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We study the time dependence of the electrical conductivity of single-crystalline YBa2Cu3O7-x with varying oxygen content. We show that the accelerated transport of the oxygen ions in the initial stage of the process occurs along one-dimensional clusters of nonstoichiometric vacancies through the single-file diffusion mechanism. The final stage of the oxygen ion redistribution in the studied compound is described with a classical mechanism of bulk diffusion. At the same time, the degree of deviation from the oxygen stoichiometry significantly influences the change in duration of the time intervals corresponding to the mechanisms of single-file and bulk diffusion of the labile oxygen.

This paper discusses experimental data which show that with increasing thermal processing time, oxygen doping of crystals of YBa2Cu3O7−x with x > 0.65 (tetragonal phase) is characterized by two stages with substantially different kinetics. In the first (initial annealing) stage, oxygen ions enter at a faster rate with an activation energy of approximately 0.4 eV. The second (end of annealing) stage is characterized by significantly slower transport of oxygen ions with an activation energy on the order of 1 eV. The kinetics of the oxygen doping process is analyzed in terms of the time variation in the electrical resistance of the compound. It is shown that the faster transport of oxygen ions in the initial stage of the implantation process can take place along one-dimensional nonstoichiometric vacancies in a single-file diffusion mode. The final stage of oxygen ion implantation in this compound is described by an ordinary classical diffusion mechanism.

The aim of the work – to determine the level of adaptive cellular stress and reactivity of patients with infectious mononucleosis associated with Epstein-Barr virus. To increase the knowledge on the pathogenesis of infectious mononucleosis associated with WEB (IM-AVEB), it was advisable to establish the level of adaptive tension and cellular reactivity of the body of these patients. Conclusions. Infectious mononucleosis associated with Epstein-Barr virus is confirmed in heterogeneous immunological test for antibodies by characteristic clinical and laboratory manifestations, which shows the growth in the relative number agranulocyte 51.45 %, the absolute number agranulocyte – by 80.52 %. The growing number agranulocyte done by increasing the absolute and relative number of lymphocytes respectively 2.22 times and 19.18 % (p

The effects of quenching from 600[Formula: see text]C and subsequent room-temperature annealing on the basal-plane electrical resistivity of underdoped HoBa2Cu3O[Formula: see text] single crystals are investigated. Regions with different superconducting transition temperatures, [Formula: see text], have been revealed in the sample after quenching and attributed to a non-uniform distribution of the labile oxygen in the sample volume. Room-temperature annealing has been revealed to lead to an increase of [Formula: see text] of all regions and a decrease of their number, attributed to the coalescence of clusters of oxygen vacancies. The temperature dependence of the resistance in the normal state is characterized by a decrease of the residual resistivity and the phonon scattering coefficient.

In this paper, the relaxation of the electrical resistance of a YBa[Formula: see text]Cu[Formula: see text]O[Formula: see text] single crystal that is kept for a long time at room temperature in air atmosphere is investigated. It is shown that with increasing time of keeping, relaxation of the electrical resistivity at room temperature is observed, controlled by a single channel and the classical oxygen ion diffusion mechanisms. The faster transport of oxygen ions in the initial stage of the implantation process can take place along one-dimensional nonstoichiometric vacancies in a single-file diffusion mode. The final stage of oxygen transport in this compound is described by an ordinary classical diffusion mechanism.

A general system of equations is formulated describing the evolution of the macrorelief on the surface of a solid of arbitrary stoichiometric composition under irradiation. Irradiation is treated only as an additional source of point defects (vacancies and interstitial atoms). A general formula for the smoothing of the macrorelief with time is obtained with consideration of the real conditions of the problem. A two-component substance is considered as a special case: new forms of the dependence of the surface smoothing rate on the roughness parameters appear, which are not observed for a one-component material. The surface and bulk diffusion coefficients of the material, as well as the constants characterizing the interaction of radiation with the substance, can be found by experimentally investigating the surface smoothing rate as a function of the roughness.

The general system of equations describing the smoothing of surface structure in solids under irradiation is formulated. It is shown that under real conditions the system can be reduced to a simpler form which has an exact solution. A general formula describing the smoothing of surface structure with time is derived. As a special case, this formula gives the evolution (smoothing) of the relief in the absence of radiation, which is associated with the difference in curvatures for different roughnesses. The physical reason behind the intensification of smoothing under irradiation is the difference between the positions of the centers of gravities for concentration profiles of vacancies and interstitials. The radiation gives rise to a new type of dependence of the rate of smoothing on the roughness parameters of the surface, which permits the experimental separation of the contribution from radiation to smoothing and simultaneously makes it possible to determine some parameters which are difficult to measure.

Phase formation and sintering of the ceramics YBa2Cu3O7−x are studied. Both processes are shown to be controlled by diffusion. At different stages the rate of chemical reactions as well as mass transfer are limited by the diffusion of different ions.

As a result of studying the sintering of ceramic material YBa2Cu3O7−x in a temperature field with a constant gradient the possibility of rapid mass transfer with participation of a liquid phase is established. Its formation provides rapid sintering and radial shrinkage in the high-temperature region. Redistribution and crystallization of the liquid in the low-temperature region causes ceramic swelling. The effects described are also accompanied by a change in material phase composition in a direction parallel to the temperature gradient.

Theoretical considerations, experimentally established facts, and elementary estimates lead to the conclusion that the initial stage of the sintering process may be accompanied by plastic deformation, while a later stage is controlled by diffusion-dislocation flow, in which mass transport responsible for growth of the contact neck takes place under conditions of self-consistency of the dislocation loop generation and dissolution processes. This article is concerned only with monocrystalline objects, but the conclusions arrived at in it can be extended also to real polycrystalline systems. This will necessitate regarding the structural elements of a polycrystal as obstacles to dislocation motion characterized by different degrees of penetrability. An opportunity will thus arise in particular to obtain fuller information on the initial stage of sintering of powder compacts, which are characterized by high sintering activity.

The results of model experiments confirm the validity of the hypothesis that the plastic flow of material in the contact zone is a consequence of conservative motion of dislocations in the contact region. Before the capacity for mass transport by this mechanism and hence its contribution to “activity” can be reliably assessed, it will be necessary to examine the problem of possible dislocation multiplication in the peripheral zone of the contact. At present we can only assert that this capacity is not less than that due to dislocations linked with the previous history of a material. Under conditions of a model experiment this capacity is determined by the density of dislocations generated in the vicinity of the crack mouth during cleavage. In the case of ideally brittle fracture this density might prove to be equal to zero.

A description is given of the correct procedure for processing results of model sintering experiments for the purpose of finding coefficients of self-diffusion. It is shown that the large quantity of published data on X vs t relationships has been processed without taking into account the strong influence of the initial stage of rapid contact growth, which is followed by a stage of slow growth, on the value of D determined from the X vs t relationship.