Special structural types of selected metals

4 Special structural types of selected metals. In this paragraph a few selected special structures peculiar to some metals, generally located in particular positions of the periodic table, are described. Some very simple structural types have to be considered (the simplest one is the aPo-cPl) and some having rather complex atomic arrangements, for instance otMn, cI58. 

For indications about rare crystal forms possessed only by a few, or just by one, metals see in Chapter 5 the paragraphs dedicated to the various specific elements, where structure type and lattice parameter data are listed for all the allotropes. 

structural type Cubic, space group Pm3m, N. 221. 

The simple structure of this semimetal, not very compact, has a space filling parameter p = 0.524. 

2 ctHg, hR3, structural type. The hR3-aHg structure can be considered a distorted cubic close-packed structure compressed along the three-fold axis. In the rhombohedral primitive unit cell there is one atom three atoms are in the equivalent triple primitive hexagonal cell (a = 346.0 pm, c = 670.2 pm, c/a = 1.937) in the positions 3 Hg in (a) 0,0,0 A, A, A A, A, A in the space group R3m, N. 166. The environment data are Hg CNE = 12 (122 2) (6 + 6 Hg) 

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