Elsevier

Thin Solid Films

Volume 495, Issues 1–2, 20 January 2006, Pages 78-81
Thin Solid Films

High-Tc superconducting thin film from bismuth cuprate nano-colloids

https://doi.org/10.1016/j.tsf.2005.08.304Get rights and content

Abstract

With the colloidal suspension of superconducting nanoparticles as a precursor, we have successfully fabricated well-oriented high-Tc superconducting Bi2Sr2CaCu2Oy films by an electrophoretic deposition method. The colloidal suspension of superconducting nanoparticles can be prepared by the exfoliation of Bi-based cuprates through the intercalation of long chain organic molecules. According to zeta potential measurement, the surface of the resulting nanosheets in an acetone solvent is positively charged with a potential of + 25 mV. Such a presence of surface charge allows us to apply the electrophoretic deposition process with a silver metal substrate. A post-annealing process for the as-deposited film improves significantly the electrical connectivity and the c-axis alignment of the superconductor grains. The thickness of the resulting films can be easily tuned by the control of deposition conditions such as an applied electrical potential and a deposition time.

Introduction

In the emerging field of nanotechnology, the exfoliation reaction of layered inorganic solids has attracted intense interest since it provides an effective way of preparing colloidal nanosheets and fabricating nanostructured materials such as nanohybrid, nanowires, nanosphere with them [1], [2]. Such an exfoliation process can be achieved through the intercalation of bulky guest species, leading to the minimization of interlayer interaction [3]. Due to the absence of interlayer interaction, the exfoliated monolayers are apt to form heterostructured materials with other compounds, deposit as a multiplayer film on a substrate, or experience a rolling process into nanorods or nanotubes for obtaining a lattice stabilization energy. In this regard, the intercalation−exfoliation reaction allows us to design and synthesize nanostructured materials or films at ambient temperature and pressure. Moreover, the intercalation reaction can induce some degree of modification in the geometric, chemical, electronic, and optical properties of host and guest [4], [5]. In this respect, an intercalation technique enables us to examine the validity of theoretical models predicting a role of dimensionality in the physicochemical properties of low dimensional materials [6]. Such a unique advantage of the intercalation method has expanded its application into diverse areas of solid state in materials sciences, including secondary batteries, electrochromic systems, oxidation−reduction catalysts, separating agents, sorbents, inorganic thin films, inorganic wires, and so on [6], [7], [8]. In particular, the intercalation chemistry of high-Tc superconducting (HTSC) copper oxides has received special attention since it can provide experimental tools to study the mechanism responsible for high temperature superconductivity of layered oxide and to fabricate HTSC thin films, as well. In fact, the exploration of economic method for high temperature superconducting film has been one of the most important goals in the HTSC researches [9]. Previously we have performed the systematic studies on the intercalation chemistry of Bi-based cuprates, leading to the synthesis of several new HTSC intercalation compounds [4], [5], [9], [10], [11], [12], [13], [14]. Especially we were able to develop a new series of inorganic−organic superconducting nanohybrids on the basis of an interlayer complexation concept [14]. In such intercalates, the interlayer distance of the superconductive CuO2 layer can be easily controlled by changing the number of atom in the intercalated organic chain. Hence, the intercalation of long-chain organic molecules can minimize the interaction between the cuprate building blocks, resulting in the exfoliation of superconducting lattice into isolated individual nanosheets. Such a colloidal suspension of superconducting nanoparticles can be a useful precursor for the fabrication of superconducting thin films [15].

In this paper, we report the fabrication of well-aligned HTSC Bi2Sr2CaCu2Oy (Bi2212) film through the electrophoretic deposition of colloidal suspension followed by a post-annealing process. Also, we have investigated the effect of deposition conditions like an applied electrical potential and a deposition period on the properties of the resulting films.

Section snippets

Experimental

The pristine Bi2212 sample was prepared by a conventional solid-state reaction, in which the stoichiometric mixture of Bi2O3, SrCO3, CaCO3, and CuO was calcined at 790 °C for 24 h and sintered at 840 °C for 48 h in ambient atmosphere. As illustrated in Fig. 1, the Bi2212 film was fabricated on the basis of the exfoliation−electrophoretic deposition method. First, HgI2-intercalation compound was obtained by heating a vacuum-sealed silica tube containing the pristine material and excess mercuric

Results and discussion

A schematic diagram for the exfoliation−deposition route to the HTSC Bi2212 film is illustrated in Fig. 1. In the first step, the organic salt, (Py-C12H25)2HgI4, was intercalated into the expanded interlayer space of HgI2-Bi2212 through an interlayer complexation reaction. The weak van der Waals interaction between the Bi2O2 layers in layered Bi-based cuprate superconductors allows these compounds to be good host materials for intercalation reaction. The X-ray diffraction (XRD) analyses

Conclusion

We were successful in fabricating well-oriented high-Tc superconducting Bi2212 film on the silver metal substrate by electrophoretic deposition of superconducting colloidal suspension. The exfoliation of bismuth cuprates could be achieved by the intercalation of long-chain organic molecules and followed by the subsequent sonication process. After post-annealing process of the as-deposited film, the well-aligned HTSC Bi2212 film could be fabricated without any non-superconducting impurity

Acknowledgment

This work is financially supported by a grant from the ETEP institute in Korea Electric Power Research Institute (KEDPRI) and partly by the Korean Ministry of Science and Technology through the STAR project. BK 21 fellowship for J.J.C. is also appreciated.

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