POSTER SESSION 4PO6: Microstructure/HTS Properties

Thursday, Feb. 24, 1:45 p.m. – 3:45 p.m., Hall D (GRB)

*4PO6-1 Study of a novel transition radiation detector utilizing superconducting microspheres for measuring the energy of relativistic high energy charged particles

Luke C.L. Yuan 1, C.P. Chen 2, C.Y. Huang 3, S.C. Lee 2, G. Waysand 4, P. Perrier 4, D. Limagne 4, V. Jeudy 4, and T. Girard 4. 1 Synchrotron Radiation Research Center, Hsinchu, Taiwan. 2 Institute of Physics, Academia Sinica, Taipei, Taiwan. 3 Center for Condensed Matter Sciences, National Taiwan University, Taipei, Taiwan. 4 GPS, University Paris 7, 75251 Cedex 05, Paris, France.

Presenting Author: C.Y. Huang

In want of a detector capable of measuring accurately the energy of relativistic high energy charged particles, a novel transition radiation detector (TRD) utilizing superheated superconducting microsphees of tin of 22-26 m m, 27-32 m m and 32-38 m m in diameter respectively has been constructed. For the purpose of enhancing the TR effect, the TRD is operated at ~ 100mK. Test has been conducted in a high energy electron beam facility at the CERN PS in the energy range of 1-10 GeV showing an energy dependence of the TR X-ray photon produced and hence the value g =E/mc² of the charged particle.

4PO6-2 Microstructure and Superconductivity of the Melt-textured YBCO Grown with the Addition of SnO₂

Z.H. He 1,2, O.B. Surzhenko 1, T. Habisreuther 1, M. Zeisberger 1, and W. Gawalek 1. 1 Institut fur Physikalische Hochtechnologie e. V., Postfach 100239, D-07702, Jena, Germany. 2 Department of Physics, Zhongshan University, Guangzhou, 510275 P.R. China.

Presenting Author: Z.H. He

Large domain YBa₂Cu₃O_7-d /Y₂BaCuO₅ (123/211) samples were prepared by top-seeded melt-textured process, with the addition of SnO₂ and CeO₂ or PtO₂. It was found that the microstructure and the superconducting critical current density J_c of the PtO₂-doped sample were different from those of the CeO₂-doped sample. In comparison to those in CeO₂-doped sample, the 211 particles in the PtO₂-doped sample were larger on average and less homogeneously distributed. Some of them were long in shape. A more obvious second peak effect was observed. This sample had also higher J_c values at high magnetic field and higher irreversibility fields (B_ir). The enhancement of J_c in the PtO₂-doped sample is related to the microstructure inhomogeneity, and also some lower T_c(B) clusters that act as flux pinning centers at high magnetic field. The pinning mechanism will also be discussed.

The work was partially supported by the German BMBF project (contract number 13N6854), the Alexander von Humboldt Foundation, the Chinese NNSF, and the Guangdong NSF (P.R. China).

4PO6-3 Pinning enhancement in zone-melting-growth (Sm_0.5Y_0.5)Ba₂Cu₃O_7-d superconductor by CeO₂ addition

Kyu-Won Lee 1, So-Jung Kim 2, Dong-Han Ha 1, Jin-Tae Kim 1, Yong-Ki Park 1, and Jong-Chul Park 1. 1 Korea Research Institute of Standards and Science, P.O. Box 102,Yusong, Taejon 305-600, Korea. 2 Korea Advanced Institute of Science and Technology, Kusong-dong, Yusong, Taejon 305-701, Korea.

Presenting Author: K.-W. Lee

For the flux pinning enhancement of (Sm_0.5Y_0.5)Ba₂Cu₃O_7-d superconductor we have developed a fabrication method of zone-melting growth with CeO₂ addition to the calcined (Sm_0.5Y_0.5)Ba₂Cu₃O_7-d powder before zone-melting process. To analyze the effect of CeO₂ addition, a zone-melted sample without CeO₂ addition was fabricated using the same process. Microstructure analysis of the CeO₂ added sample showed that fine ellipsoidal (Sm_0.5Y_0.5)₂BaCuO₅ particles were uniformly dispersed in a large (Sm_0.5Y_0.5)Ba₂Cu₃O_7-d grain.

Magnetization hysteresis at various temperature was measured to analyze the flux pinning effect using a SQUID magnetometer. The sample with CeO₂ addition showed more than three times larger magnetization hysteresis at 77 K and 1 T than the sample without CeO₂ addition. Critical current density of the CeO₂ added sample calculated by Bean's formula was 1.8 ~ 104 A/cm² at 77 K and 1 T.

4PO6-4 Influence of cuprate rods on the determination of the J_c of Bi 2212 tapes

Pierre Régnier 1*, Fabrice Legendre 2, Concetta Bifulco 1, Gaëlle Villard 2, Sylvie Poissonnet 2, and Giovanni Giunchi 1. 1 Research and Development Division, Edison Termoelettrica, Foro Buonaparte 31, 20121 Milano, Italy. 2 Section de Recherches de Métallurgie Physique, CEA Saclay, 91191 Gif sur Yvette, CEDEX, France. *Previously at 2.

Presenting Author: P. Régnier

Highly textured Bi 2212 tapes were prepared on both sides of 50 µm thick Ag substrates in alternating electrolytic depositions and heat treatments. Their critical current density was determined using double pairs of current leads and potential taps, one pair was directly connected to the superconducting material and the second one to the Ag backing. It was found that the voltage drop per unit length was higher between the pair of taps connected to the Ag backing than between the other, whatever the current lead pair used.

It was inferred that this could be due to a possible heterogeneity in the thickness of the superconducting ceramics layer. To elucidate that point, glancing sections of the tapes were polished using an original technique and studied in a CAMECA SX50 electron microprobe. Though the ceramic was 3.5 µm thick only, it was found that the density of (Sr,Ca)₁₄Cu₂₄O₄₁ cuprate rods was considerably higher near the Ag substrate than on the free surface of the tape.

Further optimisation of the process has allowed to significantly reduce the density of these underlying cuprates and hence to increase the critical current density at 77K of our Bi 2212 ceramics from 25 000 to 40 000 A/cm².

A simple model is proposed to explain how cuprate rods prevent the Bi 2212 flaky grains to lay parallel to the substrate.

4PO6-5 Microstructure Control of an Oxide Superconductor on Interaction of Pinning Centers and Growing Crystal Surface

Masanobu Awano 1, Yoshinobu Fujishiro 1, and Fatih Dogan 2. 1 National Industrial Research Institute of Nagoya, Hirate-cho, Kita-ku Nagoya 462-8510. 2 Materials Science and Engineering, University of Washington, 302 Robert Hall, Box 352120, Seattle, WA 98195-2120.

Presenting Author: M. Awano

Interaction of Ultrafine BaZrO₃ particles with growing crystal surface of YBCO superconductor was investigated by microscopic and in-situ analysis technique. Nanoparticles were dispersed in superconducting matrix when the growing rate of grain boundaries was accelerated by the pressure sintering under the solid state reaction. On contrary, existance of liquid phase resulted in squeezing of nanoparticles out of superconducting grains. High temperature observation of the interaction of nanopaticles and solid/liquid interface of superconducting phase suggested the optimum condition of heating and composition for uniform dispersion of pinning centers in matrix grains. Stress induced grain gowth of superconducting grains under uniaxial pressure resulted in highly oriented bulk body of the superconductor with improved magnetic flux pinning property by well dispersed pinning centers involved in the matrix under solid state growing of interface.

4PO6-6 Crystallographic studies of superconducting thin films and tapes by EBSD

Robert J. Fairhurst, H.Y. Zhai, L. Zhang, J.K. Meen, and D. Elthon, TcSUH, University of Houston, Houston, TX 77204-5932

Presenting Author: R.J. Fairhurst

Electron backscatter diffraction (EBSD) using an SEM provides a method to analyze the crystallography of materials on a scale of less than a micron. Some of the electrons in the primary beam are backscattered within a crystalline material and, while moving back toward the sample surface, are incoherently scattered and produce a Kikuchi pattern, detected above the sample. Comparison of the experimental pattern with that calculated for a crystalline material establishes the orientation of that crystal.

The preparation of the surface is critical to determination of EBSD patterns. Mechanical polishing produces a damaged surface layer that does not yield diffraction patterns and the surface must be prepared by ion milling or chemical polishing.

Dot-mapping with EBSD allows an orientation image of the sample to be built up, showing the orientation of individual grains, sub-grains, and twins. This, combined with x-ray maps to indicate impurities, allows a particularly full characterization of superconductor bulk samples and thin films. We have constructed EBSD and compositional maps of bulk (PIT) BSCCO and YBCO thin films and measured the degrees of grain alignment in these materials. These results will be presented and the degree of alignment of grains related to conducting properties of the superconductors.

*4PO6-7 Analytical and Structural Transmission Electron Microscopy Study of Normal-Superconductor Interfaces in Melt Textured Nd_1+xBa_2-xCu₃O_y

E. Conolly 1, F. Sandiumenge 2, H.W. Zandbergen 1, T. Puig 2, and X. Obradors 2. 1 National Centre for HREM, Laboratory of Materials Science, Delft University of Technology, The Netherlands. 2 Institut de Ciencia de Materials de Barcelona (CSIC), Spain.

Presenting Author: E. Conolly

Energy dispersive X-ray analyses (EDX) and high resolution electron microscopy (HREM) imaging have been carried out on melt-textured Nd_1+xBa_2-xCu₃O_y/Nd₄Ba₂Cu₂O₁₀ (Nd-123/422) composites around 422 particles in order to elucidate the possible occurrence of antisite disorder and lattice distortions. The motivation is the understanding of the microstructural origins of the distinctive interface pinning behaviour found in Nd-123 compared to Y-123. Since such behavior depends on P(O₂) treatments, samples processed under 1 bar and 90 bar oxygen were investigated for comparison. Thin foil specimens cut parallel to the (001) planes were used. Nd and Ba elemental profiles were taken across several Nd-123/422 interfaces and around 422 particles with a spot size of 5 nm and step sizes within the range 25 - 100 nm using a field emission gun and a extraction voltage of 4.2 kV. Notably the composition appears to depend on the local thickness of the foils as follows: In the thicker regions, ~ 10-20 nm, the measured Ba:Nd ratio was typically ~1.85, indicating a value of x of ~ 0.05. Conversely, for thinner areas of the samples, ~ 3 - 10 nm, the EDX analyses indicated Ba:Nd ratios strongly varying from place to place, from values typically within 1 - 1.6 nm up to values close to 2. The same trend was found for samples processed under 1 bar and 90 bar oxygen. Since the Nd-123 compound has a layered structure, as the analyzed number of layers increases, the measured Ba:Nd ratio will be closer to the overall sample composition, while decreasing the number of analysed layers the results will be more sensitive to the effect of local compositional fluctuations. With this in mind, the present results indicate that there are indeed fluctuations of the Ba:Nd ratio, i.e. antisite disorder, within a scale length of about 10 nm or approximately ten unit cells, relevant to the superconducting properties. This interesting effect seems independent of the distance from the 422 particles, as well as the P(O₂) treatment. In addition, the overall composition is slightly enriched in Nd. HREM imaging revealed a variety of structures including strain accommodation via interfacial dislocations, stepped interfaces, and occasionally the occurrence of a strongly distorted nanometric layer separating both phases. These results are discussed in connection with the observed J_c(H,T) behavior.

4PO6-8 Effect of PAIR Process on Microstructure of Ag-Sheathed Bi-2212 Tapes

Jodi L. Reeves 1, Mark O. Rikel 1,2, Darin Adolphs 3, David Zwicky 1, and Eric E. Hellstrom 1. 1 Applied Superconductivity Center, University of Wisconsin, Madison, WI 53706, USA. 2 Lebedev Physics Institute, Russian Academy of Sciences, Moscow, 117924 Russia. 3 Ceramic Engineering Dept., Iowa State University, Ames, IA, 50012, USA.

Presenting Author: J.L. Reeves

Record-setting critical current densities of >500,000 A/cm² (4.2K, 10T) have been produced in Bi₂Sr₂CaCu₂O_x (Bi-2212) conductors using the Pre-Anneal and Intermediate Rolling (PAIR) process (Miao et al. Physica C 301 (1998)). In this study, we have applied the PAIR process to Ag-sheathed monocore Bi-2212 tapes. The samples underwent a two-step pre-anneal, with the first pre-anneal in partial vacuum at 700°C for 24 hours followed by a second pre-anneal at elevated temperature (835-850°C) for varying lengths of time (0-48 hours). Samples with 150 micron initial thickness were rolled after the high-temperature pre-anneal step; the percent reduction varied from 0-40%. Scanning electron microscopy and x-ray diffraction were used to study the change in second phase content and grain alignment of PAIR processed tapes. Initial results show that increasing the precent reduction decreased the amount of 14:24 AEC and Cu-free particles while increasing the amount of the Bi-2201 phase. However, grain alignment was adversely affected by sausaging in tapes with the highest percent reduction. Critical current measurements are underway to determine the optimum rolling percentage and preanneal time and temperature.

4PO6-9 Microstructural Development of BSCCO-2223 Fabricated by Modified Two Powder Process

Jae-Woong Ko, Jaimoo Yoo, and Hai-Doo Kim, Ceramic Materials Group, Korea Institute of Machinery and Materials, 66, Sangnam-dong, Changwon-si, Kyungnam-do, 641-010, Korea

Presenting Author: J.W. Ko

BSCCO 2223 was fabricated by modified two powder process, and studied in terms of 2223 phase formation and grain growth. Phase evolution and reactivity of 2223 were remarkably sensitive to size of 2212 grains and liquid phase. Larger size of 2212 phase increased liquid formation temperature. The Avrami relation was well suited for describing the kinetics of grain growth in BSCCO 2223.