Raman scattering study of monoclinic and cubic tetracyanoethylene under high pressures

Chaplot, S. L.; Mierzejewski, A.; Pawley, G. S.

doi:10.1080/00268978500102211

Cited by 22 publications

(16 citation statements)

References 22 publications

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“…Finally, high pressure polymerization reactions of TCNE at room temperature have been observed when starting from either the monoclinic or cubic phases. [6][7][8]21,22,[24][25][26] The most recent investigations indicate that when using no pressure medium, the monoclinic phase completely polymerizes above 6.4 GPa while the cubic phase is stable up to 14 GPa. 22 Interestingly, the polymerized material is a form of amorphous carbon with 52% less nitrogen than crystalline TCNE, and the C : N ratio obtained from neutron/X-ray diffraction was 7 : 1 for the polymerized product compared to 3 : 2 for the original material.…”

Section: Introductionmentioning

confidence: 99%

“…The temperature-induced phase transition is first order, appearing as an irreversible (down a Department of Chemistry, The Pennsylvania State University, FayetteThe Eberly Campus, 1 University Dr, Uniontown, PA, 15401, USA. E-mail: bxs54@psu.edu to 4 K) cubic to monoclinic evolution at temperatures above 318 K. [17][18][19]23 The pressure-induced phase transitions have also been extensively investigated, [6][7][8]21,22,[24][25][26] where the monoclinic phase converts to an intermediate 'disordered' metastable phase when pressurized between 2.0-6.3 GPa. Upon release of pressure, the intermediate phase is followed by conversion to either a) the cubic phase (provided sufficient time under high pressure) or b) the original monoclinic phase.…”

Section: Introductionmentioning

confidence: 99%

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Phase transition between cubic and monoclinic polymorphs of the tetracyanoethylene crystal: the role of temperature and kinetics

Schatschneider

Liang²,

Jezowski

et al. 2012

CrystEngComm

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Prediction of the relative stabilities and phase transition behavior of molecular crystalline polymorphs is highly coveted as distinct phases can possess different physical and chemical properties while having similar energies. Crystalline tetracyanoethylene (TCNE, C 6 N 4 ) is known to exhibit rich solid state phase behavior under different thermodynamic conditions, as demonstrated by a wealth of experimental studies on this system. Despite this fact, the role of temperature and kinetics on the phase diagram of TCNE remains poorly understood. Here, first-principles calculations and highresolution Fourier-transformed infrared (HR-FTIR) spectroscopy experiments are used to study the relative stabilities of the cubic and monoclinic phases of TCNE as a function of temperature. Specifically, density-functional theory with the van der Waals interactions method of Tkatchenko and Scheffler (DFT+vdW) is employed. The accuracy of this approach is demonstrated by the excellent agreement between the calculated and experimental structures. We find that the cubic phase is the most stable polymorph at 0 K, but becomes less favorable than the monoclinic phase at 160 K. This temperature-induced phase transition is explained on the basis of varying close contacts and vibrational entropies as a function of temperature. These findings are supported by a temperaturedependent HR-FTIR linewidth study of the CMN vibrons.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Phase transition between cubic and monoclinic polymorphs of the tetracyanoethylene crystal: the role of temperature and kinetics

Schatschneider

Liang²,

Jezowski

et al. 2012

CrystEngComm

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“…Figures 5 and 6 display two different (ordered or disordered) crystal-to-amorphous transitions leading to a quasi-similar description of the amorphous state. Pressure-induced amorphizations have been observed in many other compounds [15][16][17][18][19][20][21][22][23][24][25][26][27], among which are several recognized to be typical molecular crystals [15][16][17][18][19][20][21]. However, the evidence for two different routes to a single amorphous state is unusual.…”

Section: High-pressure Dependence Of Cnamentioning

confidence: 99%

Pressure-induced transformations and high-pressure behaviour in cyanoadamantane plastic crystal

Hédoux

Guinet

Derollez

et al. 2003

J. Phys.: Condens. Matter

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Raman scattering investigations of cyanoadamantane (CNa) plastic crystals were performed in the 0–10 GPa pressure range. A phase transition towards an ordered high-pressure (HP) phase is clearly identified. However, this transition can be easily bypassed upon pressurization, placing the initial plastic phase in a metastable situation. Between 0.3 and 0.7 GPa the escape from metastability is observed through the isobaric transformation towards the ordered HP phase. Above 0.7 GPa, the lifetime of the metastability appears to be infinite with respect to the experimental timescale, suggesting that the glassy crystal state was reached upon pressurization. Above 10 GPa, the metastable plastic phase, as well as the ordered HP phase, convert into a conventional amorphous state. The structural features of the ordered and the glassy crystal HP phases, determined from Raman investigations, were compared to those of the ordered and glassy crystal phases usually obtained upon cooling.

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“…Once the potential function parameters have been chosen, it is straightforward to calculate the structure and dynamics as a function of pressure for zero temperature [ 111; the method has also been adopted in more recent work [18]. First the structure is found by minimising the total of the potential and pressure energy ( p V ) with respect to the structure variables, the lattice parameters and molecular coordinates, keeping the space group symmetry unchanged.…”

Section: Interatomic Potentialmentioning

confidence: 99%

Pressure and temperature studies of Raman scattering of the molecular crystal sym-C₆Cl₃F₃

Chaplot¹,

Mierzejewski²,

Pawley³

et al. 1990

J. Phys.: Condens. Matter

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Earlier experimental results have been considerably strengthened by Raman scattering from crystalline sym-C,CI,F3. Measurements have been made as a function of temperature at ambient pressure, and as a function of pressure at room temperature. Apart from a new first-order phase transition observed at 62 kbar but as yet uncharacterised, the crystal structure maintains the P6& space group symmetry. Anomalies in phonon frequencies and line-widths at 296 K indicate a phase transition, which is 'isostructural' order-disorder. Similar features are seen at 15 kbar, suggesting that the phase transition is of the same nature as that observed at 296 K. The half-width of the phonon associated with dynamic disorder is found by fitting to be r,,2(T) = 0.032 + 0.0061 T + 3400exp(-AE,/ k T ) cm-', with A E , = 35 kJ mol-'. Although in-plane 120" molecular reorientational jumps may play a role, this may not be a major role at room temperature due to a rather high activation energy. The full understanding of the results requires there to be another minor activation process that also obeys A, symmetry. The variation in the crystal structure parameters and the external mode frequencies with pressure up to 60 kbar is calculated using a 6-exp atom-atom potential with the rigid-body approximation. The molecular orientation changes by only 0.5" between 0 and 60 kbar. The calculated external mode frequencies agree with Raman experiment up to 60 kbar within 5 1 5 % . A molecular dynamics simulation for 300 K indicates a residence time between reorientations greater than 500 ps, giving a quasielastic Lorentzian broadening of less than 0.01 cm-'.

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Raman scattering study of monoclinic and cubic tetracyanoethylene under high pressures

Cited by 22 publications

References 22 publications

Phase transition between cubic and monoclinic polymorphs of the tetracyanoethylene crystal: the role of temperature and kinetics

Phase transition between cubic and monoclinic polymorphs of the tetracyanoethylene crystal: the role of temperature and kinetics

Pressure-induced transformations and high-pressure behaviour in cyanoadamantane plastic crystal

Pressure and temperature studies of Raman scattering of the molecular crystal sym-C₆Cl₃F₃

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Raman scattering study of monoclinic and cubic tetracyanoethylene under high pressures

Cited by 22 publications

References 22 publications

Phase transition between cubic and monoclinic polymorphs of the tetracyanoethylene crystal: the role of temperature and kinetics

Phase transition between cubic and monoclinic polymorphs of the tetracyanoethylene crystal: the role of temperature and kinetics

Pressure-induced transformations and high-pressure behaviour in cyanoadamantane plastic crystal

Pressure and temperature studies of Raman scattering of the molecular crystal sym-C6Cl3F3

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Pressure and temperature studies of Raman scattering of the molecular crystal sym-C₆Cl₃F₃