Synthesis of high-oxidation Y-Ba-Cu-O phases in superoxygenated thin films

TL;DR

This study demonstrates a new method for synthesizing high-oxidation Y-Ba-Cu-O superconducting phases in thin films using superoxygenation, which could lead to discovering more complex superconducting oxides.

Contribution

The paper extends superoxygenation synthesis to thin films, enabling stabilization of high-oxidation phases not achievable in powders, opening new avenues for complex cuprate phase discovery.

Findings

High-oxidation phases Y2Ba4Cu7O15-δ and Y2Ba4Cu8O16 were formed in thin films.

No phase conversion observed in powders under the same annealing conditions.

Superoxygenation in thin films enables synthesis of complex cuprate phases.

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 $\rm{YBa_2Cu_3O_{7-\delta}}$ grown by pulsed laser deposition are annealed at up to 700 atm O$_2$ and 900$^\circ$C, in conjunction with Cu enrichment by solid-state diffusion. The films show clear formation of $\rm{Y_2Ba_4Cu_7O_{15-\delta}}$ and $\rm{Y_2Ba_4Cu_8O_{16}}$ as well as regions of $\rm{YBa_2Cu_5O_{9-\delta}}$ and YBa$_2$Cu$_6$O$_{10-\delta}$ phases, according to scanning transmission electron microscopy, x-ray diffraction and x-ray absorption spectroscopy. Similarly annealed $\rm{YBa_2Cu_3O_{7-\delta}}$ powders show no phase conversion. Our results demonstrate a novel route of synthesis towards discovering more complex phases of cuprates and other superconducting oxides.