FABRICATION AND PROPERTIES OF HIGH Jc Y—Ba—Cu—O SUPERCONDUCTOR BY (MTG) PROCESS

Superconducting Y—Ba—Cu—O bulk materials were fabricated by melt—textured growth (MTG) method, where cooling slowly under temperature gradient produces an aligned structure exhibiting high Jc value. The critical current density was measured by continuous dc four—probe method with criterion of 1μV/cm. Jc value has reached 23, 800 A/cm 2 at 77K under 2T magnetic field perpendicular to the current. The magnetic field dependences of Jc from 1 to 7 Tesla show the anisotropy for two orientations (H┴I, H┴a—b plane and H┴I, H//a—b plane). The X—ray diffraction patterns show the crystals preferentially aligned. The SEM and TEM observations of the MTG sample reveal that the sample has dense layered—structure with regular alignment of plate—shaped crystals. Twinning planes of fairly high density exist. A great quantity of dislocations, dislocation loops and stacking faults exist around 211 phase. These crystal defects may be main flux pinning centers. We have measured the zero—field cooled (ZFC) and the field cooled (FC) magnetizations as functions of temperature at various external dc magnetic field. The dependence of irreversibility point T * on 2/3 power of field H for MTG sample was demonstrated. The flux jumping was found in the hysteresis loop below 10K.