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19F/119Sn/207Pb NMR Studies on Ion Dynamics in Tetragonal PbSnF4: Spectroscopic Evidence for Defect-Driven Conductivity
journal contribution
posted on 2017-01-13, 00:00 authored by Miwa Murakami, Yoshiyuki Morita, Motohiro MizunoIon
dynamics in tetragonal PbSnF4, which shows high
conductivity ∼10–3 S cm–1 at room temperature, was examined by using 19F/119Sn/207Pb solid-state NMR at 7 and 14 T. While the observed
temperature dependence of 19F spin–lattice relaxation
time (T1) decreases monotonously with
increasing temperature at the temperature range studied (ca. 230–360
K), 119Sn and 207Pb T1 bear T1 minima. From the short 119Sn T1 minimum value at 14 T
(ca. 0.85 ms) and its dependence on the strength of the static magnetic
field, it was concluded that the relaxation mechanism of 119Sn is fluctuation of the chemical-shift anisotropy (CSA). The activation
parameters for the motion responsible for the CSA relaxation were
found to be τ0 = (8.8 ± 3.1) × 10–15 s and Ea = 26.9 ± 0.1 kJ/mol. We
showed that mutual exchange of two F– ions does
not affect the size and orientation of the CSA tensor and thus cannot
be the CSA-relaxation mechanism. As a mechanism to affect the CSA
tensor, we invoked exchange between a F– ion and
a defect (the defect-diffusion motion). As the activation energy of
the defect-diffusion motion is consistent with that obtained from
temperature-dependent conductivity (∼28 kJ/mol), we concluded
the defect-diffusion motion is the motion responsible for ion conduction.