title: Phase stability, chemical bonding and mechanical properties of titanium nitrides: a first-principles study.
abstract: We have performed first-principles evolutionary searches for stable Ti-N compounds and have found, in addition to the well-known rock-salt TiN, new ground states Ti3N2, Ti4N3, Ti6N5 at atmospheric pressure, and Ti2N and TiN2 at higher pressures. The latter nitrogen-rich structure contains encapsulated N2 dumbbells with a N-N distance of 1.348 Å at 60 GPa. TiN2 is predicted to be mechanically stable and quenchable. Our calculations on the mechanical properties (bulk modulus, shear modulus, Young's modulus, Poisson's ratio, and hardness) are in excellent agreement with the available experimental data. Further analyses of the electronic density of states, crystal orbital Hamilton population and the electron localization function reveal that the hardness is enhanced by strengthening directional covalent bonds and disappearance of Ti-Ti metallic bonding.
authors: Science and Technology on Thermostructural Composite Materials Laboratory, School of Materials Science and Engineering, Northwestern Polytechnical University, Xi'an, Shaanxi 710072, P. R. China. yushuyin2014@gmail.com.
authors: Shuyin
authors: S
authors: Yu
authors: Qingfeng
authors: Q
authors: Zeng
authors: Artem R
authors: AR
authors: Oganov
authors: Gilles
authors: G
authors: Frapper
authors: Litong
authors: L
authors: Zhang