Journal of Non-Crystalline Solids: X最新文献

Phase change materials (PCMs) that store and release thermal energy via a reversible phase transition in the intermediate temperature range are a promising solution for renewable energy storage as they can be durable and inexpensive. Towards the development and understanding of new intermediate PCMs, this work describes a family of pyridinium ionic liquids and their thermophysical properties that show the potential of protic ionic liquids in the PCM field. Various pyridine structural isomers were used to explore the molecular patterns that affect the enthalpy of fusion and melting. The results show that small structural variations in the cation can change the thermophysical properties drastically; for example, melting temperatures varied between 357 ± 1 K and 499 ± 1 K, and enthalpies of fusion covered a wide spectrum from 38 to 190 J g⁻¹ ± 5%. The most promising results in terms of PCM application, and one of the best among all protic ionic liquids reported thus far, were obtained for 2-hydroxypyridinium methanesulfonate [2-OHpyH][CH₃SO₃] (T_m = 433 K and ΔH_f = 190 J g⁻¹).

The continuous development and improvement of interatomic potential models for oxide glasses have made classical molecular dynamics a powerful computational technique routinely used for studying the structure and properties of such materials on a par with the more advanced experimental techniques.

In this brief review, we retrace the development of the most used interatomic potential models from the earliest MD simulations up to now with a look at the possible future developments in this field due to the advent of the machine learning era and data-driven methods.

Thermoelectric materials capable of direct conversion between electricity and heat provide a broad prospect for power generation and refrigeration. As a family of potential thermoelectric materials, semiconducting chalcogenide glasses exhibit unique characteristics of easy to draw fiber, high Seebeck coefficient, low thermal conductivity and tunable electrical conductivity, endowing them with promising applications in wearable electronics. In this review, we summarize the recent advance on semiconducting chalcogenide glass for thermoelectric application. The design and fabrication method of semiconducting chalcogenide glasses are presented. The strategies for improving the thermoelectric performance of chalcogenide glasses are reported. Besides, the extensive applications of chalcogenide fibers in the fields of thermal sensing and positioning are overviewed. In the end, the challenges and perspectives for the future development of semiconducting chalcogenide glasses and fibers are discussed.

The mechanism of non-congruent growth of a crystal from glass has been sought using molecular dynamics simulations. Specifically, as a model of this process, the growth of a lithium niobate (LiNbO₃) crystal seed sandwiched between two lithium niobosilicate (LNS) glass slabs has been simulated as a function of time and temperature. The growth of pre-existing crystal is strongly affected by the orientation of crystal seed, temperature, and the SiO₂ concentration in the surrounding LNS glass matrix. The orientation of LiNbO₃ seed surface that has inherently larger interplanar distance results in a relatively slower crystal growth. The addition of SiO₂ to LNS system significantly decreases the crystal growth, which primarily occurs in the region devoid of Si. The suppressive effect of SiO₂ on growth rate can be traced to the existence of defect complex comprising of Si substituted at the Nb site and a nearby Nb vacancy.

Glasses in the systems Me₂O-ZnO-B₂O₃ with Me = Li, Na, K, Rb (MeZB), Na₂O-ZnO-CuO-B₂O₃ (NZCuB), CaO-ZnO-B₂O₃ (CaZB), and Li₂O-PbO-B₂O₃ (LPbB) as a reference, were studied by differential thermal analysis, dilatometry, rotational viscometry, and heating microscopy. A decrease of viscosity and sintering range was found with decreasing number of fourfold coordinated boron. The viscosity of the alkali zinc borate glasses varies only slightly. LPbB and CaZB stand out by their reduced and increased viscosities, respectively. Sodium, potassium, and calcium zinc borate glasses possess a fragility above 76. All glasses were sintered to full density before crystallization. Mostly binary zinc borate phases govern crystallization. A ternary crystalline phase was detected only in the potassium containing sample. The Weinberg glass stability parameter ranges between 0.07 and 0.12. This is caused by the presence of several crystalline phases and varying melting points of even the same crystalline phase in different glass matrices.

Glass transition temperature and related dynamics play an essential role in amorphous materials research since many of their properties and functionalities depend on molecular mobility. However, the temperature dependence of the structural relaxation time for a given glass former is only experimentally accessible after synthesizing it, implying a time-consuming and costly process. In this work, we propose combining artificial neural networks and disordered systems theory to estimate the glass transition temperature and the temperature dependence of the main relaxation time based on the knowledge of the molecule's chemical structure. This approach provides a way to assess the dynamics of molecular glass formers, with reasonable accuracy, even before synthesizing them. We expect this methodology to boost industrial development, save time and resources, and accelerate the scientific understanding of structure-properties relationships.

Combining thermal and pressure effect represents a novel approach to modify glass properties. However, the microscopic structural origin of these property modifications is complex and far from fully understood, especially in multicomponent glasses with mixed glass formers. In this paper, we have utilized classical molecular dynamics simulations with a set of composition dependent potentials to investigate pressure-quenching effect on sodium borosilicate glasses. Processes including hot compression, cold compression and subsequent annealing on the structures and properties are investigated and compared. It was found that applying pressure up to 10 GPa at the glass transition temperature led to permanent densifications and a dramatic increase of elastic moduli by 90%, while thermal annealing reversed the increase and applying pressure at ambient temperture did not increase the modulus. The main structural change of the hot compressed sample is the increase of four-fold coordinated boron while silicon remains four-fold coordinated. The sodium environment shows an increase of coordination number and a decrease of NaO and NaNa bond distances. Medium range structure is also changed with an increase of 8-membered rings. These results provide atomistic insights of the pressure quench effect on borosilicate glasses.

Inorganic glasses have been the one of the most important families of inorganic materials used by human society. The ability to fabricate glasses with customized shapes is of high significance for a diverse range of applications. We review the recent advances in the development of techniques for fabricating glass items with pre-designed geometries. Most of these methods are based on the high-temperature densification of the green parts, which are formed by the preshaping of the composites containing inorganic feedstock (e.g., SiO₂) by molding, nanoimprinting and 3D printing, with resolutions down to the sub-micron level. These methods have also enabled the fabrication of multicomponent glass systems and the incorporation of traces of metal ions or nanoparticles as dopants with optical functionalities. In this review, these low-temperature routes are compared with the direct 3D printing route for the fabrication of glass by selective laser melting and fused deposition molding, which rely on high-temperature melting/sintering of glass powers or filaments. Finally, the benefits of different methods for fabricating glass in a customizable manner are discussed and potential future directions are highlighted.

The viscoelasticity of glass-forming fluids contains sustantial information about space-time rigidity. Viscoelasticity and rheology provide alternative experimental, computational and theoretical ways to asses chemical composition effects in the relaxation of supercooled liquids near the glass transition. In particular, the transverse current correlation and transversal dynamical structure factor contain space-time information allowing to relate the dynamical gap of transversal vibrational modes with floppy modes and relaxation times in the liquid. Here, a short revision is made of the subject, including simulations of Tellurium, a typical chalcogenide glass. Our results are similar to those obtained for typical metallic liquids. To rationalize this result, an statistical mechanics analysis in the strain ensemble is performed by using a model that incorporates flexibility and hard-core potentials. This shows that the entropy is akin to a hard-cord fluid as angular bonds only renormalize the entropy if they are not substantially affected by temperature effects. Finally, a comparison is made with Selenium, where bond breaking effects do not allow such a straight-forward treatment.