Preparation and characterization of high J_c Y-Ho-Ba-Cu-O Bulk superconductors by a powder melting process

摘要

We have successfully prepared high J_c-Ho-Ba-Cu-O bulk samples by a `powder melting process' method and investigated their superconducting properties, flux pinning mechamism and melting temperature. The best J_c value estimated from a magnetic hystersis loop is about 1.6x10~5 A/cm~2 (70K, 1T) when the magnetic field is parallel to the c-axis. The results indicate that critical current density is improved by the Ho doping. The average size of the 211 particles is below 1 mu m and many clusters of the stacking faults (around 300nm wide) have been observed by TEM. It is considered that the magnetic pinning, clusters of stacking faults, stress-field pinning and the reduction of the size of the 211 particle created by the substitution of Ho for Y may be responsible for the enhancement of Jc.