Ideal Glass Transition Temperature Research Articles

Mixed ionic and electronic conductivity in the quaternary V2O5–Na2O–ZnO–P2O5 glass system

The melt quenching method was adopted to synthesize glasses with the formula xV2O5–(0.4-x) Na2O–0.35ZnO–0.25P2O5 (x = 0.05, 0.1, 0.15, 0.2, and 0.25). X-ray diffraction patterns for the x = 0.05 sample showed the complete amorphous structure, whereas other composites revealed the development of nanocrystallites over the amorphous glassy networks. DSC measurement showed that glass transition temperature reduced as V2O5 concentration rose, and values were consistent with modified CBH model theoretical (fitting) data. DC conductivity for x = 0.05 and 0.1 composites followed an Arrhenius-type relation and linearity against the reciprocal of temperature, revealing ionic conductivity. On the contrary, the electronic or small polaron hopping mechanism was responsible for DC conductivity for all other composites. AC conductivity mechanism was described by the modified correlated barrier hopping model, and ideal glass transition temperatures were predicted (361 °C (x = 0.05) to 412 °C (x = 0.25)). It was observed that with rising V2O5 content (x), there was blockage of ionic pathways of Na+ ions, causing the ionic conductivity to decline and the electronic or small polaronic conductivity to enhance, as the radius of small polaron reduces. AC conductivity scaling property established that the time-temperature superposition principle and the BNN relation did not hold for the systems.

A thermodynamic framework for the additive manufacturing of crystallizing polymers. Part I: A theory that accounts for phase change, shrinkage, warpage and residual stress

A rigorous, comprehensive, and thermodynamically consistent theory has been developed for the fused deposition modelling (FDM) of semi-crystalline polymers. It is sufficiently general in that it can accommodate multiple phase transition mechanisms (crystallization, glass transition, and melting) during the heating and cooling cycles of the process encountered during FDM. The theory predicts the residual stresses and the resulting warpage in the polymer part due to the temperature-dependent, spatially varying specific volumes of each phase, precipitated by the inhomogeneous distribution of temperature. The theory treats the semi-crystalline polymer as a constrained mixture of multiple phases, where glass is assumed to be a new phase of the polymer. The statistically based Avrami kinetics for crystallization, modified for non-isothermal processes, is recovered as a particular case of our non-equilibrium thermodynamic analysis. Moreover, the theory predicts the temperature corresponding to the local free energy minima as the ideal glass transition temperature analogous to that of Franz and Parisi’s mean field theory with a statistical basis.

Structural relaxation, dynamical arrest, and aging in soft-sphere liquids.

We investigate the structural relaxation of a soft-sphere liquid quenched isochorically (ϕ = 0.7) and instantaneously to different temperatures Tf above and below the glass transition. For this, we combine extensive Brownian dynamics simulations and theoretical calculations based on the non-equilibrium self-consistent generalized Langevin equation (NE-SCGLE) theory. The response of the liquid to a quench generally consists of a sub-linear increase of the α-relaxation time with system's age. Approaching the ideal glass-transition temperature from above (Tf > Ta), sub-aging appears as a transient process describing a broad equilibration crossover for quenches to nearly arrested states. This allows us to empirically determine an equilibration timescale teq(Tf) that becomes increasingly longer as Tf approaches Ta. For quenches inside the glass (Tf ≤ Ta), the growth rate of the structural relaxation time becomes progressively larger as Tf decreases and, unlike the equilibration scenario, τα remains evolving within the whole observation time-window. These features are consistently found in theory and simulations with remarkable semi-quantitative agreement and coincide with those revealed in a previous and complementary study [P. Mendoza-Méndez et al., Phys. Rev. 96, 022608 (2017)] that considered a sequence of quenches with fixed final temperature Tf = 0 but increasing ϕ toward the hard-sphere dynamical arrest volume fraction ϕHS a=0.582. The NE-SCGLE analysis, however, unveils various fundamental aspects of the glass transition, involving the abrupt passage from the ordinary equilibration scenario to the persistent aging effects that are characteristic of glass-forming liquids. The theory also explains that, within the time window of any experimental observation, this can only be observed as a continuous crossover.

Prigogine-Defay ratio and its change with fictive temperature approaching the ideal glass transition

According to equilibrium thermodynamic theory, a liquid of zero configurational entropy would undergo an Ehrenfest type second order transition to another disordered structure at a temperature T2 known as the ideal glass transition temperature, but glass formation prevents one from observing it. The heat capacityCp, isothermal compressibility, κT, and isobaric thermal expansion coefficient, αp, change by an amount Δ at the Ehrenfest temperature, TEH=T2, and also at the glass transition temperature Tg. The Ehrenfest ratio RE at TEHorT2, ΔCp,EHΔκT,EHTEHVEH(Δαp,EH)2≡1. In contrast, experimentally determined Prigogine-Defay ratio, ∏P−D at Tg, ΔCpΔκTTV(Δαp)2>1, where V is the volume at the respective temperatures. Angell and Sichina [Ann. N. Y. Acad. Sci. 279 (1976) 53-67] discussed how ∏P−D would change to RE if a liquid could be cooled slowly enough to reach T2. After critically reviewing the basic aspects of RE and of experimental and theoretical values of ∏P−D, we use generic variations of ΔCp, ΔκT, ΔαP and V with the fictive temperature, Tf, and the extrapolated values of these quantities for o-terphenyl at T=T2, and calculate RE and ∏P−D. We find that RE<∏P−D, thus contributing to Angell-Sichina's discussion of the unique structure of the low temperature disordered phase. We then consider how ∏P−D would change if the entropy of a liquid were extrapolated such that it did not violate the third law of thermodynamics and there was no need for the conjecture of an Ehrenfest transition.

Comparative Study of the Measured and Two Ideal Glass Transition Temperatures Corresponding to the Limit of Infinitely Slow Heating Rate and the Infinite Barriers with Respect to Flow in Metallic Glasses and Glass-Forming Liquids

Comparative Study of the Measured and Two Ideal Glass Transition Temperatures Corresponding to the Limit of Infinitely Slow Heating Rate and the Infinite Barriers with Respect to Flow in Metallic Glasses and Glass-Forming Liquids

Dynamical Manifestations of Supercooling in Amyloid Hydration.

The effect of extreme temperature on amyloidogenic species remains sparsely explored. In a recent study (J. Phys. Chem. Lett., 2019, 10, (10)), we employed exhaustive molecular dynamics simulations to explore the cold thermal response of a putative small amyloid oligomer and to elicit the role of solvent modulation. Herein, we investigate the dynamical response of the hydration waters of the oligomer within the supercooled states. Using NMR-based formalism, we delineate the entropic response in terms of the side-chain conformational entropy that corroborates the weakening of the hydrophobic core with lowering of temperature. The translational dynamics of the protein and hydration waters reveal the coupling of protein dynamical fluctuations with solvent dynamics under supercooled conditions. Probing the translational motion as a space-time correlation indicates glassy dynamics exhibited by hydration waters in the supercooled regime. Caging of the water molecules with lowering of temperature and the resultant hopping dynamics are reflected in the longer β-relaxation timescales of translational motion. Furthermore, we utilized mode-coupling theory (MCT) and derived the ideal glass transition temperature from translational and rotational dynamics, around ∼196 and 209 K, respectively. Interestingly, rotational motion in the supercooled regime deviates from the MCT law, exhibits Arrhenius motion, and marks a fragile-to-strong crossover at 227 K. The low-frequency vibrational modes also coincide with the dynamical transition. This exposition lends dynamical insights into the hydration coupling of an amyloid aggregate under cryogenic conditions.

Glass-Transition Temperature of Cyclic Polystyrene: A Computational Study

Molecular-dynamics simulations are employed to study the glass transition of cyclic polystyrene melts. Gibbs and DiMarzio’s theory predict an increase in glass transition temperature, Tg upon lowering the length of cyclic polymer chains, which is opposite to the well-known trend for linear polymers. Their theory has been confirmed by some experiments; however, others observe a decrease in Tg upon lowering the chain length instead. When volumetric methods are employed to obtain the glass transition temperature in simulated cyclic polystyrene, a slight increase with decreasing cyclic polystyrene chain length is obtained. This increase is more pronounced when glass transition temperatures are obtained from dynamics. Both the glass transition temperature Tg obtained from diffusion data and the ideal glass transition temperature T0 obtained from the decay of the orientational autocorrelation function of the phenyl bond show a clear upturn.

High temperature strain glass in Ti–Au and Ti–Pt based shape memory alloys* *Project supported by China Postdoctoral Science Foundation (Grant No. 2019M650880), the National Natural Science Foundation of China (Grant Nos. 51901243, 61888102, and 11790291), the Natural Science Foundation of Guangdong Province, China (Grant No. 2019B030302010), and the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No.

Strain glass is a frozen short-range strain ordered state found in shape memory alloys recently, which exhibits novel properties around the ideal glass transition temperature T 0. However, the T 0 of current strain glass systems is still very low, limiting their potential applications and experimental studies. In this paper, we reported two new strain glass systems with relatively high T 0. In Ti50Au50−x Cr x alloys, the strain glass appears at x = 25, and exhibits a T 0 of 251 K, while in Ti50Pt50−y Fe y alloys, the strain glass takes place at y = 30, and shows a T 0 of 272 K. Both of them are comparable with the highest T 0 value reported so far. Moreover, the phase diagrams of main strain glass systems in Ti-based alloys were summarized. It is found that the influence of the martensitic transformation temperature of the host alloy on the T 0 of the strain glass is limited. This work may help to design new strain glass systems with higher T 0 above ambient temperature.

Fragility and Vogel-Fulcher-Tammann parameters near glass transition temperature

The strength parameter D, ideal glass transition temperature T0, and fragility parameter m are vital parameters and frequently used to analyze significant problems in various glass-forming liquids. It is found that parameters D, T0 and m will have great difference when these values for the same glass-forming liquid are obtained by fitting the measured viscosity data in different temperature ranges near glass transition temperature Tg. In order to obtain accurate parameters (T0, D and m), the temperature dependences of viscosity in different temperature ranges are studied. The results show that in the temperature range 0.97Tg~1.16Tg, the fitting viscosity data obtained by the measured data in temperature ranges (f)~(k) and Plazek's expression are close to the measured viscosity data. However, there are still great difference between the minimum and maximum values for fluctuant T0 and D values, which are 28.61 K and 24.91, respectively. The study further finds that parameters obtained using the measured viscosity data in temperature ranges (g)~(i) and (k) by VFT relation are more accurate and the maximal fluctuations of T0 and D parameters are decreased to 10.57 K and 10.79, respectively. Furthermore, parameters obtained by the measured data in (g) are the most accurate than those obtained by the measured data in any temperature range.

Predicting the Thermodynamic Ideal Glass Transition Temperature in Glass-Forming Liquids.

The Kauzmann temperature TK is a lower limit of glass transition temperature, and is known as the ideal thermodynamic glass transition temperature. A supercooled liquid will condense into glass before TK. Studying the ideal glass transition temperature is beneficial to understanding the essence of glass transition in glass-forming liquids. The Kauzmann temperature TK values are predicted in 38 kinds of glass-forming liquids. In order to acquire the accurate predicted TK by using a new deduced equation, we obtained the best fitting parameters of the deduced equation with the high coefficient of determination (R2 = 0.966). In addition, the coefficients of two reported relations are replaced by the best fitting parameters to obtain the accurate predicted TK, which makes the R2 values increase from 0.685 and 0.861 to 0.970 and 0.969, respectively. Three relations with the best fitting parameters are applied to obtain the accurate predicted TK values.

Structural properties and electrical conductivity mechanisms of semiconducting quaternary nanocomposites: Effect of two transition metal oxides

Several quaternary nanocomposites, doped with two transition metal oxides, of the generalised composition formula 0.4ZnO–0.1P2O5–0.5[xV2O5–(1-x) MoO3] were prepared via the melt quenching process. We investigated the microstructural and conductivity properties of two ternary systems and four quaternary systems to determine the better semiconductor nanocomposite system for wider application purposes. The X-ray diffraction results showed the presence of superposed nanocrystallites within amorphous networks or matrices. Analysis of ultraviolet–visible absorption spectra showed that optical bandgap energy (Eopt) values varied with V2O5 concentration, and there was an inverse relationship between Eopt and average nanocrystallite size. The responsible mechanisms of ac conductivity were examined using the model of Jonscher's universal power-law and Almond–West formalism, and it was found that ac conductivity increased as temperature rose, exhibiting semiconducting features. All the ternary (two examples) and quaternary (four examples) nanocomposite systems established non-linearity in dc conductivity, caused by the small polaron hopping process with dissimilar activation energies at different temperature regions. The power-law exponent (s) of Jonscher's universal power-law revealed that the ac conductivity mechanism could be described by correlated barrier-hopping (CBH) or non-overlapping small polaron tunnelling (NSPT) models for different samples due to major structural alterations. We applied modified CBH and NSPT models (as s > 0.8) to get realistic values of different fitting parameters, and in this process, we also obtained the values of ideal or hypothetical glass transition temperature from the theoretical models. The different activation energies associated with ac conductivity and for the small polaron migration process diminished with an increment in conductivity. Scaled ac conductivity spectra demonstrated that the conductivity relaxation process relied upon the composite structural features and did not depend on temperature. These materials can be used for such applications as gas sensors, even at higher temperatures due to their semiconducting nature and the different valence states of transition metal ions.

Measured and ideal glass transition temperatures of glass-forming liquids

Herein, measured and ideal glass transition temperatures of glass-forming liquids have been investigated. The value of T0/Tg increases with increasing fragility parameter m or decreasing strength parameter D (where Tg and T0 are the measured and ideal glass transition temperatures, respectively). We utilize T0/Tg values to classify various glass-forming liquids into three broad categories, which are strong, metallic glass-forming (intermediate) and fragile liquids. The result reveals that strong liquids with 15.25 < m ≤ 30 (or 37.3 ≤ D) have 0 < T0/Tg ≤ 0.49. By contrast, fragile liquids obtain 0.82 ≤ T0/Tg ≤ 0.94 when m values lie in 100 ≤ m ≤ 214 (or 1.8 ≤ D ≤ 9.1). Metallic glass-forming liquids have 0.52 ≤ T0/Tg ≤ 0.77 when m values have 32 ≤ m ≤ 66 (or 10.8 ≤ D ≤ 32.8).

The Effect of the Nature of Cation on Transport Properties of Bis(trifluoromethylsulfonyl)imide Ionic Liquids

The methods of viscosimetry, conductometry, densimetry, and differential scanning calorimetry are used for studying the physicochemical properties of cations (1-butyl-3-methylimidazolium [BuMeIm]+, N-butylmethylpyrrolidinium [BuMePyrr]+, and methytrioctylammonium [MeOc3Am]+) and their effect on the transport properties of bis(trifluoromethylsulfonyl)imide ionic liquids (IL). It is shown that ILs formed by cyclic amines ([BuMeIm]+ and [BuMePyrr]+) as the cations demonstrate the close values and temperature dependences of viscosity and conductivity. The cation [MeOc3Am]+ predetermines the difference in the IL structure and, thus, a substantial difference in the transport properties of the melt. For salts [BuMeIm][Tf2N], [BuMePyrr][Tf2N], and [MeOc3Am][Tf2N] at 293 К, the following transport characteristics are observed: viscosity 57.7, 88.1, and 726.5 mPa s; specific conductivity 0.376, 0.252, and 0.005 S m–1; activation energy of conductivity 21, 21, and 35 kJ mol–1; degree of “ionicity” 0.92, 0.94, and 1.00, respectively. Using the equation of Vogel–Fulcher–Tammann and based on the temperature dependences of specific conductivity and viscosity, the ideal glass transition temperatures are calculated for liquids under study. In the positive temperature range, a linear correlation is observed between the conductivity and the cation volume in these ionic liquids.

Structural characterization and electrical conductivity analysis of MoO3–SeO2–ZnO semiconducting glass nanocomposites

A series of glass nanocomposite samples of the general composition formula xMoO3–(1-x) (0.5SeO2–0.5ZnO) for x = 0.05, 0.1, 0.2, and 0.3 have been prepared by solid-state reaction, i.e., slow cooling process. The structural characteristics have been explored by analyzing X-ray diffraction patterns, Fourier-transform infrared, and UV–Vis spectra. The superposition of different nanophases SeO2, SeO3, ZnO, MoO3, Zn (SeO3), Zn (SeO4), Zn(MoO4), Zn2Mo3O8 and ZnMo8O10 over the amorphous glassy matrices have been identified, and their crystallite sizes have been evaluated as well. Fourier transform infrared (FTIR) spectra reveal different types of bonding like Zn–O–Se type and stretching vibrations of MoO6 octahedral units. It is observed that with increasing MoO3 concentration, the estimated values of optical bandgap energy, Urbach energy, and average crystallite size reduce. The dependency of electrical conductivity on frequency and temperature have been analyzed using Almond-West formalism and Jonscher's universal power-law. The non-linear character of DC conductivity and different activation energies at low and high-temperature regions affirm that the present glassy systems exhibit semiconducting nature. Moreover, DC conduction process is due to small polaron hopping through localized or defect states. The decreasing trend of power-law exponent (s) with temperature rise reveals that AC conduction mechanism is consistent with the correlated barrier-hopping (CBH) model. The existing correlated barrier-hopping model has been modified to attain reasonable values of fitting parameters and to obtain theoretical values of ideal thermodynamic glass transition temperature. The AC conductivity activation energy and free energy required for small polaron migration reduce with increasing conductivity. The scaling property emphasizes that conductivity relaxation process is subjected to the structure of the composition and does not depend on temperature.

The Temperature Effect on the Transport Properties of 1-Alkyl-3-methylimidazolium Bis(trifluoromethylsulfonyl)imide Ionic Liquids

The temperature dependences of specific and equivalent conductivities, viscosity, density, and crystallization temperature are determined for three 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide ([C n MeIm] [Tf2N], n = 2, 3, 4) ionic liquids saturated with water vapor at room temperature. It is established that in the area of positive temperatures, the relationship between viscosity and conductivity obeys the fractional Walden rule with exponents of 0.97, 0.92, and 0.92 for ionic liquids with ethyl-, propyl-, butylradicals, respectively. The temperature dependences of conductivity and viscosity are approximated using the Vogel–Fulcher–Tammann equation (R2 > 0.999), and ideal glass transition temperatures T0 are calculated for the investigated liquids. The obtained values of T0 depend largely on the chosen range of temperatures. It is shown that [C2MeIm][Tf2N] occupies a separate position with regard to [C3MeIm][Tf2N] and [C4MeIm][Tf2N].

Calorimetric study on Ge23Se67Sb10–0.5CsCl glass

The mechanical behavior of Ge23Se67Sb10 glass can be improved by adding CsCl facilitating the nano-crystaline formation. Understanding the crystallization mechanism of chalcogenide glass can help in directing the subsequent annealing processing and tuning the microstructure and physical properties. In this work, 99.5Ge23Se67Sb10–0.5CsCl glass was prepared and its transformation kinetics was investigated under non-isothermal conditions with heating rate up to 400 K min−1. Using Vogel–Fulcher–Tammann equation, the ideal glass transition temperature was determined as T 0g = 434.1 K. Using the classical JMA theory, the average activation energy and average growth exponent were determined as 135.0 and 2.4 kJ mol−1, while using the model considering impingements (MCI), the two parameters were determined as 120.9 and 3.2 kJ mol−1, respectively. Compared to JMA theory, the MCI model can fit the transition curves better, and it shows that the growth mode of the present glass is between two-dimension and three-dimension. By comparing with the result of Ge23Se67Sb10 glass, it is found that addition of CsCl can reduce the growth dimension and activation energy during crystallization.

Frequency and temperature dependent conductivity spectra of mixed transition metal oxide doped semiconducting glassy system

Frequency and temperature dependent conductivity of mixed transition metal oxide (TMO) doped semiconducting glassy system, xV2O5–(1−x) (0.05MoO3–0.95ZnO) have been investigated in the wide range of frequency and temperature. The dc conductivity (σdc), crossover frequency (ωH), frequency exponent (n) and power law exponent (s) have been computed from the best fitted plots of experimental data. We have estimated the values of activation energy of ac conduction (Eac) and free energy of polaron migration (EH). Dc conductivity of the as-prepared samples shows thermally activated non–linear nature, which has been interpreted with Vogel–Tammann–Fulcher (VTF) model. From the fitting, pseudo activation energy (Ea) and thermodynamic ideal glass transition temperature (T0) have been estimated. Nature of variation of conductivity and the power law exponent (s) data exhibit that non–overlapping small polaron tunnelling (NSPT) model is suitable to interpret these data for compositions x=0.3, 0.5 and 0.7. On the other hand, correlated barrier hopping (CBH) model is most applicable mechanism for ac conduction for compositions x=0.9 and 0.93. Formation of some complex Mo-O-V structures may be possible reason for applicability of CBH model for composition x=0.9, 0.93. It is also observed that conductivity relaxation process of charge carriers (polarons) is independent of temperature, but depends upon composition.

Calorimetric studies on Ge23Se67Sb10-0.5%RbI glass

Understanding the crystallization mechanism of chalcogenide glass can help in directing the subsequent annealing processing, thus tuning the microstructures and physical properties. In this work, the transformation kinetics of Ge23Se67Sb10-0.5%RbI was investigated under non-isothermal conditions. From VFT equation, the ideal glass transition temperature was determined as T0g=427.74K. The fragility index m was estimated to be 64.74, indicating a relatively fragile liquid. From the classical JMA theory, the activation energy was determined as 222.9kJ/mol, growth index was 1.26, while from the model considering the impingement modes(MCI) activation energy was determined as 90.99kJ/mol and growth index was 1.38, which indicated that the growth mode of crystallization of the present glass was between one dimension and two dimension. The result shows that addition of RbI can reduce the growth dimension and activation energy.

Kinetics and thermal stability of the Ni62Nb38–x Ta x (x=5, 10, 15, 20 and 25) bulk metallic glasses

We studied thermal stability and its relationship to the glass-forming ability (GFA) of the Ni62Nb38–xTax (x=5, 10, 15, 20, 25) bulk metallic glasses (BMG) from a kinetic point of view. By fitting the heating-rate dependence of glass transition temperature (Tgonset) and crystallization temperatures (Txonset and Txpeak) of the Ni62Nb38–xTax BMG using the Vogel-Fulcher-Tammann (VFT) equation, we obtained the ideal glass transition and crystallization temperatures (Tg0 and Tx0) and the fragility parameter (m), and also constructed continuous heating transition (CHT) diagrams for crystallization of the BMG. The CHT diagrams of the BMG indicate enhanced thermal stability by Ta addition; the Tg0 as well as the Tx0 also illustrates this improved stability limit. The compositional dependence of m, which agrees well with that of the reduced glass-transition temperature, indicates a strong correlation between liquid fragility and glass-forming ability in the present alloy system. These results provide new evidence for understanding thermal stability, liquid fragility, and GFA in BMG.

Study on glass transition temperature and kinetics of Cu–Zr glassy alloys

Ideal glass transition temperatures and transition activation energies of Cu46Zr45Al9 metallic glass was investigated using differential scanning calorimetry (DSC). The Vogel–Fulcher–Tammann temperature T 0 and Kauzmann temperature T k were determined, respectively, and T 0 is greater than T k. Meanwhile, activation energies of glass transition E g, onset crystallization E x and crystallization peak E p were deduced to be 634.2 ± 15, 444 ± 16.1 and 366.8 ± 25.1 kJ mol−1, which indicates that glass transition is harder than crystallization process to proceed.