Nonlocal self-organization of long stacking faults from highly strained nanocomposite film of complex oxide

Abstract

Elastic strain and defects are important key words for controlling structure and properties in films. While epitaxial strain and misfit dislocations have been discussed in conventional films, the evolution of strain and defect can be significantly varied by nanocomposite strain and complicated defects in oxides. In the present study, long stacking faults with a spacing of 5--30 nm and a length of $>500\phantom{\rule{0.16em}{0ex}}\mathrm{nm}$ were self-organized by ex situ annealing highly strained nanocomposite films of $\mathrm{YB}{\mathrm{a}}_{2}\mathrm{C}{\mathrm{u}}_{3}{\mathrm{O}}_{7--\ensuremath{\delta}}(\mathrm{YBCO})+\mathrm{BaM}{\mathrm{O}}_{3}\phantom{\rule{4pt}{0ex}}(M=\mathrm{Hf},\phantom{\rule{0.28em}{0ex}}\mathrm{Sn})$. It is surprising that the nonlocal nature of stacking faults, namely, the structural correlation over $>500\phantom{\rule{0.16em}{0ex}}\mathrm{nm}$, was observed in spite of the local configuration of the nanocomposite interface. This kind of structural variation was not observed in the pure $\mathrm{YBCO}$ film without nanorods, even when the same annealing was performed. A strain energy analysis showed that the stacking fault formation led to the strain energy minimum by reducing the nanocomposite strain. The layered structure of YBCO stacking faults and the large nanocomposite strain realized the present nonlocal self-organization, which is not observed in the conventional systems with epitaxial strain and misfit dislocations.