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ORIGINAL PAPER

Improved Fabrication of Electrophoretically Deposited Bi2 Sr2 CaCu2 O8 Films via Supporting Electrolyte Optimization in Ethanol M. M. Rosete1,2

· MA. H. Zosa3 · R. V. Sarmago4

Received: 24 April 2020 / Accepted: 2 September 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020

Abstract This paper describes the effect of the addition of supporting electrolytes sodium chloride (NaCl), potassium chloride (KCl), and lithium chloride (LiCl) on the stability of Bi2 Sr2 CaCu2 O8 (Bi-2212) suspension for improved electrophoretic deposition (EPD) of Bi-2212 films. The optimal concentrations are found to be 7.15, 5.21, and 8.09 wt% for NaCl, KCl, and LiCl, respectively. They exhibit characteristic high zeta potential, small particle size, and low settling velocity entailing that well-stabilized Bi-2212 suspensions are produced. The resulting films possess a relatively smooth surface, high transition temperature (Tc ), and high c-axis orientation. Further analysis shows that LiCl is the most suitable supporting electrolyte for the Bi-2212 suspension. The mechanism of action of this supporting electrolyte is influenced by the Hofmeister effects, which yields an electrostatic stabilization mechanism. The synthesized film using the optimal LiCl concentration demonstrates the highest Tc (87.25 K) and is c-axis oriented and well-textured. Keywords Superconductors · Films · Electrochemical techniques · Stabilization · Supporting electrolytes

1 Introduction The bismuth strontium calcium copper oxide (BSCCO) system is a popular member of the high transition temperature (Tc ) family of superconductors. Among the BSCCO compounds, Bi2 Sr2 CaCu2 O8 (Bi-2212) is particularly promising because of its chemical stability and ease of synthesis [1–4]. High-quality Bi-2212 films with high Tc s and smooth surfaces are of interest for various applications such as superconducting quantum interference devices (SQUIDs), terahertz radiation sources, and Josephson junctions [5– 8]. The electrophoretic deposition (EPD) technique which  M. M. Rosete

[email protected] 1

Department of Mining, Metallurgical and Materials Engineering, College of Engineering, University of the Philippines Diliman, 1101, Quezon City, Philippines

2

Materials Science and Engineering Program, University of the Philippines, Diliman, 1101, Quezon City, Philippines

3

Institute of Laser Engineering, Osaka University, 2-6 Yamadaoka, Suita, Osaka, 565-0871, Japan

4

National Institute of Physics, University of the Philippines Diliman, 1101, Quezon City, Philippines

preferably uses non-aqueous media for suspension preparation has been used to produce Bi-2212 films [9]. A stable Bi-2212 suspension has a significant influence on the quality of Bi-2212 films. Stable suspensions are generally characterized by a zeta potential of at least ±30 mV [10–13]. The two basic mechanisms that result in the stabilization of a suspension are electrostatic stabilization, which is described by the theory of Derjaguin, Landau, Verwey, and Overbeek (DLVO)