Effects of processing parameters on the levitation force of melt-processed YBa 2 Cu 3 O x
- PDF / 1,385,780 Bytes
- 6 Pages / 576 x 792 pts Page_size
- 103 Downloads / 186 Views
V. Pavate and E. P. Kvam School of Materials Science and Engineering, Purdue University, West Lafayette, Indiana 47907 (Received 27 January 1995; accepted 24 May 1995)
Melt processing of YBa2Cu30;i: (Y-123) with a NdBa 2 Cu 3 (V123 single-crystal seed has been used to grow large single-grain Y-123 samples. Processing parameters have been varied to observe the resulting differences in the levitation force of the samples. Increased hold time above the peritectic temperature and increased undercooling temperature have been observed to be beneficial in enhancing the levitation force of the samples. The levitation force measurements have been correlated with magnetization measurements on the crushed domains.
I. INTRODUCTION Seeded melt processing of Y B a ^ ^ O * is widely used to grow large domains which are useful in applications such as magnetic levitation and trapped flux magnets. '~7 Some earlier studies were aimed at understanding the factors responsible for the growth of large 123 domains. Ohtsu et al. have reported8 that with an increase in undercooling, the growth rate of 123 domains increases. Use of a concentration gradient to produce large grain samples has also been attempted.9 There are also reports10 on the applicability of other seed materials (e.g., Pt, ZrO 2 , Sm 2 O 3 , Nd 2 O 3 , etc.) to obtain large 123 single grains. Nd 2 O 3 and Sm 2 O 3 powders were observed to perform better as compared to Pt and ZrO 2 seeds. Although large domains of Y-123 are now frequently obtained by using various high temperature RE-123 single-crystal seeds (RE = Sm, Nd, etc.) during melt processing, there is little work reported on the effects of processing parameters to further enhance the levitation force of the samples. One of the important factors in obtaining good levitation force is the flux pinning characteristics of the superconductor. While there are many ways to improve flux pinning (e.g., second-phase additions,1 '~13 mechanical deformation,14 shock compaction,15 etc.), often they result in a decreased domain size (or are not practical for commercial use), which is not beneficial from the point of view of levitation applications. As the trapped flux or levitation force also depends upon the size of the 123 domains,1 one desires to increase the flux pinning force without decreasing the domain size. Thus, processing that allows one to enhance the flux pinning without adversely affecting the domain size is of great interest. The present work is aimed at studying the effects of processing parameters on the levitation J. Mater. Res., Vol. 10, No. 9, Sep 1995 http://journals.cambridge.org
Downloaded: 13 Mar 2015
force of Y-123 samples by varying the time of hold and undercooling temperatures as compared to a standard melt processing cycle. II. EXPERIMENTAL The starting composition of all the samples used in the present experiments was the same in order to observe any process-induced differences in the properties of the samples. Pure Y-123 (supplied by Superconductivity Components, Inc.) powder was mixed with 20 w
Data Loading...
