J. Phys. IV France 03 (1993) C4-213-C4-215
Structural characteristics of Bi-based superconductors studied by positron annihilationS.J. WANG1, Z. TANG1, X.H. GAO2 and Z.X. ZHAO3
1 Department of Physics, Wuhan University, Wuhan 430072, P.R. of China
2 Department of Chemistry, Central-South University of Technology, Changsha 410083, P.R. of China
3 Institute of Physics, Chinese Academy of Sciences, Beijing, 100080, P.R. of China
We have measured the positron lifetime spectra as a function of temperature from 80 to 300 K and Doppler-broadening annihilation radiation (DBAR) spectra in normal and superconducting states for three kinds of Bi-based superconductors : Bi2212, Pb-and F-doped Bi2223. For Pb-doped Bi2223 superconductor, anomalies in the temperature dependence of positron lifetimes indicate the structural instabilities. However, a continuous increasing in the mean lifetime is observed for F-doped Bi2223 system and interpreted in terms of a simple thermal expansion with an average linear expansion coefficient « [MATH] 35x10-6. The difference spectra of DBAR spectra after deconvolution between two states show an evidence for charge transfer between the Cu-O and Bi-O planes in Bi-based superconductors. The role of oxygen defects in charge transfer was discussed.
© EDP Sciences 1993