3, Karlsrhue Institute of Technology, Eggenstein-Leopoldshafen, , Germany
2, IFW Dresden, Dresden, , Germany
4, University of Turku, Turku, , Finland
5, BASF SE, Ludwigshafen, , Germany
6, Deutsche Nanoschicht, Rheinbach, , Germany
The implementation of YBa2Cu3O7-δ (YBCO) coated conductors in power applications generally has a potential to change the paradigm in large-scale energy applications. Unfortunately, pure YBCO thin films typically exhibit a strong reduction of the critical current density (Jc) with increasing magnetic field strength caused by vortex motion. There are many different synthetic strategies available to produce superconducting YBCO thin films, of which many are not commercially viable. Here, we collaborated with companies in the field, choosing the approach that will be used for production. It is based on chemical solution deposition (CSD) of a precursor solution with several fluorine contents.
Hereby, the incorporation of preformed nanocrystals (PNCs) as artificial pinning centers was introduced as an adequate approach to achieve flux pinning, preventing the drastic decrease of the critical current density Jc at moderate-to-high magnetic fields as well as its angular dependency on the magnetic field. To achieve this, we have produced nanocomposite thin films starting from PNCs in combination with fluorine-based chemical solution deposition. The use of PNCs generally offers a better control of the final microstructural properties of the nanocomposite films when compared to self-assembled nanoparticles formation during YBCO processing.
In this work, small crystalline single (ZrO2 and HfO2) and double (SrTiO3 and BaZrO3) metal oxide nanocrystals were synthesized with diameters in the range of 4-10 and capped with hydrophobic ligands to ensure colloidal stability in apolar solvents. However, as the YBCO precursor typically provides a more polar environment, e.g., methanol, an important aspect of this research involves ligand exchange and the appropriate stabilization procedure. We are able to stabilize these nanocrystals in different types of fluorine-based YBCO precursor solutions, leading to highly stable nanocomposite precursors with long shelf-lives.
Afterwards, the YBCO-PNC solutions were deposited on single crystal LaAlO3 (LAO) substrates via ink-jet printing method. The main focus of this research pointed to understanding the factors which control the microstructure development and the physical properties of the nanocomposite thin films. By strict optimization on both the precursor and processing level, we achieved nanocomposite thin films exhibiting Jc of 4-5 MA/cm2 at 77 K in self-field as well as a much smoother decay of Jc as a function of magnetic field. This is reflected by a strong pinning force enhancement (up to 17 GN/m3 at 77 K) and a reduced effective anisotropy compared to undoped YBCO films.
This newly developed approach delivers scalable and high quality superconducting films, capable of meeting the strict requirements for the successful implementation and distribution of coated conductors throughout energy market.