Structural transition of secondary phase oxide nanorods in epitaxial YBa₂Cu₃O_7−δ films on vicinal substrates

Abstract

A theoretical study of a structural transition of secondary phase oxide nanorods in epitaxial YBa₂Cu₃O_7−δ films on vicinal SrTiO₃ substrates is presented. Two possible types of film/substrate interface are considered, with one assuming complete coherence, while the other is defective as manifested by the presence of antiphase grain boundaries. Only in the former case does the increase of the vicinal angle of the substrate lead to a substantial change of the strain field in the film, resulting in a transition of the nanorod orientation from the normal to the in-plane direction of the film. The calculated threshold vicinal angle for the onset of the transition and lattice deformation of the YBa₂Cu₃O_7−δ film due to the inclusion of the nanorods is in very good agreement with experimental observations. This result sheds lights on the understanding of the role of the film/substrate lattice mismatch in controlling self-assembly of dopant nanostructures in matrix films.

Keywords:

• cuprate superconductors
• nanostructured thin films
• structural transitions
• strain
• nanocomposites
• vicinal substrates
• YBCO

Acknowledgments

This work is supported in part by NSF and ARO under contract no. NSF-DMR-0803149, NSF-DMR-1105986, NSF EPSCoR-0903806, and ARO-W911NF-0910295.