Experiment for growing large Gd–Ba–Cu–O–Ag bulk superconductor N. Sakai a, * , K. Inoue a , S. Nariki a , A. Hu a , M. Murakami a,b , I. Hirabayashi a a Superconductivity Research Laboratory, ISTEC, 10-13, Shinonome 1-Chome, koto-ku, Tokyo 135-0062, Japan b Shibaura Institute of Technology, 9-14 Minato-ku, Tokyo 108-8548, Japan Received 23 November 2004; accepted 12 February 2005 Available online 24 August 2005 Abstract Unmanned space experiments were performed with the aim of growing large grain Gd–Ba–Cu–O superconductors in space. The advantage of the space experiment was the support of a large precursor block by a small seed crystal alone. Three samples were safely returned from space. It was interesting to note that one of the samples was mainly composed of Gd 2 BaO 4 pillar shaped crystals. Detailed characterization of this new phase showed that the phase is very stable under severe conditions and will be a firm framework for the melt growth process. Infiltration of Ba–Cu–O phase into a precursor Gd 2 BaO 4 block enabled us to grow a large grain bulk Gd–Ba–Cu–O 14 cm in diameter. Ó 2005 Elsevier B.V. All rights reserved. PACS: 74.80.Bj; 74.72.Jt; 74.62.Bf Keywords: Large bulk superconductor; Gd 2 BaO 4 ; Infiltration process 1. Introduction Single grain RE–Ba–Cu–O (RE: rare earth ele- ments) bulk superconductors can trap magnetic fields much stronger than conventional permanent magnets [1], which is attractive for various indus- trial applications. The magnetic field trapped by a RE–Ba–Cu–O bulk is proportional to its grain size and critical current density (J c ). Microstructural control enabled us to dramatically enhance J c val- ues of bulk RE–Ba–Cu–O, and the maximum J c has already exceeded 10 5 A/cm 2 at 77 K in self field [2], which is sufficient for most engineering applica- tions. Hence, for the promotion of practical appli- cations, it is desirable to enlarge the grain size of bulk RE–Ba–Cu–O superconductors without dete- riorating the homogeneity and the high J c values. However, it has been difficult to grow high quality 0921-4534/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.physc.2005.02.156 * Corresponding author. Tel.: +81 3 3536 5707; fax: +81 3 3536 5705. E-mail address: nsakai@istec.or.jp (N. Sakai). Physica C 426–431 (2005) 515–519 www.elsevier.com/locate/physc