RELATION BETWEEN CRITICAL CURRENT DENSITIES AND EPITAXY OF YBA2CU3O7 THIN-FILMS ON MGO(100) AND SRTIO3(100)

The preferred orientation of YBa2Cu3O7 thin films grown on single-crystal MgO(100) and SrTiO3(100) substrates has been investigated using x-ray diffraction and transmission electron microscopy. Various types of microstructural defects were identified in the films and correlated with a lowering of the critical current density J(c). On MgO substrates it was found that a film with 5% of its grains rotated 45-degrees with respect to the dominant orientation and a high density of small-angle grain boundaries had J(c) reduced by 75% compared to a film with no 45-degrees grain boundaries and a low density of small-angle grain boundaries. On SrTiO3 substrates it was found that an increase in the amount of a-axis oriented material from 0.6% to 8.3% lead to a reduction in J(c) by 70%. In general, higher critical current densities were found on SrTiO3 than on MgO substrates. This fact is attributed to the closer lattice match of YBa2Cu3O7 with SrTiO3, resulting in an in-plane mosaic spread of only 0.38-degrees for the best film on SrTiO3 compared to 0.86-degrees for the best film on MgO.