Structure types and unit cell Pearson symbol

3 Structure types and unit cell Pearson symbol 

The use of the so-called Pearson notation (Pearson 1972) is highly recommended (IUPAC, Petzow and Effenberg 1988 etseq, Leigh 1990, Villars etal. 1995) for the construction of a compact symbolic representation of the structure of the phase. As far as possible, it should be completed with a more detailed structural description by using the prototype formula which defines, as previously mentioned, a certain structure type. 

In this book, the Pearson symbol will be used throughout and the convention has been adopted indicating in every case the number (ideal or effective) of atoms contained in the chosen unit cell. In the case, therefore, of rhombohedral substances for which the data of the (triple primitive) hexagonal cell are generally reported, the number of atoms is given which is in the hexagonal cell and not the number of atoms in the equivalent rhombohedral cell (Ferro and Girgis 1990). So, for instance, 

If the structure is not known exactly, the prototype indication cannot be added to the Pearson symbol. In some cases, moreover, only incomplete Pearson symbols (such as o 60, cF , etc.) can be used. 

Criteria similar to Pearson s for the unit cell designation were used by Schubert (1964) and Frevel (1985). 

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