Patents Relating to Production of Bulk Ternary LRE-Ba2Cu3Oy Materials Intended for Applications at High Magnetic Fields and Temperatures
Miryala Muralidhar, Milos Jirsa and Masaru Tomita
Affiliation: Railway Technical Research Institute (RTRI), Applied Superconductivity, Materials Technology Division, 2-8-38, Hikari-cho, Kokubuni-shi, Tokyo 185-8540, Japan.
In this patent review the progress in technology and prospects of bulk ternary LRE-Ba2Cu3Oy “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-Tc 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 Birr (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 Tc, 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 Birr increased twice due to a nanoscale planar substructure correlated with the regular twin structure.
Keywords: Critical current density, flux pinning, levitation at 90.2K, mesoscopic defects, micro-structure, ternary LRE-123 compounds, High electromagnetic forces, superconductors, liquid nitrogen, interfacial energy
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