Critical current density-magnetic field curve for untwinned orthorhombic Nd1+xBa2-xCu3O7 +/-delta single crystal and its microstructure

Critical current density-magnetic field (J(c)-H) curves with H parallel to c-axis for untwinned orthorhombic Nd1+x, Ba2-x,Cu3O7+/-delta (Nd123, x = 0. 07) single crystals were investigated. Untwinned single crystals were prepa red by two different fabrication processes under uniaxial stress: a detwinn ing process and a twin-free process. The peak effects for twin-free crystal s were larger than those for detwinned crystals. The results of evaluation of the Nd/Ba configurations in these single crystals by extended X-ray abso rption fine structure (EXAFS) spectroscopy and transmission electron micros copy (TEM) suggested that a larger number of pinning centers of Nd rich pha ses were distributed more finely in twin-free crystals, so that the peak ef fects in their J(c)-H curves increased. Furthermore, it is possible that th e heat treatments under uniaxial stress affected the progress of Nd/Ba rati o fluctuation by means of the spinodal decomposition mechanism, which cause d the fine distribution of Nd-rich phases in twin-free crystals.