Defects borides

Refractory Compounds. Refractory compounds resemble oxides, carbides, nitrides, borides, and sulfides in that they have a very high melting point. In some cases, they form extensive defect stmctures, ie, they exist over a wide stoichiometric range. For example, in TiC, the C Ti ratio can vary from 0.5 to I.O, which demonstrates a wide range of vacant carbon lattice sites. 

Table 2. Crystal Structures and Boron Coordination of Platinum Metal Borides WITH Isolated B Atoms (Owing to Defect Boron Sublattice)...

Little information is available on homogeneity ranges and defect structures in the dodecaborides. The only variation from stoichiometry in these borides is for YB,2i the limiting phase determined by density measurements is Yq92B,2. This result can be attributed to the size of Y which is the maximum for metals that form the dodecaborides. Attempts to prepare DyB,2 with a nonstoichiometric composition are conclusive. ... 

Point Defects Nitrogen and boron are ubiquitous atomic-scale impurities in synthetic diamonds. The free energy of formation of nitrides and borides in the solvent/catalyst melt will determine the extent to which these impurities are... 

As shown in the above table, the Group IV carbides (and Groups V and VI carbides as well) are good electrical conductors and have an electrical resistivity only slightly higher than that of the parent metals, reflecting the metallic character of these compounds. The nitrides and especially the borides have even lower resistivity. The large spread in the reported values may be attributed to differences in composition and the presence of defects and impurities. 

CH de Novion, B Beuneu, T Priem, N Lorenzellii, A Finel. Defect structures and order-disorder transformations in transition metal carbides and nitrides. In R Freer, ed. The Physics and Chemistry of Carbides, Nitrides and Borides. Dordrecht Kluwer Academic Press, 1990, p 329. 

Lundstroem, T. (1985). Structure, defects, and properties of some refractory borides. Pure and Applied Chemistry, 57(10), 1383-1390. doi 10.1351/pac 198557101383. 

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