Self-diffusion in Pure and Impurity Doped dl - Camphene

dl-Camphene has been ultra-purified and the process of self-diffusion in well-annealed crystals studied as a function of added dopants and temperature using radiotracer and plastic deformation techniques. Impurities of equivalent size and shape to the host form solid solutions which do not perturb significantly the sub-structure of prepared crystals. As the size of the impurity departs from that of the host, segregation and precipitation occur either during or following solidification to yield an increased sub-grain-boundary and strain-induced dislocation sub-structure. In some cases this sub-structure was stable to annealing and the influence of a high equilibrium density of such imperfections on the self-ditrusion process could be examined. In the pure solid radiotracer self-diffusion proceeds in a manner similar to that observed for other pure rotator-phase solids. The introduction of imperfections produces the expected increase in overall diffusion rates and correspdnding decrease in activation energy. These changes are mirrored by the plastic deformation experiments but not by a parallel pulsed n.m.r. examination. As found previously the latter yields results for both pure and imperfect samples which equate most closely with the radiotracer results for the defective samples.