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.
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.
We have developed a new method to measure the viscosity of micrometric films by thermomechanical analysis with a hemispherical probe of millimetric diameter. The loading curve (displacement vs. time) recorded as the probe tip crosses the whole film at constant load until it touches the substrate is fitted to a theoretical curve shape that has been obtained after solving the problem of liquid flow under the probe tip. The method has been validated by measuring the viscosity of rosin films. It has been applied to analyze the thermal evolution of unstable liquid films that appear on Ba propionate, Ce(III) propionate and a low-fluorine precursor film of YBa2Cu3O6+x. During pyrolysis of the last two films, viscosity first diminishes due to heating and then it increases as solid oxide particles are formed inside the liquid.
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