Study of the synthesis process and structural defects in Y-123 superconducting systems by positron experiment

Using positron annihilation,X-ray diffraction and scanning electron microsc opy experiments,the structural characteristics and preparation techniques f or YBa2Cu3O7-delta systems are systematically studied. The results show tha t,for the samples sintered at 950 degreesC,the orthorhombic disorder increa ses with the duration of sintering time. On the whole,with the increase of sintering temperature and time, the positron lifetime increases until it re aches a saturation value. It is proved that,under the condition of 920-950 degreesC for 12-72 h,the structural characteristics and superconductivity o f Y-123 have good stability. The changes of defect with the sintering tempe rature and time are also discussed. This experimental results indicate that the positron experiment shows good stability and reliability.