Lattice defects in plastic organic solids. Part 2.—Anomalous self-diffusion in succinonitrile

A comparative study of tracer self-diffusion and creep has been carried out for the high-temperature plastic phase of succinonitrile. The results indicate that, as for other plastic solids, plastic deformation is self-diffusion controlled. Self-diffusion rates varied with temperature according to D=(4.3±1.3)× 10–4 exp [(57.3 ± 0.8 kJ mol–1)/RT] m2 s–1. The pre-exponential factor and activation energy are anomalous in that they are relatively lower than the values previously found for this class of solid. This anomaly is ascribed to the generation of an excess of non-thermal “point” defects in the crystal lattice by the presence of isomeric “impurity”.