The outstanding ability of YBa₂Cu₃O_7−x (YBCO) films to carry high-currents at high-magnetic fields offers an unprecedented opportunity to be used in large-scale superconducting power applications and high-field magnets. In an essential need of high-performance and low-cost manufacturing, chemical-solution deposition (CSD) has become a very competitive cost-effective and scalable methodology to grow epitaxial YBCO-films [1]. However, their growth-rates are rather small (0.5-1 nm/s). For this purpose, we have developed a novel growth-approach, entitled, Transient Liquid Assisted Growth (TLAG) [2], which is able to combine CSD methodologies with ultra-fast growth-rates (100-1000 nm/s) by facilitating a non-equilibrium liquid-mediated approach. Critical current-densities up to 5 MA/cm² at 77K are already realized in TLAG-CSD grown thin films, but in order to further improve the current carrying properties, understanding of initial nano-phases in pyrolysis process and fine-tuning of growth parameters are essential in thicker films. Therefore, the microstructure of multideposited pyrolyzed and grown YBCO films, investigated via high-resolution transmission electron microscopy (HR-TEM), scanning-TEM (STEM), electron-energy loss spectroscopy (EELS) and energy-dispersive X-ray spectroscopy (EDX), will be presented.

Furthermore, the critical current-density capabilities of high-temperature superconductors (HTS) are determined by its microstructure and it can be enhanced by the presence of well-controlled nano-defects inside the epitaxial superconducting matrix acting as vortex-pinning-centers. TLAG-CSD has demonstrated the growth of nanocomposites to increase flux-pinning at high magnetic-fields by incorporating pre-formed NPs to the metal-organic initial inks [2]. Therefore, using aberration-corrected STEM combined with high angle annular dark field (HAADF) and EELS, the detailed microstructure of grown TLAG-CSD YBCO films, nanocomposites, and coated-conductors, with a focus on new defects landscape at the atomic-level, secondary phases, and strain-effects, will be presented. Finally, the recent progress in TLAG-CSD films and nanocomposites, in terms of microstructure correlation with growth mechanisms and growth rate will be discussed.

[1] J. Gutierrez, A. et al., Nat. Mat., 6, 367 (2007)
[2] L. Soler et al, Nat. Commun., 11, 344 (2020)

Figure Caption: STEM-HAADF images of TLAG-CSD YBCO films indicating the different microstructures for a) 0.4 ºC/s, (b) 20º/s, highlighting the tunability of TLAG-CSD for vortex pinning, and (c) a 12% BaZrO3 (BZO) nanocomposite, where inset shows that BZO nanoparticles grow epitaxial with the YBCO matrix contrary to the other CSD processes [2].

Keywords: YBCO, TLAG-CSD, TEM, Superconductivity