Observation of mesoscopic structures in NdBa2Cu3O7-δ by small-angle neutron scattering

In order to clarify the origin of the high critical current density (J(c)) of NdBa2Cu3O7-delta (Nd123), we investigated the inhomogencities in this material by small-angle neutron scattering (SANS) experiments. As a result of numerical calculations, it was found that the anisotropic scattering patterns and radial intensity profiles can be explained by the existence of elliptic cylindrical objects of which the cylindrical, axis is parallel to the crystallographic c-axis. Long and short elliptic axis lengths and the height of the elliptic cylinders in the high-J(c) sample are about 400, 200 and 100 nm, and those of the low-J(c) sample are about 200, 100 and 50 nm. Since these two samples have been heat-treated in different manners, it is suggested that sizes of the elliptic cylinders are affected by the heat treatments and this change in scale, as a result, increases or decreases the J(c) characteristics of the samples.