Black phosphorus, Crystalline structure

Black phosphorus is the third major adotropic form of phosphorus. It occurs in two forms, one is an amorphous modification having a laminar structure similar to graphite and the other is an orthorhombic crystalline form. The density of black phosphorus may vary between 2.20 to 2.69 g/cm. Black phosphorus is obtained from white phosphorus by heating the latter at 220°C under an extremely high pressure of about 10,000 atm. 

Crystalline black phosphorus has a corrugated layer structure. - ... 

A review of the alleged allotropes of phosphorus reduces their number to four, namely, the a- and/3-forms of yellow phosphorus, red or violet phosphorus, and black phosphorus. Most of the work of various investigators has been directed towards elucidating the nature of red phosphorus, and of the transformation of yellow to red phosphorus and conversely. Red phosphorus was formerly considered to be amorphous, and it was often called amorphous phosphorus. The term amorphous, however, here referred more to the general appearance of the powder rather than to its minute structure. J. W. Retgers 5 showed that the particles of ordinary red phosphorus are rhombohedral crystals, which are well developed in those of W. Hittorf s violet phosphorus. All four varieties are therefore crystalline. J. W. Terwen has reviewed this subject in a general way and M. Copisarow discussed the theory of allotropy,... 

The most thermodynamically stable, and least reactive, form of phosphorus is black phosphorus, which exists as three crystalline (orthorhombic-, rhombohedral- and metallic, or cubic, and one amorphous, allotrope. All are polymeric solids and are practically nonflammable. Both orthorhombic and rhombohedral phosphorus appear black and graphitic, consistent with their layered structures. 

Black Phosphorus. Polymorphic. Orthorhombic crystalline form stable in air resembles graphite in texture produced from the white modification under high pressures Bridgman, J. Am. Chem. Soc. 36, 1344 (1914) Jacobs, J. Chem. Phys. 5, 945 (1937) Krebe, Inorg. Syn. 7, 60 (1963), d 2.691. Does not catch fire spontaneously. Insol in organic solvents. Amorphous form prepd at lower pressures Ja-cobe, loc. cit At higher pressure the orthorhombic form undergoes reversible transition to a rhombohedral structure, d 3.56, and a cnbic structure, d 3.83 Jamieson, Science 139, 1291 (1963). 

Black phosphorus, which is one of the crystalline modifications of elemental phosphorus, has a crystal structure of three-dimensional network as shown in Figure 2a (45). A plane diagram of its structure is illustrated in Figure 2b-. On the other hand, various structures have been proposed for commercial red phosphorus, which is one of the amorphous modifications of elemental phosphorus. The fact that s... 

There have been many studies of the crystalline structures of elemental phosphorus [10,45], and the microscopic structures of the amorphous modifications (red, black, grey vitreous) are still the subjects of considerable attention. Gas phase clusters have been of interest for many years, and Martin [19] has detected mass spectroscopically clusters up to > 6000. Nevertheless, little experimental information was available until recently on the structure of clusters with > 4, and this is also true for arsenic clustere, As . 

Phosphorus also exists in several allotropic modifications. White phosphorus in the crystalline state consists of discrete P4-tetrahedral molecules and is soluble in carbon disulfide. However, on the addition of catalysts and the application of pressure, it changes first to red, then to violet, and finally to black phosphorus. For this it is necessary to have 35,000 bar at 20°C, and 12,000 bar at 200 C. Thus, the ceiling temperature in this equilibrium polymerization must lie below the melting point of white phosphorus at 1 bar. Black phosphorus possesses a complicated parquet structure similar to graphite and is a type 2 polymer that is no longer soluble in CS2. Both red and violet phosphorus possess a lower degree of polymerization. 

Amorphous black phosphorus is made from white by the application of somewhat lower temperatures and pressures than are needed to make the crystalline varieties, and it represents a transition structure. 

Figure 20.18 (a) The P4 molecule found in white phosphorus, (b) The crystalline network structure of black phosphorus, (c) The chain structure of red phosphorus. 

Whereas single-crystalline flakes of black phosphorus can be grown from a bismuth solution [138], crystallization from liquid lead leads to red platy crystals of another modification, called Hittorf s phosphorus. Its monoclinic structure [137] (Cih—P2c, Z = 84, all atoms in 4g) consists of cage-like Pg and P9 groups which are linked alternately by pairs of P atoms to form tubes of pentagonal cross section. Parallel tubes form double layers in which tubes of different layers are approximately perpendicular (at 89.6°) to each other. In one layer, the tubes are parallel with [110], in the crossed layer, parallel with [iTO]. Each tube is /... 

It seems likely that all forms of red phosphorus (like black (4.26b)) are built from pyramidally linked atoms, the different crystalline varieties representing various kinds of ordered framework, or differing degrees of polymerisation. It is believed by some [49] that nitrogen under very high pressures will form a similar structure to (4.26b). 

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