In the context of CSD-MOD growth of coated conductors for low cost and scalable production of YBCO coated conductors, new solutions are proposed in accordance with the new requirements concerning environmental safety and product performance. Looking at these objectives we will present here our work in the preparation of metallorganic precursor solutions with reduced fluorine content, which fulfill the requirements of superconducting YBCO epitaxial layers, leading to high superconducting performance. Solutions with low fluorine precursors with different solvents and amounts of additives have been stabilized and their rheology modified for substrate wettability. Thermal decomposition analysis and infrared spectroscopy performed directly in films, have revealed the different decomposition steps and NMR analysis could unveil the chemical reactions taking place in the solution. Upon optimization of the growth process parameters, T c and J c (77K) of 90 K and 3-4 MA/cm 2 are obtained.

The achievement of high critical currents in ‘all-chemical’ YBa2Cu3O7−δ thick films from low cost and versatile chemical solution deposition (CSD) methodology is still an open issue. Here we report a study of the nucleation and growth conditions to achieve YBa2Cu3O7−δ films in excess of 1 micron using single pass inkjet printing or multideposition of low-fluorine metalorganic precursors. Growth conditions of thick YBa2Cu3O7−δ layers are first investigated on LaAlO3, where there is no interfacial chemical reactivity. The second architecture investigated is an ‘all-chemical’ CSDCe0.9Zr0.1O2(CZO)/YSZ multilayer on single crystal substrates which serves as model system for coated conductors. Finally, the ‘all-chemical’ coated conductor architecture CSDYBa2Cu3O7/CSDCZO/ABADYSZ/stainless steel, where ABAD stands for alternating beam assisted deposition, is investigated. The nucleation conditions of YBa2Cu3O7−δ films on top of CΖΟ cap layers have been selected to minimize the formation of the BaCeO3 phase at the interface. We demonstrate that by combining the use of Ag additives in the starting YBCO solution and processing conditions leading to low supersaturation (high water pressure and low temperature) we can achieve ∼1 μm thick YBa2Cu3O7−δ films and coated conductors with high critical currents of  = 390 and 100 A/cm-w, respectively, at 77 K and self-field. The achieved control of the interfacial reactivity with CeO2 cap layers opens a route for further increasing film thickness and critical currents in ‘all-chemical’ YBa2Cu3O7−δ coated conductors.

In-field angular pinning performances at different temperatures have been analysed on chemical solution deposited (CSD) YBa 2 Cu 3 O 7−x (YBCO) pristine films and nanocomposites. We show that with this analysis we are able to quantify the vortex pinning strength and energies, associated with different kinds of natural and artificial pinning defects, acting as efficient pinning centres at different regions of the H-T phase diagram. A good quantification of the variety of pinning defects active at different temperatures and magnetic fields provides a unique tool to design the best vortex pinning landscape under different operating conditions. We have found that by artificially introducing a unique defect in the YBCO matrix, the stacking faults, we are able to modify three different contributions to vortex pinning (isotropic-strong, anisotropic-strong, and isotropic-weak). The isotropic-strong contribution, widely studied in CSD YBCO nanocomposites, is associated with nanostrained regions induced at the partial dislocations surrounding the stacking faults. Moreover, the stacking fault itself acts as a planar defect which provides a very effective anisotropic-strong pinning at H//ab. Finally, the large presence of Cu-O cluster vacancies found in the stacking faults have been revealed as a source of isotropic-weak pinning sites, very active at low temperatures and high fields.

Superconducting nanocomposites are the best material choice to address the performances required in power applications and magnets working under high magnetic fields. However, it is still challenging to sort out how to achieve the highest superconducting performances using attractive and competitive manufacturing processes. Colloidal solutions have been recently developed as a novel and very promising low-cost route to manufacture nanocomposite coated conductors. Well dispersed and stabilized preformed nanoparticle solutions are first prepared with high concentrations and then mixed with the YBa 2 Cu 3 O 7 metalorganic precursor solutions to generate colloidal solutions to grow the nanocomposite films. Here we demonstrate, for the first time, that non-reactive BaZrO 3 and BaHfO 3 perovskite nanoparticles are suitable for growing high quality thin and thick films and coated conductors with a homogeneous distribution and controlled particle size. Additionally, we extend the nanoparticle content of the nanocomposites up to 20-25 % mol without any degradation of the superconducting properties. Thick nanocomposite films, up to 0,8 µm, have been prepared with a single deposition of low-fluorine solutions using an Ink-Jet Printing dispenser and we demonstrate that the preformed nanoparticles display only a very limited coarsening during the growth process and so high critical current densities J c (B) under high magnetic fields. These films show the highest critical currents achieved so far based on the colloidal solution approach, I c = 220 A/cm-w at 77 K and self-field, and they still have a high potential for further increase of the film thickness. Finally, we also show that nanocomposite YBa 2 Cu 3 O 7-BaZrO 3 coated conductors based on Alternating Beam Assisted Deposited YSZ buffer layer on Stainless Steel metallic substrates can be developed based on these novel colloidal solutions. Non-reactive preformed oxide perovskite nanoparticles are therefore very promising elements to further advance the colloidal solution approach in the implementation of low-cost and high-performance coated conductors for high magnetic field applications.

Pyrolysis transformations, wrinkling and cracking, of thick solution-derived epitaxial superconducting YBa₂Cu₃O₇ films are disclosed through in situ analytical studies.

Inkjet printing (IJP) is a very appealing cost-effective deposition technique to achieve large-area solution-derived functional films. For many applications, it is very challenging to increase the film thickness in order to achieve competitive performance, for instance, high critical currents in superconducting films. In this paper, the preparation of superconducting YBa2Cu3O7 thick films (∼1.1 μm) using a single deposition is reported. Specific rules for ink design, deposition protocols, and pyrolysis processes are provided. The most important aspect is to formulate an ink with a solvent having a high boiling point that keeps the whole film wet during deposition to avoid liquid movement due to coffee-ring effects. An additional success has been to modify the ink with a photocurable polyacrylic ester varnish which after polymerization with a UV LED lamp helps keep homogeneous thickness. This varnish also helped avoid the generation of film instabilities (wrinkling or cracking) during pyrolysis. Homogeneous pyrolyzed thick films are transformed into epitaxial thick films with high critical currents. The IJP process is shown to be valid to prepare nanocomposite films using colloidal inks including pre-prepared BaZrO3 nanoparticles. The nanocomposite thick films display enhanced vortex pinning, thus keeping high critical currents under high magnetic fields.

High-performing superconducting YBa2Cu3O7–x (YBCO) films are fabricated by a chemical solution deposition methodology through novel barium-deficient low-fluorine solutions. The precursor solutions, distinguished for being straightforward, inexpensive and eco-friendly, allow us to reduce the growing temperature of YBCO down to 750 °C. We investigated the influence of the growing temperatures on both the microstructure and superconducting properties of YBCO films by using conventional thermal annealing and flash-heating approaches. A clear correlation between the growing temperature (Tg) and the superconducting performance of the films was obtained with improved performances observed at low Tg.

Cuprate coated conductors are promising materials for the development of large-scale applications, having superior performances over other superconductors. Tailoring their vortex pinning landscape through nanostructure engineering is one of the major challenges to fulfil the specific application requirements. In this work we have studied the influence of the growth temperature on the generation of intrinsic pinning defects in YBa2Cu3O7-δ (YBCO) films grown by chemical solution deposition using low Ba precursor solutions. We have analysed the critical current density as a function of the temperature, applied magnetic field magnitude and orientation, Jc(T,H,θ), to elucidate the nature and strength of pinning sites and correlate the microstructure of the films with their superconducting performance. An efficient pinning landscape consisting of stacking faults and associated nanostrain is naturally induced by simply tuning the growth temperature without the need to add artificial pinning sites. Samples grown at an optimized temperature of 750°C show very high self-field Jc values correlated with an overdoped state and improved Jc(T,H,θ) performances.