Borides layered compounds

A. .. A etc. contacts between the layers (see later). The reason for the great importance of the most closely packed structures is that in many halides, oxides, and sulphides the anions are appreciably larger than the metal atoms (ions) and are arranged in one of the types of closest packing. The smaller metal ions occupy the interstices between the c.p. anions. In another large group of compounds, the interstitial borides, carbides, and nitrides, the non-metal atoms occupy Interstices between c.p. metal atoms. 

Borides with two-dimensional nets. These are represented by MB2 and M2B5 compounds and include some of the best electrically conducting, hardest, and highest-melting of all borides. The crystal structures of the MB2 compounds are unusually simple, consisting of alternating layers of close-packed metal atoms and chicken wire sheets of boron atoms, as shown in Fig. 8-1. 

Much of surface science research to date has focussed on the physical and chemical properties of clean metal surfaces, a state of matter that is only obtainable under ultrahigh vacuum. However, under practical, real world conditions most metals are covered by an oxide layer or take the form of various compounds, eg. sulfide, carbide, etc. For the last several years my research group has investigated the properties of "chemically modified" molybdenum surfaces which serve as models for the surface of molybdenum compounds. Surfaces that are models for the oxides, carbides, sulfides, and borides of molybdenum are fabricated by the reaction,... 

Boron compounds with nonmetals, i.e., boron hydrides, carbides, nitrides, oxides, silicides, and arsenides, show simple atomic structures. For example, boron nitride (BN) can be found in layered hexagonal, rhombohedral, and turbostratic or denser cubic and wurtzite-like structures, as well as in the form of nanotubes and fullerenes. Boron compounds with metalloids also differ from borides by electronic properties being semiconductors or wide-gap insulators. 

AIB2-Type Analogous Tiling Compounds. A series of layered graphitic boride compounds (AlB2-fype analogous... 

Boronize (substrate) The process of diffusing boron into a surface region containing Mo, Cr, Ti, etc. so as to form a surface layer (Case) containing boride compound particles dispersed through the layer. 

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