"Aging" of the structure of crystals of hard colloidal spheres

We study the development of the structure of crystals of colloidal hard sph eres in time when gravity effects are minimal and polydispersity is small ( <3%). The initial stacking of the close-packed hexagonal layers that make u p the crystals is varied by applying various types of shear stress during n ucleation of the crystals. The experimental powder diffraction patterns are consistent with a fraction of a faulted-twinned face-centered cubic (fcc) structure that grows at the expense of randomly stacked crystallites. If a faulted-twinned fcc structure is generated initially, no change is found ov er a considerable time. The present observations rule out the possibility t hat a randomly stacked structure is the equilibrium structure of colloidal crystals of (nearly) hard spheres, and point to the thermodynamic or kineti c stability of faulted-twinned fcc crystals in these systems. (C) 2000 Amer ican Institute of Physics. [S0021-9606(00)70307-2].