Kotvytska K. Influence of different morphology defects on magnetoresistive properties single crystals ReBa2Cu3O7-delta (Re = Y, Ho, Pr).

Object: Connections of family of ReBa2Cu3O7 - delta. The purpose: the goal of the thesis is to determine influence physics of point and flat defects on magnetoresistive properties of ReBa2Cu3O7-delta (Re = Y, Ho, Pr) compounds, and to establish the laws for forming conduction state as metal-insulator transition, superconductor-Fermi-liquid metal-nonsuperconductor under carrier concentration variation and labile component concentration change in a wide range or constituent element substitution. Methods: The single crystals YBa2Cu3O7-delta were grown in a gold crucible with the solution-melting method. Structural studies carried out by X-ray diffraction and electronic and optical microscopy. The concentration of point defects (oxygen vacancies) changed by varying the temperature annealing the crystals in oxygen atmosphere. The resistive measures in the standard four-probe geometry were done. Results: It was first showed that high pressure application leads to substantial increase of baric derivative dТс/dP value in low praseodymium-doped single crystal samples Y1-xPrxBa2Cu3O7-delta in contrast with pure samples YBa2Cu3O7-delta . It was first showed that degree decrease oxygen doped in samples ReBa2Cu3O7 - delta (Re=Y, Ho) leads to amplification of effects of localisation and embodying in system of phase transition metal-insulator which always precedes superconducting transition. It was first established that the application of constant magnetic field (up to 15 kOe) to single-domain single crystals YBa2Cu3O7-delta with small oxygen deficit leads to appearance of an additional coherent transition on temperature dependences of excess conductivity in basis ab-plane. It is caused by suppression of dynamic phase transition as vortex liquid-vortex lattice. Field of application: solid state physics, semiconductor physics.