Two Ultrahigh-Energy-Density Layered Cerium Polynitrides with Molecular Sieve Channel

Abstract

Two high-pressure stable phases (<i>I</i>4₁/<i>a</i>-CeN₄ and <i>R</i>3̅<i>m</i>-CeN₆) and two metastable phases (<i>P</i>6<i>mm</i>-CeN₁₄ and <i>P</i>6<i>mm</i>-CeN₁₇) were proposed in Ce-N compounds at 150-300 GPa. The polymeric nitrogen units include quadruple helical chains, N₆ rings, and first reported layered molecular sieves structures. <i>I</i>4₁/<i>a</i>-CeN₄ can be quenched to ambient conditions and its thermal stability can be maintained up to 500 K. <i>P</i>6<i>mm</i>-CeN₁₄ is dynamically and mechanically stable at ambient pressure. The electronic properties analyses show that charge transfer between the Ce and N atoms makes a significant contribution to the structural stability by promoting the formation of Ce-N ionic bond and N-N covalent bond. The Ce atom provides a suitable coordination environment and an excellent bonding state for the fully sp³ hybridized layered molecular sieve to enhance the stability of <i>P</i>6<i>mm</i>-CeN₁₄. Surprisingly, the energy density (8.45 kJ/g) and explosive performance of <i>P</i>6<i>mm</i>-CeN₁₄ are the highest among all metal polynitrides, refreshing a new record for high-energy metal polynitrides.