Preparation and properties of PMP YBCO bulk with submicrometre Y₂BaCuO₅ particles

The microstructure, critical current density and relaxation behaviour of a YBCO sample fabricated by the powder melting process technique have been studied by using a transmission electron microscopy and SQUID magnetometer. It is found that many 211 particles are very small with diameter of submicrometre size. Also, some 211 particles with 250 nm in diameter exist in this sample. A high density of stacking faults and dislocations is observed. In the low field region, J_c decreases with the field according to a power law at temperatures above 60 K. An exponential temperature relationship between the critical current density (J_c) and temperature is established in the high field region. In addition, the field and temperature dependence of the relaxation rate exhibits a plateau over a temperature region from 30 K to 65 K, illustrating the collective pinning nature of the pinning centres.