The nature of oxygen exchange in ZrW2O8 revealed by two-dimensional solid-state 17O NMR

Abstract

17O magic angle spinning (MAS) NMR has been used to determine the nature of oxygen exchange in ZrW(2)O(8). A highly effective isotopic labelling technique has been developed and 1D NMR and 2D exchange spectroscopy (EXSY) experiments have revealed that mutual exchange occurs between all oxygen sites, even at temperatures considerably below the alpha to beta order-disorder phase transition.

Quadrupolar transients, cosine correlation functions, and two-dimensional exchange spectra of non-selectively excited spin-3/2 nuclei: A 7 Li NMR study of the superionic conductor lithium indium phosphate

“…One can either attempt to remove the anisotropic spectral broadening, e.g., by sample rotation techniques, and aim at resolving potential differences of isotropic chemical shifts at different probe sites. This strategy has been used for a diverse array of nuclei, see, e.g., [5,6,7,8,9,10,11,12]. Alternatively, like often employed for spin-1/2 nuclei, one may exploit the anisotropic part of the interaction, a strategy that we will focus on in the present work.…”

“…Therefore, an important question is whether their NMR powder spectra are moderately broad (up to a few 100 kHz)so that they can be irradiated nonselectivelyor whether they are several MHz wide allowing only their central transition to be excited using standard techniques. Nonselective excitation of quadrupolar probes is typically achievable for spin-1 nuclei such as 2 H and 6 Li or for the spin-3/2 nuclei 7 Li and 9 Be. In general, relatively narrow ---# e-mail: michael.storek@tu-dortmund.de quadrupolar satellite spectra emerge only if the charge distribution near the nuclear site deviates not too strongly from cubic symmetry [13].…”

17O NMR in room temperature phase of La2Mo2O9 fast oxide ionic conductor

“…If site exchange has occurred during the mixing time, magnetization shows up as off-diagonal cross peaks in the two-dimensional spectrum. 13,14 In the exchange spectra obtained at room temperature (Fig. 6, t m D 50 ms) all the intensity remains on the unexchanged diagonal line, broadened by T 2 effects.…”

“…Dynamic processes on time-scales of milliseconds to hundreds of milliseconds could also affect the 17 O spectra and could be evidenced by exchange experiments. 13,14 An exchange experiment correlates the spectral signature of the system at two different times separated by a given mixing or exchange time. The magnetic system of the central transition is spectrally encoded during a first evolution time t 1 , stored along the principal field during the mixing or exchange time, and finally recalled for observation during time t 2 .…”

“…13,14 In this work, we used 17 O highresolution solid-state NMR to characterize the˛-phase of La 2 Mo 2 O 9 at room temperature. Oxygen NMR parameters (chemical shifts and electric field gradients) are very sensitive to the nature of oxygen bonding.…”