Transmission electron microscope observations of interfaces in YBa₂Cu₃O_x/BaSnO₃/YBa ₂Cu₃O_x trilayers

A new insulating material, BaSnO₃ with a relatively large mismatch to YBa₂Cu₃O_x is investigated as a barrier material in a superconductor/ insulator/ superconductor (SIS) structure. All c-axis oriented YBa₂Cu₃O_x/ BaSnO₃/ YBa₂Cu₃O_x SIS structures are grown by an in situ sequential pulsed laser deposition technique. Transmission electron microscopy (TEM) reveals that BaSnO₃ thin films cover well c-axis oriented YBa₂Cu₃O_x thin films. Moreover, c-axis oriented YBa₂Cu₃O_x thin films grow epitaxially on BaSnO₃ thin films with very good wetability. The relatively large mismatch provides periodical lattice discontinuity, which is probably associated with the generation of dislocations in one third of c-axis unit of YBa₂Cu₃O_x thin films. This study provides guidelines for selecting insulating materials.