Search for efficient pinning centers in high-temperature cupric oxide superconductors

Our recent efforts to search for efficient flux pinning centers which are indispensable to attain a high critical current density (J(c)) in high-temperature cupric oxide superconductors (HTSCs) are reviewed. A series of studies have been carried out through careful investigations of relationships between physical properties and microstructures of HTSCs. It is demonstrated that specific chemical substitutions result in novel microstructures which are generally associated with chemical instability for a phase separation. Two topics are presented: characteristic two-phase microstructures found in heavily Ph-substituted Bi2Sr2CaCu2O8+delta With a superconducting critical temperature (T-c) of about 85 K, are suggested to be remarkably efficient correlated defects that can suppress a thermally activated flux flow and thus dramatically improve J(c) at high temperatures and high magnetic fields. Interesting segregation phenomena in (Hg,Re)Ba2Can-1CunOy with T-c = 132 K, which occur on heating by a weak electron beam are also reported. The manipulation of these microstructures could be a key for future large-scale applications of HTSCs. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.