Prediction of Molybdenum Nitride from First-Principle Calculations: Crystal Structures, Electronic Properties, and Hardness

Abstract

Transition metal (TM) nitrides has been widely used in many scientific and technical areas because of their unique physical and mechanical properties. However, most of the well-known transition metal nitrides are nitrogen deficient. The reports on nitrogen-rich TM nitrides are rather scarce and sometimes even show discrepancy in their crystal structures. Herein, the microstructure, stability, electronic property, and hardness of nitrogen-rich molybdenum nitride MoN2 compound have been investigated systematically by using an unbiased structure search method crystal structure analysis by particle swarm optimization combined with first-principle calculations. Our study demonstrates a stable configuration orthorhombic Cmc21 (no. 36) for MoN2 crystal, which is even lower in energy than the experimental synthesized structure rhombohedral R 3 m -MoN2 at ambient pressure condition. The formation enthalpies with respect to the reactant Mo + N2, mechanical stabilities, and phonon dispersions further confirm the stability of Cmc21-MoN2 phase at the whole ambient condition, indicating that it can be synthesized in experiment. According to the density of states, it is seen that all the considered MoN2 exhibit metallic behavior and have two types of bonds (covalent and ionic). The Vicker hardness of Cmc21-MoN2 is calculated as 11.987 GPa, and the strength and number of covalent bonds may dominate its hardness.

Guidelines for the synthesis of molybdenum nitride: Understanding the mechanism and the control of crystallographic phase and nitrogen content

“…Density of states (DOS) were calculated for MoO3, β-Mo2N, and γ-Mo2N. Our results agree with previously published works for β-Mo2N, and γ-Mo2N [49,50]. For MoO3 good agreement is also obtained, but the value of the band gap on our DOS is inferior to experimental value of band gap (around 3 eV), as expected while using a GGA functional.…”

“…Both spectral features highlight a strong metallic character [49]. Although theoretical studies have been used to predict the electronic structure of molybdenum nitrides [49,50,80], none of these were corroborated by an experimental analysis of the valence band by UPS. The UPS spectra were analyzed following an analytical procedure developed to precisely determine quantitative parameters, such as position and relative intensity [42].…”

Computational Design of Mixed-Valence Tin Sulfides as Solar Absorbers

“…It provides reliable predictions of the ground state and metastable structures of the known stable compositions of SnS, SnS 2 , and Sn 2 S 3 . Many higher-energy metastable structures are also predicted that are yet to be experimentally verified, but may be feasible under high temperature or high-pressure growth conditions. ,− An important finding is the mixed-valent Sn 3 S 4 composition that appears as a marginally stable phase. Its occurrence has been alluded to, but not definitively observed in previous studies.…”

High-pressure synthesis and crystal structures of molybdenum nitride Mo3N5 with anisotropic compressibility by a nitrogen dimer

“…Although dense molybdenum nitrides, unlike other transition-metal dense nitrides, have not been synthesized using the LHDAC so far, theoretical calculations predicted the existence of several dense molybdenum nitrides. [34][35][36] Herein, we report the synthesis conditions, crystal and electronic structures, compression behavior, and phase stability of a novel molybdenum nitride Mo 3 N 5 , successfully synthesized under high-pressure and high-temperature conditions using the LHDAC.…”