Pressure-induced isosymmetric phase transition in sulfamic acid: A combined Raman and x-ray diffraction study

Abstract

High-pressure behaviors of hydrogen-bonded molecular crystal, sulfamic acid (NH3(+)SO3(-), SA), have been investigated using Raman spectroscopy and synchrotron X-ray diffraction (XRD) techniques up to the pressure of ~20 GPa. Under ambient conditions, molecules of SA are arranged in puckered layers and held together by hydrogen bonding and electrostatic interactions. It is proved by the Raman results that SA undergoes the molecular conformation changes in the pressure range 8.1-10.2 GPa. Then between 10.2 and 12.7 GPa, a phase transition is observed in both Raman and XRD patterns. Both the ambient and high-pressure phases of SA crystallize in Pbca symmetry with similar unit-cell dimensions. The mechanism of the phase transition involves relative movements of adjacent hydrogen-bonded molecules, accompanied by the rearrangement of hydrogen bonds and the enhancement of electrostatic interactions.

Effect of pressure on heterocyclic compounds: Pyrimidine and s-triazine

“…As displayed in Figure 6(b), the lattice modes exhibit high rates of blue shifts owing to reduction in intermolecular distances. 46,47 The υ 1 mode weakens progressively above 6.8 GPa, shown in the inset of Figure 6(a). Overall, the four modes in phase II can still be observed even at the highest pressure of 14.3 GPa in this experiment.…”

High‐Pressure Band‐Gap Engineering in Lead‐Free Cs2AgBiBr6 Double Perovskite

“…To determine the in situ local and global structural variations of Cs 2 AgBiBr 6 , Raman spectroscopy and angle‐dispersive synchrotron X‐ray diffraction (ADXRD) experiments are conducted at high pressure. In Raman experiments, we obtain the abnormal discontinuities of lattice modes and octahedral bending modes of ν (F 2g ) between 3.5 and 4.2 GPa (Figure S3), which are indicative of the phase transition of Cs 2 AgBiBr 6 . And the gradual broadening of lattice vibrations and weakening of ν (F 2g ) with further compression may involve with the structural amorphization of high pressure phase .…”

“…The splitting of two diffraction peaks as marked with asterisks at 3.1 GPa is observed (enlarged in Figure S5), confirming the occurrence of phase transition that we inferred from Raman and UV/Vis absorption experiments. For high pressure Cs 2 AgBiBr 6 above 6.5 GPa, the broad diffraction background, as well as the peak weakening, exhibits the gradual structural amorphization . Furthermore, Cs 2 AgBiBr 6 is reverted into its original phase after fully releasing pressure (Figure S6).…”

Can We Predict the Isosymmetric Phase Transition? Application of DFT Calculations to Study the Pressure Induced Transformation of Chlorothiazide

“…Isosymmetric structural phase transition (IPT, type 0), in which there are no changes in the occupation of Wyckoff positions, the number of atoms in the unit cell, and the space group symmetry are relatively uncommon [5]. However, there are some well-known and recently discovered examples of such transitions: sodium oxalate [6], 1,3-cyclohexandione [7] L-serine [8], sulfamic acid [9], biurea [10], and α-glycylglycine [11].…”