Elements high-pressure modifications

U. Schwarz, Metallic high-pressure modifications of main group elements. Z. Kristallogr. 219 (2004) 376. 

The polymers which have been used to illustrate problems of inorganic polymer formation have been lieteroatomic. that is, their chains are built from different atoms alternating with each other. The other structure mentioned has been homoatomic—all the atoms in the chain are the same. There aie only a few homoatomic polymers of airy promise. Most elements will form only cyclic materials of low molecular weight if they polymerize at all. In addition to the silane polymers, black phosphorus, a high-pressure modification of the element, forms in polymeric sheets. 

Parts C of the tables present crystallographic data for allotropic and high-pressure modifications of the elements. The left-hand columns contain data for allotropic modifications that are stable at a pressure of 100 kPa over the temperature ranges indicated, and the right-hand columns contain data for modifications stable at higher pressures as indicated. The modifications stable at 100 kPa are denoted by Greek letters... 

Table 2.1-6B(a) Elements of the first period (hydrogen and helium). Crystallographic properties (for alio tropic and high-pressure modifications, see Table 2.1-6C)... 

Table 2.1-7C Elements of Group lA (CAS notation), or Group 1 (new lUPAC notation). Allotropic and high-pressure modifications...

Table 2.1-17C Elements of Group VIA, or Group 16. Allotropic and high-pressure modifications, cont. ...

The Zn- and Cd-lattices are hep. As a rule, the hep elemental metals, even including high-pressure phases, do not deviate from the ideal ratio of the lattice constants (e/a = 8/3 = 1.633) of this structure type by more than 4%. Zn, Cd and the high-pressure modification of Hg," however, constitute conspicuous exceptions, showing extreme values of eja (1.86 and 1.89 for Zn and Cd, respectively), deviating by 14% and 16%... 

---