Some examples of theory and computation of properties of transition metal nitrides – Sanjay Khare

Date: Mon. April 7th, 2008, 12:30 pm-1:30 pm
Location: Rockefeller 221

A convergence of many factors has caused the emergence of growing synergy between theoretical and experimental research in condensed matter and materials science. Our current research interests that are benefiting from this symbiosis will be briefly discussed. Part of this co-development is due to first principles computational approaches that have ripened to such a degree that they can simulate materials properties with predictive power. With such ab initio methods, macroscopic properties can be theoretically correlated to microscopic causes such as bonding between individual atoms. As a specific example of such theoretical work, using density functional theory (DFT) we will show the structure of the recently discovered noble metal nitride of Pt and N. Calculations reveal the nature of this material which has had an ambiguous history of theoretical and experimental characterization. [S. K. R. Patil et al., Phys. Rev. B 73, 104118 (2006). Motivated by these initial results, we embarked on a systematic study of mechanical and electronic properties of 32 cubic phases of nitrides of the transition metals M (M = Hf, Ta, W, Re, Os, Ir, Pt, Au), in zinc-blende, rocksalt, pyrite, and fluorite structure using ab initio computations. Our results reveal that MN2 (M = W, Re, Os, Ir, Pt, Au) in pyrite phase, have a bulk moduli greater than 330 GPa, MN2 (M = Re, Os, Ir) in fluorite phase have a bulk moduli greater than 350 GPa and TaN in rocksalt phase has a bulk modulus of 380 GPa making them candidates for super hardness. Based on the bulk and shear modulus for stable phases, potential hard coating materials for cutting tools were identified. The local density of states of all phases was obtained and linked to mechanical stability. The high values of bulk moduli were attributed to strong bonding of transition metal d-orbitals with nitrogen p-orbitals. The trend in the bulk modulus was related to the valence electron density of these materials.