Rigid molecular glass-formers with no internal degrees of freedom nonetheless have a single secondary β-relaxation. For a rigid and planar molecule, 1-methylindole (1MID), although a secondary relaxation is resolved at ambient pressure, its properties do not conform to the rules established for rigid molecules reported in early studies. By applying pressure to the dielectric spectra of 1MID, we find the single secondary relaxation splits into two. The slower one is pressure sensitive showing connections to the α-relaxation as observed in other rigid molecules, while the faster one is almost pressure insensitive and dominate the loss at ambient pressure. The two secondary relaxations, identified to associate with the out-of-plane and in-plane rotations of the rigid and planar 1MID, are resolved and observed for the first time by increasing density via elevating pressure.

•Two step changes of the caged dynamics found at Tgα and THF below Tgα in IPB and cis-decalin by QENS.•THF coincides with Tgβ, the secondary glass transition temperature.•The generality of the finding is explained by Coupling Model.In several publications we studied the fast caged dynamics of many glass-formers observed in the glassy state at high frequencies above circa 1 GHz by various techniques, including neutron scattering, Brillouin scattering, 2H NMR spin-lattice relaxation, and THz dielectric spectroscopy. On increasing temperature, the intensity of the caged dynamics exhibit two step increases in intensity at two temperatures, first at THF below the glass transition temperature Tgα and subsequently at Tgα. THF is nearly coincident with the Johari-Goldstein (JG) β-glass transition temperature Tgβ. The phenomenon is general and found in polyalcohols, pharmaceuticals, many amorphous polymers, and two small molecular van der Waals glass-formers. It is remarkable since THF is determined from measurements of fast caged dynamics at short time scales typically in the ns to ps range, while Tgβ characterizes the JG β-glass transition at which the JG β-relaxation time τβ reaches a long time ~ 103 s. The phenomenon was explained by coupling of the caged dynamics to the JG β-relaxation. In this paper we analyze exceptionally high quality quasielastic neutron scattering data of two molecular van der Waals glass-formers, cumene (isopropylbenzene) and cis-decalin (cis-decahydro-naphthalene) to demonstrate the generality of the phenomenon and validity of its theoretical explanation.

The crystallization kinetics of the newly developed (Ga2Te3)x(SnTe)100 − x (x = 32, 34, 36 mol%) chalcogenide glasses were investigated by differential scanning calorimetry under non-isothermal conditions. The kinetic parameters such as activation energies and Avrami exponents were determined using Kissinger, Ozawa, Augis–Bennett, and Matusita–Sakka methods. The thermal stability is evaluated and consistency is suggested for various criteria. The thermal stability of these glasses was evaluated by various criteria, revealing the relatively higher stability of the (Ga2Te3)34(SnTe)66 sample. The analyses of the crystallization phases by X-ray diffraction upon annealing suggest that the SnTe crystalline phase can be effectively controlled and independently precipitated from the glass matrix, generating promising thermoelectric glass–ceramic materials.

•The effect of dynamic parameters on the glass transition width is analyzed.•The relations generated by the TNMH model are reproduced by experimental results.•An empirical equation of ΔTg/Tg = 2.20*(1/m + 0.0026)*(1/βKWW-0.59) is proposed.The dependence between the calorimetric glass transition width ΔTg defined in heat capacity curves and structural relaxation dynamics is studied in analytical and experimental fashions. The Tool–Narayanaswamy–Moynihan–Hodge model is analyzed to extract the relations between the normalized glass transition width ΔTg/Tg and three dynamic parameters: fragility (m), stretching exponent (βKWW) and non-linear factor (x). When the other two dynamic parameters are fixed, ΔTg/Tg is found to scale linearly with 1/m or 1/βKWW, but not to show marked variation with x in the range of practically accessible values. Experimental data of more than 50 glass formers covering molecular, metallic and oxide systems are examined, and the linear relations are reproduced for m (or βKWW) among the chemicals of comparable βKWW (or m). Joint consideration of m and βKWW makes an empirical equation of ΔTg/Tg = 2.20 * (1/m + 0.0026) * (1/βKWW − 0.59) with high accuracy for all the materials. For the glass formers with similar βKWW, Moynihan's relation can be approximately restored.

•The connection of glass forming range with T0 curves has been reviewed.•The thermodynamics of the partitionless solidified solid solutions of four eutectic alloys have been studied.•A thermodynamic reasoning of the glass forming ability is proposed.T0 curves in the phase diagrams have been proven useful to understand thermodynamically glass formation in metallic alloys, emphasizing the importance of the metastable solid solutions crystallized partitionlessly. Here we focus on four typical binary eutectic alloys with distinct glass-forming abilities and interatomic interactions, Ag60Cu40, Sb17.5Pb82.5, Au81.4Si18.6, and Ni24Zr76. The thermodynamics involved in the liquid–solid solution transition at T0 temperatures for the alloys of eutectic compositions are quantified, and the validity of the thermodynamic properties is evaluated. The comparison of the melting entropies for the equilibrium and partitionless solidifications reveals a basic relation. Based on the thermodynamics of the equilibrium phases and the solid solutions, an understanding of the glass formation of metallic alloys is proposed.

A quantitative evaluation of the contribution of mixing thermodynamics to glass transition is performed for a binary eutectic benzil and m-nitroaniline system. The microcalorimetric measurements of the enthalpy of mixing give small and positive values, typically ∼200 J mol−1 for the equimolar mixture. The composition dependence of the glass transition temperature, Tg, is found to show a large and negative deviation from the ideal mixing rule. The Gordon–Taylor and Couchman–Karasz models are subsequently applied to interpret the Tg behavior, however, only a small fraction of the deviation is explained. The analyses of the experimental results manifest quantitatively the importance of the mixing thermodynamics in the glass transition in miscible systems.

The relaxation dynamics of a series of molecular liquids with modified structures from aldehyde with a fixed number of carbon atoms is studied. Structural modification is made by introducing oxygen into the main chain, or by incorporating end group moieties such as ethyl, acrylate, methacrylate and dihydroxyl. Broadband dielectric measurements were performed on the glass-formers. The experimental results emphasize the importance of intermolecular interactions and molecular rigidity in determining the kinetic fragility and non-exponential parameters of the structural α-relaxation.Graphical abstractHighlights► Relaxation dynamics of molecular liquids with related structures are examined. ► Enhanced intermolecular interactions increase non-exponential parameter. ► Increasing molecular rigidity decreases non-exponential parameter.

The dielectric strength of the Debye relaxation in the binary mixtures of two isomeric monohydroxy alcohols, 2-ethyl-1-butanol (2E1B) and 4-methyl-2-pentanol (4M2P), is studied at low temperature near glass transition. Enhanced dielectric strength is exhibited in the mixtures, remarkably different from the mixing behaviors of the structural (α-) relaxation of generic liquids. A similar result is observed when analyzing the dielectric data of the binary mixtures of 2-ethyl-1-hexanol and 2-methyl-1-butanol reported in an early study. The unusual behavior of the dielectric strength in the mixtures reveals a new feature of the Debye relaxation in monohydroxy alcohols. Yet, the calorimetric measurements of the glass transition temperature in 2E1B–4M2P mixtures show a distinct negative deviation from the ideal mixing law. The explanation of the Debye relaxation is discussed with the results.

The glass transition and glass-forming ability in a binary eutectic system of methyl o-toluate (MOT) versus methyl p-toluate (MPT) are studied across the whole composition range. The phase diagram is constructed to explore the best glass-forming composition as the characteristic temperatures of the glass transition, crystallization, eutectic, and liquidus are determined. The best vitrification region is found to locate between the eutectic and the midpoint compositions of the eutectic line, indicating a remarkable deviation from the eutectic composition. The compilation of various simple binary eutectic systems covering inorganic, metallic, ionic, and molecular glass-forming liquids reproduces the rule. Kinetics and thermodynamics in binary systems are investigated to associate with the rule. The composition dependence of the structural relaxation time and the kinetic fragility are presented with dielectric measurements. It is found that whereas mixing of binary miscible liquids kinetically favors glass formation, thermodynamic contribution to the deviation of the best glass-forming composition from eutectics is implied.

The glass transition and structural relaxation dynamics of various binary glass-forming liquids are investigated with dielectric relaxation measurements across the entire composition range. Three categories of solutions with weak, intermediate, and strong mixing effects, namely methyl-m-toluate in methyl o-toluate, methyl m-toluate in di-n-butyl phthalate, and 1,2-propandiol in 2-hexylamine, are selected to address the mixing behaviors from near-ideal to nonideal cases. The glass transition temperatures, fragility indices, and stretching exponents of the solutions are determined and their composition dependence is the focus of this study. The experimental measurements show that mixing generally generates a negative deviation of fragility m relative to the composition average of the results of two neat components (ideal mixing law). This excess negative fragility proves to be a universal feature of binary systems, and the increase of the nonideal mixing degree results in a more pronounced negative deviation. In contrast, the composition dependence of the stretching exponents is more complex, and a transition from the negative to positive deviation is observed for substantial nonideal character. The study assists understanding the dynamics of multicomponent glass formers.

Relaxation enthalpies in the vicinity of glass transitions were recorded on the basis of the heat capacity curves measured in nine glass-forming molecular liquids and solutions in the well defined cooling and subsequent heating cycles. It is observed that enthalpy hysteresis in the cooling/heating cycles is less significant in liquids with increasing fragility. A notable correlation of the fragility index m with relaxation enthalpy ΔHR, glass transition temperature, and heat capacity jump from glasses to liquids is demonstrated. The introduction of ΔHR favors the thermodynamic evaluation of fragility in the glass forming multicomponent systems such as solutions and alloys.

•Novel Ga2Te3-SnTe glasses are successfully synthesized.•The glass-forming region of Ga2Te3-SnTe system is determined.•A reliable strategy is proposed to vitrify the SnTe-based chalcogenide systems.Using specified telluride glasses to prepare the glass-ceramics containing narrow band-gap telluride crystals as the main precipitated phase would be an effective route to developing high-efficiency thermoelectric materials. Unfortunately, such telluride glasses are extremely difficult to achieve. In this paper, a strategy is proposed to vitrify these narrow band-gap tellurides by jointly focusing on the glass formation thermodynamic and kinetic factors. Novel Ga2Te3-SnTe glasses are successfully synthesized and the glass-forming region is found to be located at the SnTe-rich compositions.

A quantitative evaluation of the contribution of mixing thermodynamics to glass transition is performed for a binary eutectic benzil and m-nitroaniline system. The microcalorimetric measurements of the enthalpy of mixing give small and positive values, typically ∼200 J mol−1 for the equimolar mixture. The composition dependence of the glass transition temperature, Tg, is found to show a large and negative deviation from the ideal mixing rule. The Gordon–Taylor and Couchman–Karasz models are subsequently applied to interpret the Tg behavior, however, only a small fraction of the deviation is explained. The analyses of the experimental results manifest quantitatively the importance of the mixing thermodynamics in the glass transition in miscible systems.