We have investigated at room temperature and at 7 K the "0 NMR spectrum of a chemically and structurally characterized "0-enriched powder of Bi2Sr2CaCu208+, superconductor.Using the frequency dependence of the spectrum and TI relaxation-time measurements, we were able to infer that the two lines constituting the spectra can be assigned to the oxygen nuclei in the SrO planes and to the oxygen nuclei in the Cu02 planes. The absence of the expected BiO line is accounted for, on the basis of the incommensurate superstructure existing in these compounds.The interest of ' 0 nuclear magnetic resonance (NMR) measurements of high-T, superconducting oxides has been often underlined. Indeed, band-structure calculations have shown that the 2p 0 orbitals in the Cu02 planes contribute in a central manner to the formation of the charge-carrier bands. ' Up to now, "0 NMR results concerning YBa2Cu307 "powders ' and oriented powders, 3LaSrCu04-oriented powders and some oxides, precursors to the high-T, superconductors, 9 have been published."0 NMR studies of YBa2Cu307 ", with x 0 and 0.35, have confirmed experimentally that the doped holes are predominantly (0 2p)-like rather than (Cu 3d)-like, and that the spin susceptibility originates from the Cu02 plane. 6 Moreover, these measurements have allowed the specification that, at the 02, 03, and 04 oxygen sites, the spin density involves the p orbitals. In the Bi-Sr-Ca-Cu-0 system, NMR studies were essentially performed on the copper nuclei by nuclear quadrupole resonance (NQR) in the compounds Bi2$r2Ca2Cu30y (Ref. 10) and Bi2Sr2CaCu20s+, . " Very recently, Oldfield et al. ' have published an extensive study of ' 0 NMR in high-T, superconductors which includes spectra concerning the so-called 2:2:1:2phase of the Bi-Sr-Ca-Cu-0 system whose building blocks contain two copper planes. The authors pointed out difficulties in interpreting the spectra; namely only two lines were observed where three are expected. Difficulties in the interpretation of the NMR spectra in superconductors are not specific to the bismuth compounds. Indeed, the assignment of ' 0 NMR peaks is still controversial in YBa2Cui07, though the studies were performed on oriented powders. ' In this Rapid Communication, we present new experimental results concerning the ' 0 NMR of a chemically and structurally characterized enriched ' 0 powder sample of the 2:2:1:2phase of the Bi-Sr-Ca-Cu-0 type of superconductors.Using the frequency dependence of the spectrum and an appropriate pulse sequence, as well as Tm easurements, we were able to infer an assignment of the lines in the spectra, which is in agreement with the structural data available for this phase. In addition, we present the first preliminary results at temperatures located well below the critical temperature.With the view of elaborating ' 0-enriched material, pellets of the 2:2:1:2 phase were prepared by standard solid-state reactions. The ' 0 isotopic exchange was realized by two consecutive annealings of the pellets at 800'C, in a static atmosphere of enrich...
