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

Two high-pressure stable phases ( I 4 ₁ / a -CeN ₄ and R 3̅ m -CeN ₆ ) and two metastable phases ( P 6 mm -CeN ₁₄ and P 6 mm -CeN ₁₇ ) were proposed in Ce-N compounds at 150-300 GPa. The polymeric nitrogen units include quadruple helical chains, N ₆ rings, and first reported layered molecular sieves structures. I 4 ₁ / a -CeN ₄ can be quenched to ambient conditions and its thermal stability can be maintained up to 500 K. P 6 mm -CeN ₁₄ 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 sp ³ hybridized layered molecular sieve to enhance the stability of P 6 mm -CeN ₁₄ . Surprisingly, the energy density (8.45 kJ/g) and explosive performance of P 6 mm -CeN ₁₄ are the highest among all metal polynitrides, refreshing a new record for high-energy metal polynitrides.