Transition metal borides, crystal structures

The hardest of the transition-metal borides are the diborides. Their characteristic crystal structure (Figure 10.6) consists of plane layers of close-packed metal atoms separated by plane openly-patterned layers of boron atoms ( chicken-wire pattern). If the metal atoms in the hexagonal close-packed layer have a spacing, d, then the boron atoms have a spacing of d/V3. 

Parth6, E. and Chabot, B. (1984) Crystal structures and crystal chemistry of ternary rare earth-transition metal borides, silicides and homologues. In Handbook on the Physics and Chemistry of Rare Earths, ed. Gschneidner Jr., K.A. and Eyring, L. (North-Holland, Amsterdam), Vol. 6, p. 113. 

E. Parthe and B. Chabot, Crystal structures and crystal chemistry of ternary rare earth-transition metal borides, silicides and homologues 113... 

Combinations of diborides of different transition metal borides have been studied, especially in the TiB2/CrB2 and TiB2/W2B5 systems, for wear applications and to a minor extent for eleetrodes in Hall-Herould cells [135,139,140,293-295], Since the transition metal diborides crystallize in the same structure type, namely the AIB2... 

Parthd, E. Chabot, B. (1984). Crystal Structures and Crystal Chemistry of Ternary Rare Earth - Transition Metal Borides, Silicides and Homologues in "Handbook on the Physics and Chemistry of The Rare Earths", edited by K.Gschneidner, Jr. and L. R. Eyring, Vol. 6, ppl 13-334, Amsterdam North Holland. 

While most of the binary carbides and nitrides considered above form unlimited homogeneous solid solutions, some other 5 and p elements (B, Be, Al, Mg, etc.) have only a low solubility in these phases. As their content in carbides and nitrides increases, ternary compounds with very specific crystal structures are formed which were reviewed by Alyamovsky et al (1981) and Goldschmidt (1967). It is well known (see Samsonov, Serebryakov and Neronov (1975)) that B or transition metal borides do not form unlimited solid solutions, when interacting with MX phases (X = C, N) and single-phase TiNjBj, compounds exist over a narrow composition range for example, when z + y = 0.62-0.94, y < 0.03 (see Alyamovsky, Zainulin and Shveikin (1976)). As the B/N ratio increases. 

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