Savych S. Structural Relaxation and the Impact of Aging on Transport Processes in HTSC Compounds of 1-2-3 System

The thesis is devoted to the solution of the actual scientific problem on the establishment of the mechanisms of the influence of structural relaxation processes arising under the conditions of application of extreme external factors (high temperature, hydrostatic pressure, magnetic field) and prolonged aging for electro- and mass transfer in single-crystal ReBa2Cu3O7-δ compounds (Re = Y, Ho), as well as phase separation and the appearance of dynamic phase transitions as a result of doping with hafnium and zirconium of YBa2Cu3O7-δ ceramics. The experimental studies of the effect of prolonged annealing (17 years) at room temperature of an optimally doped YBa2Cu3O7-δ single crystal by oxygen were carried out. A stratification of the sample into phases with different transition temperatures to the normal state is revealed. Mechanisms of redistribution of labile oxygen ions in the process of fast annealing at room temperature of single-crystal ReBa2Cu3O7-δ samples (Re = Y, Ho) with different degree of non-stoichiometry of the oxygen subsystem are analyzed. The two-stage process of redistribution is established. At the initial stage of the movement of oxygen ions occurs in the regime of single-channel diffusion, which over time is replaced by the classical mechanism of ion diffusion. The influence of hydrostatic pressure 4.8 kbar on the structural relaxation of a HoBa2Cu3O7-δ single crystal (δ = 0.35), which is low-doped with oxygen. The changes in the resistive characteristics of a single crystal were analyzed within the framework of the diffusion coalescence model of oxygen clusters under the influence of high pressure. The influence of doping of ceramic samples of compound YBa2Cu3O7-δ by impurities of hafnium on resistive characteristics over a wide range of temperatures and magnetic field values is experimentally investigated. It has been established that doping significantly affects the parameters of the pseudogap and fluctuation anomalies, and in the case of application of the magnetic field, the vortex liquid-vortex lattice suppresses the dynamic phase transition and the vortex-vortex "Bragg" glass forms in the transition system. Keywords: single crystals of high-temperature superconductors, single file diffusion, diffuse coalescence, oxygen clusters, excess conductivity, pseudogap anomaly, fluctuation conductivity, dynamic phase transitions.