Synthesis of high-oxidation Y-Ba-Cu-O phases in superoxygenated thin films
Abstract
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 YBa2Cu3O7-δ grown by pulsed laser deposition are annealed at up to 700 atm O2 and 900, in conjunction with Cu enrichment by solid-state diffusion. The films show clear formation of Y2Ba4Cu7O15-δ and Y2Ba4Cu8O16 as well as regions of YBa2Cu5O9-δ and YBa2Cu6O10-δ phases, according to scanning transmission electron microscopy, x-ray diffraction and x-ray absorption spectroscopy. Similarly annealed YBa2Cu3O7-δ powders show no phase conversion. Our results demonstrate a novel route of synthesis towards discovering more complex phases of cuprates and other superconducting oxides.
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