Y-Ba-Cu-O系超伝導性セラミックスの水による劣化

概要

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Y-Ba-Cu-O ceramics (mixing atomic ratio (Y:Ba:Cu)=(1 to 4):(1 to 5):(1 to6) were prepared by solid state reactions at 950℃ for 17 hrs in O_2, starting with Y_2O_3, BaCO_3 and CuO. When kept in water at 20℃, most of the superconducting black ceramics became white within 1 to 2 days, due to the H_2O attack. However, the ceramics made of mixing atomic ratio 1:1:2 was still black and had Meissner effect up 20 days. J_c of the 112 ceramics (25 A/cm^2) was smaller than 39 A/cm^2 of 123 ceramics. The mixing composition of the 112 was the same as that of 123 and YCuO_<2.5>(20.5 wt%). It is expected that the water resistivity and superconducting properties of the ceramics composed of 123 and YCuO_2.5 (3 to15 wt%) may be better thsn those of the 123 or 112 ceramics. The T_c(zero) and J_c(77K) of these ceramics (123-YCuO_2.5) were about 92K and 2〜860 A/cm^2, respectively. However, the J_c of these ceramics when kept in water at 20℃ for only 1 day decreasedbelow 5 A/cm^2, in spite of these ceramics beinge black and having Meissner effect. When kept in salad oil, these ceramics were still black, and T_c(zero) and J_c were about 92K and 18〜53 A/cm^2 even after 90 days.it is concluded that the H_2O attack is very sever, but the superconducting properties are not so much damaged when kept in oil, due to the lack of water.
社団法人日本材料学会の論文
1990-12-15