Silicon binary borides

In the above methods, the borides are notated in the form of a simple binary boride MB . However, we have discovered that small additions of 3rd elements like carbon, nitrogen, and silicon can lead to the formation of new higher borides, and this will be presented in detail in the appropriate sections. For the synthesis of such compounds, it has been found to be expedient to first obtain MB (n > 10) and then add the desired amounts of carbon powder, or BN powder, or Si powder plus additional B powder if necessary to react again to obtain the desired compounds. 

Binary borides are formed with transition and inner transition elements, with alkali and alkaline-earth elements, and with the p elements, aluminum, and silicon. In addition, a group of more electronegative elements (C, 0, P, S, As, Se) form compounds with boron, which display properties and structures closely related to those of some borides. This group of compounds is also briefly described in the present article as well as the polymorphs of elemental boron. 

The occurrence of the binary borides of the alkaline, alkaline earth, aluminum, and transition elements has been collected in Table 1, together with boron compounds of the right main group elements (carbides, etc.). Only relatively well-established phases have been included. Noncorroborated and/or badly characterized borides lacking precise composition and structure data are not included. The reader is referred to other sources for references. There are no binary borides among the Cu, Zn, Ga, and Ge group elements with the exception of a noncorroborated early report on diborides in the Ag-B and Au-B systems. Two silicon borides have been established, namely, SiB3 4 and SiBe. 

Niobium combines with carbon, boron, silicon and other elements at very high temperatures, forming interstitial binary compounds of varying compositions. With carbon, it forms niobium carbide having compositions varying from NbCo.7 to NbC [12069-94-2]. With boron, the products are orthorhombic niobium boride, NbB [12045-19-1], and the hexagonal diniobium diboride, Nb2B2[12007-29-3]. 

Figure 9. (a) The binary B-Si system according to experimental results with powders of technical purity. Homogeneity fields of the silicon borides according to Ettmayer et al. [76], Lugscheider et al. [77], Armas et al. 1981 [82], (b) The binary B-Si system according to recent calculations by Lim and Lukas [52],... 

Krypyakevych (1977) has proposed the systematics of structure types of intermetallic and related compounds based on the analysis of the coordination polyhedra of the smallest atom. This author distinguishes 17 groups to which the coordination polyhedra of the smallest atoms belong. In analyzing the crystal structures of intermetallic compounds some problems, connected with choice of the smallest atom, arise. In the case of the metal compounds with boron, carbon, silicon, and phosphorus the nonmetal element is always the smallest. Kuz ma (1983) successfully used this concept for the analysis of the structure types of borides. In analyzing the structure types of the binary and ternary phosphides we will hold to the systematics developed by Krypyakevych (1977) also because the CPs of phosphorus atoms are given in the figures. 

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