ИСТИНА

Nowadays YBa2Cu3O7-x (YBCO) films are beengused in HTS coated conductors (CC). For high-field applications the introduction of pinning centers is essential to immobilize fluxoids penetrating the superconducting layer. In this work pinning centers have been created through the production of nanocomposites of YBCO with Ba2Y(Nb,Ta)O6 (BYNTO) or BaHfO3 (BHO) nanocolumns. Variation of the substrate temperature and deposition rate alters the defect structure of the film resulting in changes of the superconducting transition temperature and of the critical current density in magnetic fields. Through transmission electron microscopy (TEM) we investigated the micro- and nanostructure of the nanocomposites producedby pulsed laser deposition on a SrTiO3 (STO) substrate at different conditions. Under optimal deposition conditions the YBCO matrix contains homogenously distributed nanocolumns of the addend. The columns start at the YBCO/STO interface and run through the whole YBCO layer. In most cases, a thin layer of highly distorted YBCO is present at the substrate/superconductor interface. In these areas the nanocolumns are generated above the distorted YBCO layer. Columns are about 2 to 10 nm thick and are distributed with ~ 1 column per 20-30 nm. Non-optimal deposition conditions lead to an inhomogeneous second phase distribution, interruption of the nanorods or formation of planar precipitates. All of them will be discussed in this presentation. The structural relationship between columns and YBCO is: (001)BYNTO/BHO // (001)YBCO, (100)BYNTO/BHO // (100)YBCO. Nanocolumns cause expansion of the YBCO structure in the [001]YBCO and [100]YBCO direction and induce defects, such as stacking faults, dislocations and extra planes. Non-optimal deposition conditions lead to an inhomogeneous second phase distribution, interruption of the nanorods or formation of planar precipitates. All of them will be discussed in this presentation. This work is supported in part via EC FP7 EUROTAPES.