High-energy-density pentazolate salts: CaN10 and BaN10

The search for high energy density materials (HEDMs) in polymeric nitrogen compounds has gained considerable attention. Previous theoretical predictions and experiments have revealed that metal ions can be used to stabilize the pentazolate (N 5 − ) anion. In this work, by employing a machine learning-accelerated crystal structure searching method and first-principles calculations, we found that the new pentazolate salts, CaN10 and BaN10, are energetically favorable at high pressures. Phonon dispersion calculations reveal that they are quenchable at ambient pressure. Ab initio molecular dynamics simulations verify their dynamic stability at finite temperature. Bader charge and electron localization function illustrates that alkaline earth atoms serve as electron donors, contributing to the stability of N5 rings. Bonding calculations reveal covalent bonds between nitrogen atoms and weak interactions between N5 rings. Similar to other pentazolate salts, these polymeric nitrides have high energy densities of approximately 2.35 kJ/g for CaN10 and 1.32 kJ/g for BaN10. The predictions of CaN10 and BaN10 structures indicate that these salts are potential candidates for green nitrogen-rich HEDMs.