On the schematic representations of crystal structures

As in previous chapters, the reader will find below for a number of structures a schematic representation, generally through a number of sections and/or projections of the unit cells, often together with a few adjacent cells. As an exercise and an introduction to the subsequent descriptive paragraphs, a few examples with indications about their interpretation are given here. 

1 Structure and structure component sections the tI2-cxPa, cI2-W, cF8-ZnS and tI8-NbAs types as examples. 

Above and below the position of the Zn atom at level 0 or 1 in the centre of the square base of the unit cell there are two pairs of S atoms, at levels 0.25 and 0.75 

in order to give a more realistic indication of the structure, more that one single unit cell is shown. The structure results from placing identical three-dimensional (3D) repetitive cells side by side. In every section, therefore, a small group of unit cells is generally shown (the one in bold for easier comparison with the listed numerical data, parameters, etc.). 

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