The achievement of high growth rates in YBa 2 Cu 3 O 7 epitaxial high-temperature superconducting films has become strategic to enable high-throughput manufacturing of long length coated conductors for energy and large magnet applications. We report on a transient liquid assisted growth process capable of achieving ultrafast growth rates (100 nm s −1) and high critical current densities (5 MA cm −2 at 77 K). This is based on the kinetic preference of Ba-Cu-O to form transient liquids prior to crystalline thermodynamic equilibrium phases, and as such is a non-equilibrium approach. The transient liquid-assisted growth process is combined with chemical solution deposition, proposing a scalable method for superconducting tapes manufacturing. Additionally, using colloidal solutions, the growth process is extended towards fabrication of nanocomposite films for enhanced superconducting properties at high magnetic fields. Fast acquisition in situ synchrotron X-ray diffraction and high resolution scanning transmission electron microscopy (STEM) become crucial measurements in disentangling key aspects of the growth process.

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.

The investigation of the atomic structure of individual defects is critical to the understanding and precise controlling of the physical properties of materials. And although defects are sometimes detrimental to functionality, in high temperature superconductors (HTS) are necessary for providing pinning of magnetic flux and allowing high currents to be carried. Moreover, a strong enhancement on the vortex pinning in HTS YBa 2 Cu 3 O 7 (YBCO) films is also found to be controlled by nanostrain [1], which is attributed to elastic distortions of the crystal lattice at the nanoscale level. Using aberration‐corrected Scanning Transmission Electron Microscopy (STEM) we explore the complex defect landscape of YBCO nanocomposite thin films. Combining High Angle Annular Dark Field (HADDF) with Low Angle Annular Dark Field (LAADF) and local strain analyses we are able to map and quantify the lattice deformations associated to the defects, which will ultimately determine their self‐assembling behavior as well as their mutual interaction. Our atomic scale investigation shows that the presence of mainly randomly oriented nanoparticles generates incoherent interfaces within the epitaxial YBCO matrix, which drastically increases the density of defects, yielding a ramified network of inhomogeneously distributed nanostrained regions where the crystalline perfection of the superconductor is perturbed. Finally, we will compare the microstructure of conventional high‐quality solution‐derived trifluoroacetate‐YBCO nanocomposites with new fluorine‐free films based on a novel transientliquid assisted growth method (TLAG), which provides ultra‐high growth rates with a consequent influence on the defects landscape. Accordingly, TLAG envisages an enormous potential for lowcost and high‐performance coated conductors.

Transient liquid assisted growth (TLAG) is an ultrafast non-equilibrium growth process mainly governed by kinetic parameters, which are only accessible through fast in situ characterizations. In situ synchrotron X-ray diffraction (XRD) analysis and in situ electrical resistivity measurements are used to derive kinetic diagrams of YBa 2 Cu 3 O 7−x (YBCO) superconducting films prepared via TLAG and to reveal the unique peculiarities of the process. In particular, diagrams for the phase evolution and the YBCO growth rates have been built for the two TLAG routes. It is shown that TLAG transient liquids can be obtained upon the melting of two barium cuprate phases (and not just one), differentiated by their copper oxidation state. This knowledge serves as a guide to determine the processing conditions to reach high performance films at high growth rates. With proper control of these kinetic parameters, films with critical current densities of 2-2.6 MA cm −2 at 77 K and growth rates between 100-2000 nm s −1 are reached. These growth rates are 1.5-3 orders of magnitude higher than those of conventional methods.