Fabrication of Large Melt-textured RE-Ba-Cu-O (RE = Gd, Dy) Superconductors and Their Trapped Magnetic Fields
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Fabrication of Large Melt-textured RE-Ba-Cu-O (RE = Gd, Dy) Superconductors and Their Trapped Magnetic Fields Shinya Nariki, Naomichi Sakai and Masato Murakami Superconductivity Research Laboratory, ISTEC, Shibaura, Minato-ku, Tokyo, 105-0023, Japan ABSTRACT We have succeeded in synthesizing RE-Ba-Cu-O (RE = Gd and Dy) bulk superconductors with excellent field trapping properties. Large c-axis oriented single-domain Gd-Ba-Cu-O bulk samples with Ag addition were melt-textured under controlled oxygen partial pressure of 1.0%. The Gd-Ba-Cu-O sample 50 mm in diameter could trap a high flux density of 2.4 T at 77 K. In addition, we measured the trapped field between two Gd-bulks in order to minimize the demagnetizing effect and found that it reached 3.3 T. The single-domain Dy-Ba-Cu-O/Ag bulk 48 mm in diameter was also fabricated in air and its trapped field was 1.9 T at 77 K.
INTRODUCTION Melt-textured RE-Ba-Cu-O (RE: rare earth element) superconductors are promising candidates for practical applications such as flywheel energy store systems, magnetic bearings and quasi-permanent magnets with high trapped magnetic fields, since their trapped magnetic fields far exceed those of conventional permanent magnets [1-5]. For the enhancement of field trapping capabilities of bulk superconductors, it is important to increase the critical current density (Jc) and/or the size of single-domain. As for the melt-processing of Gd-Ba-Cu-O bulk, we previously reported that the employment of fine Gd2BaCuO5 (Gd211) starting powder led to the size reduction of Gd211 inclusions in GdBa2Cu3Oy (Gd123) matrix, leading to an enhancement of the Jc value [6]. Furthermore, we could fabricate large c-axis oriented Ag-added Gd-Ba-Cu-O bulks using a top-seeded melt-growth technique. The trapped magnetic fields of the bulk samples 32 and 48 mm in diameters reached 1.5 and 1.8 T at 77 K, respectively [7-9]. Recently, a similar approach was adapted to the Dy-Ba-Cu-O system [10]. Employing fine Dy211 powder in a starting material reduced the size of Dy211 particles dispersed in the melt-textured bulk and enhanced the Jc. In the present study, we report on the processing of large single domain Gd- and Dy-Ba-Cu-O/Ag bulks with an excellent field trapping ability.
EXPERIMENTAL Fabrication of Gd-Ba-Cu-O bulk The Gd211 starting powder was prepared from commercial Gd2O3, BaO2 and CuO powders, which were well mixed and calcined at 1173 K for 8 h. The particle size of the Gd211 powder was determined to be 1.0 µm through BET specific area measurements. In addition, the finer Gd211 powder with the mean size of 0.4 µm was also prepared by ball-milling of the calcined powder using Y2O3-ZrO2 ball in acetone for 10 min. These Gd211 powders were added to
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commercial Gd123 powders in a molar ratio of Gd123 : Gd211 = 10 : 5. 0.5 wt% Pt and 10 wt% Ag2O were also added to the mixtures. These mixed powders were first uniaxially pressed into pellets with the diameter of 60 mm, and subjected to cold-isostatic pressing (CIP) under a pressure of 200 MPa. Me
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