Nuclear magnetic resonance evidence of disorder and motion in yttrium trideuteride

Abstract

Three samples of YD x , with x ranging from 2.9 to nearly 3.0, were studied with deuterium nuclear magnetic resonance to gain insight into the locations of the D atoms in the lattice and their motions. Line shapes at low temperatures ͑200-330 K͒ show substantial disorder at some of the deuterium sites. Near 355 K, the spectrum sharpens to yield three uniaxial Pake patterns, reflecting a motional averaging process. However, the three measured intensities do not match the ratios expected from the neutron-determined, HoD 3 -like structure. This is strong evidence that the structure and space group of YD 3 are different than reported, or that the current model needs adjustment. At still higher temperatures near 400 K, the Pake doublet features broaden, and a single sharp resonance develops, signalling a diffusive motion that carries all D atoms over all sites. The temperature at which line shape changes occur depends on the number of deuterium vacancies, 3Ϫx. The changes occur at lower temperatures in the most defective sample, indicating the role of D-atom vacancies in the motional processes. The longitudinal relaxation rate T 1 Ϫ1 displays two regimes, being nearly temperature independent below 300 K and strongly thermally activated above. The relaxation rate depends on the number of deuterium vacancies, 3Ϫx, varying an order of magnitude over the range of stoichiometries studied and suggesting that D-atom diffusion is involved. Also, the activation energy describing T 1 Ϫ1 (Ӎk B ϫ5500 K) approximately matches that for diffusion. An unusual 0 Ϫ0.7 frequency dependence of T 1 Ϫ1 is observed. A relaxation mechanism is proposed in which diffusion is the rate-determining step and in which frequency dependence arises from a field-dependent radius of the relaxation zones.

Correlated Electromigration of H in the Switchable MirrorYH3−δ

“…In total, we performed 11 experiments on two samples at temperatures between 292 and 408 K. Both y 0 and D exhibit Arrhenius behavior, the latter with activation energy E a 0.45 6 0.03 eV (see Fig. 3a), a value comparable to the estimate obtained from NMR measurements by Balbach et al (0.5 6 0.1 eV) [23].…”

Proton magnetic resonance spectra ofYH3andLuH3

“…A sample of YH 2.96 was also studied, having been hydrided years ago by Hoffmann 9 following the same procedure as used for YD 3 by Balbach et al 10 and then stored in a flame-sealed glass tube. Data were taken for YH 2.96 at 186± 4 K, and for LuH 3 at 173± 2 K; at these temperatures both samples are in the NMR rigid-lattice limit.…”

The nature of deuterium arrangements in YD3 and other rare-earth trideuterides

“…Different spectroscopic probes such as neutron vibrational spectroscopy (NVS) [18,21,22,[32][33][34], Raman spectroscopy [35,36], infrared (IR) spectroscopy [35][36][37], and nuclear magnetic resonance (NMR) [38][39][40] have provided further clues concerning the local structural symmetry. Initial scrutiny of NV spectra for YH 3 and related hexagonal rare-earth trihydrides [19,22,32] led to the suggestion that the hydrogen vibrational lineshapes best reflected a local P 3 3c1 symmetry, although a more rigorous modeling of the data was needed to confirm this.…”