Deuterium Exchange Dynamics in Zr_2NiD_(4.8) Studied by ^2H MAS NMR Spectroscopy

Variable temperature (VT) ^2H magic angle spinning (MAS) spectroscopy was employed to measure deuterium diffusion behavior in the Zr_2NiD_(4.8) phase. ^2H MAS NMR spectrum at ∼190 K provides with well-resolved 4 different site occupancies which can be assigned based on the crystal structure (16k (Zr_2Ni_2), 32m (Zr_3Ni), Zr_4 (16/ and 4b)). As the temperature rises, the ^2H peaks sensitively reflect the exchange behavior among the sites with evident change at around 230 K and reaching a uniform distribution of site occupancies, indistinguishable in NMR timescale, above 245 K. This behavior is reflected by the collapse of the ^2H MAS spectrum into a single peak. From analyses of VT MAS NMR spectra, we were able to extract multiple hopping rates and activation energies among face sharing interstices: for example, 32m ↔ 16/ hopping shows _(τc)=2.8×10^(-4)s at 245 K and E_a = 62.2 kJ/mol.