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SUPERCONDUCTING

YBa 2 Cu 3 O7 _x THIN FILM ON METAL CHEMICAL VAPOR DEPOSITION PROCESS.

SUBSTRATE

BY

T.YAMAGUCHI, S.AOKI, N.SADAKATA, and O.KOHNO Fujikura Ltd., 1-5-1, Kiba, Koto-ku, Tokyo 135, Japan

ABSTRACT Superconducting YBa 2 Cu 3 07_x thin films were prepared by chemical vapor deposition using beta-diketonate chelates on various oxide substrates and metal substrates. According to X-ray diffraction patterns, the existence of a well-oriented orthorhombic YBa 2Cu 3 07_x structure has been confirmed in all specimens. The temperature of complete superconducting transition were observed at 89K on single-crystalline oxide substrate, and 84K on metal substrate. Reduced critical current density of the film on single-crystalline substrate in magnetic fields up to 600mT at 77K remained one or two order of magnitude higher than that of the film on metal substrate.

INTRODUCTION Since the discovery of the high-Tc superconducting materials in 1986, A number of technique have been established to prepare the thin films on single-crystalline substrates [1-3]. The use of the high-Tc superconductor for conductor requires rapid formation of the film with excellent critical parameter on various substrates. Chemical vapor deposition method has a great advantage in this viewpoint. The use of high-Tc superconducting materials for application has been eagerly expected though the materials has some intrinsic properties like anisotropic current flow and weak links at grain boundaries which may greatly reduce Jc" Thin film fabricating method are attractive because highly oriented or even single-crystalline films could be obtained. In particular, chemical vapor deposition process is promising because its deposition rate is superior to the other thin film processes. In this paper, we report the preparation procedure and properties of superconducting YBa 2 Cu 3 o 7 _x (YBCO) thin films on oxide or metal substrates using beta-diketonate chelates.

EXPERIMENTAL The source materials that have sufficient vapor pressure are necessary to realize the chemical vapor deposition method. At first, we searched these volatile compounds of Y, Ba and Cu and not containing halogen elements in order to obtaining the controllable vapor phases and pure oxide films. At present, we judge that beta-diketon chelates without halogen elements, so called (thd) complexes of 2,2,6,6-tetramethyl-3,5heptanedione -yttrium (Y(thd) 3 ), -barium (Ba(thd) 2 ) and -copper (Cu(thd) 2 ) are the most suitable for chemical vapor deposition of YBCO. Mat. Res. Soc. Symp. Proc. Vol. 169. 1990 Materials Research Society

598

At the beginning of this study, we measured thermochemical behavior of several metal chelates with beta-diketon ligand by thermogravimetry (TG) and differential thermal analysis (DTA). The temperature dependence of vaporizing rate of the source materials proved the vaporizing temperature for Y, Ba and Cu at 110-1350 C, 190-240 0 C and 120-130)C respectively. Figure 1 shows a configuration for chemical vapor deposition used in this experiment. Source materi