Phase diagram of carbonyl sulfide: An analogy to carbon dioxide and carbon disulfide

Abstract

The application of pressure, internal or external, transforms molecular solids into nonmolecular extended network solids with diverse crystal structures and electronic properties, ranging from optically nonlinear CO2–V to high Tc superconducting CS2-III. While these transformations can be understood in terms of pressure-induced electron delocalization, the governing mechanisms are complex and often result in unusual phase/chemical transformation diagrams with a large number of polymorphs, metastable phases, and path-dependent phase behaviors. This complexity, commonly shared in many molecular systems at high pressures, poses both theoretical and experimental challenges in understanding high-pressure behaviors of dense molecular solids, particularly in the transition regime where the long-range interactions become comparable or even greater than hydrogen bonding at collapsed interatomic distances. In this paper, we describe the phase diagram of OCS, highlighting (i) the significance of long-range dipolar interaction that leads to the transition from linear phase I (R3m) to bent phase II (Cm) at 11 GPa, (ii) the molecular-to-nonmolecular transformations to highly disordered one-dimensional (1D) polymer phase III (modeled Cm) at 22 GPa and 3D network phase IV (modeled P212121) at ∼35–45 GPa that becomes a semiconductor at around 100 GPa, and (iii) the intermediate nature of extended OCS between the two end members of CO2 and CS2 — an important chemical concept for molecular alloys. These results are based on our present low temperature and previous ambient temperature data obtained from confocal micro-Raman spectroscopy, synchrotron X-ray diffraction, and four-probe electric conductivity measurements.

Seven-Coordinated “Metallic” WO3 at High Pressures

“…The present X-ray diffraction results confirm that WO 3 undergoes a series of structural phase transitions from one six-fold coordinated triclinic P 1̅ phase I ,− to another six-fold coordinated monoclinic P 2 1 / c phase II and then to a seven-fold coordinated P 2 1 / c phase III at ∼27 GPa and another seven-fold coordinated Pc phase IV at ∼37 GPa. These transitions are also complemented by the present Raman and resistivity measurements.…”

“…Upon compression, the resistance drops to ∼10 4 Ω at ∼10 GPa and 200 Ω at 24 GPa. These resistance values measured for phase II and III are typical for a semiconductor and a “poor” metal in the present four-probe configuration in DAC. ,− Upon further increasing the pressure above 24 GPa, the resistance value initially drops to 74 Ω at 30 GPa and then steadily increases to 186 Ω at 60 GPa. It is important to note that the slight increasing trend in the resistivity starts at around ∼33 GPa, which roughly corresponds to the phase III-to-IV transition pressure observed in both Raman and X-ray diffraction measurement (37 GPa in hydrostatic pressure).…”

Promotional effect of H2O introduction on the NH3-SCR activity of the gas-phase sulfated CeO2 catalyst by organic CS2+COS: Influence of H2O concentration

“…Compared to inorganic SO2, organic carbonyl sulfide (COS) and carbon disulfide (CS2) are linear triatomic molecules similar to carbon dioxide (CO2), which are less reactive and difficult to be removed [11,12]. At present, catalytic hydrolysis [13,14], hydrogenation [15,16], adsorption and absorption [17][18][19] have been developed to reduce the emission of organic sulfur.…”