Slow secondary relaxation in simple glass formers

Kudlik, A.; Tschirwitz, C.; Blochowicz, Thomas; Benkhof, S.; Rössler, E. A.

doi:10.1016/s0022-3093(98)00510-9

Cited by 120 publications

(110 citation statements)

References 16 publications

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“…This is the so-called Debye time, characteristic of local, non-cooperative thermally activated processes [6]. For this system, as well as for others, the TSDC data does not support the authors that claim a cooperative character for the b-relaxation [7,8].…”

Section: Three Levels Of Tsdc Data Presentationcontrasting

confidence: 73%

TSDC as a tool to study slow molecular mobility in condensed complex systems

Ramos

Correia

2006

Journal of Non-Crystalline Solids

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Section: Three Levels Of Tsdc Data Presentationcontrasting

confidence: 73%

TSDC as a tool to study slow molecular mobility in condensed complex systems

Ramos

Correia

2006

Journal of Non-Crystalline Solids

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“…, promoted in [21,58], is also accomplished taking into account the aforementioned uncertainty in the determination of ∆H a because of non-equilibrium effects for T < T g (∆H a /(k B T g ) = 30 in our case). Furthermore, if we check now if the 50% mixture of 2-picoline in tri-styrene follows the correlation between the stretching exponent of the α-relaxation and the β relaxation time [53], it fails as in the case of Freon112, again because of the extremely small slope of the high-frequency flank of the primary relaxation peak.…”

Section: Discussionmentioning

confidence: 99%

α and β relaxation dynamics of a fragile plastic crystal

Pardo

Lunkenheimer

Loidl

2006

The Journal of Chemical Physics

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We present a thorough dielectric investigation of the relaxation dynamics of plastic crystalline Freon112, which exhibits freezing of the orientational degrees of freedom into a glassy crystal below 90 K. Among other plastic crystals, Freon112 stands out by being relatively fragile within Angell's classification scheme and by showing an unusually strong β-relaxation. Comparing the results to those on Freon112a, having only a single molecular conformation, points to the importance of the presence of two molecular conformations in Freon112 for the explanation of its unusual properties. 1 INTRODUCTIONGlass phenomena occur when a dynamically disordered system (e. g. aliquid, plastic crystal or paramagnet) freezes as a function of external temperature or pressure devoid of long range order. In this freezing process, one or more degrees of freedom of atoms or molecules continuously slow down, reaching the so called glass transition when their dynamics has a characteristic time, generally chosen to be 10 2 s (for recent reviews on glass transition see, e.g., [1]). Since in the liquid phase there is translational and orientational disorder, the glass transition of canonical glass formers is associated with the freezing of these two degrees of freedom. But a mesophase can exist between the completely ordered crystalline phase and the translationally and orientationally disordered liquid phase, the so called plastic phase or orientationally disordered (OD) phase [2,3]. In the plastic phase, the centers of mass of the molecules have spatial long range order, forming a lattice which generally has high symmetry (such as cubic, quasi-cubic or rhombohedral [2, 3, 4]), but there is only short-range order with respect to the orientational degrees of freedom [5].As for glass-forming liquids, the typical phenomenology of a glass transition also can be realized in various plastic crystals when the temperature is decreased, but in this case only the orientational degrees of freedom are frozen, yielding the formation of a "glassy crystal"[6], also called OD glass.Concerning the dynamics of OD phases, dielectric spectroscopy has been revealed to be a useful tool to understand the complex dynamics of these phases [7,8,9,10,11,12,13].Based on these works there seem to be some general dynamic features of OD phases and its glasses: They are rather strong (following the definition of Angell [14]) and they follow the Böhmer relation between non-exponentiality of the α relaxation and fragility [15,16].On the contrary, the so called Nagel scaling [17] does not seem to work for these phases [7,11,18]. In addition there is only a weak or no β-relaxation at all and the excess wing, showing up as a second power law at the high frequency flank of the α peak in many canonical glass formers [17,19,20,21], is either absent in plastic crystals [11] or can be ascribed to a weak secondary relaxation [7,9].

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“…1, suggests that in the case of ethylcyclohexane a secondary relaxation would appear able to 'survive' through the cross-over with the α−relaxation, becoming slower than the α-process at higher temperatures, whereas usually a merging between the α-and the β-relaxation is observed at some (bifurcation) temperature T β above T g . [6,40,41]. In many glass-forming liquids the possible existence of such a slow secondary process would be likely hidden by the almost ubiquitous dc conductivity contribution [42,43,18], arising for instance from residual ionic impurities.…”

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confidence: 99%