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Pressure-induced isosymmetric phase transition in sulfamic acid: A combined Raman and x-ray diffraction study
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10.1063/1.4807864
/content/aip/journal/jcp/138/21/10.1063/1.4807864
http://aip.metastore.ingenta.com/content/aip/journal/jcp/138/21/10.1063/1.4807864
View: Figures

Figures

Image of FIG. 1.
FIG. 1.

Crystal structure of SA at ambient conditions: (a) the five hydrogen bonds originated from one NH group (show in pink), (b) the unit cell of SA, and (c) the hydrogen-bonds system view along axis.

Image of FIG. 2.
FIG. 2.

(a) Selected high-pressure Raman spectra of SA in the range 65–320 cm, (b) Lattice modes at ambient conditions, and (c) Peak positions of the lattice modes as a function of pressure. Linear fits are performed for clarity and the neighboring numbers are the pressure confidence of the corresponding mode. (The unit is cm/GPa.) The shadow represents the phase-transition region.

Image of FIG. 3.
FIG. 3.

Selected high-pressure Raman spectra of SA in the spectral range: (a) 165–510 cm, (b) 505–850 cm, and (c) 1000–1050 cm. The dotted lines are illustrated for the sake of clarity of lattice modes’ evolution.

Image of FIG. 4.
FIG. 4.

Frequency shifts of major internal modes ranging from 165 to 1050 cm as a function of pressure. Linear fits are performed for clarity and the neighboring numbers are the slopes of the corresponding modes. (The unit is cm/GPa.) The vertical dotted line stands for the beginning of the variations in Raman spectra. And the shadow represents the phase-transition region.

Image of FIG. 5.
FIG. 5.

Representative high-pressure Raman spectra of NH related modes: (a) NH deformation, (b) N–H stretching, (c)–(f) Decompositions of the N–H stretching region are conducted for clarity, (g) The comparison of calculated and experimental N–H stretching modes, and (h) Pressure dependence of the peak positions for these NH related modes. The vertical dotted line stands for the beginning of the variations in Raman spectra. And the shadow represents the phase-transition region. Linear fits are performed for clarity and the neighboring numbers are the slopes of the corresponding modes. (The unit is cm/GPa.)

Image of FIG. 6.
FIG. 6.

Representative ADXRD diffraction patterns of SA at selected pressures. The top pattern is the one collected after releasing the pressure, which shows the reversibility of the phase transition.

Image of FIG. 7.
FIG. 7.

Rietveld refinement of the ADXRD pattern collected at 13.7 GPa. The blue line denotes the difference between the observed (black) and the simulated (red) profiles. The refined structure crystallizes with symmetry.

Image of FIG. 8.
FIG. 8.

Compression of (a) lattice constants and (b) unit cell volume of SA with respect to pressure. Shadow represents the phase-transition region.

Image of FIG. 9.
FIG. 9.

The geometry optimized structure of ambient phase (left) and the crystal structure of high-pressure phase (right). (a) The structure in ab plane, (b) SA molecules projected down the S–N bond axis, and (c) The sliding trends along the c axis. The black arrows show the moving trends of the molecular chains.

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/content/aip/journal/jcp/138/21/10.1063/1.4807864
2013-06-06
2014-04-18
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Pressure-induced isosymmetric phase transition in sulfamic acid: A combined Raman and x-ray diffraction study
http://aip.metastore.ingenta.com/content/aip/journal/jcp/138/21/10.1063/1.4807864
10.1063/1.4807864
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