The formation and stability of 80 K phase in the BiPbSrCaCuO system
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The formation and stability of 80 K phase in the BiPbSrCaCuO system W. Zhu,a) C. K. Kuo, and P. S. Nicholson Ceramics Engineering Research Group, Department of Materials Science and Engineering, McMaster University, Hamilton, Ontario, Canada L8S 4L7 (Received 2 October 1995; accepted 14 March 1996)
The formation of Pb-doped 80 K phase from nitrate precursors was studied in the Bi1.84 Pb0.34 Sr1.91 Ca2.00 Cu3.04 O10.05 system. Sr(Pb, Bi)O3 , Ca5 Bi14 O26 , CuO, and CaO were found to be the intermediate compounds reacting to produce 80 K phase between 600 and 820 ±C. Synthesis was complete at 800 ±C for 24 h. 110 K phase formed at the expense of 80 K phase at temperatures above 820 ±C. Partial melting was detected and 80 K and 110 K phases were unstable in the presence of liquid phase. They decomposed to 2201, Cu2 O, and (Ca, Sr, Cu) complex oxides. The melting and decomposition were accompanied by oxygen loss.
I. INTRODUCTION
Bi(Pb)SrCaCuO 80 K superconducting phase (Bi2 Sr2 CaCu2 O8 , 2212) has been extensively studied as films, wires, and current-leads.1,2 The starting powder is synthesized via solid-state reaction. Precursors used are oxides, carbonates, nitrates, or organometallics. Although single-phase 80 K superconductor material has been fabricated by solid-state reaction and sintering procedures, its formation mechanism is not well established. Several intermediate compounds and reaction routes have been proposed. The formation of 80 K phase was studied by Lo and Glowacki3 using oxide/carbonate raw materials and attributed to reactions between 2201 (Bi2 Sr2 CuO6 ), Ca5 Bi14 O26 , CuO, and SrCO3 . The 2201 intermediate phase was produced by the reactions between Bi–Sr–Cu–OyBi–Sr–O compounds and SrCO3yCuO or between Bi2 CuO4 and SrCO3 . Bohacek et al.4 proposed the formation reaction was through 2201 with CaO and CuO. On the other hand, Huang et al.5 believed SrCaCu2 Ox and BiSrOy but not 2201 were the main reactants leading to the 80 K product. Zorn et al.6 used high temperature x-ray to follow the 2212 phase formation from the mixture of oxides and carbonates, and found that 2212 started to form at 800 ±C with consumption of 2201, Ca2 PbO4 , and Sr2 PbO4 . 2201 coexisted with 2212 up to 880 ±C. Oh and Osamura7 studied the carbonate mixture from 800 –950 ±C. 2212 was found to be the major phase at 800–845 ±C, 2201 was detected at 800 –820 ±C and 860 –950 ±C, which suggested that 2201 was a reactant for 2212 formation and a product of 2212 decomposition.
a)
Present address: IREQ, Hydro Quebec, Canada. J. Mater. Res., Vol. 11, No. 8, Aug 1996
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In the study on the preparation of BiSrCaCuO 110 K superconducting phase (Bi2 Sr2 Ca2 Cu3 O10 , 2223),8 it was found that the 80 K phase, in addition to being a BiSrCaCuO superconducting compound, was an intermediate product which formed at low temperatures. It transformed to 110 K phase at .820 ±C in the presence of extra Cu and Ca oxide components. The present work
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