ORAL SESSION 1D1: Bulk Processing
Monday, Feb. 21, 4:30 p.m. - 6:30 p.m., Room 301F (GRB)
Chairs: D.C. Larbalestier (UW-Madison)
1D1.1 Recent progress in processing and applications of bulk high temperature superconductors
Masato Muarkami, Superconductivity Research Laboratory, 1-16-25 Shibaura, Minato-ku, Tokyo 105-0023, Japan
Presenting Author: M. Murakami
Recent advancement in melt processing enabled us to grow a large single-grain RE-Ba-Cu-O (RE: rare earth elements) bulk superconductors with high critical current density (Jc). Such high Jc bulk superconductors can be used for various power applications. A heavy object can be levitated in midair by using a combination of permanent magnets and bulk superconductors. Many groups have successfully made magnetic bearings without contact. Low rotational loss in such bearings led to the development of flywheel energy storage system. Large bulk superconductors can also trap large fields much greater than those of permanent magnets, and thus they can be used as quasi-permanent magnets. The trapped field already reached 10 T at 50K. The possibility to use such bulk magnets for second generation Maglev has been studied in Japan. Bulk superconductors can also be used for conductor applications. The employment of YBCO rod for current leads in superconducting magnets saved the consumption of liquid helium. Recent studies showed that a current of 2500 A can be passed without heat generation in the current lead made by melt-textured YBCO. The application of melt textured RE-Ba-Cu-O to fault current limiters is now under consideration in Japan and Europe.
1D1.2 Texturing of bulk Bi2212/MgO by melt processing in a magnetic field and effect of post-annealing on the critical current density
Sybille Pavard 1, Daniel Bourgault 1, Robert Tournier 1, and Catherine Villard 2. 1 Laboratoire de Cristallographie/CRETA, CNRS, BP 166, 38042 Grenoble, France. 2 CRTBT/CRETA, CNRS, BP 166, 38042 Grenoble, France.
Presenting Author: R. Tournier
Bulk Bi2212 containing 10 wt. percent MgO are melt processed in a magnetic field. The texture induced by magnetic melt processing (MMP) is demonstrated using superconducting and microstructural characterizations: the c-axis tends to be parallel to the processing field direction.
The magnetic susceptibility of the material is followed during the MMP. This in-situ measurement is used to study the effect of the maximum processing temperature on the orientation degree and the critical current density (Jc) of the material. The temperature window where texturing is largely efficient is narrow. High Jc values are obtained at low temperatures for bulk Bi2212/MgO optimally MMP. By magnetic measurements, Jc of 161 kA/cm2 is obtained on a "as made" sample (i.e. with no annealing treatment applied after processing).
Hot forging (HF) applied after MMP slightly increases the orientation degree of the c-axis in the material as well as the critical current density. Transport Jc in self field is of about 10 kA/cm2 at 40 K after post-annealing in air and then in argon. Without any post-annealing, the magnetically measured Jc is 165 kA/cm2 at 4 K. The enhancement of Jc by post-annealing in air and in reduced atmosphere is studied.
1D1.3 YBCO - Monoliths with Peak Effect and Trapped Fields More than 14 T
Gernot Krabbes 1, Günter Fuchs 1, Peter Schätzle 1, Stefan Gruss 1, Jai W. Park 2, Ferdinand Hardinghaus 2, Roland Hayn 1, and Stefan - Ludwig Drechsler 1. 1 IFW - Institute of Solid State and Materials Research Dresden, D-01171 Dresden. 2 Solvay Barium Strontium GmbH, D-30002 Hannover, Germany.
Presenting Author: G. Krabbes
The present paper reports on the trapped fields of 14.3 and 11.4 T measured in the gap between two YBCO cylinders and on top of a single YBCO cylinder, respectively. The magnetic flux has been trapped at 17 and 22 K, respectively. The composite material consists of a YBCO-matrix with Ag inclusions and was reinforced by a bandage from steel. A modified melt crystallisation process was applied to grow the superconducting bulk which takes into account the previously determined features in the phase diagram due to the additional silver component. On the other hand, the trapped fields at 77 K benefit from the newly proposed chemical doping by Zn on Cu plane sites which results in a well pronounced peak effect near 3 T. This peak in relatively high fields is thought to result from pair breaking by locally induced magnetic moments due to in plane substitution of Cu by Zn. Thus, more than 1.1 T has efficiently been trapped at 77K in a cylindrical sample of only 25 mm in diameter.
1D1.4 Growth and Properties of Nd1+xBa2-xCu3Oy Large Grains for Device Applications
Wai Lo and K. Salama, Texas Center for Superconductivity, University of Houston, Houston, TX 77204, USA
Presenting Author: W. Lo
Nd1+xBa2-xCu3Oy (NdBCO) bulk materials are known to have superior superconducting properties than YBa2Cu3O7-d (YBCO). They have higher Tc, Jc, Hirr, growth rate and also exhibit pronounced Jc(H) peak effect. NdBCO can therefore enhance the performance of devices fabricated on the basis of large YBCO grains if they can be grown in similar forms using an industrially viable processing technique. Several barriers need to be overcome in order to develop this processing technique. One of these barriers is the control of processing oxygen partial pressure p(O2), which dictates the degree of Nd substitution onto Ba-site and consequently affects both Tc and Jc. Another barrier is the search for an appropriate seed with similar lattice structure, chemically stable and higher melting point, due to the nearly highest peritectic temperature of the NdBCO in the RE-BCO series and the presence of chemically active Ba-Cu-O liquid in the peritectic state. This talk will present the growth of NdBCO large grains under different p(O2) using both MgO and NdBCO seeds introduced either at room temperature or near the peritectic temperature of NdBCO. The seeding process, growth process and transport properties of these materials as revealed by microscopy, magnetization, transport current measurement and levitation force characterization techniques will be discussed in detail. Comparison of these features with the growth and properties of YBCO large grains will also be made.
1D1.5 Fabrication of Large Grain Nd-Ba-Cu-O by Seeded Melt Growth
David A. Cardwell, Nadendla H. Babu, Makoto Kambara, Patrick J. Smith, and Yunhua Shi, IRC in Superconductivity, University of Cambridge, Madingley Road Cambridge, CB3 0HE. United Kingdom
Presenting Author: D.A. Cardwell
Large, single grain Nd-Ba-Cu-O (NdBCO) composite samples consisting of NdBa2Cu3O7-d (Nd-123) containing various amounts of non-superconducting Nd4Ba2Cu2O10 (Nd-422) phase inclusions have been fabricated successfully by a variety of techniques based on top-seeded melt growth under reduced oxygen partial pressure. Specifically, individual grains up to 2cm in diameter have been grown using (100) oriented MgO seeding, self (NdBCO) seeding at elevated temperature and self seeding of Ag and Au doped precursor powder pellets which exhibit a reduced peritectic decomposition temperature compared with the parent NdBCO compound. These techniques, which vary in degree of difficulty and hence reliability, yield grains with a range of microstructural homogeneity. This paper will describe the general aspects of large NdBCO grain fabrication and present the results of the different fabrication techniques. Finally, a brief overview of the magnetisation and irreversibility behavior of the grains will be presented, providing evidence for the significant potential of NdBCO for bulk engineering applications.
1D1.6 Competition effects between random quenched and linearly correlated disorders in MTG-YBCO
T. Puig, J. Figueras, and X. Obradors, Institut de Ciència de Materials de Barcelona, CSIC, 08193 Bellaterra, Spain
Presenting Author: T. Puig
Melt textured grown (MTG) YBCO has been shown to be a superconducting material which microstructure can be tailored while still keeping the intrinsic characteristics of YBa2Cu3O7. However, detailed studies of combined effects from different types of defects (211 precipitates, twin boundaries, dislocations...) are required in order to design the desired microstructure for specific applications. We have studied the competition between random quenched disorder induced by the 211 precipitates, and twin boundary pinning in the liquid vortex state of MTG-YBCO, by angular dependent in-plane magnetoresistance measurements. The contribution of both types of defects to the irreversibility line and activation energy has been analyzed. We have identified a partially entangled liquid vortex phase arising from the competing effects between the quenched disorder and linearly correlated twin boundaries. This new phase is characterized by a short range c-axis vortex correlation length which is temperature and magnetic field independent. Extension of this analysis to MTG-YBCO free of 211 precipitates allows us to determine the effect of twin boundaries in MTG-YBCO avoiding the dominant effect from the 211 quenched disorder.