EPR spectra of deoxygenated high T-c superconductors

EPR spectra of deoxygenated Bi-2201, Bi-2212, Bi-2223, Y-123, Tl-2223 and H g-1223 have been investigated. Different types of Cu-clusters as octamers, tetramers, dimers and monomers have been identified. EPR spectra were recor ded for more than 100 samples of these materials, from different batches of preparations and from different portions of the same batch with the aim of recording all varieties of the spectra in these materials. Different sampl es of the same compound gave different spectra, some of which were repetiti ve but some spectra of the samples of different compounds were also similar . In different samples of the same compounds, different combinations of the spectra of octamers, tetramers, dimers and monomers appeared. In all 20 di fferent types of spectra could be observed. The role of Cu-tetramers in the mechanism of high temperature superconductivity has been hinted at. (C) 20 01 Elsevier Science B.V. All rights reserved.