In-Situ Preparations and Properties of High Tc Ybco Poly-Crystalline Thin Films
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IN-SITU PREPARATIONS AND PROPERTIES OF HIGH Tc YBCO POLY-CRYSTALLINE THIN FILMS
N.HARADA, K.SATO, K.YAMAMOTO The Furukawa Electric Co., Ltd., 2-4-3, Nishi-ku, Yokohama 220 Japan
Okano,
ABSTRACT Highly oriented YBCO films were produced on MgO(100) single crystal substrates. The direction of c axis was perpendicular to the film plane, whereas those of a and b axes were at random directions. The critical current density of the films was significantly high ca. 7x10W A/cm2 . The critical transition temperature (Tc) of the YBCO film formed on a metal substrate, predeposited with YSZ as a buffer layer, was similar to those of the YBCO on MgO substrate. The possibility for the formation of superconductor films on metal substrates is suggested from these results. INTRODUCTION In order to fabricate a high Tc superconductor film on a metal substrate, the following key points have been presented; (a) lattice matching between film and substrate, (b) smoothness of the substrate surface, and (c) interdiffusion of the metallic elements from the substrate into the film." 1 ) The techniques on the preparation of superconductor films at low temperature and the introduction of a buffer layer are needed to avoid these problems. In the present study, the YBCO films were prepared on both the MgO(100) single crystal and Ni-alloy (Hastelloy) with buffer layer by the co-evapolation technique. The surface morphology and electric properties of these films were evaluated by SEM, TEM and four-probe. FILM PREPARATION Figure 1 shows a schematic diagram of the co-evapolation system. Y and Ba metals were evaporated by heating with electron beam gun and the heating of Cu metal was made electrically. The substrate of MgO(100) single crystal was kept at 650-750 "C in the atmosphere
of
ozone
at 10-5
-
10-3 Torr during the film growth. After the deposition, ozone gas was introduced gradu-
Figure 1. Schematic figure of multi-source evaporation apparatus
Mat. Res. Soc. Symp. Proc. Vol. 169. O1990 Materials Research Society
676
ally up to ca. 2 Torr, and then the substrate heater was turned off in order to promote the oxidation of the deposited metal elements. MORPHOLOGY AND ELECTRIC PROPERI diffractio The X-ray pattern (XRD) of the deposite film is shown in Fig.2. Typica (001) diffraction related t were clearl YBCO structure observed. The film is highl oriented to the direction of axis perpendicular to the fil plane. Figure 3 shows the re sults of TEM observation an electron diffraction pattern which indicates the produce film to be poly-crystallin structure with random a and axes. R-T and Jc-B propertie Fig.4 and 5, re are shown in spectively. The Tc and Jc values, 85K and 7x105' A/cm2 , were obtained for the YBCO film at 77K Excellent and 0 tesla. superconducting properties are demonstrated for the poly-crystalline YBCO film
20
40
60
CuKa 20(deg)
Figure 2. X-ray diffraction pattern of YBCO film
with random a and b axes.
(a) BUFFER LAYER PREPARATION
o2v.
(b)
Figure 3. (a)TEM observation and (b)electron diffraction pattern of the YB
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