Ink-jet printing of YBa₂Cu₃O₇ superconducting coatings and patterns from aqueous solutions

ABSTRACTIn this paper, we combine the use of Drop-on-Demand (DOD) ink-jet printing with completely water- based inks as a novel approach to the CSD process for coated conductors. This method holds the promise of improved scalability due to lower ink losses, continuous processing and a drastically increased precursor lifetime due to the prevention of solvent evaporation and dust incorporation. Moreover, ink-jet printing has the potential to switch quite easily from continuous coatings to a multi-filamentary pattern, which is particularly important for alternating current (AC) or field applications of coated conductors. The fluid properties, often expressed with dimensionless constants, like the Reynolds and Weber numbers, for printable liquids were determined. For proof-of-concept, single crystals of SrTiO3 with a low mismatch towards YBCO, were used as substrates.</jats:p

Chemical solution deposition of functional ceramic coatings using ink-jet printing

This paper discusses the development of environmentally-friendly precursor inks suited for ink-jet printing of functional ceramic coatings. We synthesized superconducting materials, SrTiO3 thin films for coated conductor applications and transparent TiO2 photocatalytic coatings. Here, we discuss all aspects of ink formulation, including the stabilization of metal ions, nanoparticle inks or combination of both. This demands the investigation and determination of the inks rheological parameters. Ceramic nanoparticles are often incorporated in our inks to decrease thermal processing temperatures (e.g., TiO2 or YSZ coatings...) or enhance the properties of the functional ceramic coating (e.g., pinning centres in superconducting coatings). These ceramic nanoparticles (ZrO2, HfO2, TiO2...) are synthesized through methods based on microwave heating from aqueous and/or organic solutions. With that, we aim at developing smart and environmentally friendly processes that require lower energy input

Ink-jet printed BaTiO₃ for photonics

ABSTRACTA water-based BaTiO3 precursor solution, suited for ink-jet printing of hetero-epitaxial BaTiO3 layers on LaAlO3 single-crystal substrates was developed. First, a study on the simultaneous stabilization of Ba2+ and Ti4+ions in a neutral, aqueous environment was performed. Thermal analysis of the precursor was used to select appropriate temperature programs and the rheology of the solutions is studied to optimize dipcoating and later ink-jet printing parameters. On both substrates, it was possible to obtain epitaxial layers of about 200 nm thickness after sintering at temperatures above 1000 °C. Currently, we are adapting the thermal program and heating atmosphere in order to reduce the sintering temperatures, decrease the surface roughness and increase density.</jats:p

Fast, microwave-assisted synthesis of monodisperse HfO₂ nanoparticles

A conventional solvothermal synthesis was compared to a microwave-assisted method for the synthesis of HfO2 nanoparticles. In a microwave, the reaction could be completed in 3 h, compared to 3 days in an autoclave. In the microwave synthesis, the ensemble of particles was found to have a better size dispersion and a smaller average size (4 nm). The reaction mechanism was investigated and proof for an ether elimination process was provided. Post-synthetic modification with dopamine or dodecanoic acid permitted the suspension of the synthesized particles in both polar and apolar solvents, which is an advantage for further processing

Digitally printed superconducting coatings and patterns

The most suitable way to implement superconducting materials in large scale applications is as wires. To overcome the brittle nature of ceramic high-temperature superconductors and to increase the overall performance of the wire, a coated conductor design was developed. In this thesis, we focus on the development of ink-jet processing as a new technique for chemical solution deposition of Y(Gd)Ba2Cu3O7-δ [Y(Gd)BCO] coatings and patterns. For this, cheap and fluorine-free metal salts are used as starting products, which were dissolved in water. The research is mainly focused on the precursor’s chemical stability and printability. The addition of complexing agents is necessary to increase the total metal concentration. Still, an optimisation of the pH value is obligatory for a long shelf life of the precursor solution. A 0.185 mol L-1 YBCO ink with a viscosity of 4.77 mPa s and a surface tension of 67.9 mN m-1 was finally obtained. The printability of the solution is predicted using the ratio: Oh-1= Re/We1/2. With a value of 7.37, the ink’s properties fall within the printing value: 1< Oh-1 <10. After tuning the driving waveform, proper ink-jetting behaviour was visualised using a strobe assisted camera. The optimised deposition parameters resulted in a 350 nm thick YBCO coating, grown on SrTiO3, showing preferential c-axis orientation. This layer exhibits a critical current of 0.67 MA cm-2 at 77 K in self-field. After changing the deposition parameter, high-resolution patterns could be deposited on several substrates. The shape and dimensions of printed YBCO tracks were determined using optical microscopy and noncontact profilometry, showing 100 to 500 nm thick and 40 to 220 µm wide YBCO tracks

Ink-jet printing of aqueous inks for single-layer deposition of Al-doped ZnO thin films

In this article, Al-doped ZnO thin films deposited by a one single-layer approach are studied. An aqueous precursor solution was prepared for the deposition of Al-doped ZnO thin film via ink-jet printing. The physical properties of the ink were studied in detail by rheology measurement and drop visualization. The wetting of the ink with the substrate was studied by the use of wetting envelopes. A single layer of the ink was deposited on the substrate and fully processed. The thin films were studied by X-ray diffraction, scanning electron microscopy, resistivity measurements, and optical transmission measurements. The optimal dopant concentration was set at 3 at.%, which resulted in thin films with a resistivity of 2.54 c cm and an optical transmission larger than 90% over the visible range of the electromagnetic spectrum

Coated conductor synthesis through aqueous sol-gel chemistry

High temperature superconductors such as YBa2Cu3O7 (Tc=92 K) can't be produced in long lengths because of their brittle ceramic nature. Another problem in using bulk YBCO is the absence of texture, biaxial texture is necessary to assure the quality of the superconductor. A solution to both problems is presented by the coated conductor structure. This structure consists of a flexible metallic tape (Ni-5at%W) coated with multiple buffer layers (CeO2, La2Zr2O7) and a superconducting layer (YBa2Cu3O7). In contrast to the production of many coated conductors in the international research community, a cheaper non-vacuum technique, namely the sol-gel method is used in this work. Every layer is produced starting from an aqueous precursor solution containing the corresponding metal acetates and an organic complexing agent, such as triethanolamine. The acidity of the solution was adjusted by adding ammonium hydroxide order to obtain a clear and stable gel without precipitation. Potentiometric titrations allowed us to determine the complexation behaviour of the metalions in the gel. Using the SUPERQUAD and EQUIL software, pH-distribution curves could be generated. Through dip-coating, thin films were deposited on the substrate. At low temperatures (60°C) the solution is transformed into an amorphous gel. The crystalline and biaxially textured buffer layers are formed during a heat treatment at elevated temperatures (1000°C) under inert atmosphere (Ar-5%H2). The superconducting film was deposited on a cleaned SrTiO3 substrate and heat treated at temperatures of 815°C under nitrogen with 200 ppm oxygen. Characterisation of the morphology and microstructure of the thin films were carried out using XRD, pole figures, SEM, AFM and TEM. The buffer layers show good in an out-of-plane alignment and a smooth surface with little impurities. The superconducting film has a critical temperature of 89 K and shows a sharp transition from normal to superconducting phase