Preparation of Fibrous Bi(Pb)-Sr-Ca-Cu-O Crystals Containing the High-T c Phase
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PREPARATION OF FIBROUS Bi(Pb)-Sr-Ca-Cu-O CRYSTALS CONTAINING THE HIGH-Tc PHASE I. MATSUBARA, H. TANIGAWA, T. OGURA, H. YAMASHITA, M. KINOSHITA AND T. KAWAI+ Government Industrial Research Institute, Osaka Midorigaoka, Ikeda, Osaka 563, Japan +The Institute of Scientific and Industrial Research, Osaka University, Ibaraki, Osaka 567, Japan
ABSTRACT Fibrous crystals containing the high-Tc phase (2223 phase) of the Bi(Pb)-Sr-Ca-Cu-O superconductor have been prepared by heating a glassy meltquenched plate in a stream of oxygen gas. Each fiber is composed of several platelike single crystals which are stacked in a layered structure. The fibers show two stepdrops in resistance at 105K and 73K, and a zeroresistance state around 70K. From the results of SQUID measurements, the volume fraction of the high-Tc phase is found to be about 0.6%. The high-Tc phase is also detected with a microarea X-ray diffractometer, and it is stacked in the interlayer between the low-Tc platelike crystals. For the fibrous Bi-Sr-Ca-Cu-Li-O crystals, the volume fraction of the high-Tc phase increases to 1.5% and a zero resistance state is achieved at 81K. The J 2 value of the Li doped fiber is 30,OOOA/cm at 77K and 300,000A/cm2 at 66K in a zero magnetic field.
INTRODUCTION It is well known that the Bi-Sr-Ca-Cu-O superconductor has two different phases: one is Bi 2 Sr 2 CaCu 2 Ox(low-Tc phase, Tc=80K) and the other is Bi 2 Sr 2 Ca 2 Cu 3 Ox (high-T phase, Tc=IIOK)[I]. Since the discovery of the Bi system superconductor? 2], many studies to obtain a pure 110K phase (high-Tc phase) have been carried out. Single phase, high-Tc material was obtained by substituting Pb for Bi(3] and by reacting under low oxygen pressure[4]. We have reported that Bi(Pb)-Sr-Ca-Cu-O whiskers which mainly have the 2212 structure with a zero resistance at 70K are formed by heating a melt quenched plate in a stream of 02 gas[5,6J. From measurements of the temperature dependence of the resistivity, some whiskers were found to show a resistance drop at 105K suggesting the presence of the high-Tc phase. In this report, we determine where the high-Tc phase exists in the whisker and the volume fraction of this phase. Further, the effects of Li-doping on the resulting phases and superconductivity of the crystals are also examined.
EXPERIMENTAL Bi 2 0 3 , SrCO3 , CaCO 3 , CuO and PbO or Li 2 CO 3 powders were mixed with appropriate compositions in a ball mill and the mixed powder was melted in an alumina crucible at 1200 t for 30 minutes in an electric furnace in air. The melts were poured onto a steel plate and were pressed quickly. The thickness of the resulting quenched, glassy plate was approximately 1.0mm. The glassy plates were heated on an alumina boat at 840°C for 120h in a stream of 0 2 (150ml/min) and were cooled to room temperature in the furnace. Whiskers grew perpendicular to the surface of the quenched plates. The temperature dependence of the resistance and the critical current density (Jc) was measured by a standard four-probe method. Phase determination was carr
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