For 7,7,8,8- etracyanoquinodimethane (TCNQ)-treated (Bi,Pb) 2Sr2Ca2Cu3Oz[(Bi,Pb) -2223 super- conductors, a superstructure which can be described as 2a 0×2b0×c0 has been observed by electron diffraction. Superconductivity is virtually destroyed in the TCNQ-treated (Bi,Pb)-2223 cuprate. Superconductivity (with Tc up to 110 K) may be recovered for a TCNQ-treated sample by being annealed in flowing oxygen gas. Then the 2a0×2b0×c0 superstructure is found to disappear. This suggests that the superstructure may be caused by an ordering of oxygen vacancies. High resolution transmission electron microscopic observations reveal that the oxygen vacancies reside not only in the CuO2 sheets, but also likely in the SrO sheets. A model for the superlattice in both CuO2-x and SrO1-y sheets is proposed.
All Science Journal Classification (ASJC) codes
- Physics and Astronomy(all)