In this chapter we describe the results of theoretical studies of the electronic structure and properties of refractory nitrides, as compared with the properties of binary carbides. We shall consider here only those compounds with ideal crystal lattices, without any defects or impurities. The electronic structure and chemical bonding in nonstoichiometric nitrides will be discussed in Chapter 4.

Cubic nitrides of iva and va d-metals

Cubic nitrides have been the subject of many theoretical and experimental investigations. A list of references for the theoretical studies of the electronic structure of this group of compounds is given at the end of this chapter.

The band structure of TiN (Neckel et al, 1975), Fig. 3.1, can serve as a typical example of the electronic structure of such compounds with NaCl B1 structure. The composition of energy bands is illustrated in Fig. 3.2, which shows the total DOS for TiN decomposed into the partial N2s, N2p, Ti3d, Ti4p, and Ti4p contributions as calculated by the LMTO method (Zhukov et al, 1988a). Fig. 3.3 presents the t2g and eg contributions to the density of 3d states.

The characteristic feature of the bands of cubic nitrides, which is different from those of the isostructural carbides (see Chapter 2), is the position of the N2s-bands, which, due to the lower energy of the 2s states of free N atoms is situated at a lower energy. Hybridised Mmd-bands have almost the same energy as their counterparts in the carbides. But their width in nitrides is essentially less than in the carbides, and this results in the large interval between the edges of the hybridised and metallic state bands.