Mechanical and electrical characteristics of silver stabilizer layer prepared by using nano silver paste for coated conductor J.B. Lee a , S.U. Lee b , S.S. Kim b , B.J. Kim a , H.J. Kim a , Y.S. Yoo a , J.G. Kim c , G.W. Hong a,c , H.G. Lee a, * a Graduate School of Knowledge-Based-Technology and Energy, Korea Polytechnic University, 2121 Jungwang-dong, Siheung-si, Kyonggi-do 429-793, Republic of Korea b CMS TECHNOLOGY INC., 8-5BL, Jiksan-eup, Mosi-ri, Cheonan-si, Chungnam, 330-314, Republic of Korea c Institute for Superconducting and Electronic materials, University of Wollongong, Wollongong NSW2522, Australia article info Article history: Available online 6 June 2009 PACS: 74.25.Sv 74.72.Bk 74.78.Bz 81.70.Bt 81.07.Wx Keywords: Nano silver paste Stabilizer layer Coated conductor YBCO abstract Mechanical and electrical properties of silver stabilizer layer of coated conductor, which was prepared using nano silver paste as starting materials, have been investigated. Nano silver paste was coated on YBCO (Y 1 Ba 2 Cu 3 O 7Àd ) film by a dip coating method with a speed of 25 mm/min. Coated film was dried in air and heat treated at 400–700 °C in a flowing oxygen atmosphere. Adhesion strength between YBCO and silver layer was measured by Tape test (ASTM D 3359). The hardness and electrical conductivity of the sample were measured by pencil hardness test (ASTM D 3363). Surface and volume resistance were measured by using LORESTA-GP (MITSUBISHI). The sample heat treated at 500 °C showed poor adhesive- ness of 1B but it is clearly enhanced to 5B when samples were heat treated at higher than 600 °C. The silver layer heat treated at 700 °C showed a high hardness value of higher than 9H and a volume resis- tance of 1.417 Â 10 À7 X mm at room temperature. SEM observations showed that a dense silver layer was formed with a thickness of about 2 lm. Dip coated silver layer prepared by using nano silver paste showed superior electrical and mechanical characteristics which is comparable to those that sputter deposited Ag layer. Ó 2009 Elsevier B.V. All rights reserved. 1. Introduction Coated conductor is expected to be used widely as electric wire for the application in electric power devices due to its superior electric current carrying capacity even under magnetic field at a boiling temperature of liquid nitrogen. For the commercialization of coated conductor, there are three key elements to be solved; (1) fabrication of long-length wire with high critical current (I c ), (2) low ac loss, high I c under high magnetic field and (3) high pro- ductivity and low cost. In order to achieve those issues, intensive research and development efforts have been made and long-length coated conductor with high performance has been realized by SuperPower Inc. [1]. The high I c under high magnetic field and the anisotropy has been achieved by incorporation of second phase particles [2–4] and partial or complete substitution of yttrium by light rare earth elements [4–6]. Low ac loss of coated conductor has been decreased by reducing the width of superconducting layer using laser, photolithography and scalpel [7–9]. On the other hand, a wind-and-flip technique has been introduced for the fabri- cation of a persistent mode magnet which is essential for the appli- cation of MRI (Magnetic Resonance Imaging) and NMR (Nuclear Magnetic Resonance) [10]. Fabrication of coated conductor contains a various processing steps such as polishing of metallic substrate, texturization of metal substrate or ceramic buffer, epitaxial deposition of cap layer, epi- taxial deposition of YBCO superconducting layer, silver deposition by sputtering, electrodeposition or soldering of copper layer. Therefore, it is not easy to achieve high productivities in all the above processing steps. However, on the long run, SuperPower Inc. has achieved high production speed of over 100 m/h in all important processes [1]. Even though there have been so big progresses in the develop- ment of production technologies, the efforts for the development of alternative processing techniques in order to reduce the produc- tion and capital cost are also very important for the fabrication of low cost coated conductor. For instance, silver stabilizer layer with a thickness of 1–3 lm is provided by using sputtering method in order to get low contact resistance and provide bottom layer for the electrodeposition of copper layer [11]. Coated conductor sur- rounded by copper electroplating is advantageous in being used at high voltage due to its round corner. For the electrodeposition of copper, double side deposition of silver layers is preferable. Nano silver paste is an important substance to give both of good electrical conductivity and adhesion for various devices [12]. 0921-4534/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.physc.2009.05.250 * Corresponding author. Tel.: +82 031 8041 0586; fax: +82 031 8041 0599. E-mail address: hglee@kpu.ac.kr (H.G. Lee). Physica C 469 (2009) 952–955 Contents lists available at ScienceDirect Physica C journal homepage: www.elsevier.com/locate/physc