Advances in sustainable fluorine-free CSD YBa 2 Cu 3 O 7 thin films
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Advances in sustainable fluorine-free CSD YBa2Cu3O7 thin films Pieter Vermeir1,2, Jonas Feys2, Glenn Pollefeyt2, Bram Verslyppe1, Asha De Brabandere1, Kim Verbeken3, Michael Bäcker4, Petra Lommens2, Joseph Schaubroeck1, Klaartje De Buysser2 and Isabel Van Driessche2 1 University College Ghent, Faculty of Applied Engineering sciences, Belgium. 2 Ghent University, Department of Inorganic and physical chemistry, Belgium. 3 Ghent University, Department of Materials Science and Engineering, Belgium. 4 Deutsche Nanoschicht, Germany. ABSTRACT Chemical solution deposition techniques are a very competitive low cost method to achieve coated conductors. Recently, fluorine-free CSD methods have made a great progress for the preparation of YBCO thin films and became a sustainable alternative for the well-known trifluoroacetate CSD approach. By elucidating the reaction mechanism behind this new approach, finally giving an answer to the question why it is possible to fabricate YBCO films without TFA, different processing routes were discovered giving rise to high superconducting YBCO films (>1MA.cm-2). Each route has it's own benefits. One specific route offers the opportunity to tune the crystallographic orientation. By changing one process parameter, a shift from complete c-axis to complete a-axis orientation is observed. This can be very useful for e.g. Josephson Junctions. We particularly investigated the fundamental reaction mechanism of each reaction route, with the focus on the corresponding barium compound. Although good superconducting properties are obtained, still one major drawback limits industrial implementation: thickness. It is observed that a critical thickness of ~500 nm eliminates the superconducting properties. Therefore, this paper gives a summary of all progress made regarding to fluorine-free waterbased CSD YBCO thin films with emphasis on the possibility to control the crystallization rate. INTRODUCTION Since the discovery of the so-called high-temperature superconductors, cheap liquid nitrogen (77K) could be used as a cooling agent raising the economical feasibility of many applications to a realistic level [1]. A major application territory is the production of superconducting cables enabling heat losses during transportation of current [2]. Currently, all high-temperature superconductors are ceramic materials which are inherently very brittle of nature. When used as bulk material, this characteristic hampers easy operability within practical cable applications (flexibility). To overcome this difficulty, coated conductors were introduced [3,4]. A coated conductor is a composition of a thin superconducting layer deposited on a flexible substrate template. For coated conductor designs, the most promising high-temperature superconducting ceramic is YBa2Cu3O7 (YBCO) [5]. The most common techniques to deposit YBCO on the substrate template require expensive vacuum equipment and are limited in production speed [6]. An alternative for this vacuum technology lies in synthesizing a layer by coating a metal-contain
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