Self-Diffusion in the Molecular Crystal Adamantane; Comparison of NMR and Plastic-Flow Methods

Abstract

Ultraslow-motion NMR and plastic-flow-rate techniques, both applied here for the first time to diffusion in a molecular crystal, each yield an activation enthalpy for self-diffusion of ∼36 kcal/mol. Mechanical properties of so-called plastic crystals have long been considered anomalous, but the relation between diffusion and plastic flow shown here renders the creep properties as well understood as those in metals.