Patents relating to production of bulk ternary LRE-Ba₂Cu₃O_y materials intended for applications at high magnetic fields and temperatures

In this patent review the progress in technology and prospects of bulk ternary LRE-Ba₂Cu₃O_y 'LRE-123' (LRE=light rare earth, Nd, Eu, Sm, Gd) superconductors are presented. Number of experiments has proven that ternary LRE-123 melt processed materials exhibit excellent properties appropriate for development of bulk high-field high-T_c superconducting magnets. The key prerequisite for success in controlling flux pinning in these materials at high magnetic fields is creation of pinning defects with distinct superconducting properties compared to the superconducting matrix. In (Nd,Eu,Gd)-123 critical current density achieved the level of 10⁵A/cm² at 65K in self-field and 5T and the irreversibility field B_irr (the field limit above which the superconductor looses its ability to carry electric current) approached 15T at 77K. The high critical current density at low and intermediate fields, persisting up to the boiling point of liquid oxygen (90.2K), close to T_c, is mainly due to size reduction of normal-conducting or insulating pinning defects up to nanoscale level. Such pinning sites are e.g. nanoscale secondary phase particles, Zr-, Nb-, Mo-, or Ti-oxides. In some particular (Nd,Eu,Gd)-123 compositions B_irr increased twice due to a nanoscale planar substructure correlated with the regular twin structure.