processes occurring on cleaving tempered NaCl crystals have been studied by decoration methods on the scale of electron microscopy. The decorating agent, gold, was evaporated at the moment of performing the cleavage. The obtained decoration pictures differed from those described in the literature. Features similar to the propagation of waves were observed. They begin on cleavage steps and are mostly parallel to 〈100〉. On interaction of the “waves” with the steps or with other “waves” there arise black “threads” distinguished, the same as the wave boundaries, owing to a very high contrast on account of the higher density of decorating particles. The waves and threads are interpreted as microbreakdowns, which have also a two-stage character - stages of wave and thread formation, propagate along definite crystallographic directions, and occur at the boundary of strained sites. The charge sign of the waves is determined from the degree of coalescence of decorating gold particles. The detected waves reflect the occurrence of specific polarization states in local sites of the surface. These states are induced by local electric fields of a very high intensity occurring on cleaving the crystals. These polarization states disappear in 10-15 s after the cleavage is made due to neutralization of the charges. Analogy is drawn between polarization structures in form of waves and stable linear polarization bridges occurring in crystals between oppositely charged point defects and their assemblies.     

Solid-state polymerization of diacetylenes under the action of outside forces on crystalline monomer lattice

The polymerization of crystalline diacetylenes TS and DCH with different lattice structure was studied under high hydrostatic pressures (up to 4 kbar). It was shown that pressure increases the deformation of chain growing in monomer crystal. The features of such deformation depend on lattice structure that governs the influence of pressure on polymerization rate. We studied also polymerization of diacetylene HD crystals obtained in the pores of stretched polymer (PP). The field of polymer matrix influences the crystal state and the rate of polymerization. It was shown that the interaction of monomer crystals with the matrix leads to growth of more strained chains in these crystals.