PRZEGLĄD ELEKTROTECHNICZNY (Electrical Review), ISSN 0033-2097, R. 88 NR 7a/2012 161 Katarzyna L. JUDA 1 , Mariusz WOŹNIAK 1 , Mariusz MOSIADZ 1 , Simon C. HOPKINS 1 , Bartłomiej A. GŁOWACKI 1,2 , Tadeusz JANOWSKI 3 University of Cambridge (1), Institute of Power Engineering (2), Lublin University of Technology (3) Superconducting properties of YBCO coated conductors produced by inkjet printing Abstract. Current methods of producing YBa 2 Cu 3 O 7-δ coated conductors (YBCO CC) require expensive processing. A new technology combining chemical solution deposition (TFA-MOD) with inkjet printing, demonstrated successfully in this paper as confirmed by Hall probe magnetometry, shows considerable potential as a cost-effective replacement. The flexible control of ink stoichiometry and rheology, and the ease of introducing additions, offered by CSD inkjet printing has the potential to reduce the strong I c anisotropy of YBCO CCs revealed by goniometric I c measurements. Streszczenie. Nowa technologia produkcji nadprzewodzących taśm YBa 2 Cu 3 O 7-δ , łącząca procedurę chemicznej depozycji roztworu za pomocą drukowania, ma szansę zastąpić obecne, kosztowne metody produkcji. Pomiar magnetometryczny czujnikiem Halla potwierdził nadprzewodnictwo próbki YBCO otrzymanej wyżej wymienioną metodą, która umożliwia łatwą kontrolę stechiometrii i reologii roztworu, a także wprowadzanie dodatkowych komponentów, mających na celu redukcję silnej anizotropii I c w filmach YBCO, ukazanej przez pomiar goniometryczny. (Nadprzewodzące właściwości taśm YBCO otrzymanych metodą drukowania roztworu). Keywords: YBCO, sol-gel, Hall probe measurement, goniometric measurement. Słowa kluczowe: YBCO, sol-gel, pomiar czujnikiem Halla, pomiar goniometryczny. Introduction The current methods of producing YBa 2 Cu 3 O 7-δ coated conductors (YBCO CC) require expensive equipment and often vacuum conditions. An especially promising new chemical solution deposition (CSD) technology combining sol-gel synthesis, based on the trifluoroacetate metalorganic deposition (TFA-MOD) route, with inkjet printing, presents clear opportunities for industrial application. The method enables the controllable deposition of liquid sol on the metallic substrate and does not require expensive equipment and vacuum conditions, significantly decreasing manufacturing costs [1]. Because of the anisotropic properties of superconducting YBCO, the dependence of its superconducting properties on oxygen content, and the weak grain boundaries which impede critical current transport, the deposition and subsequent heat treatment of the YBCO ink must be optimised to obtain a crystallographically well textured and superconducting film. After optimising processing parameters, the YBCO CC obtained from this TFA-MOD route was confirmed to be superconducting by scanning Hall probe magnetometry. Goniometric critical current measurements performed on commercially available YBCO CC indicate a new direction of research towards controlling the anisotropy of this superconductor, as the sol-gel method enables flexible control of the ink stoichiometry and rheology. Experimental The YBCO precursor ink was prepared using the trifluoroacetate (TFA) route, from YBa 2 Cu 3 O 6.9 powder (SSC Inc.) previously desiccated in a vacuum furnace at 150 °C for 24 h. Anhydrous acetone was mixed with the YBCO powder in the ratio of 15 cm 3 to 3 g. Trifluoroacetic acid (TFAH) was added drop-wise under stirring at room temperature in 10 vol. % excess to the stoichiometric molar ratio of 13:1 (Reaction 1) to ensure full reaction of the YBCO powder. The reaction was run for 24 h at 85 ºC in an N 2 atmosphere. The resulting blue solution was cooled to room temperature and a stoichiometric amount of trifluoroacetate anhydride (TFAA), according to reaction (2), was added drop-wise. The solution was kept for approximately 1 h at 85 ºC (until it became clear and green). Subsequently the resulting green solution was mixed with anhydrous methanol and heated under vacuum in a rotary evaporator three times in turn, at a temperature ranging between 65 and 80 ºC. This product was diluted to the appropriate concentration with anhydrous methanol, resulting in a clear green solution, passed through a 1 μm glass microfibre filter and sealed in a vial under a nitrogen atmosphere. Stored in this way, the ink remained stable and suitable for printing for several months. (1) YBa 2 Cu 3 O 7-δ + 13 TFAH → Y(TFA) 3 + 2 Ba(TFA) 2 + 3 Cu(TFA) 2 + 6.5 H 2 O (2) 6.5 H 2 O + 6.5 TFAA → 13 TFAH Fig.1. Schematic of the drop on demand inkjet printing system with electromagnetic nozzle. To print continuous tracks, the drivers are set to deliver pulses of current at a rate synchronised with the positioning system velocity. The prepared ink was deposited on a Ni-5%W rolling-assisted biaxially textured substrate (RABiTS) with a double La 2 Zr 2 O 7 (LZO) buffer layer and a single CeO 2 cap layer (Ni-5%W/2LZO/CeO 2 ) provided by Zenergy Power GmbH (Germany). The buffered tape was cleaned with ethanol for 3 min and additionally with isopropanol or acetone for 3 min in an ultrasonic bath before each deposition, and used as soon as possible to prevent degradation of the wettability. The ink was deposited on the substrate by means of drop on demand printing using an electromagnetic nozzle (a solenoid micro-valve modified from a Domino MacroJet printer) and other equipment schematically presented in Figure 1. After outgassing, the YBCO ink was supplied to the nozzle from a reservoir under