Bonding, Lattice Parameter, Density and Defect Structure of TiN Containing an Excess of N


From combustion analyses (TiN → TiO 2), Kjeldahl N-determinations, and gas analyses, it was found that the composition of the titanium nitride used was Ti 0.904±0.010 N, which agreed very well with that obtained by the lattice parameter and density method. From its chemical behavior (dissolution in HF with NH 4 + formation in the presence of oxidizers, especially KMnO 4, and N 2-production at elevated temperatures) and furthermore, from the heats of formation, lattice energy, hardness and high melting point, the conclusion is drawn that the bonding in the nitride is of a mixed type. It appears to be predominantly ionic and to some extent metallic. The partially metallic character of the bonding is evidenced in the release of N 2 during heating, and accounts for the high electrical conductivity and magnetic properties of the nitride. Since the N atoms do not accept all the available valence electrons (from Ti) the radius of the N-anions is smaller than found for N 3-. Using Pauling's formula and a ligancy of 5, a value of r = 1.426 Å is obtained for N. With this value and r = 0.69 Å (for Ti 3+, a lattice parameter α = 4.232 Å is calculated in reasonable agreement with the experimental value a = 4.23986 ± 0.00007Å. The thermal expansion coefficient α 25 is 5.71 × 10 -6 ° C -1 (between 10 and 65° C). The experimental density d 25 is 4.975 ± 0.004 g cm -3 (X-ray density, 5.394 g cm -3). There are 4.94% vacancies in the cationic and 0.175% vacancies in the anionic sublattice of all the sites, 8 per unit cell, of the nitride. © 1967.


Materials Science and Engineering

Second Department


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Article - Journal

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© 1967 Elsevier, All rights reserved.