Chemical ordering beyond the superstructure in long-range ordered systems

TL;DR

This paper extends the Warren-Cowley short-range order parameters to long-range ordered systems, enabling better analysis of chemical ordering beyond superstructure arrangements, demonstrated on a B2-ordered alloy.

Contribution

The authors generalize the Warren-Cowley parameters for long-range order and apply the theory to a non-stoichiometric alloy using Monte Carlo simulations.

Findings

Extended parameters describe chemical order beyond superstructure.

On-lattice and off-lattice methods show different effects.

Quantitative analysis of long-range order in alloys.

Abstract

To describe chemical ordering in solid solutions systems Warren-Cowley short-range parameters are ordinarily used. However, they are not directly suited for application to long-range ordered systems, as they do not converge to zero for large separations. It is the aim of this paper to generalize the theory to long-range ordered systems and quantitatively discuss chemical short-range order beyond the superstructure arrangements. This is demonstrated on the example of a non-stoichiometric B2-ordered intermetallic alloy. Parameters of interatomic potentials are taken from an embedded atom method (EAM) calculations and the degree of order is simulated by the Monte Carlo method. Both on-lattice and off-lattice methods, where the latter allows individual atoms to deviate from their regular lattice sites, were used, and the resulting effects are discussed.