Lattice boron compounds

Boron creates an electron deficiency in the siHcon lattice resulting in a -type semiconductor forp—n junctions. Boron compounds are more commonly used as the dopant, however (see Boron hydrides). 

The first ionization potential of boron, 8.296 eV, is rather high, and the next two are much higher. Thus the total energy required to produce B3 + ions is far more than would be compensated by lattice energies of ionic compounds or by hydration of such ions in solution. Consequently, simple electron loss to form a cation plays no part in boron chemistry. Instead, covalent bond formation is of major importance, and boron compounds usually resemble those of other non-metals, notably silicon, in their properties and reactions. 

A problem with this phosphor is that without precautions it usually contains a small amount of unreacted V2O5 which lowers the light output. For application in high-pressure mercury vapor lamps this pho.sphor is usually prepared with an excess of boric acid. The material has then a white body color and, in addition, the particle size can be controlled. The boron is not built into the lattice in some way or another the boron compound acts as a flux. 

The diamondoid shape that the boron compound forms demonstrates how it can be bonded into a diamond crystal without causing strain in the diamond lattice due to its similarity of structure. This also demonstrate how the properties of a material at the macro scale (visible to the naked eye) is determined by bonding at the atomic scale. 

The modifications of boron and boron compounds are characterized by nets or chains of boron atoms bound to each other by covalent bonds. The coordination number of the boron atoms varies between 1 and 7. The nets have the form of linked icosahedra, cuboctahedra, octahedra, graphite-like planes, or linear branched boron chains. Two-electron three-center bonds in boron-cornered triangles are the rule in the lattice structure. Boron can only form ions in combination with hydrogen (BH4 ) and oxygen (BOj ). The borates (boron oxide derivatives) form covalent nets like the silicates. They are often amorphous. 

Lithium Nitride. Lithium nitride [26134-62-3], Li N, is prepared from the strongly exothermic direct reaction of lithium and nitrogen. The reaction proceeds to completion even when the temperature is kept below the melting point of lithium metal. The lithium ion is extremely mobile in the hexagonal lattice resulting in one of the highest known soHd ionic conductivities. Lithium nitride in combination with other compounds is used as a catalyst for the conversion of hexagonal boron nitride to the cubic form. The properties of lithium nitride have been extensively reviewed (66). 

Boron and carbon form one compound, boron carbide [12069-32-8] B C, although excess boron may dissolve ia boron carbide, and a small amount of boron may dissolve ia graphite (5). Usually excess carbon appears as graphite, except for the special case of boron diffused iato diamonds at high pressures and temperatures, eg, 5 GPa (50 kbar) and 1500°C, where boron may occupy both iaterstitial and substitutional positions ia the diamond lattice, a property utilized ia synthetic diamonds (see Carbon, diamond, synthetic). 

The stabilizing influence of small amounts of B (M/B > 0.25) in the voids of the metal host lattice varies with the mode of filling (partial or complete) of the interstitial, mostly O, sites and whether the compounds develop from the binary-intermetallic host lattice. The structures of B-rich compounds (M/B < 4) are mainly determined by the formation of regular, covalent B polyhedra (O, icosahedron) and the connections between them (B frame structures). Typical metal (M) borides therefore are found within a characteristic ratio of metal to boron 0.125 < M/B < 4. 

Table 2. Structure Types, Boron Coordination and Representatives op Metal Borides with Isolated B Atoms (Filled Metal Host Lattice Compounds)...

Cubed compound, in PVC siding manufacture, 25 685 Cube lattice, 8 114t Cubic boron nitride, 1 8 4 654 grinding wheels, 1 21 hardness in various scales, l 3t physical properties of, 4 653t Cubic close-packed (CCP) structure, of spinel ferrites, 11 60 Cubic ferrites, 11 55-57 Cubic geometry, for metal coordination numbers, 7 574, 575t. See also Cubic structure Cubic symmetry Cubic silsesquioxanes (CSS), 13 539 Cubic structure, of ferroelectric crystals, 11 94-95, 96 Cubic symmetry, 8 114t Cubitron sol-gel abrasives, 1 7 Cucurbituril inclusion compounds,... 

E. O. Fischer and H. P. Fritz Recent Studies of the Boron Hydrides William N. Lipscomb Lattice Energies and Their Significance in Inorganic Chemistry T. C. Waddington Graphite Intercalation Compounds W. Riidorff... 

An interstitial compound consists of a metal or metals and certain metalloid elements, in which the metalloid atoms occupy the interstices between the atoms of the metal lattice. Compounds of this type are, for example. TaC, TiC, ZrC. NbC, and similar compounds of carbon, nitrogen, boron, and hydrogen with metals. 

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