An investigation of the invariant reactions in the BiPbSrCaCuO system
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An investigation of the invariant reactions in the BiPbSrCaCuO system Libin Liu and Zhanpeng Jin Department of Materials Science and Engineering, Central South University of Technology, Changsha, Hunan 410083, People’s Republic of China (Received 14 December 1994; accepted 23 May 1996)
The phases present around the (Bi, Pb)2 Sr2 Ca2 Cu3 Ox (2223) phase between 830–880 ±C have been studied by x-ray diffraction (XRD) and electron probe microanalysis (EPMA) methods. The decomposition and melting temperatures of the 2223 phase in these samples have been measured by the differential thermal analysis (DTA) method. Partial substitution of Bi with Pb (Pb : Bi 3 : 22) does not change the 850 ±C phase relations around 2223 phase. 2223 decomposes to liquid, Sr7 Ca7 Cu24 O41 (7724), and Ca2 CuO3 at 875 ±C. The invariant reactions (degree of freedom is zero) among 2223, 7724, Ca2 CuO3 , CuO, Bi2 Sr2 CaCu2 O8 (2212), and liquid were proposed to be L 1 7724 1 Ca2 CuO3 ! 2223 1 2212, L 1 7724 1 Ca2 CuO3 ! 2223 1 CuO, L 1 7724 ! 2223 1 2212 1 CuO. The reaction temperatures were estimated to be 860 ±C, 860 ±C, and 854 ±C, respectively. An invariant reaction scheme and a tentative liquidus projection were sketched out.
I. INTRODUCTION
Since the discovery of high temperature superconductivity in the Bi(Pb)SrCaCuO system,1 much effort has been made in the determination of the phase diagram of this system, and many phase diagram data have been obtained. These results mainly concern (i) the isothermal section of quasiquaternary2–4 and quasiternary phase diagrams3–6 (usually in the subsolidus range), (ii) the quasibinary phase diagrams,5–7 (iii) the composition range of superconductor phases,8,9 and (iv) more detailed studies of certain compositions of interest.10–14 But, up until now, the phase diagram in the vicinity of the (Bi, Pb)2 Sr2 Ca2 Cu3 O10–y) (2223) phase and in the interesting temperature range 830 –880 ±C is still not clear enough to be used to explain the formation mechanism of the 2223 phase and guide its synthesis. Only a Bi1.6 Pb0.4 Sr2 CuO6 –CaCuO2 isopleth was reported by Strobel et al.16 No general agreement has been reached about the decomposition reaction of the 2223 phase. The whole invariant reaction series between 2223 and its adjoining phases has not been published. No liquidus fields of 2223 and its adjoining phases have been discussed. In order to optimize the condition of synthesizing the 2223 phase and grow large crystals with a good quality, a detailed investigation of these problems is of great interest. In the present study, we intend to confirm the 850 ±C subsolidus phase relations reported by Schulze et al.,4 discuss the decomposition reaction of the 2223 phase, and investigate the invariant reactions existing in the Bi-poor region around the 2223 phase. On the basis of these results, a reaction scheme will be proposed and a 2142
http://journals.cambridge.org
J. Mater. Res., Vol. 11, No. 9, Sep 1996
Downloaded: 30 Mar 2015
tentative liquidus projecti
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