Abstract
Deuterium NMR spectra of were obtained at 8.0 and 8.4 T from 163 to 398 K, revealing only minor changes with temperature. The resonance has an outer, uniaxially symmetric quadrupolar doublet, arising from atoms in the unit cell. An inner resonance with quadrupolar asymmetry and approximately twice the intensity is assigned to the nominally tetrahedral atoms. Using partial alignment of the powder particles in the magnetic field and subsequent freezing in wax, the NMR line shape has been studied as a function of field direction, allowing the orientation of the electric-field-gradient tensor to be partly determined. In addition, the agreement of the aligned line shapes with simulations confirms that the spectrum has only two components, from and atoms; specifically, there is no evidence for two subgroups of atoms. The decays of two-pulse echoes and three-pulse spin-alignment echoes indicate fluctuations in the quadrupole splittings due to atomic motions. The spin-lattice relaxation rate above 300 K is an approximately thermally activated function of temperature; in this region is determined by atomic diffusion to relaxation centers. Comparisons are made between the NMR behaviors of and
- Received 18 November 2002
DOI:https://doi.org/10.1103/PhysRevB.67.174115
©2003 American Physical Society