Bulletin of the Chemical Society of Japan
Online ISSN : 1348-0634
Print ISSN : 0009-2673
ISSN-L : 0009-2673
Ionic Motion and Phase Transition in Potassium Hydrogendifluoride KHF2 Studied by Pulsed NMR
Yoshihiro FurukawaHideko Kiriyama
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1978 Volume 51 Issue 12 Pages 3438-3442

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Abstract

Nuclear spin-lattice relaxation times, T1 and T, have been measured above room temperature for 1H and 19F nuclei in powdered KHF2 and its deuterated analogue. Below 400 K and in the high-temperature β-phase (Tt=469.8 K), the magnetization recovery for both nuclei in KHF2 is strongly non-exponential owing to the heteronuclear H–F interaction. In the low-temperature α-phase the T1 vs. 1/T curves show broad minima ascribable to the 180°-flip motion of linear [FHF] anions. The activation energy Ea of this motion was determined to be 50.5±2 kJ/mol. The phase transition, which is defined by discontinuous changes in both T1 and T, is associated with diffusional disorder superimposed on rapid isotropic reorientation of the HF2 ion. The relaxational process in the β-phase is governed by self-diffusion of the anions with an Ea of 80±6 kJ/mol deduced from the T data. In contrast to the earlier suggestion from electrical measurements, the NMR results indicate that the dominantly mobile species in the conducting high-temperature β-phase are not single F ions but complex [FHF] anions.

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