Abstract
Molybdenum mononitrides (MoN) exhibit superior strength and hardness among the large class of transition-metal light-element compounds, but the underlying atomistic mechanisms for their outstanding mechanical properties and the variations of those properties among various MoN phases adopting different crystal structures remain largely unexplored and require further investigation. Here we report first-principles calculations that examine the stress-strain relations of these materials, and systematically compare results under pure and indentation shear deformations. In particular, we examine the distinct bonding structures and the associated mechanical properties in four different crystal phases of MoN that have been experimentally synthesized and stabilized under various physical conditions. Our results reveal evolution patterns of bonding configurations and the resulting structural deformation modes in these MoN phases, which produce diverse stress responses and unexpected strength variations. These findings elucidate the structural and bonding characters that are responsible for the rich and distinct mechanical properties in various MoN structures, providing insights for understanding the experimentally observed phenomena and further exploring advanced superhard materials among the promising transition-metal nitrides, borides, and carbides.
Highlights
Transition metal (TM) nitrides constitute a remarkable class of materials, which have drawn considerable interest and attention because of their excellent physical properties, such as low electrical resistivity, high melting point, superconductivity, and high strength and hardness [1,2,3,4,5,6,7,8,9,10]
The Vienna ab initio simulation package (VASP) code [26] was employed, and the total energy calculations and structural relaxations were carried out using the density functional theory (DFT) within the generalized gradient approximation (GGA) [27]
We performed systematic first-principles calculations to examine the stress responses, especially under pure and indentation shear strains that are most relevant to the experimental hardness measurements, for four reportedly synthesized crystal phases of MoN along various deformation modes
Summary
Transition metal (TM) nitrides constitute a remarkable class of materials, which have drawn considerable interest and attention because of their excellent physical properties, such as low electrical resistivity, high melting point, superconductivity, and high strength and hardness [1,2,3,4,5,6,7,8,9,10]. This class of materials has a wide range of scientific and industrial applications ranging from wear-resistant coatings to cutting tools.
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