Ionic motion and phase transition in potassium hydrogendifluoride KHF2 studied by pulsed NMR.
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概要
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Nuclear spin-lattice relaxation times, <I>T</I><SUB>1</SUB> and <I>T</I><SUB>1ρ</SUB>, have been measured above room temperature for <SUP>1</SUP>H and <SUP>19</SUP>F nuclei in powdered KHF<SUB>2</SUB> and its deuterated analogue. Below 400 K and in the high-temperature β-phase (<I>T</I><SUB>t</SUB>=469.8 K), the magnetization recovery for both nuclei in KHF<SUB>2</SUB> is strongly non-exponential owing to the heteronuclear H–F interaction. In the low-temperature α-phase the <I>T</I><SUB>1</SUB> <I>vs.</I> 1/<I>T</I> curves show broad minima ascribable to the 180°-flip motion of linear [FHF]<SUP>−</SUP> anions. The activation energy <I>E</I><SUB>a</SUB> of this motion was determined to be 50.5±2 kJ/mol. The phase transition, which is defined by discontinuous changes in both <I>T</I><SUB>1</SUB> and <I>T</I><SUB>1ρ</SUB>, is associated with diffusional disorder superimposed on rapid isotropic reorientation of the HF<SUB>2</SUB><SUP>−</SUP> ion. The relaxational process in the β-phase is governed by self-diffusion of the anions with an <I>E</I><SUB>a</SUB> of 80±6 kJ/mol deduced from the <I>T</I><SUB>1ρ</SUB> 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<SUP>−</SUP> ions but complex [FHF]<SUP>−</SUP> anions.
- 公益社団法人 日本化学会の論文
著者
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Furukawa Yoshihiro
The Institute of Scientific and Industrial Research, Osaka University
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Kiriyama Hideko
The Institute of Scientific and Industrial Research, Osaka University
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