Properties of hexasubstituted benzenes with one or two nitro groups. Dielectric, DSC, X-ray and Raman studies

Kołodziej, H.A.; Orzechowski, Kazimierz; Szostak, Roman; Freundlich, P.; Głowiak, Tadeusz; Sorriso, Salvatore

doi:10.1016/0022-2860(95)09211-0

Cited by 6 publications

(7 citation statements)

References 14 publications

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“…For pentachloronitrobenzene ͑see inset of Fig. 6 for a sketch of the molecular structure͒ from dielectric investigations a plastic phase was reported above 223 K extending well up to the melting point of 415 K. [50][51][52] Those measurements covered a relatively restricted overall frequency range of 20 Hz to 1 MHz and temperatures between 175 and 430 K. They did not reveal any results on processes beyond the ␣-relaxation.…”

Section: Pentachloronitrobenzenementioning

confidence: 93%

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Relaxation dynamics in plastic crystals

Brand¹,

Lunkenheimer²,

Loidl³

2002

The Journal of Chemical Physics

312

355

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We report dielectric data on six different plastic crystalline materials, namely 1-cyanoadamantane, adamantanone, pentachloronitrobenzene, cyclo-hexanol, ethanol, and meta-carborane, covering a frequency range of up to 14 decades and up to 20 GHz. Information on phase transitions, the α-relaxation, and relaxation processes beyond the α-relaxation are provided. The α-relaxation shows clear non-Debye behavior and varying degrees of deviation from thermally activated behavior. Our results reveal a generally rather low fragility of plastic crystals. In some of the investigated materials evidence for Johari–Goldstein type β-relaxations is obtained. In addition, the question of the so-called excess wing of the α-relaxation peak is addressed in detail. In all cases, it is either absent or can be ascribed to a β-relaxation submerged under the α-peak. Overall, the present work provides a broad database on the dielectric behavior of plastic crystals, and may be taken as a review of the dynamic phenomena occurring in these materials, many of them being observed also in structural glass formers.

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Section: Pentachloronitrobenzenementioning

confidence: 93%

“…15,16,[50][51][52] Their molecules having a circular disk structure, the rotation is most easy about the axes perpendicular to the disk. For pentachloronitrobenzene ͑see inset of Fig.…”

Section: Pentachloronitrobenzenementioning

confidence: 99%

Relaxation dynamics in plastic crystals

Brand¹,

Lunkenheimer²,

Loidl³

2002

The Journal of Chemical Physics

312

355

View full text Add to dashboard Cite

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“…refs [30][31][32][33][34]. The fact that such disorder appears to be responsible for unusual dielectric behaviour [35][36][37][38] adds a substantial materials-centred interest to the problem. The results of this case study are shown to rationalize the role of molecular disorder on the dielectric properties observed.…”

Section: The Case Study Of Pentachloronitrobenzenementioning

confidence: 99%

Distinction of disorder, classical and quantum vibrational contributions to atomic mean-square amplitudes in dielectric pentachloronitrobenzene

2011

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The solid-state molecular disorder of pentachloronitrobenzene (PCNB) and its role in causing anomalous dielectric properties are investigated. Normal coordinate analysis (NCA) of atomic mean-square displacement parameters (ADPs) is employed to distinguish disorder contributions from classical and quantum-mechanical vibrational contributions. The analysis relies on multitemperature (5-295 K) single-crystal neutron-diffraction data. Vibrational frequencies extracted from the temperature dependence of the ADPs are in good agreement with THz spectroscopic data. Aspects of the static disorder revealed by this work, primarily tilting and displacement of the molecules, are compared with corresponding results from previous, much more in-depth and time-consuming Monte Carlo simulations; their salient findings are reproduced by this work, demonstrating that the faster NCA approach provides reliable constraints for the interpretation of diffuse scattering. The dielectric properties of PCNB can thus be rationalized by an interpretation of the temperature-dependent ADPs in terms of thermal motion and molecular disorder. The use of atomic displacement parameters in the NCA approach is nonetheless hostage to reliable neutron data. The success of this study demonstrates that state-of-the-art single-crystal Laue neutron diffraction affords sufficiently fast the accurate data for this type of study. In general terms, the validation of this work opens up the field for numerous studies of solid-state molecular disorder in organic materials.

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“…The frequency position and temperature dependence of the main peak are in agreement with early normal pressure dielectric studies at on PCNB. [34][35][36] In addition to a well-pronounced main peak (hereafter α relaxation), an excess wing (hereafter called α process) is clearly visible as a shoulder to the main peak. The fact that this loss process appears as a shoulder indicates that its dielectric strength is lower than that of the main loss (see also below).…”

Section: Resultsmentioning

confidence: 99%

“…The phase behaviour of this molecule, which forms a layered structure of triangular planes, has been extensively studied. 19,23,24,[34][35][36][37][38][39][40][41] A glass transition was observed by adiabatic calorimetry at approximately 185 K, which was assigned to the freezing of the orientational disorder within the hexagonal planes. 37 Similar results were found by Correia et al by DSC and thermally stimulated currents, with a reported transition temperature of 191 K. 38,39 Here, we show by means of broadband dielectric spectroscopy (BDS) that such phase is characterized by a double primary (collective) relaxation which is related to the low-dimensional character of the system and which results in a spectral landscape reminiscent of α relaxations characterized by an excess wing.…”

Section: Introductionmentioning

confidence: 99%

Double Primary Relaxation in a Highly Anisotropic Orientational Glass-Former with Low-Dimensional Disorder

et al. 2016

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The freezing of the cooperative reorientational motions in orientationally disordered (OD) molecular crystals marks the so-called "glassy" transition, which may be considered a lower-dimensional version of the structural glass transition. While structural glasses display both positional and orientational disorder, in fact, in orientational glasses the disorder involves exclusively the orientational degrees of freedom of the constituent molecules, while the molecular centres of mass form an ordered lattice. We report here on a glass-forming system with even less degrees of freedom, namely the OD phase of a dipolar benzene derivative, pentachloronitrobenzene (C 6 Cl 5 N O 2 ). We probe the orientational dynamics of PCNB as a function of temperature and pressure * To whom correspondence should be addressed † Universitat Politècnica de Catalunya ‡ Università di Pisa 1 by means of dielectric spectroscopy at normal and high pressure and high-pressure density measurements, and show that the system exhibits a double primary relaxation feature associated with two distinct motions of the molecular dipole moment. After ruling out an interpretation in terms of primitive or intramolecular relaxations, we discuss an assignment of the double relaxation feature based on the material's anisotropy and on the comparison with discotic liquid crystals.

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Properties of hexasubstituted benzenes with one or two nitro groups. Dielectric, DSC, X-ray and Raman studies

Cited by 6 publications

References 14 publications

Relaxation dynamics in plastic crystals

Relaxation dynamics in plastic crystals

Distinction of disorder, classical and quantum vibrational contributions to atomic mean-square amplitudes in dielectric pentachloronitrobenzene

Double Primary Relaxation in a Highly Anisotropic Orientational Glass-Former with Low-Dimensional Disorder

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