ATOMISTIC MODELLING OF SUPERSTRUCTURE REFINEMENT IN CRYSTALLINE MATERIALS 
Rafal Kozubski ^{3}, Ewa Partyka ^{3}, Mirosław Kozłowski ^{3}, Véronique PierronBohnes ^{1}, Wolfgang Pfeiler ^{2} 
1. Institut de Physique et Chimie des Materiaux de Strasbourg, UMR7504, CNRS  ULP, 23, rue du Loess, BP 43, Strasbourg CEDEX 2 67034, France 
Abstract 
Chemical ordering in multicomponent crystalline systems is of fundamental technological importance and knowledge of its dynamics (kinetics) is crucial in materials engineering. The process, however, always competes with the general tendency for entropy maximization and hence, at any nonzero temperature T finite concentration of antisite defects is observed and increases with increasing T. Consequently, a change of system temperature is followed by generation/annihilation of antisite defects, socalled "orderorder" relaxation, whose mechanism (atomic migration) is the same as that of diffusion. The kinetics of both phenomena are different due to non steadystate conditions during relaxation. "Orderorder" relaxation may be successfully modeled by computer simulations, which involves the following tasks: (i) approximation of system energetics (Hamiltonian), (ii) energetics and thermodynamics of structural defects (vacancies, interphases, surfaces), (iii) implementation of particular atomicjump mechanism, (iv) adaptation/elaboration of computer codes.
