Oxygen nonstoichiometry, point defects and critical temperature in superconducting oxide Bi2Sr2CaCu2O8+Delta

Oxygen nonstoichiometry of the high-T-c superconductor Bi2Sr2CaCu2O8+4 has been investigated by thermogravimetric techniques from 300 degreesC to the phase stability limits with oxygen partial pressure ranging from 1 to 10(-4 ) atm. Although it was not possible to remove the entire oxygen excess due to phase decomposition, Delta could be reversibly varied from 0.23 to 0.15. Depending on the annealing temperature, two different behaviours have been observed. At low temperature, the oxygen exchange consists in the intercal ation of O2- ions, while over 800 degreesC, oxygen vacancies are likely to be created in the lattice. The consequences on the superconducting transiti on temperature are revealed. It appears that the physical properties of the material (e.g., T-c) can be governed at constant oxygen content through th e control of the oxygen excess distribution. (C) 2000 Elsevier Science B.V. All rights reserved.