LOCAL ELECTRON-STRUCTURE AND VACANCY PROPERTIES FOR OXYGEN-DEFICIENT YBA2CU3O7-DELTA(DELTA=0.06-SIMILAR-TO-0.68) BY POSITRON LIFETIME DATA

We report the positron lifetime results for oxygen deficient YBa2Ca3O7 -delta(delta = 0.06-0.68) systems and calculate the local electron den sity n(e) and vacancy concentration C-v as a function of delta at 77K and 300K. The results show that there exist a significant dependence o n oxygen-deficient and near delta = 0.4, corresponding only right to O -T transition, an anomalous change occurses. These may be explained by the electronic weak localization and orthorhombic structural characte ristic of Y(123) cuprate.