1PO5-11 to 1PO5-19

1PO5-11 Effect of Nickel Purity on Cube Texture Formation in RABiT-Tapes

J. Eickemeyer 1, D. Selbmann 1, R. Opitz 1, E. Maher 2, and W. Prusseit 3. 1 Institut für Festkörper- und Werkstofforschung Dresden, Germany. 2 Oxford Instruments, Eynsham, Witney, Oxon, United Kingdom. 3 Theva Dünnschichttechnik, Eching-Dietersheim, Germany.

Presenting Author: J. Eickemeyer

Highly cube textured nickel tapes are favoured flexible substrate materials for the deposition of layer systems with high temperature superconducting properties. The impurity content of the base metal was suspected to influence the resulting recrystallization texture after intense cold rolling. The effect of impurities and micro-alloying elements on cube texture quality was therefore investigated. Impurity and micro-alloying contents, respectively, were less than 0.1 atomic percent.

It was shown that detrimental effects with regard to cube texture formation due to the usual metallurgical trace elements in nickel can be compensated by specific micro-alloying. The refractory elements molybdenum and tungsten revealed this beneficial influence. The cube texture of the micro-alloyed tapes was excellent as the results of X-ray investigations and electron back scattering mappings showed. Furthermore, the thermal stability of the strongly aligned microstructure was maintained at coating temperatures during buffer and YBCO layer deposition. Preliminary depositions resulted in a maximum value of the critical current density of YBCO films at 77 K of j_c= 0.5 MA/cm².

1PO5-12 Fabrication of Y123 Disk by Seeded Infiltration and Growth Method

H. Fang and K. Ravi-Chandar, Department of Mechanical Engineering and Texas Center for Superconductivity, University of Houston, Houston, TX 77204-4792

Presenting Author: H. Fang

Y123 disks were prepared by a newly invented seeded infiltration and growth process to produce net-shape products with a uniform distribution of 211 inclusions. At the beginning of this process, a Y123 disk was placed on the top of a Y211 disk and a Sm123 seed was introduced at the interface. Above the peritectic temperature, the top Y123 decomposed into the peritectic liquid phase and 211; the liquid phase flowed down into bottom Y211 disk and a well textured Y123 was formed there with slow cooling. The microstructure shows that a slower cooling rate results in more complete peritectic reaction. The 211 area fraction is between 30% and 50% for a cooling rate in the range of 1 ° C/hr and 1.5 ° C/hr. The critical current density at 77K is at least 100000 A/cm² under zero field and about 20000 A/cm² under 1.5 T magnetic field, which indicates that this method is a promising way to fabricate bulk Y123 superconducting materials. Furthermore, we have reduced the particle size of bottom Y211 disk to less than 100 nanometer, which further decreases the particle size of 211 inclusions in final textured material. Better transport property is highly expected, and these results will also be reported.

1PO5-13 Computer Simulations of TSMG-YBCO Processing and Properties

Ivan A.Parinov and Lyubov I. Parinova, Mechanics & Applied Mathematics Research Institute, Rostov-on-Don 344090, Russia

Presenting Author: I.A. Parinov

It is known, that the bulk YBCO prepared by the top-seeded-melt growth (TSMG) method is one of the most promissing superconductors for applications. However, the successful applications of this material demand sufficiently high superconductive and mechanical properties. The main problems of the high properties attainment are connected with heat treatment during processing, formation undesirable microstructure (i.e., pores, microcracks, secondary phases, grain misorientation, etc.) and with composition features of superconductor.

The aim of this report is the computer modeling of the TSMG-YBCO processing, in particular, the development of the next models for seeded YBCO samples: (i) planar growth, (ii) cellular growth, (iii) cellular growth with undesirable nuclei, and (iv) random nucleation. Also, it will be considered YBCO microstructure with included Ag particle dispersion used usually for healing of defects. For YBCO model microstructures two problems of compromise will be studied, namely: (i) an optimum concentration of the normal 211 phase into superconductive 123 phase (a size and concentration growth of the high-modulus 211 particles increases YBCO strength properties but diminishes superconductive ones), and (ii) an optimum concentration of the Ag particle dispersion in the YBCO matrix (a growth of the Ag concentration improves YBCO fracture resistance but decreases critical current). The corresponding estimations for some microstructural, strength, toughness and conductive properties of the model samples will be obtained.

1PO5-15 Structure and Formation Mechanism of Subgrains in Melt-processed REBa₂Cu₃O_y (RE = Y, Nd, Sm) Bulk Superconductors

Kei Ogasawara, Naomichi Sakai, and Masato Murakami, Superconductivity Research Laboratory, International Superconductivity Technology Center, 1-16-25, Shibaura, Minato-ku, Tokyo 105-0023, Japan

Presenting Author: K. Ogasawara

Some low-angle grain boundaries such as subgrain boundaries, present in melt-grown REBa₂Cu₃O_y (RE = Y or rare earth elements) bulk superconductors, have been reported to act as weak-links in high magnetic fields. Thus it is important to control the formation of subgrains for high field applications along with the enlargement in the grain size of bulk materials. In this study, we adopted a new approach to characterize the subgrains in melt-grown REBa₂Cu₃O_y (RE = Y, Nd, Sm) bulk superconductors. A pole-figure measurement technique combined with x-ray micro diffraction system was employed to quantify the misorientation angles of the subgrains in these materials. This enables us to acquire the crystal orientation in an area as small as 10 microns in diameter, which could effectively be applied to the characterization of the subgrains. We will propose possible subgrain formation mechanisms through a systematic study of how the subgrains are formed depending on positions, growth conditions and the second-phase distribution, and also by comparing the results with previous research works studied in similar systems.

This work is supported by the New Energy and Industrial Technology Development Organization (NEDO) as Collaborative Research and Development of Fundamental Technologies for Superconductivity Applications.

1PO5-16 Comparative study of morphological and structural properties between top seeding growth and Bridgman-based directional solidification of NdBaCuO

Antonio Vecchione, Patrizia Tedesco, Marcello Gombos, and Sandro Pace, Instituto Nazionale per la Fisica della Materia and Department of Physics, University of Salerno, Via S. Allende, Baronissi (Sa) 84081, Italy

Presenting Author: A. Vecchione

We have studied the morphological and structural properties of bulk Nd₁Ba₂Cu₃O₆₊_dgrown by means of two different techniques. Starting from the same Nd₁Ba₂Cu₃O₆₊_d/ Nd_3.8Ba_2.4Cu_1.8O_10-_dmixtures, top seeding growth and Bridgman-based directional solidification in air were employed to produce bulk samples.

The resulting microstructures, analyzed by using a scanning electron microscope, have shown Nd₁Ba₂Cu₃O₆₊_ddomains, pores and Nd₄Ba₂Cu₂O_10-_dsize distribution and shape depending on the fabrication technique. Moreover, even if the fabrication relevant parameter, the cooling rate, was the same for both the techniques, the structural features of the samples were different.

We interpret the experimental results pointing out the role played by both undercooling degree and temperature gradient in controlling the sample growth. We show that the undercooling degree is a function of the fabrication technique of the samples.

1PO5-17 Melt processing of La_1+xBa_2-xCu₃O_7-_dwith Pt and CeO₂ addition

Goro Osabe 1, Naomichi Sakai 1, Masato Murakami 1, and Kazuhiko Yasohama 2. 1 Superconductivity Research Laboratory, ISTEC, 1-16-25 Shibaura, Minato-ku, Tokyo 105-0023, Japan. 2 College of Science and Technology, Nihon University, 1-8 Kanda, Surugadai, Chiyoda-ku, Tokyo 101-8308, Japan.

Presenting Author: G. Osabe

Unlike Y-Ba-Cu-O, the La-Ba-Cu-O system forms a La_1+xBa_2-xCu₃O_7-_dtype solid solution (La123ss) due to similar ionic radius of La³⁺ and Ba²⁺. Recently, it was found that high T_c and J_c La123 bulk can be synthesized by melt processing in a reduced oxygen atmosphere to use the Ba-rich composition. In the case of Y-Ba-Cu-O, it is known that Pt or CeO₂ addition is effective in reducing the size of Y₂BaCuO₅ particles. However, it was found that Pt addition had no appreciable effects on the size reduction for Nd₄Ba₂Cu₂O₁₀ (Nd422) particle in Nd_1+xBa_2-xCu₃O_7-_d, while CeO₂ addition led to the refinement of Nd422 particle. In this paper we studied the effect of the Pt and CeO₂ addition on the size of La₄Ba₂Cu₂O₁₀ (La422) particle in La-Ba-Cu-O in low oxygen partial pressure to use the Ba-rich La422 precusor.

1PO5-18 Superconducting Properties of (Nd, Eu, Gd)-123

M. Muralidhar and M. Murakami, Superconductivity Research Laboratory, ISTEC-SRL, Division 3, 1-16-25, Shibaura, Minato-ku, Tokyo, 105, Japan

Presenting Author: M. Muralidhar

Recent experiments have demonstrated the superior performance of (Nd_0.33Eu_0.33Gd_0.33)Ba₂Cu₃O_y (NEG) bulk superconductors as compared to Y-123 or Bd-123. Originally we started from the mixture of Bd, Eu, and Gd elements with an even ratio both in the matrix and the 211 particles. Recently we began to explore the effect of mixing ratio of these three rare earth elements on the superconducting properties. Previous investigations showed that the Nd-123 and Gd-123 plays an important role in determining the peak J_c and the peak position, respectively. With this in mind, we prepared two groups of (Nd, Eu, Gd)-123 samples. For the first group we kept the Nd content constant and varied the Gd ration, and for the second group the Gd content was kept constant and the Nd content was varied. The samples were grown by the oxygen-controlled-melt-growth (OCMG) process. The heat treatment profiles for melt processing were determined based on the peritectic decomposition temperatures obtained from the thermal analysis measurements. The sample with Gd=0.25 exhibited a large critical current density (J_c) of 90000 A/cm² at 77 K and 1.7 T. However, the peak position and irreversitbility field were not systematically varied with either Gd or Nd content.

This work was supported by New Energy and Industry Science and Technology Development Organization (NEDO).

*1PO5-19 Fabrication of Large Melt-textured Gd-Ba-Cu-O Superconductor with Ag Addition

Shinya Nariki, Naomichi Sakai, and Masato Murakami, Superconductivity Research Laboratory, ISTEC,1-16-25 Shibaura, Minato-ku, Tokyo 105-0023, Japan

Presenting Author: S. Nariki

Large c-axis oriented Gd-Ba-Cu-O bulk superconductors with Ag addition were melt-textured under an oxygen partial pressure of 1.0%. Nd123 was used as a seed for the growth of single domain bulk. The bulk samples with diameters of 32mm and 48mm were successfully fabricated with no macro-sized cracks. The size of 211 particles dispersed in the bulk was remarkably reduced by using fine Gd211 powder as a starting material. As a result, high critical current density (J_c) of 60000A/cm² was obtained at 77K and 0T. The trapped magnetic field of the sample with a 32mm diameter was 1.5T at 77K. This value is comparable to that of a melt-textured Sm-Ba-Cu-O bulk in a similar size, and exceeds that of a Y-Ba-Cu-O bulk. The superconducting properties of the larger sample 48mm in diameter will also be reported.