1H NMR study of the phase transitions of trissarcosine calcium chloride single crystals at low temperature

Abstract

The 1H NMR line-width and spin–lattice relaxation time T 1 of TSCC single crystals were studied. Variations in the temperature dependence of the spin–lattice relaxation time were observed near 65 and 130 K, indicating drastic alterations of the spin dynamics at the phase transition temperatures. The changes in the temperature dependence of T 1 near 65 and 130 K correspond to phase transitions of the crystal. The anomalous decrease in T 1 around 130 K is due to the critical slowing down of the soft mode. The abrupt change in relaxation time at 65 K is associated with a structural phase transition. The proton spin–lattice relaxation time of this crystal also has a minimum value in the vicinity of 185 K, which is governed by the reorientation of the CH 3 groups of the sarcosine molecules. From this result, we conclude that the two phase transitions at 65 and 130 K can be discerned from abrupt variations in the 1H NMR relaxation behavior, and that 1H nuclei play important roles in the phase transitions of the TSCC single crystal.