Characteristic of local electron structure, O-T phase transition and superconductivity for oxygen-deficient YBa2Cu3O7-delta systems

The oxygen deficient YBa2Cu3O7-delta (delta = 0.06 similar to 0.68) has bee n studied by positron lifetime experiment at normal state 300 K. It is foun d that there exists an abrupt change of positron lifetime parameter near Or thorhombic-Tetragonal phase transition. The local electron density n(e) and vacancy concentration C-nu are evaluated as a function of oxygen deficienc y delta. The effect mechanism of local electronic structure on charge trans fer and superconductivity is given in detail. The results show the existenc e of weak localization of electrons in tetragonal phase. The positron annih ilation mechanism and its relation with superconductivity are also discusse d. (C) 1999 Published by Elsevier Science B.V. All rights reserved.