O17NMR spectroscopy of magnetically orderedY

Abstract

We have obtained ' 0 nuclear-magnetic-resonance spectra of powder samples of YBa2Cu307and EuBa2Cu30& -, as well as magnetically ordered YBa2Cu307-". Two major features are observed in YBa2Cu307 -. 'a sharp resonance at =1800 ppm (from external H2' 0, International Union of Pure and Applied Chemistry 8 scale) and a broader series of features centered at =400 ppm. The 1800-ppm feature undergoes a diamagnetic shift of =800 ppm on cooling to 77 K, and a similar magnitude shift on Eu substitution, suggesting assignment to the plane oxygens, O(2, 3). Measurements on magnetically ordered samples at 8.45 and 11. 7 T give the magnitude of the diagonal terms of the electric-field-gradient tensor, which are 2.3, 3.5, and 5.8 MHz. For the column oxygen, O(1), we find e q2g/h 7.7 MHz, with a chemical shift anisotropy of =660 ppm.All of the new high-T, superconducting oxides' are, in principle, excellent candidates for study using ' 0 nuclear-magnetic-resonance (NMR) spectroscopy. We show in this Rapid Communication that such studies are indeed possible, and by using magnetically aligned materials, ' we are able to investigate both chain and plane sites in ' 0-labeled YBa2Cu307 . We observe large changes in the ' 0 resonance frequency shifts (of the plane oxygens) upon formation of the superconducting state. Additionally, we have determined the nuclear quadrupole coupling constants (e qQ/h), electric-field-gradient tensor asymmetry parameters (rl), and chemical shift anisotropies (t5, 8) for selected oxygen sites. Given the ubiquitous nature of oxygen in high-T, superconductors, such atomic level probes of both magnetism and structure oN'er considerable hope for elucidating the details of superconductivity in these systems. Unlabeled YBa2Cu307 -, (and EuBa2Cu 307 -") was prepared from Y203(Eu203), BaCO3, and CuO (99.99%,

Oxygen-17 NMR spectroscopy: Basic principles and applications (part II)

“…by Oldfield and collaborators [103,963]. Spectra of the diamagnetic oxides contain relatively sharp resonances in a region of $À200 to +700 ppm.…”

Tris(pyrazolyl)hydroboratomagnesium and aluminum alkyl derivatives: alkyl exchange with methyl iodide and enolate formation with acetone

“…-1514 -------^Mg-X 2.130 (10), Mg-N22 = 2.137 (7), N11-N12 = 1.375 (13), N21-N22 = 1.390 (8), B-N11 = 1.524 (16), B-N21 = 1.532 (11); N12-Mg-N22 = 91. 3 (3), N22-Mg-N22' = 90.6 (4), N11-B-N21 = 109.7 (7), 21--2 = 108.8 (10).…”

Radio-Spectroscopic Studies of Magnetic Properties of High Temperature Superconductors

“…2), denoted by a, ß, and y. As the spectrum recorded in the c || H orientation should not contain any broadening due to the anisotropy of the quadrupolar and magnetic shift interactions, the intensity ratio 4:2:1 of the lines a, ß, and y, respectively, corresponds to the already established [12,13] assignment. Therefore the line a corresponds to oxygens in the Cu0 2 plane sites 0(2, 3), ß to the oxygen bridging the CuO planes and chains 0(4), and the smeared line y to the oxygen in the CuO chains, O(l).…”