Deuterium NMR study of structure and motion inLuD3

Abstract

Deuterium NMR spectra of ${\mathrm{LuD}}_{3}$ 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 ${\mathrm{D}}_{m}$ atoms in the unit cell. An inner resonance with quadrupolar asymmetry $\ensuremath{\eta}=0.68$ and approximately twice the intensity is assigned to the nominally tetrahedral ${\mathrm{D}}_{t}$ 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 $\ensuremath{\eta}\ensuremath{\ne}0$ 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 ${\mathrm{D}}_{m}$ and ${\mathrm{D}}_{t}$ atoms; specifically, there is no evidence for two subgroups of ${\mathrm{D}}_{t}$ 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 ${R}_{1}$ above 300 K is an approximately thermally activated function of temperature; in this region ${R}_{1}$ is determined by atomic diffusion to relaxation centers. Comparisons are made between the ${}^{2}\mathrm{D}$ NMR behaviors of ${\mathrm{LuD}}_{3}$ and ${\mathrm{YD}}_{3}.$