O-17 NMR CHARACTERIZATION OF THE OXYGEN SITES IN THE BI2SR2CAN-1CUNO4+2N (N = 1, 2, 3) HIGH-TEMPERATURE SUPERCONDUCTORS

O-17 NMR measurements have been performed on the Bi2Sr2Ca(n-1)Cu(n)O4+2n (n = 1, 2, 3) phases allowing the different oxygen sites to be identified. Detailed study of the n = 3 phase in different applied magnetic fields has allowed extraction of the shift and quadrupole interaction parameters at the oxygen sites. For this phase the two distinct sets of copper planes have markedly different oxygen shifts, 1590 ppm and 1285 ppm, shift anisotropies, 1300 ppm and < 50 ppm, and quadrupolar coupling constants, 2.8 MHz and < 0.5 MHz, with the additional CuO2 plane having the smaller shift and anisotropy. This implies that the local susceptibility is lower in this plane and that the 2p occupancy is less. There is only a small shift difference for the CuO2 plane oxygens between the superconducting n = 2 phase and the nonsuperconducting (for our samples) n = 1 phase. Only one resonance, at 265 ppm, is observed in all three phases for the SrO, BiO planes. We suggest that this is from the SrO plane and that the electric field gradient at the oxygen site produced by the incommensurate modulation of the Bi-O distances broadens the line from the BiO plane beyond detection.