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Direct Observation of Defect Dynamics in Nanocrystalline CaF2: Results from 19F MAS NMR Spectroscopy

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journal contribution
posted on 16.12.2015, 16:31 authored by Pragati Jain, Sangtae Kim, Randall E. Youngman, Sabyasachi Sen
The structure and F-ion dynamics in nanocrystalline CaF2 is studied using 19F fast magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy in the temperature range 22 °C ≤ T ≤ 240 °C. The 19F MAS NMR spectra of nanocrystalline CaF2 (diameter ∼ 25 nm) shows the presence of ∼0.55% of the F ions in interstitial sites that are found to be highly mobile at elevated temperatures and undergo rapid site exchange with regular fluorine sites in the lattice via hopping. It is shown that an increased concentration of these defects formed in nanocrystalline CaF2 may result in an enhancement in ionic conductivity by nearly 3 orders of magnitude compared to that of bulk CaF2.