Nitrogen in black phosphorus structure

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Science Advances  03 Jun 2020:
Vol. 6, no. 23, eaba9206
DOI: 10.1126/sciadv.aba9206
  • Fig. 1 XRD characterization and illustration of the crystal structure of BP-structured nitrogen.

    (A) Le Bail fit of XRD data at 132 GPa. Black circles, red line, and green line represent experimental data, Le Bail fitting, and residual, respectively. Blue, pink, and purple ticks mark reflections for BP-structured nitrogen, CG-nitrogen, and Re, respectively. Inset shows the microscopic image of the sample under illumination with both reflected and transmitted light, with the white circle marking the sample position being measured. BP and CG stand for BP-structured nitrogen and CG-nitrogen, respectively. (B) 2D x-ray diffraction (XRD) image from grain #2. White boxes mark the diffraction spots of BP-structured nitrogen. Numbers indicate corresponding Miller indices. Image is obtained by merging selected step scan patterns that contain BP-structured nitrogen reflections for demonstration. (C) Crystal structure of BP-structured nitrogen. (D and E) Single nitrogen layer in BP-structured nitrogen. (F and G) Dihedral angles in BP-structured nitrogen and CG-nitrogen calculated at 132 GPa, respectively. a.u., arbitrary units.

  • Fig. 2 Identification of the BP structure by Raman spectrum.

    (A) Raman spectra from sample 1 measured at 138 GPa and sample 2 measured at 112 GPa compared with the superposition of two calculated spectra for BP-structured nitrogen (black) and CG-nitrogen (red) at 138 GPa. Gray shade marks the region of phonon from stressed diamond anvil, which hides B3g of BP-structured nitrogen. Inset shows photomicrograph of the sample, with the white arrow marking the sample position being measured. A mode of CG-nitrogen at 112 GPa shifts to a lower frequency compared with the spectrum at 138 GPa. Red arrow between the experiment spectra correlates the two A modes of CG-nitrogen at different pressures. (B and C) Schematic of atomic displacements of the Ag and Ag′ modes.

  • Fig. 3 Measured and calculated pressure-dependent evolution of unit cell volume, lattice parameters, and Raman phonons of BP-structured nitrogen.

    (A) Unit cell volumes of BP-structured nitrogen and CG-nitrogen. (B) Lattice parameters a, b, and c of BP-structured nitrogen. (C) Measured Raman shift compared with calculations and previously reported values (10, 11). All measurements were performed during decompression. In (C), LP stands for LP-N (11).

  • Fig. 4 Calculated enthalpies of BP-structured nitrogen under high pressure at the ground state and at high temperature.

    (A) Calculated enthalpies as functions of pressure for various structures of solid nitrogen with respect to CG-nitrogen. Pba2, C2/c, P42bc, and chain structures are reported in (12), (20), (13), and (19), respectively. “N2” denotes the enthalpy of the molecular solid of N2, calculated using the lowest-enthalpy structures (21) in respective pressure ranges. (B) Finite-temperature energy (H + Fvib) of BP-structured nitrogen relative to CG-nitrogen.

  • Table 1 List of 23 reflections indexed with the BP-structured nitrogen structure at 140 GPa.

    dobs and dcal represent the d-spacing of observed and calculated reflections, respectively. Dcal was obtained using unit cell parameters a = 2.1438 Å, b = 6.5554 Å, and c = 2.8534 Å.

    #h k ldobs (Å)dcal (Å)dobs-dcal (Å)
    10 2 03.27793.27770.0002
    20 2 12.15312.15210.0010
    31 1 11.66061.65820.0024
    40 4 01.63831.6389−0.0006
    50 0 21.42691.42670.0002
    60 4 11.42121.42110.0001
    71 3 11.34751.3486−0.0011
    81 1 21.16781.1687−0.0009
    92 0 01.07331.07190.0014
    101 5 11.04211.04140.0007
    112 2 01.01971.01880.0009
    122 2 10.95970.95950.0002
    130 2 30.91460.91350.0011
    141 1 30.86160.8619−0.0003
    152 4 10.85470.8558−0.0011
    160 4 30.82300.82260.0004
    170 8 10.78740.7876−0.0002
    182 6 00.76460.7652−0.0006
    191 7 20.73470.7354−0.0007
    201 5 30.72450.7246−0.0001
    210 6 30.71780.71740.0004
    222 2 30.69440.6953−0.0009
    232 8 00.65170.65100.0007

Supplementary Materials

  • Supplementary Materials

    Nitrogen in black phosphorus structure

    Cheng Ji, Adebayo A. Adeleke, Liuxiang Yang, Biao Wan, Huiyang Gou, Yansun Yao, Bing Li, Yue Meng, Jesse S. Smith, Vitali B. Prakapenka, Wenjun Liu, Guoyin Shen, Wendy L. Mao, Ho-kwang Mao

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