Relevance of the Formation of Intermediate Non-Equilibrium Phases in YBa2Cu3O7–x Film Growth by Transient Liquid-Assisted Growth

Silvia Rasi, Laia Soler, Júlia Jareño, Juri Banchewski , Roger Guzman, Cristian Mocuta, Martin Kreuzer, Susagna Ricart, Pere Roura-Grabulosa, J Jordi Farjas, Xavier Obradors and Teresa Puig
Journal of Physical Chemistry C 124, 15574-15584, 2020
DOI: 110.1021/acs.jpcc.0c03859

Transient liquid-assisted growth (TLAG) is a non-equilibrium ultrafast method to grow YBa₂Cu₃O_7–x (YBCO) superconducting films at up to 100 nm/s using chemical solution deposition. In this work, we study the formation of non-equilibrium crystalline intermediate phases prior to the growth of YBCO through TLAG. We analyze the thermal decomposition and microstructural evolution of a propionate-based fluorine-free solution used as precursor to YBCO epitaxial films. Thermal analyses (TGA, DSC), coupled with techniques to monitor the volatiles (TG-IR), were applied in situ during film pyrolysis in humid O₂, while the thermal evolution of the solid residue was characterized by infrared spectroscopy and X-ray diffraction, both ex situ and in situ in synchrotron radiation sources, and by scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS) cross-sectional analysis. Unexpected effects, observed during the decomposition of the ternary solution, are the formation of intermediate non-equilibrium phases: Cu₂O or Cu(0) and monoclinic BaCO₃. We emphasize that working with anhydrous solutions and anhydrous deposition conditions promotes the formation of the expected equilibrium phases. Finally, in situ X-ray diffraction permits monitoring the influence of the non-equilibrium monoclinic BaCO₃ phase on the formation of binary oxide phases, precursors of TLAG YBCO film growth. Understanding the evolution of non-equilibrium phases is shown to be fundamental for the control of the final YBCO film’s microstructure and performance, since the latter are strongly affected by the film’s thermal history after solution deposition.