Transient liquid-assisted growth (TLAG) is a non-equilibrium ultrafast method to grow YBa2Cu3O7–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.This work was funded by Ministerio de Ciencia, Innovation y Universidades (RTI2018-095853-B-C21 and RTI2018-095853-B-C22) cofinanced by the European Regional Development Fund, and the EU Ultrasupertape project (ERC ADG-2014-669504). We also acknowledge the Center of Excellence Severo Ochoa (SEV-2015-0496), the Generalitat de Catalunya (2017-SGR-1519) and the COST -action NANOCOHYBRI (CA16218). In situ FTIR experiments were performed at the MIRAS beamline of the ALBA Synchrotron with the collaboration of ALBA staff. We also thank the DiffAbs beamline at SOLEIL Synchrotron facility and the beamline staff support for the in situ XRD experiments. We thank the ICMAB, INA-Zaragoza and UdG scientific services and technical staff for the support on the experiments. S.R. thanks the Universitat de Girona (UdG) for the IFUdG grant. L.S. and J.J. also acknowledge their FPU-MINECO PhD grant.Peer reviewe
