Pearson symbol code

Pearson symbol and prototype Space group symbol and number Lattice parameters (pm) Wyckoff positions (WP) Representative coordinates x,y, z of the 1st WP Occupancy Coordination polyhedron code Average polyhedron radius (pm) AET... 

Pearson symbol - A code for designating crystallographic information, including the crystal system, the lattice type, and the number of atoms per unit cell. 

These structural characteristics can be easily represented by using specific codes and symbols, which can be very useful for a compact presentation and comparison of the structural features of several structures. Many different notations have been devised to describe the stacking pattern (for a summary see Parthe 1964, Pearson 1972). A few of them will be presented here. 

As noted in section 6.2, when the material of interest is an intermetallic alloy, the solution of its crystal structure may be simplified because intermetallics often form series of isostructural compounds. In contrast to conventional inorganic and molecular compounds, stoichiometries of the majority of intermetallic phases are not restricted by normal valence and oxidation states of atoms and ions therefore, crystal structures of metallic alloy phases are conveniently coded using the classification suggested by W.B. Pearson. According to Pearson, each type of the crystal structure is assigned a specific code (symbol), which is constructed from three components as follows ... 

The compositions, space groups and Pearson s classification symbols for the members of this series are listed in table 2. For n = 00 the octahedra are replaced by an infinite three-dimensional framework of centred trigonal prisms that is known as the Alc B -type. This type is found with 67(75) 0( 2581.75)2 (GIB, 65) and many other R(T, Si)2 or R(T, Ge)2 compounds. Since, in the known examples of R-Ni-Si alloys, no regularity of the Ni/Si ratio at the prism centre sites is shown, and since the homogeneity ranges of these phases have not been investigated, the last two digits of the composition code have not been specified in table 2. Thus the compositions of the different members of this series can be correlated only by their content of rare earth (or non-rare-earth) element. 

LC Code Ternary compound Pearson s classif. symbol Space group Relation to binary types Class m n number of slabs of type Hypothetical composition for order a) Hypothetical composition Fig. 

LC Code Hypo- thetical formula Pearson s classif. symbol Space group m n... 

Code Compound Structure type Pearson s classif. symbol Space group a-Mn unit C + TT+T+CO bcc unit C + CB + OH + CO y-brass unit IT-l-OT-l-OH-l-CO CajAgg unit OH + CB + CO Ti2Ni unit OH + T + CO... 

Code R-T-M compound Structure type Pearson s dassif. symbol Space group Antiprism Octahedron Crystal-chemical formula... 

Structure type and composition of slabs Predicted stoichio- metry Composition code for known compound Compound formula Pearson s classic symbol Space group Fig. 

Code R-T-M compound discussed in the text Ternary structure type Related binary structure type Pearson st classif. symbol Space group g a 2 rt o> 0 C/3... 

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