Critical phenomena and renormalization-group theory

Dynamic properties, derived from dielectric relaxation spectra of glass-formers at variable temperature and pressure, are used to characterize and classify any resolved or unresolved secondary relaxation based on their different behaviors. The dynamic properties of the secondary relaxation used include: (1) the pressure and temperature dependences; (2) the separation between its relaxation time τβ and the primary relaxation time τα at any chosen τα; (3) whether τβ is approximately equal to the independent (primitive) relaxation time τ0 of the coupling model; (4) whether both τβ and τ0 have the same pressure and temperature dependences; (5) whether it is responsible for the “excess wing” of the primary relaxation observed in some glass-formers; (6) how the excess wing changes on aging, blending with another miscible glass-former, or increasing the molecular weight of the glass-former; (7) the change of temperature dependence of its dielectric strength Δeβ and τβ across the glass transition temperature Tg; ...

Classification of secondary relaxation in glass-formers based on dynamic properties.

An intriguing problem in condensed matter physics is understanding the glass transition, in particular the dynamics in the equilibrium liquid close to vitrification Recent advances have been made by using hydrostatic pressure as an experimental variable These results are reviewed, with an emphasis in the insight provided into the mechanisms underlying the relaxation properties of glass-forming liquids and polymers

https://iopscience.iop.org/article/10.1088/0034-4885/68/6/R03/pdf

Supercooled dynamics of glass-forming liquids and polymers under hydrostatic pressure

Evaluation of amorphous solid dispersion properties using thermal analysis techniques.

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Dislocations in solids

Broadband dielectric spectroscopy (BDS) studies for a remarkable temperature range (230 K) in a supercooled orientationally disordered phase given rise to an orientational glass have been performed in mixed crystal formed between NPG ((CH3)2C(CH2OH)2) and NPA ((CH3)3C(CH2OH)) compounds. The α-relaxation slows down and the width of the dielectric spectra becomes broader with decreasing temperature without any additional relaxation process, making easy the fitting procedure of the relaxation loss spectra. The existence of three dynamic domains is made evident: For the high temperature region the relaxation time obeys an Arrhenius behavior, while when decreasing temperature two crossover temperatures define the temperature intervals for which two different VFT regimes are clearly visible. The shape parameters α and α·β according to the fit of HN function have been determined. Approaching T g , the common feature of many structural glass forming materials (decrease of the shape parameters with temperature) is found, indicating the strong deviation from the Debye behavior. Both parameters seem to reach the claimed universal value of 0.5.

Orientationally disordered glassy phases

The shape of the critical anomaly of the Nonlinear Dielectric Effect has been analysed. In binary critical solutions of ordinary liquids the best results have been obtained when the first correction-to-scaling term has been taken into account. For three different solutions almost the same value of the critical exponent has been obtained: ψ = 0.370 ± 0.005.

Influence of an additional power term on the critical exponent of the nonlinear dielectric effect in critical solutions

Several simple, non-mesogenic liquids can exists in two or more different liquid forms. When the liquid-liquid line, separating two liquid forms, meets the melting line, one can expect some kind of break on the melting line, caused by the different freezing/melting behaviour of the two liquid forms. Unfortunately recently several researchers are using this vein of thinking in reverse; seeing some irregularity on the melting line, they will expect a break and the appearance of a liquid-liquid line. In this short paper, we are going to show, that in the case of the high-pressure nitrogen studied recently by Mukherjee and Boehler, the high-pressure data can be easily described by a smooth, break-free function, the modified Simon-Glatzel equation. In this way, the break, suggested by them and consequently the suggested appearance of a new liquid phase of the nitrogen might be artefacts.

About the shape of the melting line as a possible precursor of a liquid-liquid phase transition

We present a study of the dynamics and structural changes for trans-1,2-dichloroethylene between high and low density liquids using neutron scattering techniques (diffraction, small angle neutron scattering and time of flight spectroscopy) and molecular dynamics simulations We show that changes in the short range ordering of molecules goes along with a change of the molecular dynamics: both structure and dynamics of the high density liquid are more cooperative than those of the low density liquid The microscopic mechanism underlying the cooperative motions in the high density liquid has been found to be related to the backscattering of molecules due to a strong correlation of molecular ordering

Erratum: Microscopic structures and dynamics of high- and low-density liquid trans-1,2-dichloroethylene [Phys. Rev. B 81, 092202 (2010)]

A new nanocomposite material was prepared by high pressure processing of starting glass of nominal composition NaFePO4. Thermal, structural, electrical and dielectric properties of the prepared samples were studied by differential thermal analysis (DTA), X-ray diffraction (XRD) and broadband dielectric spectroscopy (BDS). It was demonstrated that high-pressure–high-temperature treatment (HPHT) led to an increase in the electrical conductivity of the initial glasses by two orders of magnitude. It was also shown that the observed effect was stronger than for the lithium analogue of this material studied by us earlier. The observed enhancement of conductivity was explained by Mott’s theory of electron hopping, which is more frequent in samples after pressure treatment. The final composite consisted of nanocrystalline NASICON (sodium (Na) Super Ionic CONductor) and alluaudite phases, which are electrochemically active in potential cathode materials for Na batteries. Average dimensions of crystallites estimated from XRD studies were between 40 and 90 nm, depending on the phase. Some new aspects of local dielectric relaxations in studied materials were also discussed. It was shown that a combination of high pressures and BDS method is a powerful method to study relaxation processes and molecular movements in solids. It was also pointed out that high-pressure cathode materials may exhibit higher volumetric capacities compared with commercially used cathodes with carbon additions.

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Sylwester J. Rzoska

Papers

Orientationally disordered glassy phases

Influence of an additional power term on the critical exponent of the nonlinear dielectric effect in critical solutions

About the shape of the melting line as a possible precursor of a liquid-liquid phase transition

Erratum: Microscopic structures and dynamics of high- and low-density liquid trans-1,2-dichloroethylene [Phys. Rev. B 81, 092202 (2010)]

Novel High-Pressure Nanocomposites for Cathode Materials in Sodium Batteries