Relation between critical current densities and epitaxy of YBa2Cu3O7 thin films on MgO(100) and SrTiO3(100)

Abstract

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° 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° 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° for the best film on SrTiO₃ compared to 0.86° for the best film on MgO.