Deuterium NMR Study of Unstable Phenomena and Water Molecular Dynamics in Samarium Nitrate Hexahydrate Crystal

Abstract

Deuterium NMR spectra, spin−lattice relaxation time T1, and differential thermal analysis (DTA) were measured for Sm(NO3)3·6D2O. The magnetization recovery can be divided into two components. From deuterium NMR spectra and T1, the short and the long components of T1 were found to be mainly dominated by the 180° flip of the crystallization and the coordinated water molecules, respectively. For the nonannealed sample, the reproducibility of T1 was observed. The influence of the instability was not seen in the long component of T1. The results of the long component of T1 gave the activation energy Ea = 20 kJ mol-1 and the correlation time at infinite temperature τc0 = 7.8 × 10-12 s for the 180° flip of the coordinated water molecule. The motion of the crystallization water at low temperatures can be explained by the 180° flip in the asymmetric double minimum potential. τc0 = 1.2 × 10-12 s, Ea = 16 kJ mol-1, and the energy difference in the potential wells ΔE = 2.0 kJ mol-1 were obtained for the 180° flip of ...