19F-NMR Study in Phase Transition of [(CH2OH)3CNH3]2SiF6

Abstract

Measurements of 19F and 1H-NMR absorption lines have been carried out in [(CH2OH)3CNH3]2SiF6 below room temperature. It was found that the 19F-NMR absorption line width becomes narrow with the increase of temperature above around 100 K and becomes almost constant above Tc= 178 K. This result indicates that motional narrowing of 19F-NMR line accompanied by the phase transition at 178 K is observed. It is deduced from this narrowing that the SiF6 2− anions are reoriented with the correlation time which is fast enough to narrow the 19F-NMR absorption line above Tc. Moreover, we have observed the drastic change of 1H-NMR absorption line above Tc. This result indicates that the ─CH2OH groups begin to reorient by the phase transition at Tc. It is deduced from these results that the motions of SiF6 2− anions and ─CH2OH groups play an important role in the phase transition at 178 K.