Moshchil V. Mechanism of formation of the structure of melt-textured YBaCuO ceramics with a high level of superconducting and mechanical properties under conditions of controlled isostatic oxygen pressure

Dissertation for a scientific degree of the Candidate of Sciences (Engineering) in specialty 05.02.01 - "Materials Science". V. N. Bakul Institute for Superhard Materials of the National Academy of Sciences of Ukraine, Kyiv, 2019. In the dissertation the actual scientific and technical problem was solved: the regularities of structure formation of melt-textured YBaCuO ceramics with a high level of superconductive and mechanical properties under conditions of controlled isostatic oxygen pressure at high temperatures, resulting in a reduction of the time of saturation by oxygen. The oxygen saturation of the MT-YBaCuO leads for attaining of a record values of the jc, Hirr, and HV and for preventing or essential reduction of cracks formation. It has been established that the increase of jc is due to the increase of the density of twins and essential suppression of microcracking. It has been experimentally proved for the first time that twins play a more significant role in achieving high values of the critical current density than dislocations and stacking faults. It is shown that the density of twins and microcracks depends on the size of the Y2BaCuO5 grains, their distribution. The obtained characteristics make promising application of the developed materials in superconducting electric motors and fault current limiters. Key words: bulk and thin-walled melt-textured MT-YBaCuO ceramics, superconducting and mechanical properties, twins, dislocations, stacking faults, critical current density, trapped magnetic field, microhardness, fracture toughness.