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Figure 1. Crystal structure of AlN3. (a) Energy of AlN3 with planar, chair, and boat N6 rings units. (b) and (c) The structure of R-3m-AlN3 phase. (d) Separate chaired N6 ring structure. (e) The structural unit of 4-fold bonded N. Light blue and gray spheres represent Al and N atoms, respectively.
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Figure 2. The dynamical and thermodynamic stabilities of the R-3m-AlN3 structure. (a) and (b) Phonon spectra and phonon DOS, respectively. (c) Fluctuations of the total energy of R-3m structure at the temperature of 300 K during FPMD simulations. The inset shows the structure pictures after 10 ps simulations at 300 K.
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Figure 3. Electronic properties of the R-3m structure of AlN3. (a) Band structure. (b) and (c) Partial densities of states (PDOS) for Al and N, respectively. (d) and (e) The COHP between Al and N atoms and between N atoms, respectively.
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Figure 4. Schematic of the SSAdNDP chemical bonding pattern for AlN3 unit cell. (a) 36 2c-2e Al–N σ bonds, occupation number threshold: 1.75|e|, the isosurface value = 0.15. (c) 18 2c-2e N–N σ bonds, occupation number threshold: 1.75|e|, the isosurface value = 0.2. (b) and (d) The bonding modes of Al–N and N–N, respectively. (e) The calculated ELF, the isosurface value = 0.8.
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Figure 5. Occupied orbitals of the
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Figure 6. Pressure-driven reaction mechanism between AlN with N2. (a) The relationship between atomic distance and external pressure. The blue line represents the sum (1.96 Å) of Al-3p and N-2p covalent radii; the green line indicates the N–N distance for cg-N. (b) Calculated enthalpy difference (ΔH), internal energy (ΔE), and volume term (PΔV) with pressure for the formation of AlN3. For the chemical reaction of AlN + N2 → AlN3, we defined ΔH = HAlN3–HAlN–HN2, ΔE = EAlN3–EAlN–EN2, PΔV = PVAlN3–PVAlN–PVN2, where P and V represent the pressure and volume per formula unit, respectively.
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Figure 7. Enthalpy of formation of R-3m-AlN3 relative to AlN and N2.
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