Ab Initio molecular dynamics study of threshold displacement energy in Zirconium Nitride

Zirconium nitride (ZrN) is a promising matrix candidate for advanced nuclear fuels and transmutation of minor actinides. This study investigates the displacement process induced by low-energy recoils in ZrN using ab initio molecular dynamics (AIMD) simulations to evaluate the threshold displacement energy (E_d). Observations of the collision processes of primary knock-on atoms (PKAs) for both Zr and N atoms were performed for seven different directions: [100], [110], [111], [210], [211], [221], and [321], which cover most regions of the stereographic triangle. The values of E_d ranged from 15 eV to 50 eV, and the collision processes were dependent on the crystallographic orientations. The weighted average values of E_d evaluated from the PKA directions investigated in this study were 33 eV and 29 eV for the Zr and N atoms, respectively. Anti-site defects were not formed for either Zr or N PKAs. Sequential replacement collisions along the [110] atomic row played an important role in the collision process, providing a lower value of E_d in the crystallographic directions. Furthermore, configurations of interstitials were different between the Zr and N atoms, which also influenced E_d values.