skip to main content

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


Title: A novel all-nitrogen molecular crystal N 16 as a promising high-energy-density material
All-nitrogen solids, if successfully synthesized, are ideal high-energy-density materials because they store a great amount of energy and produce only harmless N 2 gas upon decomposition. Currently, the only method to obtain all-nitrogen solids is to apply high pressure to N 2 crystals. However, products such as cg-N tend to decompose upon releasing the pressure. Compared to covalent solids, molecular crystals are more likely to remain stable during decompression because they can relax the strain by increasing the intermolecular distances. The challenge of such a route is to find a molecular crystal that can attain a favorable phase under elevated pressure. In this work, we show, by designing a novel N 16 molecule (tripentazolylamine) and examining its crystal structures under a series of pressures, that the aromatic units and high molecular symmetry are the key factors to achieving an all-nitrogen molecular crystal. Density functional calculations and structural studies reveal that this new all-nitrogen molecular crystal exhibits a particularly slow enthalpy increase with pressure due to the highly efficient crystal packing of its highly symmetric molecules. Vibration mode calculations and molecular dynamics (MD) simulations show that N 16 crystals are metastable at ambient pressure and could remain inactive up to 400 K. The initial reaction steps of the decomposition are calculated by following the pathway of the concerted excision of N 2 from the N 5 group as revealed by the MD simulations.  more » « less
Award ID(s):
1848141
PAR ID:
10403397
Author(s) / Creator(s):
; ; ; ; ; ; ; ; ;
Date Published:
Journal Name:
Dalton Transactions
Volume:
51
Issue:
24
ISSN:
1477-9226
Page Range / eLocation ID:
9369 to 9376
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ; ( , Physical Chemistry Chemical Physics)
    null (Ed.)
    Polymeric nitrogen (PN) belongs to a general family of materials containing all-nitrogen molecules or clusters. Although it is rare and challenging to synthesize PN members, they are attracting increasing scientific attention due to their high energy storage capacity and possible use as a green catalyst. A few theoretical calculations predicted the possible PN phases from N 2 gas, but they all require extremely high pressures and temperatures to synthesize. In this work, a practical way to synthesize N 8 polymeric nitrogen from an N 3 − precursor is elucidated using density functional theory calculations. The detailed mechanism, , is determined. The calculated energy barriers indicate that the first step is the rate-limiting step. This result guides us to rationally synthesize N 8 under UV (254 nm) irradiation, chosen based on the calculated absorption spectrum for the azide anion. As expected, UV irradiation enhances N 8 yields by nearly four times. This provides an interesting route to the scalable synthesis of high energy density N 8 compounds. 
    more » « less
  2. ; ; ; ; ; ; ; ; ; ; et al ( , Advanced Functional Materials)
    Abstract Magnetic and electronic properties of quantum materials heavily rely on the crystal structure even in the same chemical compositions. In this study, it is demonstrated that a layered tetragonal EuCd 2 Sb 2 structure can be obtained by treating bulk trigonal EuCd 2 Sb 2 under high pressure (6 GPa) and high temperature (600 °C). Magnetization measurements of the newly formed layered tetragonal EuCd 2 Sb 2 confirm an antiferromagnetic ordering with Neel temperature ( T N ) around 16 K, which is significantly higher than that ( T N ≈ 7 K) of trigonal EuCd 2 Sb 2 , consistent with heat capacity measurements. Moreover, bad metal behavior is observed in the temperature dependence of the electrical resistivity and the resistivity shows a dramatic increase around the Neel temperature. Electronic structure calculations with local density approximation dynamic mean–field theory (LDA+DMFT) show that this material is strongly correlated with well‐formed large magnetic moments, due to Hund's coupling, which is known to dramatically suppress the Kondo scale. 
    more » « less
  3. ; ; ; ; ( , Zeitschrift für Naturforschung B)
    null (Ed.)
    Abstract An unprecedented NiSn 2 intermetallic with CoGe 2 -type crystal structure has been recovered (at ambient conditions) after high-pressure high-temperature treatment of a Ni 33 Sn 67 precursor alloy at 10 GPa and 400 °C. The orthorhombic structure with Aeam space group symmetry is pseudotetragonal. Based on the evaluation of powder X-ray diffraction data, lattice parameters of a  =  b  = 6.2818 Å and c  = 11.8960 Å have been determined. Complicated line broadening and results of a further microstructure analysis, however, imply a defective character of the crystal structure. First-principles calculations with different model structures and a comparison with structural trends in the literature suggest that at the high-pressure high-temperature conditions a CuAl 2 -type crystal structure might be stable, which transforms to the recovered CoGe 2 -type crystal structure upon cooling or the release of pressure. 
    more » « less
  4. ; ; ; ; ; ; ; ( , Dalton Transactions)
    We present the combined results of single crystal X-ray diffraction, physical properties characterization, and theoretical assessment of EuSnP under high pressure. Single crystals of EuSnP prepared using Sn self-flux crystallize in the tetragonal NbCrN-type crystal structure (S.G. P 4/ nmm ) at ambient pressure. Previous studies have shown that for Eu ions, seven unpaired electrons impart a 2+ oxidation state. Assuming the oxidation states of Eu to be +2 and P to be −3, each Sn will donate one electron, with one p valence electron left for forming a weak Sn–Sn bond. According to the high-pressure single crystal X-ray diffraction measurements, no structural phase transition was observed up to ∼6.2 GPa. Temperature-dependent resistivity measurements up to 2.15 GPa on single crystals indicate that the phase-transition temperature occurring at the Néel temperature ( T N ) is significantly enhanced under high pressure. The robust crystallography and enhanced antiferromagnetic transition temperatures can be rationalized by the electronic structure calculations and chemical bonding analysis. The increasing Eu–P bonding interaction is consistent with the lattice parameter changing and enhanced T N . Moreover, the molecular orbital diagram shows that the weak Sn–Sn bond can be squeezed under pressure, acting as a compression buffer to stabilize the structure. 
    more » « less
  5. ; ; ( , Physical Chemistry Chemical Physics)
    Neural network potentials (NNPs) trained against density functional theory (DFT) are capable of reproducing the potential energy surface at a fraction of the computational cost. However, most NNP implementations focus on energy and forces. In this work, we modified the NNP model introduced by Behler and Parrinello to predict Fermi energy, band edges, and partial density of states of Cu 2 O. Our NNP can reproduce the DFT potential energy surface and properties at a fraction of the computational cost. We used our NNP to perform molecular dynamics (MD) simulations and validated the predicted properties against DFT calculations. Our model achieved a root mean squared error of 16 meV for the energy prediction. Furthermore, we show that the standard deviation of the energies predicted by the ensemble of training snapshots can be used to estimate the uncertainty in the predictions. This allows us to switch from the NNP to DFT on-the-fly during the MD simulation to evaluate the forces when the uncertainty is high. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email