Twins in superconducting melt-textured grown Y-Ba-Cu-O as related to critical current densities

Twin spacings in melt-textured grown (MTG) Y-Ba-Cu-O (YBCO) are refined by annealing at higher 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, employing transmission electron microscopy. We observe that twin spacing decreases from 190 nm to 54 nm as the temperature increases from 450 to 680 degrees 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).