Displacive phase transition, structural stability, and mechanical properties of the ultra‐incompressible and hard MoN by first principles

Abstract

Abstract The structural stability, electronic, and mechanical properties of MoN were investigated by use of the density functional theory. Nine structures were considered, i.e ., hexagonal δ 1 ‐MoN, δ 2 ‐MoN, $\delta '_2$ ‐MoN, δ 3 ‐MoN, δ 4 ‐MoN, and wurtzite ZnS structures, cubic NaCl, zincblende, and CsCl structures. The calculated results indicated that δ 3 ‐MoN is the ground state among the considered structures. The second‐order displacive phase transition has been found from δ 3 ‐MoN to $\delta '_2$ ‐MoN with increase in pressure, in agreement with the experimental observation. $\delta '_2$ ‐MoN has the largest calculated bulk and shear moduli among the considered structures, followed by δ 3 ‐MoN. The estimated hardness of $\delta '_2$ ‐MoN and δ 3 ‐MoN is 34 and 29 GPa, respectively. Both of them are thermodynamically and mechanically stable. The compressibility along the c ‐axis for both compounds is smaller than that for diamond and cubic boron nitride (c‐BN). The ideal strengths of $\delta '_2$ ‐MoN were discussed. magnified image The stress–strain relationship for $\delta '_2$ ‐MoN shows that the ideal tensile strength of 107.0 GPa along the 〈0001〉 direction is very large, which might have potential technological and industrial applications.