Journal of Non-Crystalline Solids: X最新文献

We discuss possible extraneous effects entering in the conventional measures of “fragility” at atmospheric pressure that may obscure a characterization of the genuine super-Arrhenius slowdown of relaxation. We first consider the role of density, which increases with decreasing temperature at constant pressure, and then the potential influence of the high-temperature dynamical behavior and of the associated activation energy scale. These two effects involve thermodynamic parameters and the strength of the “bare” activation energy reflecting the specific bonding between neighboring molecules. They vary from system to system with, most likely, little connection with any putative collective behavior associated with glass formation. We show how to scale these effects out by refining the definition of fragility and modifying the celebrated Angell plot. We dedicate this note to our great and so inspiring friend, Austen Angell, and associate in this tribute another dear colleague who died too soon, Daniel Kivelson.

Lithium-ion-conducting oxide glass electrolytes in the multicomponent systems Li₂O–B₂O₃–SiO₂–P₂O₅-LiX (LiX = Li₃N, Li₂SO₄, Li₂CO₃, and LiI) were synthesized using a mechanochemical technique. The crystallization temperature and ionic conductivity of multicomponent glasses with added lithium salts or Li₃N were evaluated. Because the crystallization temperature is a measure of the ability of glasses to resist crystallization at high temperature, glasses with high conductivity and high crystallization temperature are desirable electrolytes. In this study, the lithium-ion conductivity of the glasses was found to be correlated with the crystallization temperature, and it was difficult to increase both the conductivity and crystallization temperature. The addition of lithium salts (Li₂SO₄, Li₂CO₃, and LiI) increased the conductivity but decreased the crystallization temperature. Nitrogen doping by the addition of Li₃N improved both these properties of the oxide glass electrolyte. Therefore, oxynitride glasses are desirable electrolytes owing to their thermal stability and lithium-ion conductivity.

We conduct a comparative analysis of the mechanical response of a moderately fragile sodium borate melt, juxtaposing the adiabatic complex modulus measured at GHz frequencies using Brillouin light scattering and the steady-state shear viscosity measured at zero Hz. The two data sets are perfectly compatible with one another by fitting both components of the high-frequency complex modulus using a modified Maxwell-Wiechert model, transforming the loss modulus to viscosity, and extrapolating to zero frequency. This procedure yields an excellent fit to the steady-state viscosity under the condition that the static and relaxational moduli, as well as the activation energy for viscous dissipation are temperature dependent, as modulated by the logistic function, which accounts for the structural changes in the material as it transitions from liquid to glass. Accordingly, fragility of a glass forming liquid can be regarded as a measure of the rate of change with temperature in the energy landscape topography.

We present an easy-to-apply method to predict structural trends in the internal nucleation tendency of oxide glasses. The approach is based on calculated crystal fracture surface energies derived from easily accessible diatomic bond energy and crystal lattice data. The applicability of the method is demonstrated on literature nucleation data for isochemically crystallizing oxide glasses.

Plastic crystals are currently discussed as matrices for highly conducting materials. Among them, mixtures based on succinonitrile (SN) have received particular attention. Long ago, Austen Angell [J. Non-Cryst. Solids 131–133 (1991) 13] has shown that in mixtures with glutaronitrile (GN), the plastic phase of SN can deeply be supercooled. Here, a mixture of 60% SN – featuring deuterated methylene groups – and 40% GN is studied using ²H nuclear magnetic resonance (NMR), thus allowing selective access to the reorientational dynamics of SN. These dynamics agree with that inferred for partially deuterated SN-GN from dielectric spectroscopy which also reveal that a significant H/D isotope effect is absent. Additionally, in the liquid and slightly below the transition to the plastically crystalline state, mixtures of 60% SN and 40% GN are studied using field-gradient NMR diffusometry as well as rotational viscometry.

A liquid that is cooled below its melting temperature, referred to as a supercooled liquid, can solidify into an amorphous rigid state (i.e., glass), if cooling is fast enough and crystallization is avoided. The phenomenology of supercooled liquids has been in general established. However, there are pronounced exceptions (e.g., water) which do not fall into the class of ‘normal’ liquids but exhibit a transition behavior in their liquid states. The latest advances connect the unusual aspect of liquids to the properties of phase-change materials (PCMs) that are the basis for non-volatile memory and neuromorphic technologies. In this article, we review the liquid anomalies in the alloys based on group-IV, V, VI elements including technologically important compositions. Their different behaviors are rationalized in terms of liquid–liquid (metal-semiconductor, and fragile-strong) transitions. We discuss their implications for understanding unusual phase switching behaviors in these materials. Lastly, unsolved problems and new opportunities are outlined.

We build a large (~3400 structures) library of X-ray absorption (XAS) and X-ray emission (XES) spectra computed at high level, which together with their associated structures form the basis for a Monte Carlo fit to the experimental oxygen‑oxygen pair-distribution, XAS and XES spectra for ambient liquid water. The procedure results in weights giving the relative importance of each structure to reproduce the experimental properties. We show that the information content in the X-ray spectroscopic data is strongly complementary to that of X-ray diffraction, and dependent on specific structures that are still consistent with the diffraction data. We fit simultaneously to the X-ray spectroscopy and diffraction experimental data and obtain weights on each structure that give a structural distribution that is consistent with the three experimental datasets. These weights are applied to structural parameters characterizing the local environment of each structure and result in the emergence of more preferred values of these parameters.

In Austen Angell's long and fruitful scientific career, electrolyte research represented a brief and temporary “tangent” that deviated from his normal trajectory of interest. However, with this tangential touch, he left profound and rich legacies in the understanding of fundamental aspects of electrolyte science, the ripple effect of which can still be felt today.

Properties of liquid water supercooled below its melting point have been thoroughly investigated. Experiments on bulk water become increasingly difficult as the temperature is lowered, and eventually impossible when the delay before ice nucleation becomes too short, around 230 K at ambient pressure. At low temperatures, amorphous ices and their glass transition may be studied only below the temperature of crystallization during heating, around 150 K. The temperature range from around 150 to 230 K at ambient pressure thus appears as a no man's land where the properties of bulk water are not accessible. Following Austen Angell's footsteps, I provide here physically acceptable predictions for thermodynamic properties (heat capacity, entropy) of liquid water down to its glass transition, and use the Adam-Gibbs approach to predict its dynamic properties (shear viscosity, self-diffusion coefficient, rotational correlation time).