In colloidal crystals of spheres, dislocation motion was unrestricted. On the other hand, recent studies of relaxation in crystals of colloidal dimer particles had demonstrated that the dislocation dynamics in such crystals were reminiscent of glassy systems. The observed glassy dynamics arose as a result of dislocation cages formed by certain dimer orientations. In the present study, experiment and simulation were used to investigate the transition that arose when a pure sphere crystal was doped with an increasing concentration of dimers. In particular, attention was focussed upon both dislocation caging and vacancy motion. It was found that any non-zero fraction of dimers introduced finite dislocation cages; suggesting that glassy dynamics were present for any mixed crystal. However, a vacancy-mediated uncaging mechanism for releasing dislocations from their cages was also identified. This mechanism was dependent upon vacancy diffusion, which slowed by orders of magnitude as the dimer concentration was increased. It was proposed that, in mixed crystals with low dimer concentrations, vacancy diffusion was fast enough to uncage dislocations and delay the onset of glassy dislocation dynamics.

Dislocations and Vacancies in Two-Dimensional Mixed Crystals of Spheres and Dimers. S.J.Gerbode, D.C.Ong, C.M.Liddell, I.Cohen: Physical Review E, 2010, 82[4], 041404