(a) The pressure dependence of D2 vibron in the 9:1 N2 and D2 mixture and, in the inset, the microphotograph of the sample at the onset of freezing at 5.5 GPa, showing two large pieces of noncrystalline solids and surrounding liquid. The phase transition pressures of pure N2 (dotted lines at the bottom) and the pressure dependence of pure D2 vibron (Ref. 15) (open symbols) are also shown for comparison. (b) Raman spectra of D2 and N2 in the mixture showing the pressure-induced solidification to δ-N2-like lattice at 5.5 GPa and then to a novel hexagonal phase above 10 GPa.
(a) The pressure dependence of the frequency difference, Δν = ν(ν 2) − ν(ν 1), of N2 in the mixture (open circles) and pure N2 (red crosses). (b) The intensity ratio of the ν 2 and ν 1, as a function of pressure.
(a) Angle-resolved x-ray diffraction patterns up to 33 GPa. The disordered solid phase is shown below 10 GPa and N2–D2 mixture begins crystallizing at 11 GPa. Rather strong peaks at 2θ = 5 and 8° at 10.5 GPa are from the cubic δ-phase of N2. (b) Angle-resolved x-ray diffraction patterns of the crystallized N2–D2 mixture at 13 GPa plotted together with the fitted (black lines) and difference (red lines) patterns. The blue and red tick marks in 13 GPa diffraction profile (by Rietveld method) indicate reflections for the hexagonal structure (P6 3 22) with 24 N2 and the cubic (Pm-3n) structures with 8 N2, respectively.
(a) The evolution of lattice parameters as a function of pressure. (b) The pressure-dependence of the specific volume of the proposed (N2)12D2 in comparison with those of simple N2–D2 mixtures (dotted lines). The data were fitted to a third-order Birch–Murnaghan equation of state with V 0 = 644.5(24.1) Å3, B 0 = 33.2(0.9) GPa, and B′ = 3.5(0.1).
The proposed crystal structure of hexagonal (N2)12D2 with the molecular positions of 24 N2 (green) and 2 D2 (orange) on a projection of the ab-plane (a) and a 3D view (b) and the hexagonal sub-lattice of D2 (orange). Dotted-open circles represent unoccupied D2 positions.
The energy difference between the D2 vibrons observed in (N2)12D2 and pure D2 plotted as a function of the (N2)12D2 density. The energy difference between the D2 vibrons observed in (N2)12D2 and pure D2 plotted as a function of the (N2)12D2 density. Number represents a measurement pressure.
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