High resolution He diffraction and scanning tunneling microscopy images of the fivefold surface of a single-grain i-AlPdMn quasicrystal are obtained showing an almost perfect quasicrystal order. Observed configurations can be identified within the framework of polyhedral models. The terrace terminations are found to be Al-rich planes and successions of step heights agree with distances between dense Al planes in the model. This shows the ability of recent 6D polyhedral models to describe real quasicrystalline atomic configurations.

Some A 3 B fcc alloys undergo a chemical order-disorder phase transition. During the ordering process, four types of domain appear within the bulk, separated by antiphase boundaries ͑APB's͒. As for chemical ordering in the presence of a surface, scanning tunneling microscopy and He diffraction studies consistently show a contrasting behavior between vicinals, where APB's emerge at the surface, and low-index surfaces, where no APB's emerge. These differences emphasize the role of the step density in surface chemical ordering.

The kinetics of the ordering and coarsening of B2-ordered domains is studied using atomistic kinetic Monte Carlo simulations. Special emphasis is put on the effect of annealing temperature, alloy composition, and atom dynamics on the coarsening behavior. When atomic diffusion proceeds by vacancy jumps to nearest-neighbor sites, a transient slow coarsening regime is observed at temperatures below half the order-disorder transition temperature T c . It results in apparent coarsening exponents that decrease with decreasing the annealing temperature. Values as low as 0.14 are measured at 0.25T c . Slow transients take place in both stoichiometric and nonstoichiometric alloys. These regimes are correlated with the transient creation of excess antisites during domain disappearance. Since antiphase boundary mobility decreases with increasing antisite concentration, this transient excess results in the slow coarsening observed in simulations.

In this paper, we present the first quantitative determination of the divergence law of the correlation length ξ, when approaching the second order phase transition DO3→B2, by studying the behaviour of the APBs by transmission electron microscopy.