Heterogeneous Translational Dynamics of Succinonitrile in the Plastic Crystalline Phase

Abstract

A plastic crystal (PC) has a crystalline phase characterized by disordered molecular orientations while maintaining a regular lattice of molecular positions. Recent studies have reported heterogeneous dynamics within the PC phase of several ionic PCs (IPCs). This study investigates whether similar dynamics exist in a molecular PC (MPC) by examining the temperature dependence of the spin-lattice relaxation time (T 1 ) and the spin-spin relaxation time (T 2 ) of succinonitrile (NC-CH 2 -CH 2 -CN) using pulsed low-frequency nuclear magnetic resonance. The results reveal a splitting of T 2 values, which are sensitive to translational motion, within the PC phase, indicating the presence of heterogeneous translational dynamics in both MPCs and IPCs. These findings suggest that such heterogeneous dynamics are an intrinsic, yet previously overlooked, property common to plastic crystals regardless of their ionic or molecular nature.