Kinetic Study Of High Tc Bi-Pb-Sr-Ca-Cu-O System
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KINETIC STUDY OF HIGH Tc Bi-Pb-Sr-Ca-Cu-O SYSTEM W.-M. Hurng, F. Wu and P.
Y. T.
T. Huang, Wu
C.
Y.
Shei,
C.
Chiang,
H.
S.
Materials Research Laboratories, Industrial Technology Research Institute, Chutung, Hsinchu, 31015, Taiwan, R.
Koo,
S.
0. C.
ABSTRACT By studying the Bi-Pb-Sr-Ca-Cu-O system, we have found that the sintering time to form high Tc Bi-Pb-Sr-Ca-Cu-O systems was quite different as the compositions of the starting materials varied. Especially, the ratio of Sr/Ca played an important role in determining the sintering time. DTA study already showed that partial melting occurred during the reaction. The temperature of the partial melting was also related to the ratio of Sr/Ca. Our results supported the existence of a reactive liquid phase in sintering process. INTRODUCTION In the Bi-Sr-Ca-Cu-O system, two phases always coexisted; Bi2Sr 2 .xCa1xCU 2 Oy (Tc z 84 K and denoted as 2212) and Bi Sr 2 Ca Cu 3 0 (rc z 110K and denoted as 2223) [1,2]. It is diificuit to obtain a pure 2223 phase. A couple of methods were developed to yield the 2223 phase without the disturbance of 2212 including; varying the nominal compositions [3], using reduced oxygen atmosphere [4] and substituting part of the Bi with Pb [5]. Nevertheless, it always took more than sixty hours to complete sintering process [6]. We have found that the sintering time can be reduced down to twenty hours to form 2223 by varying the Sr/Ca ratio as Pb substitution is adopted and extra CuO added [7]. The real cause in shortening the sintering time was believed to be related to formation of a transient liquid phase during the 2223 formation process. In this paper, the thermal analysis of a series nominal compositions with different Sr/Ca ratio was conducted to reveal the influence in sintering time and liquid phase formation. EXPERIMENTAL A series of samples Bi1.7Pb04Sr2.xCa2÷xCU360v (x = 0.0, 0.2, 0.4, 0.6, 0.8) were prepared by mixing and grinding stoichiometric Bi 203 , PbO, SrCO3, CaC0 3 and CuO together. After calcined at 810°C in air for 30 hours with one intermediate grinding, the samples were pressed into disk like pellets. The sintering temperature was set within 840°C to 870°C
(±0.5-C).
X-ray diffraction patterns were taken using a Phillips APD1700 diffractometer with Cu Ka radiation to identify calcined or sintered products and estimate the relative yields between the 2212 and 2223 phases. For ease of comparison, the (0010) reflection of 2223 (occurred at 20 = 23.9° and abbreviated as H(0010)) and the neighboring (008) reflection of 2212 (appeared at 20 = 23.1° and abbreviated as L(008)) were utilized to evaluate the relative yield between these two Mat. Res. Soc. Symp. Proc. Vol. 180. @1990 Materials Research Society
926
phases. Differential Thermal Analysis (DTA) study of the calcined samples was carried out using a ULVAC 7000 The density of the pellets was also measured thermalanalyzer. by using absolute ethanol as solvent. RESULTS AND DISCUSSION To accurately determine the optimal condition as x increased from 0.0 to 1
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