High temperature superconductors (HTS) are unique materials to transport high electrical currents without losses up to liquid nitrogen temperatures and/or at high magnetic fields. Therefore, substantial research was promoted to demonstrate their opportunities towards efficient electrical transport and high field magnets applications. However, the high production costs of the existing technology refrain their market out-breaking. Chemical solution deposition (CSD) techniques have decisively opened possibilities for the manufacturing of low-cost nanostructured epitaxial HTS superconductors with high performances, successfully employing trifluoroacetate metal-organic precursors (TFA-route). We have developed a high-throughput growth method, the Transient Liquid Assisted Growth (TLAG), that enables to reach growth rates up to 1000 nm/s [1,2] compatible with a CSD methodology. Additionally, since it uses a fluorine-free solution approach, it follows the global need for greener chemical processes to grow epitaxial YBa₂Cu₃O₇ (YBCO) superconducting films. We designed a robust environmentally friendly propionate-based metalorganic solution using a facile low cost synthetic method which ensures a 50% higher metal concentration and very high stabilization, starting from low-cost commercial precursors [3]. This solution facilitates the preparation of highly homogeneous nanocrystalline pyrolysis layers with very low porosity (1-2 %) at least up to a thickness of 2.7 μm, resulting in the ultrafast growth of reproducible YBCO epitaxial layers of 2.5-3 MA/cm² at 77 K. Solution rheological characterization together with EPR, TGA and TEM analysis were key to obtain thick films without compromising their homogeneity [3]. Moreover, this novel preparation method is compatible with the possibility of varying the Ba/Cu molar ratio in solutions, allowing us to optimize solutions of various compositions with desired features for TLAG. The use of various liquid compositions results in a modification of the supersaturation conditions and characteristics of the transient liquid in the TLAG process, through which we can evince the differences in nucleation, epitaxy and physical properties. Employing in-situ XRD synchrotron radiation and HRTEM/STEM, we could reach a wide understanding of the TLAG mechanism by identifying the relevance of the kinetic behavior, the influence of the transient liquid composition and the correlation with the superconducting properties.

References
[1] Soler, L., Jareño, J., Banchewski, J. et al. Ultrafast transient liquid assisted growth of high current density superconducting films. Nat Commun 11, 344 (2020). https://doi.org/10.1038/s41467-019-13791-1
[2] Rasi, S., Queraltó, A., Banchewski, J., Saltarelli, L., Garcia, D., Pacheco, A., Gupta, K., Kethamkuzhi, A., Soler, L., Jareño, J., Ricart, S., Farjas, J., Roura-Grabulosa, P., Mocuta, C., Obradors, X., Puig, T., Kinetic Control of Ultrafast Transient Liquid Assisted Growth of Solution-Derived YBa2Cu3O7-x Superconducting Films. Adv. Sci. 2022, 2203834. https://doi.org/10.1002/advs.202203834
[3] Saltarelli, L., Gupta, K., Rasi, S., Kethamkuzhi, A., Queraltó, A., Garcia, D., Gutierrez, J., Farjas, Roura, P., Ricart, S., Obradors, X., Puig, T., Chemical and microstructural nanoscale homogeneity in superconducting YBa₂Cu₃O_7-x films derived from metal-propionate fluorine-free solutions, submitted.

Keywords: YBCO superconducting films, chemical solution deposition, transient liquid assisted growth, in-situ XRD synchrotron characterization