New Cadmium–Nitrogen Compounds at High Pressures

Abstract

A systematic high-pressure study of the CdN x (x = 2, 3, 4, 5, and 6) system is performed by using the first-principles calculation method in combination with the particle swarm optimization algorithm. We proposed four stable high-pressure phases (P4mbm-CdN2, Cmmm-CdN4, I4̅2d-CdN4, and C2/c-CdN5) and one metastable high-pressure phase (C2/m-CdN6), for which the structural frames are composed of a diatomic quasi-molecule N2, standard armchair N-chain, S-type bent armchair N-chain, zigzag–antizigzag N-chain, and N14 network structure. Among them, the novel zigzag–antizigzag N-chain and N14 network structure are reported for the first time. More importantly, Cmmm-CdN4 and C2/m-CdN6 possess high stability under ambient conditions, which may be quenched to ambient conditions once they are synthesized at high-pressure conditions. The high decomposition energy barrier (1.14 eV) results in a high decomposition temperature (2500 K) of Cmmm-CdN4, while a low decomposition energy barrier (0.19 eV) results in a mild decomposition temperature (500 K) of C2/m-CdN6. The high energy density and outstanding explosive performance make Cmmm-CdN4, I4̅2d-CdN4, C2/c-CdN5, and C2/m-CdN6 potential high-energy materials. The electronic structure analyses show that these predicted high-pressure structures are all metallic phases, and the N–N and Cd–N bonds are the strong covalent and ionic bond interactions, respectively. The charge transfer from the Cd atom plays an important role in the stability of the proposed structures.

Cobalt–Nitrogen Compounds at High Pressure

“…In comparison with the main group metal element, the transition metal element with the complex electronic configuration may induce richer polymeric nitrogen structures. − For example, the N-structure of R 3̅ m -WN 6 is the armchair-like N 6 ring, which is different from that of the plane N 6 rings in main group metal polynitrides . The N 14 network structure is first reported to exist in the C 2/ m -CdN 6 compound . The abnormal armchair-antiarmchair N-chain in P 1̅-ZnN 6 is different from the standard armchair N-chain structure in main group metal polynitrides .…”

“…44 The N 14 network structure is first reported to exist in the C2/m-CdN 6 compound. 45 The abnormal armchair-antiarmchair N-chain in P1̅ -ZnN 6 is different from the standard armchair N-chain structure in main group metal polynitrides. 46 Cobalt (Co) with the complex electronic configuration is a typical transition metal element.…”

Pressure-stabilized polymerization of nitrogen in manganese nitrides at ambient and high pressures

“…The stability of polynitrogen compounds under ambient conditions is also very important for their application in reality. 68 As C 2/ m -MnN 4 and C 2/ m -MnN 6 do not possess mechanical stability at ambient pressure, we look for the stable structures by considering the other four structures. The calculated phonon dispersion shows that P 4/ mmm -MnN 4 and P 1̄-MnN 8 do not possess dynamical stability at ambient pressure (Fig.…”

The New High-Pressure Phases of Nitrogen-Rich Ag–N Compounds

“…The superhard R-3m-WN 6 remains dynamically stable at ambient conditions [ 40 ]. The N-chain structures are found in MN 4 (M = Be, Cd, Fe, Gd, Re, Os, W, Ru, Zn) [ 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 ], GdN 6 [ 45 ], ReN 8 [ 49 ] and HfN 10 compounds [ 50 ]. Among them, P-1-BeN 4 , γ-P-1-BeN 4 and δ-P-1-BeN 4 with the N-chain structures can be synthesized under pressures of 25.4, 20.8 and 27.4 GPa, respectively, which is greatly lower than 110 GPa for synthesizing the cg-N.…”

“…The P-31c-CoN 8 (6.14 kJ/g) and P-1-CoN 10 (5.18 kJ/g) with high-energy density can be quenched down to ambient conditions. The three-dimensional network structures are found in the C2/m-CdN 6 , I4 1 /a-HeN 4 , R-3m-HeN 6 , P63/m-HeN 10 and C2/m-HeN 22 [ 43 , 54 , 55 ]. The C2/m-CdN 6 and C2/m-HeN 22 with respectively high-energy-density values of 3.82 kJ/g and 10.44 kJ/g may be quenchable to ambient pressure.…”