Elucidation of YBCO Growth Mechanism in KOH Flux Method
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ORIGINAL PAPER
Elucidation of YBCO Growth Mechanism in KOH Flux Method Hongbin Zhou 1 & Mengmei Chu 1 & Jing Chen 1 & Hongmei Zhu 1 & Zhiyong Liu 1,2 & Chuanbing Cai 1,2 & Minjuan Li 1 & Difan Zhou 1 Received: 22 January 2020 / Accepted: 4 September 2020 # Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract In this work, we present an extremely low-temperature (600 °C) liquid-phase synthesis method using KOH as flux to grow YBCO powder and epitaxial films. Oxides utilize solution medium KOH in which target materials are generated by cation’s physical and chemical transformations. Y123 and Y124 films could be synthesized by controlling configuration which is related to oxygen diffusion. Later, the process and mechanism of YBCO growth will be elucidated by DSC. In the presence of KOH, the decarboxylation of BaCO3 is kinetically favored with the formation of Ba (OH)2 at the first step, the same as Y2O3 and CuO. Above 350 °C, the formation of Y2Cu2O5 will take precedence over Ba2Cu3O5 due to the weak solubility of Y3+ and Cu2+ in molten KOH. With temperature increasing, liquid Ba(OH)2 begins to dehydrate, and Ba2+ subsequently reacts with Y3+ and Cu2+ to precipitate YBCO in the last step. Molten KOH provides a liquid chemical environment, which allows the synthesis of YBCO at low temperature. This low-temperature method is applicable to epitaxial superconductor and superconducting joint. Keywords YBCO . KOH flux method . Low-temperature synthesis . Process and mechanism of YBCO formation
1 Introduction The growth of high-temperature superconductor YBCO crystal and film has been widely studied over 30 years by various techniques, for example, pulsed laser deposition [1], metal organic deposition (MOD) [2], and conventional ceramic process [3], and most of them are fabricated above 750 °C [4]. Although film fabrication takes a lower crystallization temperature on LaAlO3 substrate than bulk synthesis, unfortunately, there is no evidence that YBCO could be achieved at a lower temperature 600 °C, except for the hydroxide flux method [5–9] which has been used to prepare other perovskite crystal at low temperature [10–23]. Materials in liquid phase utilize a solution medium to chemically and physically deliver cations to
* Hongmei Zhu [email protected] * Chuanbing Cai [email protected] 1
Shanghai Key Laboratory of High Temperature Superconductors, Physics Department, Shanghai University, 99 Shangda Road, Shanghai 200444, China
2
Shanghai Creative Superconductor Technologies Co. Ltd., Shanghai 201401, China
generate target materials [24]. Compared with conventional ceramic synthesis which takes a long reaction duration restricted by slow diffusion of the reactants, flux method lowers the process temperature as it allows cations to move freely in liquid. David Sandford et al. first tried molten hydroxide (NaOH, KOH) to precipitate EuBa2Cu4O8 at 475 °C in 5 h, which significantly lowers the reaction temperature and annealing time compared with traditional solid-state reaction and other fl
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