Strong pinning in thick YBa₂ Cu₃ O₇ layers mediated by catalysis of a new long-period metastable cuprate phase

Catalysts are widely utilized to promote reactions in liquid and gaseous phases but are rarely encountered in solid state synthesis. Here we use catalytically active (001) ceria buffers to modify the structure of the epitaxial high temperature superconductor YBa₂ Cu₃ O ₇. The modification is achieved by catalytically-assisted synthesis of a previously unknown metastable phase. The new phase, a long-period (3.5 nm) perovskite, intercalates into the YBa₂ Cu₃ O₇ matrix without negatively affecting the critical temperature of the film. Analysis of electron microscopy and synchrotron x-ray diffraction data allow identification of the phase as a long-period YBa₂ Cu₃ O₇ derivative formed through short-range cation displacement. The 0.8 μm thick films exhibit strong enhancement of the critical current density, reaching a maximum of 4.2 MA/ cm² at 77 K. The result emphasizes the critical role of catalysis for synthesis of novel complex materials.