⁷¹Ga Chemical Shielding and Quadrupole Coupling Tensors of the Garnet Y₃Ga₅O₁₂ from Single-Crystal ⁷¹Ga NMR

Abstract

A single-crystal (71)Ga NMR study of the garnet Y(3)Ga(5)O(12) (YGG) has resulted in the determination of the first chemical shielding tensors reported for the (71)Ga quadrupole. The single-crystal spectra are analyzed in terms of the combined effect of quadrupole coupling and chemical shielding anisotropy (CSA). (71)Ga quadrupole coupling and CSA parameters for the two (tetrahedrally and octahedrally coordinated) gallium sites with axial symmetry in YGG (Ga(IV), C(Q) = 13.1 +/- 0.2 MHz and delta(sigma) = 54 +/- 50 ppm; Ga(VI), C(Q) = 4.10 +/- 0.06 MHz and delta(sigma) = 24 +/- 3 ppm) are fully consistent with its cubic crystal structure which supports the reliability of the experimental data. In addition, the (71)Ga and (27)Al isotropic chemical shifts for YGG and YAG give further support to the linear correlation observed earlier between (71)Ga and (27)Al isotropic chemical shifts.

27Al Chemical Shielding Anisotropy

“…However, when the chemical shielding anisotropy is included as an additional interaction to the quadrupole couthe three perpendicular rotation axes 0x T (a), y T (b), and pling ( 2,14 ) , the simulations indicated by the solid lines 0z T (c) of the tenon frame (T) as defined elsewhere (13,14). For all spectra five distinct resonances correspond-in Fig.…”

Improved Hardware and Software for Single-Crystal NMR Spectroscopy

“…[7] or [8] depending on the interaction. To facilitate this assignment we have developed the software package ASICS (Analysis of Single-Crystal Spectra).…”

“…The resonances are selected using the mouse, and the optimum curvature, given by Eq. [7] or [8], is calculated interactively. Thereby, a line corresponding to the optimum curve is drawn on the screen in order to help the assignment.…”

“…This allows a determination of the relevant interaction parameters from the coefficients in Eqs. [7] and [8]. However, it is necessary to refine the parameters according to the minimum rms deviation [9] between the N experimental ( i e ) and calculated ( i c ) resonance frequencies for all three rotation axes.…”

“…Such cases include (i) complex powder spectra resulting from overlap of patterns from many different sites (4 -8), (ii) samples for which one of the interactions of interest is so weak that the effect of this interaction will be averaged by MAS even at low spinning frequencies (6,9) or is hidden in the line broadening of the dominating anisotropic interaction when observed from static spectra of powder samples (6, 7, 9 -12), and (iii) quadrupolar nuclei for which the quadrupole interaction is so strong that even the second-order broadening of the central transition is larger by more than an order of magnitude than the available spinning frequencies (7,8).…”