INFLUENCE OF OXYGEN POSTANNEALING ON SUPERCONDUCTING PROPERTIES OF NDBA2CU3OY

The onset superconducting transition temperature(Tc) for oxygen-contro lled melt-growth NdBa2Cu3Oy(Nd123) depended on the post oxygenation te mperature(Ta). The fact that the samples with hihger oxygen content ex hibit higher Tc implies that oxygen content accounts for the differenc e of Tc. The higher oxygen content in those samples which grown in the lower oxygen partial pressure P(O-2), may result from the more second phases and porosities in them, which may provide more passages for ox ygen diffusion, especially for those oxygenated at low Ta. The post ox ygenation at 250 degrees C seems to be most effective process to obtai n high onset Tc, while for Y123, a higher temperature (about 400 degre es C) may be best. The fact may be connected with the lower repulsive energy of oxygen atoms between O(1) and O(5) sites in Nd123.