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Thermodynamic and nonstoichiometric behavior of the lead-doped and lead-free Bi-2212 systems

Description: EMF measurements of oxygen fugacities as a function of stoichiometry were made on pb-doped and Pb-free superconducting ceramics at 700-815 C using oxygen titration. Equations of oxygen partial pressure vs composition and temperature were derived from the EMF measurements. Thermodynamic assessments of the partial molar quantities {Delta}{bar H}(O{sub 2}) and {Delta}{bar S}(O{sub 2}) for Pb-doped Bi- 2212 and Pb-free Bi-2212 indicate that the solid-state decomposition of these Bi cuprates at low oxygen partial pressure can be represented by the diphasic CuO-Cu{sub 2}O system. Comparison of these results with Pb-doped Bi-2223 in powder and silver sheath form is presented.
Date: February 1, 1997
Creator: Tetenbaum, M.; Hash, M.; Tani, B.S.; Luo, J.S. & Maroni, V.A.
Partner: UNT Libraries Government Documents Department

HTS coil development and fabrication. Final report

Description: The objective of this subtask (Task 2C) was to develop high-temperature superconductor (HTS) coil technology aimed specifically at superconducting generator applications. Bi-2223 tape produced in a separate subtask (Task 2A) was first wound and tested in a small circular coil. This small coil winding experience led the authors to develop a tape strengthening method using a lamination process and to develop a turn insulation method using a paper wrap process. A prototype racetrack coil was wound using 2500 feet of the laminated and insulated Bi-2223 tapes. The racetrack coil was cooled to 20K in a vacuum dewar using a unique closed-cycle helium gas refrigeration system.
Date: October 1, 1996
Creator: Herd, K.G.; Salasoo, L. & Ranze, R.
Partner: UNT Libraries Government Documents Department

Measurement of the critical current and transient characteristics of a high-temperature superconductor tube using a pulsed current supply.

Description: The transient response of a melt-cast-processed BSCCO-2212 superconductor tube is investigated by using a pulsed current source. It was found that (1) the maximum induced current and the excitation current at field penetration increase with the maximum excitation current, and (2) there is a time delay between peak excitation current and peak magnetic field inside the superconductor. These observations can be explained by the concept of magnetic diffusion. The ac steady-state critical current of the superconductor was found to depend on the magnitude of the current increment. The critical current determined by using the pulsed current system agrees fairly well with the ac steady-state critical current determined by using relatively large current increment.
Date: August 27, 1998
Creator: Cha, Y. S.
Partner: UNT Libraries Government Documents Department

Production electrolysis studies V

Description: This study seeks to determine the decomposition of bismuth trioxide by polarography. Results gained confirmed that at decomposition potentials observed that bismuth will not be reduced under normal plating conditions observed during production.
Date: December 31, 1948
Creator: Power, W.H. & Ford, M.
Partner: UNT Libraries Government Documents Department

HIGH RESOLUTION PHOTOEMISSION STUDIES OF COMPLEX MATERIALS.

Description: Recent instrumentation developments in photoemission are providing new insights into the physics of complex materials. With increased energy and momentum resolution, it has become possible to examine in detail different contributions to the self-energy or inverse lifetime of the photohole created in the photoexcitation process, Employing momentum distribution and energy distribution curves, a detailed study of the optimally doped cuprate, Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub g+{delta}}, shows that the material behaves like a non-Fermi liquid with no evidence for the quasi-particles characteristic of a Fermi liquid.
Date: October 13, 1999
Creator: JOHNSON,P.D.
Partner: UNT Libraries Government Documents Department

Chemical Solution Processing of Strontium Bismuth Tantalate Films

Description: We describe Chemical Solution Deposition (CSD) processes by which Strontium Bismuth Tantalate (SBT) thin films can be prepared at temperatures as low as 550 C. In this paper, we will present strategies used to optimize the properties of the films including solution chemistry, film composition, the nature of the substrate (or bottom electrode) used, and the thermal processing cycle. Under suitable conditions, {approximately} 1700 {angstrom} films can be prepared which have a large switchable polarization (2P{sub r} > 10{micro}C/cm{sup 2}), and an operating voltage, defined as the voltage at which 0.80 x 2P{sub r} max is switched, 2.0V. We also describe an all-alkoxide route to SBT films from which SBT can be crystallized at 550 C.
Date: December 21, 1998
Creator: Boyle, T.J. & Lakeman, C.D.E.
Partner: UNT Libraries Government Documents Department

High T{sub c} superconductors: New insights from angle-resolved photoemission

Description: Recent angle-resolved photoemission (ARPES) studies of the high T{sub c} superconductors by the Argonne group are briefly reviewed. First we discuss sum rules to establish a spectral function interpretation of the data, and the use of ARPES to obtain the momentum distribution. We then apply these ideas to the normal and superconducting state spectra for Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8}. Among the topics discussed are the Fermi surface, polarization selection rules, bilayer splitting and the superconducting gap.
Date: November 1, 1995
Creator: Randeria, M.
Partner: UNT Libraries Government Documents Department

Trilayer Josephson junctions produced by atomic layer-by-layer FORCE (Flexible Oxide Reaction Controlled Epitaxy). Final report

Description: Lawrence Livermore National Laboratory is working with Varian Associates to lay the groundwork for the routine, reproducible fabrication of high-temperature superconducting trilayer structures. The objectives of this program are: To identify high temperature, superconducting materials, metallic and insulating barrier materials and associated substrate and electrode materials for engineered trilayer structures that can provide Josephson Junction devices with desired characteristics for sensor or electronic circuit use. To identify and test potentially useful analysis techniques and to provide data appropriate for the validation and analysis of the input materials, trilayer structures and completed JJ devices. To integrate the analysis results with the existing Varian data base to optimize the growth and fabrication process to obtain more reproducible devices across each chip and from chip to chip. These objectives were defined by a detailed set of milestones for both Lawrence Livermore National Laboratory and Varian Associates all of which have been meet. The timing of the milestones was revised midway through the CRADA term to allow a longer time to pursue the objectives at no additional cost to either partner.
Date: September 30, 1995
Partner: UNT Libraries Government Documents Department

From double exchange to superexchange in charge ordering perovskite manganites

Description: The authors found dynamic ferromagnetic correlations at the room temperature in perovskite manganites which have an antiferromagnetic insulating ground state. They are replaced by antiferromagnetic correlations when the electrons order. The results indicate that the double exchange mechanism is turned off by electron localization at low temperatures.
Date: August 17, 1998
Creator: Bao, W.; Axe, J.D.; Chen, C.H.; Cheong, S.W.; Schiffer, P. & Roy, M.
Partner: UNT Libraries Government Documents Department

Computational modeling of materials processing and processes

Description: This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). Anisotropic mechanical properties of densified BSCCO powders are of paramount importance during thermo-mechanical processing of superconducting tapes and wires. Maximum current transport requires high relative density and a high degree of alignment of the single crystal planes of the BSCCO. Unfortunately this configuration causes high stresses that can lead to cracking, and thus reduce the density, and the conductive properties of the tape. The current work develops a micromechanical material mode to model is calibrated and compared to experimental results, and then employed to analyze the effects of initial texture and confinement pressure and shear strains in the core of oxide powder-in-tube (OPIT) processed tapes are calculated by finite-element analysis. The calculated deformations were then applied as boundary conditions to the micromechanical model. Our calculated results were used to interpret a set of prototypical rolling experiments. 11 refs., 5 figs.
Date: December 31, 1998
Creator: Lowe, T.C.; Zhu, Yuntian & Bingert, J.F.
Partner: UNT Libraries Government Documents Department

A 100 MVA generator utilizing high temperature superconducting windings -- design assessment & component development. Final report

Description: The operation of a high temperature superconducting generator rotor using closed-cycle refrigeration to indirectly cool the field windings was considered to be the best choice for an HTS application. The SPI program proposed to achieve the following goals: In Task 1 a 100 MVA generator with a HTS rotor field winding would be designed. An energy and economic benefits analysis was to be a key part of the program. In addition, the generator/grid interactions were to be modeled. Concurrently, Task 2 was to include further development of Bi-2223 silver-clad tape as well as an alternate Tl-1223 conductor, manufacture of 3,000 meters of tape, and development and fabrication of a prototype field coil. Details of progress have been reported in the quarterly status reports and summarized in the final reports on the tasks. Therefore this report will give a review of the original goals of each task and summary of results for each.
Date: November 1, 1996
Creator: Lay, K.
Partner: UNT Libraries Government Documents Department

Recent advances in processing of Ag-clad Bi-2223 superconductors

Description: Enhancements in the transport current properties of long lengths of multifilament Ag-sheathed (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub y} (Bi-2223) superconducting tapes were made as a function of increased packing density of precursor powder, improved mechanical deformation, and adjusted cooling rate. Improved processing parameters had a pronounced effect on the transport critical current (I{sub c}) of the superconducting tapes, at 77 K and zero applied magnetic field, an I{sub c} of 60 A was obtained in short length samples (4 cm), an I{sub c} of 54 A in a 164 m length, and 18 A in a 1,260 m length. These enhancements were based on the increase in packing density accompanied with improved mechanical deformation and cooling schedule. Maximum critical current values were two to three times higher in slow-cooled tapes than in fast-cooled tapes.
Date: August 1, 1997
Creator: Balachandran, U.; Lelovic, M.; Deis, T. & Eror, N.G.
Partner: UNT Libraries Government Documents Department

Phase formation and superconductivity in PIT-type (Bi,Pb)-1212

Description: It was shown via powder-in-tube (PIT) processing that the (Bi,Pb)-1212 phase readily forms inside a silver sheath at 920 C in air. Composition, oxygen pressure, time, and temperature were all varied to study their effects on (Bi,Pb)-1212 phase purity and superconductivity.
Date: January 13, 2000
Creator: Murphy, N. M.; Dorris, S. E.; Miller, D. J.; Luo, Z. P.; Claus, H. & Maroni, V. A.
Partner: UNT Libraries Government Documents Department

HIGH RESOLUTION PHOTOEMISSION STUDIES OF COMPLEX MATERIALS.

Description: Recent instrumentation developments in photoemission are providing new insights into the physics of complex materials. With increased energy and momentum resolution, it has become possible to examine in detail different contributions to the self-energy or inverse lifetime of the photohole created in the photoexcitation process. Employing momentum distribution and energy distribution curves, a detailed study of the optimally doped cuprate, Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}}, shows that the material behaves like a non-Fermi liquid with no evidence for the quasi-particles characteristic of a Fermi liquid.
Date: October 13, 1999
Creator: JOHNSON,P.D.; VALLA,T.; FEDOROV,A.; REISFELD,G. & HULBERT,S.L.
Partner: UNT Libraries Government Documents Department

HIGH RESOLUTION PHOTOEMISSION STUDIES OF COMPLEX MATERIALS.

Description: Recent instrumentation developments in photoemission are providing new insights into the physics of complex materials. With increased energy and momentum resolution, it has become possible to examine in detail different contributions to the self-energy or inverse lifetime of the photohole created in the photoexcitation process. Employing momentum distribution and energy distribution curves, a detailed study of the optimally doped cuprate, Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}}, shows that the material behaves like a non-Fermi liquid with no evidence for the quasi-particles characteristic of a Fermi liquid.
Date: October 13, 1999
Creator: JOHNSON,P.D.; VALLA,T.; FEDOROV,A.; REISFELD,G. & HULBERT,S.L.
Partner: UNT Libraries Government Documents Department

Critical current variation as a function of transverse stress of Bi-2212 Rutherford cables

Description: Transverse loading experiments on wire has shown that a significant drop in critical current occurs for stresses greater than 50 MPa. However, many high-energy physics applications require that the Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} conductor withstand stresses greater than 100 MPa without permanent degradation. Therefore, a study of epoxy impregnated cables, identical to those used in accelerator magnet applications, has been performed. This work presents the first results of Rutherford cables of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} with transverse stress. The results show that the cable can withstand stresses up to 60 MPa with a strain of about 0.3 % for the face loading orientation and 100 MPa for the edge loading orientation.
Date: September 10, 2000
Creator: Dietderich, Daniel R.; Scanlan, R.M.; Hasegawa, Takayo; Aoki, Yuji; Sokolowski, Robert S. & Motowidlo, Leszck R.
Partner: UNT Libraries Government Documents Department