STRUCTURAL AND SUPERCONDUCTING PROPERTIES OF MELT-GROWN Y-BA-CU-O SUPERCONDUCTORS

YBa2Cu3O7 (123) samples with varying Y2BaCuO5 (211) concentrations (0 mol %, 20 mol %, 28 mol%, and 50 mol%) were synthesized by the melt-gr owth process. Microstructural characterizations were done using x-ray diffraction (XRD), optical microscopy, scanning electron microscopy, a nd transmission electron microscopy (TEM), It was found that 123 plate let width, crack width between the platelets, and 211 particle size de creased systematically with increasing 211 concentration. TEM study sh owed that there is a critical radius of curvature (r(c) less than or e qual to 0.2 mu m-0.3 mu m) of the 123/211 interface where defects/cont rasts of strain field start to appear, and these defects are believed to be responsible for pinning the magnetic flux. Microhardness measure ments showed that Vickers hardness (VHN) increases with increasing 211 content. Critical current density (J(c)) values obtained from magneti zation measurements using a SQUID magnetometer were found to increase in melt-grown samples by the addition of 211 content.