It is known that solid-state reaction in high-pressure oxygen can stabilize high-oxidation phases of Y-Ba-Cu-O superconductors in powder form. We extend this superoxygenation concept of synthesis to thin films which, due to their large surface-to-volume ratio, are more reactive thermodynamically. Epitaxial thin films of ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-\delta }$ grown by pulsed laser deposition are annealed at up to 700 atm ${\mathrm{O}}_2$ and $900{}^{\circ }\mathrm{C}$, in conjunction with Cu enrichment by solid-state diffusion. The films show the clear formation of ${\mathrm{Y}}_2{\mathrm{Ba}}_4{\mathrm{Cu}}_7{\mathrm{O}}_{15-\delta }$ and ${\mathrm{Y}}_2{\mathrm{Ba}}_4{\mathrm{Cu}}_8{\mathrm{O}}_{16}$ as well as regions of ${\mathrm{YBa}}_2{\mathrm{Cu}}_5{\mathrm{O}}_{9-\delta }$ and ${\mathrm{YBa}}_2{\mathrm{Cu}}_6{\mathrm{O}}_{10-\delta }$ phases, according to scanning transmission electron microscopy, x-ray diffraction, and x-ray absorption spectroscopy. Similarly annealed ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-\delta }$ powders show no phase conversion. Our results demonstrate a route of synthesis towards discovering more complex phases of cuprates and other superconducting oxides.

• Received 26 September 2017

DOI:https://doi.org/10.1103/PhysRevMaterials.2.033803