ELSEVIER PhysicaC 269 (1996) 306-312 PHYSICA The increase of the critical current density of YBa2Cu307_y by a modified melt-textured-growth method C.H. Choi a, y. Zhao a,*, C.C. Sorrell a M. La Robina b, C. Andrikidis c a Superconductivity Research Group, School of Materials Science and Engineering, University of New South Wales, Sydney, NSW 2052, Australia b Australian Nuclear Science and Technology Organization, Advanced Materials Program, PMB 1, Menai, NSW 2234, Australia c CSIRO Division of Applied Physics, National Measurement Laboratory, Lindfield, NSW 2047, Australia / Received 7 June 1996 Abstract A modified melt-textured-growth (MTG) method which has a relatively low working temperature and short reaction time compared with the conventional MTG method has been developed. The number of YBa2CU3OT_y (123) nuclei during the initial slow-cooling process has been minimized which leads to the enhancement of the 123 grain growth rate and a better homogenized and smaller Y2BaCuOs (211) particles over the samples. Magnetization measurement shows that the 123 crystals have a high Jc and a good performance in high magnetic fields. 1. Introduction It is well known that the melt-textured-growth (MTG) method is one of the most promising pro- cesses to fabricate the high-T~ cuprates with a high critical current density. Since Jin et al. [1] first used a MTG process numerous modified methods have been developed [1-7]. Among these, the melt-powder- melt-growth (MPMG) process developed by Yoo et al. [8-10] showed maximum Jc values up to 2 × 104 A/cm 2 at 77 K and 2 T (H II c) for a sample substituting Nd on the Y site. Murakami et al. [11] also found that the Jc was inversely proportional to the size of Y2BaCuOs (211) grains. It is generally accepted that 211 plays an important role in the * Corresponding author. Fax: +61 2 385 5956; e-mail: y.zhao@unsw.edu.au. pinning effect, even though there are still controver- sies on the mechanism of the 211 effects. It has been found that the MPMG process can produce textured crystals with smaller 211 particle size and better liquid homogeneization, which leads to higher Jc and better performance in high magnetic field, than those of the crystals fabricated by other MTG methods. However, there are several impedi- ments to apply the MPMG owing to the following reasons [ 12]: (1) an expensive disposable Pt crucible is needed to minimize the 211 particle sizes; (2) the sample has to stay at a very high temperature (above 1350°C) for a long time, resulting in highly possible chemical reaction with the crucibles [12]. Compared with the MPMG method, the MTG process has a limit in controlling the 211 particle size and it is difficult to reach a high Jc value. 0921-4534/96/$15.00 Copyright© 1996Elsevier ScienceB.V. All rights reserved Pll S0921-4534(96)00489-3