The Structure of Boron Carbide

The combination of these various structures within a given boron carbide compound gives an overall composition from about 7.7 to 20.5 at % carbon. Each composition has slightly different lattice constants as determined by powder x-ray diffraction (see Table 7.6). Such a composition dependence provides a fast and reliable method of determining the composition, 

boron carbide, unlike SiC, has a wide range of composition and the formula B4C usually found in the literature should not be construed to represent an exact composition. Also in many cases, the composition of a boron carbide material is not fixed as localized phases having different composition may be found.l  

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Alexander, M. N., Nuclear Magnetic Resonance Studies of the Structure of Boron Carbides, in Boron Rich Solids, Am. Inst, of Physics Conf. Proc. 140, New York (1986)... 

MN Alexander. Nuclear magnetic resonance studies of the structure of boron carbides. In D Emin, T Aselage, CL Beckel, lA Howard, C Wood, eds. AIP Conference Proceedings 140. Albuquerque AIP, 1985, p 168. 

Conde O, Slivestre A.J., OUveria J.C. Influence of Carbon Content on the Crystallographic Structure of Boron Carbide Films//Surf Coat. Teehnol. 2000. V. 125. No 1. P. 141-146. 

In this work, the effect of two kinds of temperature field on boron carbide deposition was investigated. Firstly, two kinds of temperature field were compared, which were named field A and field B respectively. Then, morphologies, phase, composition and structure of boron carbide under field A and field B were characterized and compared. Finally, different deposition mechanisms were proposed to explain the difference of deposits under field A and field B. 

The boranes nido-B and m do-BioHi4 and carbaboranes n/do-2,3-Et2C2B4H6 and c/oro-l,2-C2BioHi2 have been used as precursors for boron and boron carbide thin films. ISEELS has been used to characterise the molecular precursws at solid surfaces a comparison has been made between the bond lengths determined for the molecular clusters by MNDO calculations and results from X-ray or electron diffraction and from extended EELS fine structure. A study of the deposition of boron carbide films on Si(lll) surfaces from the synchrotron radiation induced decomposition of nido-2,3-diethyldicarbahexaborane has been described. The dissociation of the cluster is the rate determining step in the process. As with the deposition of boron from nido-BioHi4, it is found that thoe is an activation barrier to the dissociation of the boron carbide precursor on Si(l 11) surfaces.43... 

Figure 7.10 Structure of boron carbide along the (112) elevation.

Marx, D., Seidler, G., Fister, T., Nagle, K., and Segre, C. (2008) Structure of boron carbide where s the carbon , in Proceedings, APS Meeting, Session Q40 Metals Nanoparticles, Compounds and Thermodynamics, March 10-14, New Orleans, Louisiana, Abstract Q40.00010. 

The idealized, most energetically favorable structure of boron carbide B13C2 (structure formula Bi2(CBC)) (206,207) was taken for reference to determine the composition dependent electron deficiency and the concentration of structural defects (202). 

As noted in Section 9, the structures of the R-B-C(N) compounds (Figure 21) are homologous to that of boron carbide which exhibits typical p-type characteristics. Boron carbide is the limit where the number of boron icosahedra and C-B-C chain layers separating the metal layers reaches infinity (i.e. no rare earth layers). It has been speculated that the 2 dimensional metal layers of these rare earth R-B-C(N) compounds are playing a role for the unusual n-type behavior, but the mechanism is not yet clear. 

The utilization of the outstanding mechanical and wear properties of cubic BN and related superhard materials has been demonstrated, although further process improvements are necessary before a more general use can be expected. Superhard cubic BN exhibits superb inertness to hot steel surfaces under conditions in which diamond would be severely attacked. Other tetrahedral structures, for instance, BCN and B2O, are anticipated to display similar attractive properties. The high-pressure phase B2O is a semiconductor with a band gap of 0.25 eV and a hardness between that of boron carbide and diamond. 

Other binary carbides. Boron and carbon form a series of boron carbide phases of which B4C appears to be the most ordered. There are several competing structural models for boron carbide which have been investigated by B and C... 

The vaporization-cold-substrate condensation process of boron carbide melted by electron-gun heating and plasma torch deposition does not give a well-organized and crystalline B4C-type structure. In CH4 [1.33.10 Pa 1 torr)] an electron-gun evaporation of boron carbide contained in a graphite crucible, followed by a condensation on a water-cooled jacket, gives crystals. Sputtering by H is possible . 

The interstitial structures comprise the compounds of certain metallic elements, notably the transition metals and those of the lanthanide and actinide series, with the four non-metallic elements hydrogen, boron, carbon and nitrogen. In chapter 8 we discussed the structures of a number of hydrides, borides, carbides and nitrides of the most electropositive metals, and these we found to be typical salt-like compounds with a definite composition and with physical properties entirely different from those of the constituent elements they are generally transparent to light and poor conductors of electricity. The systems now to be considered are strikingly different. They resemble... 

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