Journal of Non-Crystalline Solids: X最新文献

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.

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).

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.

The Gay-Berne model is studied numerically with a choice of parameters allowing for the formation of a discotic liquid crystal at low temperatures. We show that the model has strong virial potential-energy correlations in the isotropic phase at high temperatures, i.e., it obeys the criterion for the existence of isomorphs, which are curves of approximately invariant structure and dynamics. These properties are demonstrated to be approximately invariant in reduced units along the isomorph studied. The isomorph is described well by the constant density-scaling exponent 11.5, a number that is significantly larger than the density-scaling exponents of various Lennard-Jones models that are always below 6.

Austen Angell conducted pioneering work that opened up the field of supercooled water by observing the temperature dependent divergence of the thermodynamic response functions. Many different scenarios have been proposed as the origin of the anomalous properties and now it has become possible to test the various hypotheses in experimental studies of bulk supercooled water at conditions where ice crystallization becomes extremely rapid. Through the usage of x-ray lasers, ultrafast measurements could be conducted, as the sample is rapidly brought to the extreme conditions on time scales preceding ice formation. In particular the experimental observation of the existence of a liquid-liquid transition at positive pressure, one phase behavior at atmospheric conditions at temperatures down to 228 K, and the existence of maxima in several properties at 230 K indicative of a Widom line, are only consistent with the proposed liquid-liquid critical point model as the origin of the anomalous properties.

The calorimetric features that have been broadly used to assign a glass transition temperature T_g of 136 K to amorphous water are qualitatively reproduced with a phase change material. Annealing treatments and ultrafast calorimetry measurements indicate that this feature is only a shadow-T_g and that the real T_g lies at higher temperature above the glass transition. A Kissinger analysis of the crystallization kinetics confirms that crystallization occurs below T_g from the glassy state at conventional heating rates. These results strongly suggest that the amorphous water endotherm at 136 K is indeed a shadow-T_g and that the real T_g lies at higher temperature as predicted from structural relaxation considerations.