Phase transformations and vibrational properties of coronene under pressure

Abstract

Both the vibrational and structural properties of coronene have been investigated upon compression up to 30.5 GPa at room temperature by a combination of Raman scattering and synchrotron x-ray diffraction measurements. The spectroscopic and crystallographic results demonstrate that two pressure-induced structural phase transitions take place at 1.5 GPa and 12.2 GPa where the high-pressure phases are identified as monoclinic and orthorhombic crystal structures with space groups of P2/m and Pmmm, respectively. A kink in the slope of the cell parameters as a function of pressure is associated with the disappearance of several internal Raman modes, which suggests the existence of structural distortions or reorganizations at approximately 6.0 GPa. Above 17.1 GPa, almost no evidence of crystallinity can be observed, indicating a possible transformation of coronene into an amorphous phase.

Thermal expansion of coronene C24H12 at 185–416 K

“…However, no precise structural data for the high pressure modifications were reported. At pressures above 30.5 GPa, coronene appeared to be amorphous [24]. On the contrary, the Raman spectroscopy data presented in [24] indicate phase transitions at 1.3 and 3.7 GPa.…”

“…At pressures above 30.5 GPa, coronene appeared to be amorphous [24]. On the contrary, the Raman spectroscopy data presented in [24] indicate phase transitions at 1.3 and 3.7 GPa. Thus, there is a range of inconsistent phase transitions in coronene, which can be caused by the use of different pressure media and should be clarified in future studies at high pressures.…”

“…In a recent work, Zhao et al [24] argued for a transition from P2 1 /a to P2/m at 1.5 GPa and to Pmmm at 12.2 GPa. However, no precise structural data for the high pressure modifications were reported.…”

Evidence and origin of different types of sedimentary organic matter from a Paleoproterozoic orogenic Au deposit

“…(D) Raman spectra of different naturally occurring graphitic carbon samples with varying metamorphic grades from meta-anthracite (i) to graphite (v). Notes: (A) Cyclohexane (i) and benzene (ii) standard Raman spectra redrawn from McCreery (n.d.) and Mayo et al (2004) respectively; peak interpretations for both (i) and (ii) from Shimanouchi (1973) and Mayo et al (2004); Coronene Raman spectra (iii) redrawn from Colangeli et al (1992) and peak interpretations from Cyvin et al (1982), Colangeli et al (1992) and Zhao et al (2013); HBC Raman spectra (iv) redrawn from Maghsoumi et al (2016) and peak interpretations from same source. (B) Partial raman spectra of coronene (i) and HBC (ii) modified from Colangeli et al (1992) and Magsoumi et al (2016) respectively; Large PAHs Raman spectra C 60 H 22 (iii), C 72 H 26 (iv), C 78 H 26 (v), C 96 H 30 (vi) and C 132 H 34 (vii) redrawn from Mapelli et al (1999), Castiglioni et al (2001a) and Castiglioni et al (2001b) (C) Mono (i) and multi-layer (ii) pristine graphene Raman spectra modified from Yan and Barron (2010); graphite crystallite Raman spectra of inner region (iii) and edge (iv) and confocal image of G band (a) and D-band (b) showing the analysed regions (red dot) modified from Dresselhaus et al (2010); defected graphene (v) modified from Dresselhaus et al (2010); Black carbon spectra (vi) and basic structural unit (BSU) sketch redrawn from Pawlyta et al (2015).…”

Low temperature magneto-morphological characterisation of coronene and the resolution of previously observed unexplained phenomena

“…1(a). It was known that γ-coronene could be forced to form other polymorphs, but only at extremes of pressure16. What was perplexing, however, was that at low temperatures and ambient pressure, unaccountable experimental results were obtained.…”