Nitrogen crystal structures, lattice parameters

It has been established that under intense milling in a planetary mill in a nitrogen atmosphere, titanium hydride may decompose with formation of defected structure characterized by partly non-occupied tetrahedron voids in a face-centered cubic sublattice of titanium atoms. This effect is accompanied by decrease in the crystal lattice parameter of titanium hydride subjected to intense milling for 60 min. 

The carbides and nitrides of group 4-6 transition metals belong to the so-called Hagg compovmds (6). Hagg formulated a set of empirical rules for the crystal structures of interstitial solid solutions of transition metals. According to the rules, when the radius ratio r = rx/fmetai is less than 0.59, small atoms (such as carbon and nitrogen) occupy the interstitial sites of the simple crystal structures formed by the metal atoms. For the carbides and nitrides of Ti, V, Nb, Mo, and W, which have been extensively applied as catalysts, the radius ratios fall in between 0.491 r lr i) and 0.576 (rc/ry). They are indeed Hagg compounds (6). Table 1 summarizes the crystal structures and lattice parameters of carbides of Mo, W, V, Nb, and Ti. 

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