Melt textured growth YBCO superconductors were fabricated by the top seeding method using Sm1.8 $(Sm_{1.8}Ba_{2.4}Cu_{3.4}O_{7-x})$ seed. The relationship between the Y211 particles and the platelet structures was investigated by micro-structural analysis using SEM. The platelet structures were commonly observed around the Y211 particles and bent toward the Y211 particles.
The microstructures of melt processed YBCO superconductors have been examined by TEM and HRTEM. The results of TEM studies clarifies the direction of crystal growth and a variety of micro-defects such as twin structures and stacking faults that might behave as pinning centers. Our studies are focused on the stacking faults among those micro-defects by HRTEM and a formation mechanism of the stacking faults is proposed.
We investigated the twin structures using the optical microscope and SEM. The twin structures formed during the tetragonal to orthorhombic transition that occurred at 450℃ in sample oxygen annealing. The twin structures were clearly by SEM due to the chemical etching effects. The length of twin structures were increased as the oxygen annealing time increased from 1hr to 10hr. The twin lengths were considered to relate to the oxygen contents, as the platelet structures were. The results suggested an oxygen diffusion model for the formation of the twin lengths.
These results suggest a new solidification model for the formation of the platelet structures and twin structures.
