O17 nuclear-magnetic-resonance spectroscopic study of high-Tc superconductors

We have obtained solid-state O17 NMR spectra of a number of enriched17 oxides and high-temperature oxide superconductors, including Cu2IO, CuIIO, KCuIIIO2, Bi2O3, Tl2O3, La1.85Sr0.15CuO4, YBa2Cu3O7-x, Bi2Sr2CaCu2O8+x, Tl2Ba2CaCu2O8+x, and Ba0.6K0.4BiO3. Spectra of all of the simple diamagnetic oxides contain relatively sharp resonances in a diamagnetic region of -200 to +700 ppm (from H2O, International Union of Pure and Applied Chemistry scale). CuIIO exhibits a broad resonance centered at 4500 ppm. Spectra of all of the Cu-containing superconductors (at 300 K) contain a relatively broad and highly paramagnetically shifted peak, due to CuO2 planes, at 1800 ppm, together with a peak or series of peaks, in a more normal diamagnetic region, 100600 ppm from H2O. YBa2Cu3O7-x also contains a peak at 2950 ppm, assigned to the chain [O(4)] sites. The highly shifted (CuO2) features undergo a 10001300 ppm diamagnetic shift in YBa2Cu3O7-x and Tl2Ba2CaCu2O8+x upon cooling to 77 K (<Tc). These highly shifted features are absent in Ba0.6K0.4BiO3, although the resonance in Ba0.6K0.4BiO3 is 500 ppm paramagnetically shifted from that in the parent compound, BaBiO3. O17 NMR spectra of magnetically aligned samples of YBa2Cu3O7-x yield diagonal elements of the electric-field-gradient tensor (ii) for the CuO2 plane oxygens, O(2) and O(3), of (4.02,-6.46,2.44) and (3.95,-6.51,2.56) MHz. The observed resonance frequencies for both sites (H0c) are 1900 ppm from H2O. For the CuO2 plane in Bi2Sr2CaCu2O8+x (at 300 K) and in Tl2Ba2CaCu2O8+x (at 77 K) the quadrupole coupling constant (e2qQ/h) is 6.4 MHz also. For the column or bridging oxygen [O(1)] in YBa2Cu3O7-x, e2qQ/h7.3 MHz and 0, at 300 K, the isotropic frequency shift is 458 ppm, and the anisotropy of the chemical or Knight shift () is 657 ppm, with c. A similar result is found for the apical oxygen in La1.85Sr0.15CuO4, with 33=694 ppm and 11=22=474 ppm, determined on a magnetically ordered sample. For the chain site in YBa2Cu3O7-x [O(4)], we findii=(3.38,-10.94,7.56) MHz. Calculations suggest for all sites that Vzz is negative and is aligned along the Cu-O-Cu bond axis. Results on oxygen-depleted YBa2Cu3O7-x show considerable broadening of the plane-site features, consistent with the onset of antiferromagnetic ordering, while the column oxygens [O(1)] are much less affected. Temperature-dependence studies of T1 for O(2,3) in YBa2Cu3O7-x indicate Korringa-type behavior above Tc, and the Knight shift predicted is in good accord with that observed. There is no BCS-type relaxation enhancement just below Tc. Overall, our results give a broad basis for the assignment of O17 NMR resonances in most of the classes of high-temperature superconductors currently being investigated (2:1:4, 1:2:3, Bi2Cu2, Tl2Cu2, and Cu-free Bi-containing phases) and show considerable similarities in frequency shifts (and their temperature dependence), T1, e2qQ/h values, and spin-echo decay behavior, for the CuO2 planes in each system, and between the (La(Sr)O,SrO,BaO) and (TlO,BiO) planes as well.