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

• Zr2NiD4.8 was studied by 2D VT MAS NMR.
• The site occupancies among Zr4 (4b, 16l), Zr3Ni (32m), and Zr2Ni2 (16k) interstices were determined at ~ 190 K.
• Deuterium diffusion takes place to reach uniform occupancies in NMR time scale at T > 245 K.
• Multiple hopping motions among interstices were probed from analyses of 2D VT MAS NMR spectra.

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 ∼190 K 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 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 ↔ 16l   hopping shows τc=2.8×10-4s at 245 K and Ea = 62.2 kJ/mol.

2H VT MAS NMR determines the site occupancies and hopping motions of deuterium atoms among Zr4 (4b, 16l), and Zr3Ni (32m), and Zr2Ni2 (16k) interstices in Zr2NiD4.8.Figure optionsDownload as PowerPoint slide