  Materials of the Y-Ba-Cu-O (melt-textured YBa2Cu3O7-d-based materials or
MT-YBCO) and Mg-B-O (MgB2-based materials) systems with high superconducting
performance, which can be attained due to the formation of regularly
distributed nanostructural defects and inhomogenities in their structure can be
effectively used in cryogenic technique, in particular in fault current
limiters and electrical machines (electromotors, generators, pumps for liquid
gases, etc.). The developed processes of high-temperature (900-800 oC)
oxygenation under elevated pressure (16 MPa) of MT-YBCO and high-pressure (2
GPa) synthesis of MgB2-based materials allowed us to attain high SC (critical
current densities, upper critical fields, fields of irreversibility, trapped
magnetic fields) and mechanical (hardness, fracture toughness, Young modulus)
characteristics. It has been shown that the effect of materials properties
improvement in the case of MT-YBCO was attained due to the formation of high
twin density (20-22 micron-1), prevention of macrockracking and reduction (by a
factor of 4.5) of microcrack density, and in the case of MgB2-based materials
due to the formation of oxygen-enriched as compared to the matrix phase
fine-dispersed Mg-B-O inhomogenities as well as inclusions of higher borides
with near-MgB12 stoichiometry in the Mg-B-O matrix (with 15-37 nm average grain
sizes). The possibility is shown to obtain the rather high Tc (37 K) and
critical current densities in materials with MgB12 matrix (with 95 percent of
shielding fraction as calculated from the resistant curve).
