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.

Film and powder samples from a BaAc2 solution in propionic acid/MeOH were decomposed in different atmospheres and their thermal decomposition was characterized by means of thermogravimetry coupled with evolved gas analysis techniques (TG-FTIR, EGA-MS) and chemical and structural methods (EA, XRD, FTIR). The thermal behavior of the films was found to be different than the corresponding powder, in terms of volatiles, kinetics, intermediate phases and purity of final product. The mixed Ba-Prop-Ac salt obtained from solution decomposes to BaCO3 before 400°C through oxidative degradation, and above 400°C in inert atmosphere through a radical path releasing symmetrical ketones. Its double melting behavior is also highlighted and its decomposition understood by comparison with BaProp2 and BaAc2 precursors, and put into context of YBa2Cu3O7-∂ (YBCO) film pyrolysis.

The thermal decomposition of CuProp2 in the form of film and powder was studied in different atmospheres by means of thermal analysis techniques (TG-MS, TG-IR, EGA), chemical-structural methods (FTIR, XRD, EA) and computational thermochemistry (VASP/PBE). The decomposition mechanism in terms of volatiles evolved was disclosed with the aid of ab-initio modeling; it was found to be dependent on the gas diffusion in and out of the sample and accelerated by a humid atmosphere. In films, the copper redox behavior showed sensitivity to the residual atmosphere. Finally, the role of the metal center is discussed in the frame of a general decomposition mechanism for metal propionates. Volatile species evolved during decomposition can be detected by means of thermogravimetry (TG) coupled with Evolved Gas Analysis (EGA), which mainly works by infrared (EGA-FTIR or TG-FTIR) or by mass spectrometry (EGA-MS or TG-MS) detection. In fact, by EGA-FTIR and EGA-MS, it was shown that the decomposition of propionates in inert atmospheres involves formation of radicals C2H5• and C2H5CO• (along with CO2) and their recombination to form a symmetrical ketone [20-22]. For longer chain salts such as Ca(II)decanoate, techniques like pyrolysis coupled to gas chromatography (GC) revealed a more complicated scenario where normal alkanes were found along with several symmetrical ketones [23]. For odd chain length of Cu(II)carboxylates like Cu(II)propionate, only MS has been used for the in-situ EGA analysis and 2-pentanone (asymmetrical ketone) was reported to be the main decomposition product [11]. Formation of this asymmetrical ke-tone implies cleavage of a CeC(C]O) bond, instead of the expected CeC(]O) and C(]O)eO bonds. Conversely, no ketones at all were observed for even chain carboxylates of copper(II) [24], mercury(II) [25] and silver(I) [26]. In fact, references [24,25] report on the

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.

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.