| Budget Amount *help |
¥3,100,000 (Direct Cost: ¥3,100,000)
Fiscal Year 2006: ¥1,100,000 (Direct Cost: ¥1,100,000)
Fiscal Year 2005: ¥800,000 (Direct Cost: ¥800,000)
Fiscal Year 2004: ¥1,200,000 (Direct Cost: ¥1,200,000)
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| Research Abstract |
The continuous growth conditions and interface stability of directionally solidified REBa2Cu3Ox (RE123: RE=Y, Gd and Sm) superconductive oxides were investigated for achieving high transport critical current density. In the case of rods with 2 mm in diameter, the maximum pulling rates to achieve continuous growth structure with single facet interface were 8 and 12 mm/h for Gd123 and Sm123, respectively, while that of Y123 was about 2〜3 mm/h. This means that the RE123s with higher peritectic temperature can grow continuously with higher pulling rates because of the large solute diffusion rates for growth of such the RE123s with high peritectic temperature. In addition, the large temperature gradient near the growth front was favorable to achieve continuous growth structure. To see the effect of sample diameter on the continuous growth, the samples with diameters of 0.5 and 4 mm were also fabricated. The Y123 fiber with 0.5 mm in diameter could grow continuously up to 10 mm/h, and this p
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ulling rate was about 3 times higher than that of 2 mmφ sample. On the other hand, the Sm123 rods with 4 mm in diameter could not grow continuously below 4 mm/h although the 2 mmφ rods could grew up to 12 mm/h. This difference could be explained from the nucleation rate in undercooled liquid region and the stability of facet interface. The latter means that the increase in temperature difference between the top and bottom of facet interface under temperature gradient may decrease the interface stability and result the cellular structure in the sample with large diameter. To see the effect of growth anisotropy during growth, the tilt angle of the ac-plane of RE123 sample from the growth direction was evaluated, The tilt angles of the Sm123 and Gd123 samples were evaluated in the ranges of 40〜50° and 20〜30°, respectively, and no clear dependence on pulling rates was obtained, while this angle decreased as increasing pulling rate in the case of Y123 sample. This means that the temperature dependence of growth anisotropy is different for each RE123 crystal. Because of low angle at high pulling rate, Y123 fiber with 0.5 mm in diameter showed the high critical current density of lx105A/cm2. Less
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