Stability maps and correlation diagrams

1 Stability maps and correlation diagrams. As a concluding remark to some topics considered in this chapter and a recapitulation of procedures often employed in the description and classification of intermetallic systems, a little additional information about correlation diagrams is included here. 

1 Pettifor s structure maps additional remarks. We have seen that in a phenomenological approach to the systematics of the crystal structures (and of other phase properties) several types of coordinates, derived from physical atomic properties, have been used for the preparation of (two-, three-dimensional) stability maps. Differences, sums, ratios of properties such as electronegativities, atomic radii and valence-electron numbers have been used. These variables, however, as stressed, for instance, by Villars et al. (1989) do not always clearly differentiate between chemically different atoms. 

An extension of the application of these maps to the systematic description of certain groups of ternary alloys has been presented also by Pettifor (1988a, b). Composition averaged Mendeleev numbers can be used, for instance, in the description of pseudo-binary, ternary or quaternary alloys. All these maps show well-defined domains of structural stability for a given stoichiometry, thus making the search easier for new ternary or quaternary alloys with a particular structure type (and which, as a consequence, may have the potential of interesting properties and applications (Pettifor 1988a, b)). 

As a result of machine learning a model is produced of the characteristic exhibition of a property (for instance, the formation of a particular type of chemical compound) which corresponds to a distribution pattern of this property in the multidimensional representative space of the properties of the elements. The subsequent pattern recognition corresponds to a criterion for the classification of the known compounds and for the prediction of those still unknown. Examples of this approach reported by Savitskii are the prediction of the formation of Laves phases, of CaCu5 type phases, of compounds XY2Z4 (X, Y any of the elements, Z = O, S, Se, Te), etc. (Data on the electronic structures of the components were selected as 

3 Analysis of the dependence of the behaviour of alloy systems on the properties of the component elements. In an examination of the binary structure types containing more than five representatives, Villars and Girgis (1982) observed that 85% exhibited the following regularities  

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