Atomic dimensions and an example of stability multi-diagrams

As for the trivalent lanthanides (and Y) their compounds with Mg correspond to the following formulae and structure types  

The intermediate phases formed in the various binary systems have been represented, in a first approximation, as point compounds. The points, which in the different binaries correspond to phases having the same composition and structure, have then been connected, defining multi-component ternary stability fields (in this case, line fields). On each horizontal line of this multi-diagram triangle the same overall composition is found (the same Mg content and the same total 

The schemes described are useful for collecting experimental data, preparing crucial experimental work and giving some predictions , at least for selected groups of 

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