日本金属学会誌

J. Japan Inst. Metals, Vol. 63, No. 9 (1999),
pp. 1113-1116

Fabrication Process of Orthorhombic Untwinned Nd123 Single Crystaland Its Jc-H Property

Akihiro Oka, Satoshi Koyama,Teruo Izumi and Yuh Shiohara

Division IV, Superconductivity Research Laboratory, Tokyo 135-0062

Abstract:

A fabrication process of orthorhombic untwinned Nd123 single crystals was studied. In this study, in order to fabricate the complete untwinned single crystals, the Nd123 samples were cut from the as-grown tetragonal crystals into rectangular plates, of which the sides corresponded to {110} planes. Furthermore, the tetragonal cut samples were oxygenated under uni-axial compression in <{100}> direction from the corner of the samples. Almost twin-free orthorhombic Nd123 single crystals with dimensions of 2 mm×2 mm×0.5 mm, of which the sides of 2 mm×0.5 mm corresponded to {110} planes, could be obtained by modifying the heat treatment conditions from the viewpoint of the uniformity of the oxygen contents in the samples during annealing. Here, the samples were oxygenated by cooling slowly from 973 to 573 K for 200 h with a shear strain of about 1.4{×}10-3 from the corner of the samples. The critical current density (Jc)-magnetic field (H) properties for the untwinned Nd123 single crystals were compared with those for the twinned Nd123 single crystals, which were fabricated by the same heat treatment condition as that for the untwinned single crystals without the uni-axial compression. The Jc-H curve with c//H at 77 K for the untwinned single crystals showed a much larger peak effect than that for the twinned single crystals. This result suggested that the wavelength of the Nd/Ba ratio fluctuation appearing in these crystals during annealing became shorter for the untwinned single crystals so that the number of pinning centers of the Nd-rich phases increased.


(Received April 23, 1999; In Final Form June 22, 1999)

Keywords:

Neodymium 123, untwinned single crystal, heat treatment process, Jc-H property, peak effect, phase decomposition


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