Twins, Their Microstructure and Correlation to Critical Current Densities in Superconducting Melt-Textured Grown Y-Ba-Cu-O

Refinement of twin microstructure in melt-textured grown (MTG) Y-Ba-Cu-O (YBCO) is engineered by annealing at different temperatures. This isothermal method exploits the temperature dependence of twin-boundary-energy. The twin boundary energy is obtained by two independent methods: (1) twin spacing and (2) twin-tip shape. The twin boundary energy measurement is accomplished with transmission electron microscopy. Refinement of twin spacing with increasing temperature is confirmed. Twin spacing decreases from 190 nm to 54 nm as the temperature increases from 450 to 680$^{o}$C. Critical current measurements support that a sample with a higher density twin density often results in a higher pinning-force i.e. 3.4 x 10$^{8}$ N/m$^{3}$ versa 1.2 x 10$^{8}$ N/m$^{3}$.