Physica C 200 (1992) 31-42 North-Holland PHYSICA Characteristics of Bi-Pb-Sr-Ca-Cu-O powders produced by aerosol decomposition and their rapid conversion to the high-Tc phase Timothy L. Ward, Shirley W. Lyons and Toivo T. Kodas Centerfor Micro-Engineered Ceramics, Department of Chemical and Nuclear Engineering, Universityof New Mexico, Albuquerque, NM87131, USA Jorulf Brynestad, Donald M. Kroeger and Huey Hsu Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37831, USA Received 30 January 1992 Bi---Pb-Sr-Ca-Cu-O powders were produced by aerosol decomposition of nitrate solutions. The effects of reactor temperature and residence time on particle morphology and evaporative Pb loss from particles were demonstrated, and conditions necessary to control Pb loss established. Pb loss was roughly proportional to residence time, and minimal loss occurred with short residence times (3s) and T< 800 °C. Particles produced at 700 °C typically contained significant porosity, while those produced at T> 800 °C were solid. Mixtures of the Bi2Sr2CuOy (2201 ) and Bi2Sr2CaCu2Oy (2212 ) phases were produced at 700-900 °C in nitrogen and air. However, after heating in air for 16 h at 850°C, pellets of powder produced at 700°C with nominal composition Pb0.44BiLsSr2Ca2.2Cu3Oy converted to approximately 79 vol.% of the Bi2Sr2Ca2Cu3Oy (2223) phase and displayed a T~ (onset) of 110 K. Rapid conversion to 2223 was promoted by powder synthesis conditions, leading to controlled Pb loss and a homoge- neous fine-grained dispersion of mixed-oxide precursor phases within particles. 1. Introduction The Bi-Sr-Ca-Cu-O (BSCCO) family of super- conducting compounds has received a great deal of attention since the first reports of a transition tem- perature (To) exceeding 100 K with a BSCCO com- position [ 1,2 ]. The great interest in these materials stems from the higher Tc, better atmospheric stabil- ity [ 1 ], and potential processing advantages, such as ability to melt-process, relative to YBa2CuaOT_x [3,4 ]. Three superconducting phases with compo- sition Bi2Sr2Ca,_ iCu,Oy have been identified; 2201 (n= 1 ), 2212 (n=2) and 2223 (n=3) with T¢= 10, 85 and 110 K, respectively [ 5 ]. Synthesis of mate- rial with a large volume fraction of the high-T¢ phase (2223) has proven to be difficult, requiring long sin- tering times [ 6 ] within a narrow temperature range which is sensitive to 02 partial pressure [ 7 ]. Partial substitution of Pb for Bi was first reported by Tak- Author to whom correspondence should be addressed. ano et al. [ 6 ] to promote the formation and/or sta- bility of the high-Tc phase, and led to studies of Pb doping as a means of obtaining 2223 in higher purity with less effort. Solid-state reaction techniques have several dis- advantages for the synthesis of complex multicom- ponent oxides such as BSCCO, one being that it is difficult to obtain chemically homogeneous material because of transport limitations in the solid state. These inhomogeneities can result in extremely slow kinetics for 2223 formation, making it difficult to form the high-To phase in high phase purity. Endo et al. [7] reported that co-decomposition of nitrate precursors produced a uniform mixture of cations which shortened the reaction time necessary to pro- duce the high-To phase. A considerable enhancement in the formation rate of the high-To phase during powder calcination using spray-dried nitrate precur- sor powder has also been reported [ 8 ]. We have been investigating the use of aerosol de- composition to produce chemically homogeneous 0921-4534/92/$05.00 © 1992 Elsevier Science Publishers B.V. All fights reserved.