Crystal structure of SS at ambient conditions. Carbon (gray), oxygen (red), and sodium (green).
Crystal structure of SST at ambient conditions. (a) Hydrogen bonds in SST. (b) and (c) The similar structure as SS. Carbon (white), oxygen (red), hydrogen (gray), and sodium (green).
Selected high-pressure Raman spectra of SS in the range of 100–400 cm−1. The dotted lines are illustrated for the sake of clarity of lattice modes’ evolution. (Fluorescence background has been subtracted.)
Representative high-pressure Raman spectra of SS in the spectral range of (a) 550–1250 cm−1; (b) 1500–2000 cm−1 (fluorescence background has been subtracted).
(a) Enlarged view of evolution of ring bending modes. (b) Fitted curves of the ring bending modes at ambient conditions. (c) Selected Raman patterns ranging from 1550 to 2000 cm−1 with the original background.
Frequency shifts of the internal and external Raman modes as a function of pressure. The vertical dashed line presents boundaries of different phases.
Representative high-pressure Raman spectra of SS in the spectral range of (a) 550–1250 cm−1; (b) 1500–2000 cm−1. (Fluorescence background has been subtracted, Raman modes in the range of 1500–2000 cm−1 were affected by the PTM, so it will not be shown here.)
(a) Representative XRD patterns of SS at high pressures. The wavelength for data collection is 0.6199 Å. The top pattern is the one collected when pressure was released to 0.3 GPa. (b) Simulated and assignments of high-pressure XRD peaks. (c) Pawley refinement of the pattern collected at 13.5 GPa. The inset depicts the obtained space group P21. The blue line represents the fit residual beneath. (d) Pawley refinement of the released pattern of 0.3 GPa. The inset depicts the space group P21/c. The black line represents the fit residual beneath. (e) Enlarged view of the diffraction peaks of (100) and (020).
Up: (a) Squarate rings at ambient conditions. (b) Distorted squarate rings at 15 GPa. Down: Calculated unit cell at different pressures. (a) Layered structure of SS at ambient conditions. (b) Distorted layered structure of SS at 15 GPa.
Selected high-pressure Raman spectra of SST in the range of (a) 70–400 cm−1; (b) 580–1250 cm−1; (c) 1560–1940 cm−1; (d) 3400–3540 cm−1.
Unit cell parameters at ambient conditions and 15 GPa.
Three π-stacking related parameters measuring from the ambient structure and calculated model.
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