Prediction of concomitant structures in binary metallic systems from RG map: With MgCu2 structure type as an example

The efficacy of Rajasekharan–Girgis (RG) maps, constructed using Miedema's parameters, in predicting concomitant structure types in metallic binary systems is discussed taking MgCu2 structure type as an example. 22 structure types that are concomitant with MgCu2 type compounds are studied on the RG map and the salient points are discussed. The map can tell us, for instance, that in the Ho–Ni binary system where the HoNi2 compound is of MgCu2 type structure, HoNi3 and NiHo3 are likely to stabilize with NbBe3 and CFe3 type structures respectively, and not vice versa. The occurrence of CuAl2 type structure, rather than MgCu2 type, in certain binary systems with atomic radii ratio 1.225 considered ‘ideal’ for the formation of MgCu2 type compounds, is explained. The RG map can minimize the set of candidate structures on which quantum mechanical calculations need to be performed to resolve between closely competing structures for a new compound.

Research highlights▶ In this paper we have demonstrated, by taking the concomitant structure types of the MgCu2 type as examples, the efficacy of (Δϕ, Δn1/3) map in predicting concomitant and mutually exclusive structure types. ▶ We have studied the 22 structure types which are concomitant with MgCu2 type compounds in binary phase diagrams. ▶ Several typical examples are discussed in the paper. ▶ The present approach brings down the number of trial structure types that have to be investigated by ab initio methods for predicting the stable structure.