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

Abstract

Variable temperature (VT) 2H magic angle spinning (MAS) NMR spectroscopy was employed to measure deuterium diffusion behavior in the Zr2NiD4.8 phase. 2H MAS NMR spectrum at ∼190K provides with well-resolved 4 different site occupancies which can be assigned based on the crystal structure (16k (Zr2Ni2), 32m (Zr3Ni), Zr4 (16l and 4b)). As the temperature rises, the 2H peaks sensitively reflect the exchange behavior among the sites with evident change at around 230K and reaching a uniform distribution of site occupancies, indistinguishable in NMR timescale, above 245K. 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↔16l hopping shows τc=2.8×10-4s at 245K and Ea=62.2kJ/mol.