Synthesis of High-Oxidation Y-Ba-Cu-O Phases in Superoxygenated Thin Films

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 ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ grown by pulsed laser deposition are annealed at up to 700 atm ${\mathrm{O}}_{2}$ and $900{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$, in conjunction with Cu enrichment by solid-state diffusion. The films show the clear formation of ${\mathrm{Y}}_{2}{\mathrm{Ba}}_{4}{\mathrm{Cu}}_{7}{\mathrm{O}}_{15\ensuremath{-}\ensuremath{\delta}}$ and ${\mathrm{Y}}_{2}{\mathrm{Ba}}_{4}{\mathrm{Cu}}_{8}{\mathrm{O}}_{16}$ as well as regions of ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{5}{\mathrm{O}}_{9\ensuremath{-}\ensuremath{\delta}}$ and ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{6}{\mathrm{O}}_{10\ensuremath{-}\ensuremath{\delta}}$ phases, according to scanning transmission electron microscopy, x-ray diffraction, and x-ray absorption spectroscopy. Similarly annealed ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ powders show no phase conversion. Our results demonstrate a route of synthesis towards discovering more complex phases of cuprates and other superconducting oxides.