Sponsored by: Jt. EMPMD/SMD Superconducting Materials Committee, MSD Electronic, Magnetic and Optical Phenomena Committee, and FEMS (Federation of European Materials Societies)
Program Organizers: U. Balachandran, Energy Technology Division, Argonne National Laboratory, Argonne, IL 60439; Paul J. McGinn, University of Notre Dame, Notre Dame, IN 46556; Stuart Abell, University of Birmingham, Edgbaston, Birmingham B152TT, UK
Monday, PM Room: B7
February 5, 1996 Location: Anaheim Convention Center
Session Chairpersons: K. C. Goretta, Argonne National Laboratory, Argonne, IL 60439; W. Wong-Ng, National Institute of Standards and Technology, Gaithersburg, MD 20899
2:00 pm Invited
KINETICS OF FORMATION, c-AXIS ALIGNMENT, AND CRITICAL CURRENTS OF Bi(2:2:2:3)/Ag TAPES: Y.L. Wang, W. M. Bian, Y. Zhu, Y. Fukumoto, T. Thurston, M. Suenaga, Dept. of Applied Science, Brookhaven National Laboratory, Upton, NY 11973
Employing a precursor powder, which was produced by an aerosol spray pyrolysis technique, highly textured Bi(2:2:2:3)/Ag tapes were synthesized. Using the tapes, a comprehensive study was carried out for kinetics of Bi(2:2:2:3) formation, the platelets alignment, and their critical currents utilizing transmission electron microscopy, transmission x-ray diffraction, and high sensitivity V-I characteristic measurements. The results of the study will be described in detail. This work was performed under the auspices of the U.S. Department of Energy Division of Materials Sciences, Office of Basic Sciences under Contract No. DE-AC02-76CH00016.
2:20 pm Invited
FORMATION OF NUCLEATION SITES FOR GROWTH OF Bi(2223) ON Pb-DOPED Bi(2212): D. K. Finnemore, M. Xu, Ames Laboratory, Iowa State University, Ames, IA 50011; U. Balachandran, Argonne National Laboratory, Argonne, IL 60439
Scanning electron microscopy studies of mixed powders of Pb-doped Bi(2212), calcium cuprate, and CuO show that nucleation sites of 100 nm in size grow on Bi(2212) grains during the ramp up to temperature from 25 to 800deg.C. Growth of these nuclei begins at 650deg.C and seems to require the presence of Ag; it occurs at both 3 and 150 Torr of partial pressure of oxygen. The nuclei grow in the same temperature range as the rapid changes in X-ray peak heights while pellets of mixed powders are ramped from 25 to 800[[ring]]C. Work at Ames Laboratory was supported by the U.S. Department of Energy, under Contract W-7405-Eng-82; work at ANL was supported by the U.S. Department of Energy (DOE), Energy Efficiency and Renewable Energy, as part of a DOE program to develop electric power technology, under Contract W-31-109-Eng-38.
2:40 pm Invited
MELTING EQUILIBRIA OF THE HIGH Tc PHASES IN THE SYSTEM Bi-Sr-Ca-Cu-O: W. Wong-Ng, L. P. Cook, Ceramics Division, National Institute of Standards and Technology, Gaithersburg, MD 20899
Knowledge of melting equilibria in the system Ba-Sr-Ca-Cu-O (BSCCO) is important for melt processing of bulk superconductors and for melt growth of single crystals. A general procedure developed at NIST to determine melt composition has been applied to study the melting equilibria of the superconducting phases in the BSCCO system. The primary crystallization fields of the Raveau phase, 2212 and 2223 phases will be discussed. Effects of Ag addition on the melting equilibria will also be discussed.
3:00 pm Invited
THE INFLUENCE OF LEAD ON PHASE FORMATION AND MICROSTRUCTURE DEVELOPMENT IN Ag/Bi-2223 COMPOSITE CONDUCTORS: V. A. Maroni, N. Merchant, J. S. Luo, J. Leboy, A. K. Fischer, K. Wu, W. Zhong, S. E. Dorris, Argonne National Laboratory, Argonne, IL 60439
Investigations performed during the processing of Ag/Bi-2223 composite conductors have revealed that lead has numerous significant influences on Bi2223 phase formation and microstructure development. The mode of lead incorporation in the precursor powder is the dominant factor controlling the length of the induction period preceding the onset of Bi-2223 formation. Back reaction of Bi-2223 to Bi-2212 during cool down appears to be accelerated by the lead rich "liquid phase." Changes in the chemical state of lead during ramp up, heat treatment, and cool down have been monitored using Raman microscopy and x-ray diffraction. The influence of stoichiometry variations involving Bi, Pb, and Sr on Bi-2223 phase development and core microstructure has been investigated.
3:30 pm Invited
NOVEL PROCESSING ROUTES FOR BSCCO PHASES THROUGH CONTROL OF PHASE CHEMISTRY: J. L. MacManus-Driscoll, L. F. Cohen, A. D. Caplin, Centre for High Temperature Superconductivity, Imperial College, London SW7 2BZ, UK
The main limitations to the formation of long length of BSCCO conductors with good Jc performance are phase purity, microstructural inhomogeneities and large scale imperfections such as cracking and voiding. Understanding and control of the phase chemistry is essential in order to obtain reproducible properties. We have determined phase equilibria in the Bi-2212 system and phase stability of (Bi,Pb)-2212 and (Bi,Pb)-2223 as a function of temperature and reduced oxygen partial pressures. This information has allowed alternative precursor phase combinations and processing routes to be explored. In particular, reduced temperature and oxygen partial pressure processing schemes for (Bi,Pb)-2212 and (Bi,Pb)-2223 shall be discussed. For (Bi,Pb)-2212, processing in the supersolidus phase region at ~830deg.C and pO2 = 3x10-3atm. leads to well aligned, near phase pure conductors with Jc's of up to 105 A cm-2 at 4.2 K. For (Bi,Pb)-2223, rapid formation of the phase occurs when processing from reduced oxide precursor phases.
3:50 pm Invited
PHASE DEVELOPMENT IN PARTIAL-MELT PROCESSING OF SILVFR-CLAD Bi2.15Srl.83Cal.02CU20x TAPES: Ming Jiang, M. T. Lanagan, W. E. Delaney, K C. Goretta, Energy Technology Division, Argonne National Laboratory, Argonne, IL 60439
Ag-clad Bi2.15Srl.83Ca1 02Cu2Ox (Bi-2212) tapes were fabricated by the powder-in-tube method. Using the partial-melt processing approach, we heat treated the tapes in air and in various O2/Ar mixtures. The tapes were then characterized by differential thermal analysis, scanning electron microscopy energy dispersive X-ray analysis, and X-ray diffraction. Particular emphasis was placed on conditions above the peritectic melt temperature. Relationships between processing and microstructure will be discussed. Work supported by the U.S. Department of Energy (DOE), Energy Efficiency and Renewable Energy, as part of a DOE program to develop electric power technology, and Basic Energy Sciences (Materials Sciences), under Contract W-31-109-Eng-38.
4:10 pm Invited
PHASE RELATIONS AS A FUNCTION OF TEMPERATURE AND PO2 IN THE Bi2Sr2Ca2CuO8-Ag SYSTEM: R. W. McCallum, L. Margulies, M. J. Kramer, Ames Laboratory, Iowa State University, Ames, IA 50011
The promise of usable forms of high temperature superconducting wires and tapes rests on developing techniques for processing highly textured materials. Currently, melt-processing seems most suited to this goal, as the formation of liquid enhances grain alignment. Although much work has been done in determining the effect of Ag and PO2 on the first solidus temperature, there has been no detailed study of the Bi2212-Ag pseudo binary phase diagram. Understanding the effect of Ag and PO2 on the chain of peritectic reactions initiated during melting is necessary in order to optimize the melt-processing parameters of Bi2212/Ag composites. Previously, work on the solubility of Ag in the Bi2212 melt revealed a large liquid immiscibility gap and a eutectic on each side of this gap. The sub-liquidus phase reactions in this system were examined in greater detail for 0.01, 0.2, and 1.0 bar PO2. This work suggests that the initial peritectic reactions may be different than those previously reported. Supported by the United States Department of Energy under contract No. W-7405-ENG-82.
4:30 pm
EFFECT OF SINTERING PERIODS ON THE PINNING FORCE, ACTIVATION ENERGY, AND MICROSTRUCTURE OF HIGH-TC SUPERCONDUCTING Bi-(Pb)-Sr-Ca-Cu-O TAPES: N. V. Vo, H. K. Liu, S. X. Dou, Centre for Superconducting and Electronic Materials, Univ. of Wollongong, Northfields Ave., Wollongong, NSW 2522, Australia
Short and long periods of sintering of short single core Bi(Pb)-2223 tapes have been studied. Comparisons are made between three batches of these tapes with the same thermo-mechanical deformation and sintering conditions but with the starting precursor powders being different in their processing. It is found that the volume density of the macroscopic pinning force in fields up to lT is greater for a particular sintering period. Resistivity measurements further show the activation energy also reaches a higher value for the same sintering period chosen. SEM images of the surfaces indicated better morphology and density can be achieved for this particular sintering period. Prolonged sintering leads to greater porosity while short duration sintering inhibits grain growth and thus is of no assistance to the healing of cracks induced by the intermediate deformation between sintering periods.
4:50 pm Invited
COMMON MECHANISM OF TEXTURE FORMATION IN Bi-BASED HTSC PRODUCED BY DIFFERENT METHODS: T. D. Aksenova, S. V. Shavkin, ISC&SSF, RRC Kurchatov Institute, 123181, Moscow, Russia; P. V. Bratukhin, Kashirskoe sh. 31, Bochvar's Inorganic Materials Institute, 123060 Moscow, Russia
In spite of different thermomechanical processes for fabrication of the best Bi-2212-based and 2223-based Ag-sheathed composite conductors, our model of texture formation is supposed to be valid for both cases. Model treats the anisotropic crystalline growth process in quasi-2D volume of crystallization. Comparative analysis of texture in 2212 and 2223 composite tapes have been performed. We have also concluded the absence of influence of Ag sheath texture on growing oxide layer.
5:10 pm
EVOLUTION OF PHASES IN POSTANNEALED BiSrCaCuO THIN FILMS: B. Vengalis, A. Deksnys, L. Dapkus, V. Jasutis, A. Jukna, Semiconductor Physics Institute, A. Gostauto 11, 2600 Vilnius, Lithuania
Evolution of highly oriented 2201 and 2212 phases in various composition
postannealed BiSrCaCuO films has been investigated in-situ using high
temperature XRD. Magnetron sputtered amorphous Bi-Sr-Ca-Cu-O precursor films
and sequentially evaporated Bi-(SrF2, CaF2)-Cu multilayers both prepared onto
MgO(100) have been used for the investigations. The superconducting compounds
were found to be formed via the intermediate layered Bi- and Sr-based oxide
(3-x,x,0,0) following the sequence: (3-x,x,0,0) -> 2201 -> 2212.
Kinetics of the (3-x,x,0,0) -> 2201 -> 2212 structural transformations
have been investigated. Small amount of a fugitive liquid depending strongly on
the annealing schedule has been indicated at T>750deg.C. At certain
conditions the liquid stimulated oriented growth of the intermediate phase and
modified formation conditions of the phases towards liquid phase epitaxy. As a
result, we succeeded in obtaining superconducting 2212-phase films with smooth
surface being unusual for most postannealed BiSrCaCuO.
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