The preparation of bimetallic alkoxide precursors (WP1) was investigated to deliver series of bimetallic alkoxide precursors. These alkoxide precursors have shown good miscibility/solubility in benzyl alcohol and ethanol which was ideal for the nanocrystal synthesis method.
For the WP2, we have already introduced some design of experiments to synthesize double metal oxide nanocrystals via solvent-controlled non-aqueous routes. To obtain colloidally stable double metal oxide nanocrystals, we have introduced the solvothermal microwave-assisted synthesis starting from different types of bimetallic precursors. The obtained nanocrystals with the cubic crystal phase, were tunable in size, ranging from 2.5 to 40 nm in size and with a narrow size distribution. We were able to prove that definitive design screening helped to identify the factors affecting both size and total yield.
In WP3, BMO nanocrystals were stabilized in polar solvent like methanol with an appropriate ligand to have a colloidal nanosuspension. As an optimal ligand was very critical issue during YBCO growth, screening test has introduced to identify possible ligands. These nanocrystals could be transferred to the YBCO precursor solutions via introducing copolymer or carboxylate acid as stabilization ligands.
In WP4, the colloidal YBCO solution with preformed nanocrystals was deposited on LaAlO3 single-crystal substrate (lab-scale) via chemical solution deposition approach to study the growth mechanism of YBCO nanocomposite film. After this deposition and its thermal treatment, we achieved good texture of YBCO nanocomposite containing BMO nanocrystals with good critical current densities (Jc) without introduction of a seed layer. BMO-added YBCO nanocomposite shows a homogeneous distribution of the nanoparticles with an average diameter of 7 nm, leading to enhanced self-field Jc and a much smoother decay of Jc with magnetic field. Pinning force densities is also increased by a factor of 3.5 at 77 K while the Jc anisotropy is reduced by the addition of nanocrystals.
In WP5, we reported a successful fabrication of long-length RABiTS-based all-CSD coated conductors (CC) starting from colloidal YBCO solutions containing preformed BMO (M = Hf, Zr) nanocrystals. Partial optimization of the existing continuous reel-to-reel YBCO processing via DoE approach allowed us to obtain YBCO nanocomposites that retain 80-90% self-field performance of the pristine CC and show a 10 to 40% improvement of in-field critical current, which was only a moderate performance improvement compared to similar films on single-crystal substrates prepared on lab-scale. Based on XRD and TEM studies, we attributed this to worsening of the YBCO texture and strong coarsening of BMO nanoparticles, particularly, BaZrO3, during processing.
In WP6, the critical temperature Tc is studied as it depends on the oxygen contents of YBCO. It was observed that the presence of nanocrystals strongly affects the oxygenation kinetics as the lattice parameter in the nanocrystal-added YBCO films is larger than in the pristine YBCO films. Tc showed the dome like behavior versus nominal O contents and was not suppressed by the presence of nanocrystals. It is probably possible that nanocrystals inhibit rearrangement of twin boundaries (TBs) during oxidation. Therefore, in-depth studies are necessary to confirm that TBs are important short-circuit paths for oxygen diffusion.
Final, as the colloidal YBCO inks were deposited and crystallized on long-length metallic substrates, detailed cost projection for nanoparticle engineering and coating was developed. This costing model would be the basis for a transfer towards a business plan for new applications. The business plan was updated on the use of nanocomposite with efficient vortex pinning and optimized performance for superconducting properties and the use of the coatings for specific industrial applications.
