NdBCO melting and solidification by a zone-melting method
- PDF / 1,145,461 Bytes
- 6 Pages / 576 x 792 pts Page_size
- 81 Downloads / 259 Views
NdBCO melting and solidification by a zone-melting method X. Yao, K. Furuya, Y. Nakamura, J. Wen, A. Endoh, M. Sumida, and Y. Shiohara Superconductivity Research Laboratory, Division IV, Iniernational Superconductivity Technology Center, 1- 10-13 Shinonome Koto-ku, Tokyo 135, Japan (Received 20 January 1995; accepted 1 August 1995)
In the Nd-Ba-Cu-0 system, a directional structure produced by a peritectic reaction has been observed. On heating, the sintered NdlBa2Cu306+6(Nd123) precursor formed a rod-like directional structure of Nd4Ba2Cu2010 (Nd422) phase. These Nd422 rods became thicker from the melting interface to the solidified interface. The [loo] direction of Nd422 crystal is parallel to the axis of Nd422 rod and the sample pulling direction. Moreover, Nd422 rod spacing was observed as a function of growth rate and decreased with an increase of growth rate. In addition, with an increase of growth rate, Nd123 solidified interface morphologies changed from planar, cellular to equiaxed.
1. INTRODUCTION
There is now abundant evidence to indicate that critical current densities (at 77 K) of the order of 1Os A/cm2 in zero field are achievable, which will reduce to smaller values in the field of 5 T, in YBa2Cu306+8 bulk superconductors, prepared by several different melt growth processes. These processes include MTG (melttextured growth),' QMG (quench and melt growth),* and MPMG (melt powder melt growth)' methods. Recently, Nd123 made by an OCMG method has been reported to be a promising superconductor,4 showing high T , and J , values. The investigations showed that process parameters affected Ndl23 growth and, moreover, superconducting properties. In addition, in melt-textured (MT) Y123 growth the following peritectic reaction occurs at the peritectic temperature:
-
Y B a 2 C ~ 3 0 h + S Y2BaCuOS
+ Liquid
This peritectic reaction produces a high-temperature stable Y*BaCu05 (Y211) phase. However, in the Nd-Ba-Cu- 0 system, this peritectic reaction leads to a different product as follows':
-
NdBa2Cu306+S
Nd4Ba2Cu2010
+ Liquid'
Although Nd4Ba2Cu2OI0 (Nd422) phase and the Y2BaCu05 (Y211) phase have the same elemental ratio, they are different in crystal structures. The Y211 phase shows an orthorhombic crystal structure, while the Nd422 phase features a tetragonal one. This suggests that Nd422 may have a different behavior from the Y-Ba-Cu-0 system in MT growth. The aim of this work is to study the melting and solidification process of Nd 123 by using a zone-melting method. Our attention was focused on melt-textured Nd123 melting and solidification morphologies, including Nd123 and Nd422, and their relationship with meltJ. Mater. Res., Vol. 10, No. 12, Dec 1995
ing and growth rates. Moreover, the growth of Nd123 crystal has also been compared with that of Y123 for better understanding of the Ln-Ba-Cu-0 (Ln: Y and lanthanide) MT growth mechanism. II. EXPERIMENTAL
To make the NdBCO precursor, the powders of Nd203, BaC03, and CuO were mixed in a ratio of Nd : Ba : Cu = I : 2 : 3. NdBCO powders were preheate
Data Loading...
