⁹¹Zr nuclear quadrupole coupling in zircon (ZrSiO₄)

Abstract

The first measurement of 91Zr nuclear quadrupole coupling in a solid is reported. The nuclear quadrupole coupling constant (e2qQ/h) and chemical shift anisotropy ( sigma ax) for 91Zr, and the chemical shift anisotropy for 29Si, have been determined for zircon (ZrSiO4) from high-field NMR single-crystal rotation patterns. A striking variation of 91Zr linewidth with crystal orientation in the field was observed and explained in terms of local variations in the (001) tetragonal axis orientation due to crystal mosaic structure as well as a distribution of local electric-field gradients due to defects.

Multinuclear NMR study of silica fiberglass modified with zirconia

“…In the three crystalline ZrO 2 phases the spectra were dominated by quadrupolar interactions in agreement with previous reports [92], and CASTEP calculations (Table 3). Only in zircon, ZrSiO 4 , the contribution from the chemical shielding interactions is not negligible, O¼160 ppm, which agrees well with the previously reported 91 Zr singlecrystal NMR data [90]. The 91 Zr NMR spectrum recorded for orthorhombic ZrO 2 shows significant disorder, even though the sample itself is crystalline.…”

“…We note that the earlier reported 91 Zr chemical shifts in crystalline ZrO 2 oxides suffered from greater uncertainty due to lower magnetic fields used [87,[89][90]92]. The isotropic 91 Zr chemical shifts in the crystalline ZrO 2 phases and zirconia silicates fall within about the same range (Table 3), which makes them rather insensitive to zirconium coordination number by oxygen, and to the presence of silicon atoms in the second coordination sphere of ZrO x species.…”

“…Only a few 91 Zr NMR studies in materials have so far been reported in the literature [24,[28][29][30][87][88][89][90][91][92][93][94][95]. Most recent research fully utilizes advantages of performing 91 Zr NMR experiments at ultrahigh magnetic fields, some examples include microporous and layered zirconium phosphates [28,96] and metallocene catalysts [97].…”

“…This simplifies recording such spectra and also contributes to improved sensitivity. For example earlier studies in three crystalline ZrO 2 phases, monoclinic, tetragonal, and orthorhombic, required recording 91 Zr NMR spin-echo spectra in a frequency-stepped manner [29,90,92]. Later work employed 91 Zr NMR frequency-stepped QCPMG technique to record such spectra at 9.4 T with much better quality and in shorter time [24,87].…”

29Si NMR characterisation of the crystalline-amorphous transition in ZrSiO4

“…However, the broad line seen here does not mean that a wide variety of crystalline domain orientations have arisen in the crystal because of a-decay damage. The full single crystal rotation pattern for an undamaged zircon has been measured (Bastow, 1990) and the anisotropy in chemical shift is only 9 ppm across all relative orientations of zircon single crystal and magnetic field. The broadening is due to the anisotropic magnetic susceptibility introduced into the zircon by the creation of paramagnetic centres and the resulting range of local magnetic fields experienced by different Si atoms.…”