Y-Ba-Cu-O ceramics (mixing atomic ratio (Y:Ba:Cu)=(1 to 4):(1 to 5):(1 to 6)) were prepared by solid state reactions at 950°C for 17hrs in O2, starting with Y2O3, BaCO3 and CuO. When kept in water at 20°C, most of the superconducting black ceramics became white within 1 to 2 days, due to the H2O attack. However, the ceramics made of mixing atomic ratio 1:1:2 was still black and had Meissner effect up to 20 days. Jc of the 112 ceramics (25A/cm2) was smaller than 39A/cm2 of 123 ceramics. The mixing composition of the 112 was the same as that of the mixture of 123 and YCuO2.5 (20.5wt%). It is expected that the water resistivity and superconducting properties of the ceramics composed of 123 and YCuO2.5 (3 to 15wt%) may be better than those of the 123 or 112 ceramics. The Tc (zero) and Jc (77K) of these ceramics (123-YCuO2.5) were about 92K and 28-60A/cm2, respectively.However, the Jc of these ceramics when kept in water at 20°C for only 1 day decreased below 5A/cm2, in spite of these ceramics being black and having Meissner effect. When kept in salad oil, these ceramics were still black, and Tc (zero) and Jc were about 92K and 18-53A/cm2 even after 90 days. It is concluded that the H2O attack is very sever, but the superconducting properties are not so much damaged when kept in oil, due to the lack of water.
