Effect of ZrO 2 and ZnO nanoparticles inclusions on superconductive properties of the melt-processed GdBa 2 Cu 3 O 7d bulk superconductor Y. Xu a,b, * , A. Hu c , C. Xu a , N. Sakai b , I. Hirabayashi a , M. Izumi a a Laboratory of Applied Physics, Tokyo University of Marine Science and Technology, 2-1-6 Etchu-jima, Koto-Ku, Tokyo 135-8533, Japan b Superconductivity Research Laboratory, ISTEC, 1-10-13 Shinonome, Koto-Ku, Tokyo 135-0062, Japan c Department of Physics and Astronomy, University of Waterloo, 200 Unvi. Avenue West, Waterloo, Ont., Canada N2L 3G1 article info Article history: Available online 21 May 2008 PACS: 74.72.Bk 74.70.Dd 74.62.Dh Keywords: Melt processing Gd123 Nanoparticles ZrO 2 and ZnO Flux pinning abstract Single domain Gd123 bulk superconductors have been fabricated successfully with doping both ZrO 2 and ZnO nanoparticles by a hot seeded melt growth in air. Superconductive properties were studied on the specimens selected from different positions of the domain separately, along the a–b plane and c-axis. The nanosized defects induced by the nanoparticles can be effective pinning center to enhance the J c of the bulk. Atomic substitution of Cu site with Zn ion enables us to enhance the J c but the substitution suppresses the T c of the bulk. By the analysis of the pinning force, for the specimens cut along the a–b plane, the dl pinning is enhanced by the addition of nanoparticles. While for the specimens cut along the c-axis, the dT c pinning is remarkably enhanced. Ó 2008 Elsevier B.V. All rights reserved. 1. Introduction Nanoscaled precipitates inside bulk superconductors or directly doping of nanosized particles into the bulk have attracted much attention for achieving large J c and high irreversibility line at liquid nitrogen temperature [1–4]. Several species of nanoparticles have been reported to enhance the superconducting performance of YBa 2 Cu 3 O 7d (Y123) system, for example, nanoscaled BaZrO 3 , NiO and Y 2 Ba 4 MCuO 11 (M = Zr, U, Mo, W, Ta, Hf, Nb) [2,4–6]. In GdBa 2 Cu 3 O 7d (Gd123) system, the superconductive properties and the microstructure of doped bulk superconductors with addi- tion of ZrO 2 or SnO 2 nanoparticles have been intensively investi- gated [7,8]. Both additions create various micro-defects in the Gd123 bulk superconductors, such as twins, boundaries, disloca- tions and stacking faults that enhance the dl pinning and improve the J c under the self-field at 77 K. On the other hand, ZnO doping has been found to enhanced dT c pinning effectively [9] and induced an enhanced peak effect. It will be very interesting to investigate the collective pinning effect by adding two kinds of different nanoparticles. In this paper, we studied superconductive properties of Gd123 bulk superconductors by doping two kinds of nanosized additions, ZrO 2 and ZnO, both with average particle size of 50 nm. The spatial variation of the flux pinning was elucidated. The experimental results clarified that a suitable amount of nanoparticles ZrO 2 and ZnO inclusions is crucial for the enhancement of J c . The pres- ent work suggests that the systemic study of the microstructure and the optimization of the preparation conditions to improve fur- ther enhancement of J c  B performance of the bulk superconductors. 2. Experimental Commercially available Gd 2 O 3 (3 N), BaO 2 (3 N) and CuO (3 N) powders were used to prepare GdBa 2 Cu 3 O 7d (Gd123) and Gd 2 Ba- CuO 5 (Gd211) powders. For Gd211 preparation, the mixed powders sintered in air twice at 900 °C for 24 h and refined by a ball-milling for 2 h. The prepared Gd123 and Gd211 were weighed in a nominal molar ratio with 5:2 and mixed thoroughly together with ZnO and ZrO 2 nanoparticles. The precursor compositions were studied as follows: Gd123 + 0.4 Gd211 + 0.1 BaO 2 + x(ZrO 2 + ZnO), x = 0.0, 0.002, 0.004, 0.006, in molar ratio (ZrO:ZnO = 1:1, labeled the bulk sample as x ZrO 2 and ZnO here after). Both 10 wt.% Ag 2 O and 0.5 wt.% Pt were added in order to improve the mechanical prop- erty and hinder the coarsening of Gd211 second phase particles, respectively. The mixed powder was first pressed into pellets of 30 mm in diameter and 10 mm in thickness. It was further solidified via cold iso-static pressing (CIP) in a rubber bag. The 0921-4534/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.physc.2008.05.056 * Corresponding author. Address: Laboratory of Applied Physics, Tokyo University of Marine Science and Technology, 2-1-6 Etchu-jima, Koto-Ku, Tokyo 135-8533, Japan. Tel./fax: +81 3 5245 7462. E-mail address: d062030@kaiyodai.ac.jp (Y. Xu). Physica C 468 (2008) 1363–1365 Contents lists available at ScienceDirect Physica C journal homepage: www.elsevier.com/locate/physc