Structure Prediction of Binary Pernitride MN₂ Compounds (M=Ca, Sr, Ba, La, and Ti)

Abstract

Metal-pernitride compounds belong to a class of chemical systems in which both the complex ions and the non-bonding electrons may play roles in the formation of their modified crystalline structures. To investigate this issue, the energy landscapes of pernitrides of metals with different maximum valence (M=Ca, Sr, Ba, La, and Ti) were globally explored on the ab initio level at standard and high pressures, thereby yielding possible (meta)stable modifications in these systems together with information on how the landscape changed as function of the valence of the metal cation. For all of the systems in which no compounds had been synthesized so far, we predicted the existence of kinetically stable modifications that should, in principle, be experimentally accessible. In particular, TiN2 should crystallize in a new structure type, TiN2-I.

Phase stability, chemical bonding and mechanical properties of titanium nitrides: a first-principles study

“…3). The formation enthalpy of this I4/mcm structure is lower than that of the previously proposed thermodynamic ground state, the CaC 2 -V-type structure, predicted by Kulkarni et al 50 at 60 GPa. 5).…”

Phase stability, chemical bonding and mechanical properties of titanium nitrides: A first-principles study

“…At 60 GPa, we uncovered a nitrogen-rich compound TiN 2 with the CuAl 2 -type structure (SG: I4/mcm, see Figure 5a). The energy of this I4/mcm structure is lower than that of the previously proposed thermodynamic ground state, the CaC 2 -V-type structure predicted by Kulkarni et al [44] at 60 GPa. This new structure is stable against the decomposition into the mixture of TiN and N 2 at pressures above 26.6 GPa.…”

Thermodynamic Routes to Novel Metastable Nitrogen-Rich Nitrides

“…Very recently, titanium pernitride, TiN 2 , was investigated theoretically, 89,90 and was then synthesized under high-pressure synthesis at 73 GPa, with a bulk modulus in the range 360−385 GPa. 70 We calculate the Δμ N 2 for TiN 2 to be +1.18 eV/N, much higher than the precious metal pernitrides.…”