Deuterium exchange dynamics in Zr2NiD4.8 studied by 2H MAS NMR spectroscopy

Abstract

Variable temperature (VT) 2 H magic angle spinning (MAS) spectroscopy was employed to measure deuterium diffusion behavior in the Zr 2 NiD 4.8 phase.2 H 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 2 Ni 2 ), 32m (Zr 3 Ni), Zr 4 (16l and 4b)). As the temperature rises, the 2 H 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 2 H 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 16l hopping shows s c 4 10 8 . 2at 245 K and E a = 62.2 kJ/mol.