On the frequency correction in temperature-modulated differential scanning calorimetry of the glass transition

Guo, Xuan; Mauro, John C.; Allan, Douglas C.; Yue, Yuanzheng

doi:10.1016/j.jnoncrysol.2012.05.006

Cited by 19 publications

(24 citation statements)

References 36 publications

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“…Modulated Differential Scanning Calorimetry (MDSC) has proven to be a reliable (Thomas, 2005;Bhosle et al, 2012b) and rather direct means to independently establish the glass transition temperature T g , and the modulation frequency corrected enthalpy of relaxation of a glass at T g ( H nr ) with minimal scanning-rate-related kinetic upshifts. The procedure for obtaining the frequency corrected enthalpy of relaxation was developed as early as in 1995 by Len Thomas (Thomas, 2005), and more recently confirmed in numerical simulations (Guo et al, 2012). The measured H nr term is a pivotal calorimetric observable of a glass, that characterizes not merely its non-ergodic state but is crucially linked to the flexibility and rigidity of networks (Micoulaut, 2010) provided these are dry and homogenous.…”

Section: Modulated-dsc As a Probe Of The Enthalpy Of Relaxation Of Glmentioning

confidence: 99%

Evidence for a Correlation of Melt Fragility Index With Topological Phases of Multicomponent Glasses

et al. 2019

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Scores of glass compositions in the equimolar Ge x As x Se 100−2x ternary system are synthesized across the 0 < x < 26% range, and their homogeneity tracked by ex-situ Raman profiling. In synthesis, we alloyed the starting materials to homogenize until the variance, < ×> Ge , in Ge content "x," across a 1.5-g sized batch composition of <0.01% was realized. We undertook Modulated-DSC, Raman scattering, and molar volume experiments as a function of composition. Trends in T g (x) increase monotonically with x over the examined range, but the non-reversing enthalpy of relaxation at T g , H nr (x), displays a sharp square-well like reversibility window over the 9.5(2)% < x < 17.0(2)% range even in rejuvenated glasses. Trends in melt fragility index, m(x), established by measuring the T-dependence of the enthalpy relaxation time across T g , show a Gaussian-like variation with m(x) < 20 in the 9.5(2)% < x < 17.0(2)% range, and m > 20 outside that range, thus establishing a fragility window. The close correlation between the variations of m(x) and H nr (x) underscores that super-strong melts formed in the fragility window form Intermediate Phase (IP) glasses in the reversibility window, while fragile melts formed at non-IP compositions give rise to either flexible or stressed-rigid glasses. Molar volumes of glasses reveal a global reduction for IP glass compositions, thereby underscoring the compacted nature of the isostatically rigid networks formed in that phase. Evidence for specific dynamic features of the different phases is provided by molecular dynamics simulations, which indicate that the diffusivity is minuscule for x > 17% and increases substantially in the flexible phase. These results show that liquid dynamics and fragility encode glass topological phases in this ternary chalcogenide. The optimization of the glass-forming tendency for IP compositions, the stress-free nature of these networks, and the qualitative suppression of aging, are features that all point to their ideal nature. These ideas of IP glasses as ideal glasses are at variance with the notion that ideal glasses possess a low configurational entropy and form at T g values that approach the Kauzmann temperature. IP networks display, adaptability, high glass-forming tendency, stress-free nature, and high configurational entropy of networks.

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Section: Modulated-dsc As a Probe Of The Enthalpy Of Relaxation Of Glmentioning

confidence: 99%

Evidence for a Correlation of Melt Fragility Index With Topological Phases of Multicomponent Glasses

et al. 2019

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“…Frequency corrections [332] have to be taken into account in order to avoid the spurious effects arising from the frequency-dependence of the specific heat [110]. Even with this frequency correction on the non-reversing heat flow leading to a neat measurement of ∆H nr , results have been challenged by several authors who have argued that conclusions drawn from the observed anomalies (Fig.…”

Section: Experimental Signature From Calorimetrymentioning

confidence: 99%

Relaxation and physical aging in network glasses: a review

Micoulaut

2016

Rep. Prog. Phys.

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Abstract. Recent progresses in the description of glassy relaxation and ageing are reviewed for the wide class of network-forming materials such as GeO 2 , Ge x Se 1−x , silicates (SiO 2 -Na 2 O) or borates (B 2 O 3 -Li 2 O), all of them having an important usefulness in domestic, geological or optoelectronic applications. A brief introduction of the glass transition phenomenology is given, together with the salient features that are revealed both from theory and experiments. Standard experimental methods used for the characterization of the slowing down of the dynamics are reviewed. We then discuss the important role played by aspect of network topology and rigidity for the understanding of the relaxation of the glass transition, while also permitting analytical predictions of glass properties from simple and insightful models based on the network structure. We also emphasize the great utility of computer simulations which probe the dynamics at the molecular level, and permit to calculate various structure-related functions in connection with glassy relaxation and the physics of ageing which reveals the off-equilibrium nature of glasses. We discuss the notion of spatial variations of structure which leads to the picture of "dynamic heterogeneities", and recent results of this important topic for network glasses are also reviewed.PACS numbers: 61.43. Fs, 64.70.kj Relaxation and physical ageing in network glasses 2 Figure 1. Typical network-forming glasses: a) A stoichiometric glass former (SiO 2 , B 2 S 3 ) whose structure and network connectivity can be altered by the addition (b) of 2-fold coordinated atoms (usually chalcogens, S, Se) that lead to cross-linked chains. The structure can also be depolymerized (c) by the addition of a network modifier (alkali oxides or chalcogenides, Na 2 O, Li 2 S, etc.). Glassy dynamics depends strongly on the network topology, i.e. the way bonds and angles arrange to lead to a connected atomic network. Note that only chalcogenides can produce a mixture of these three kinds of basic networks, e.g. (1-x)Ge y Se 1−y -xAg 2 Se [2], and for the latter system x=0 corresponds to case (b), y=33% corresponds to case (c), and both conditions together (x=0,y=33 %) to case (a).

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“…The discovery and the experimental characterization of the IP have also led to some more unexpected developments in the field, due, in part, to the difficulty in reproducing the measurements of ΔH nr which need to be corrected [107] in order to avoid spurious effects arising from the frequency dependence of the specific heat [108]. However, once corrected, it has been furthermore discovered that this quantity is highly sensitive (Figure 8) to impurities, inhomogeneities and the relaxation status of the glass [77].…”

Section: New Directionsmentioning

confidence: 99%

Concepts and applications of rigidity in non-crystalline solids: a review on new developments and directions

Micoulaut

2016

Advances in Physics: X

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On the frequency correction in temperature-modulated differential scanning calorimetry of the glass transition

Cited by 19 publications

References 36 publications

Evidence for a Correlation of Melt Fragility Index With Topological Phases of Multicomponent Glasses

Evidence for a Correlation of Melt Fragility Index With Topological Phases of Multicomponent Glasses

Relaxation and physical aging in network glasses: a review

Concepts and applications of rigidity in non-crystalline solids: a review on new developments and directions

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