Near-neighbour diagram

Reduced dimensional parameters (strain parameters and near-neighbours diagrams) By comparing the space-filling theoretical curves and the actual values of intermetallic phases it has been observed that an incompressible sphere model of the atom gives only a rough description when discussing metallic structures. 

Figure 4.24. Near-neighbour diagrams for binary phases calculated according to Pearson (1972) for a few structural types. The lines calculated for the different interatomic contacts are shown. The numbers of contacts X-Y, Y-X, X-X, etc. are indicated. The experimental values determined for the various compounds are contained, for each structure type, within the hatched fields, (a) XY3 compounds belonging to the cP4-AuCu3 structural type (b) XY2 Taves phases of the cF24-Cu2Mg type (c) XY compounds of the cF8-ZnS structural type. Notice the importance of the high coordination contacts in the more metallic phases, whereas in the ZnS-type compounds the role of the chemical bond factor is clearly relevant.

Figure 8.24 Schcmaiic diagram of the layer structure of CuCN.NH showing the tridentate CN groups each Cu is also bonded to 1 NH molecule at 207 pm. Note also the unusual 5-coordination of Cu including one near neighbour Cu at 242 pm (13 pm closer than Cu-Cu in the metal). The lines in the diagram delineate the geometry and do not represent pairs of electrons.

Fig. 6.14 Stereoviews of the two forms of 6-XXVII. Upper, black form showing stacking of neighbouring molecules. Lower, scarlet form. In both structures the view is on the best plane of the essentially planar central portion of the reference molecule near the middle of the diagram, shown with its surroundings.

FIG. 17.1. The structure of NiAs (As atoms shaded). The Ni atom in the centre of the diagram is surrounded octahedrally by six As atoms and has also two near Ni neighbours situated vertically above and below. 

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