Journal of Non-Crystalline Solids: X最新文献

Quantitative structure-property relationship (QSPR) is a powerful analytical method to find correlations between the structure of a molecule and its physicochemical properties. The glass transition temperature (T_g) is one of the most reported properties, and its characterisation is critical for tuning the physical properties of materials. In this work, we explore the use of machine learning in the field of QSPR by developing a recurrent neural network (RNN) that relates the chemical structure and the glass transition temperature of molecular glass formers. In addition, we performed a chemical embedding from the last hidden layer of the RNN architecture into an m-dimensional T_g-oriented space. Then, we test the model to predict the glass transition temperature of essential amino acids and peptides. The results are very promising and they can open the door for exploring and designing new materials.

The mechanical behavior of a potassium phospho-aluminosilicate (KPAS) glass which is known to develop near-surface compressive stress profiles resulting from low-temperature water diffusion was explored. Region I of the macro-crack growth curve for the KPAS glass exhibited a steeper slope corresponding to a higher fatigue parameter, n, than soda-lime glass despite a lower n at crosshead speeds of 10⁻¹–10² mm/min and no decrease in strength at lower rates in dynamic fatigue testing. The fatigue limit was easily observed in 50% RH air for the KPAS glass at velocities ~10⁻⁶–10⁻⁷ m/s giving rise to the delayed restart of cracks aged below the fatigue limit. Additionally, a 75% strength increase of the KPAS glass was measured after abraded specimens were aged for 100 days in humid air relative to specimens which were tested immediately following abrasion. The effects of swelling stress, surface stress relaxation, crack healing, and crack tip blunting are discussed.

Perovskite, particularly halide perovskite has drawn increasing attention in recent years because of its remarkable photoelectric properties. However, due to its susceptibility to environmental factors, its research and application have been hampered. Recently, perovskite nanocrystals (PNCs) have been precipitated inside glass by using thermal treatment or femtosecond laser irradiation, which results in unprecedented stability because they are protected by glass matrix. This article reviews the fundamental structure and properties of PNCs, the benefits of perovskite nanocrystals-glass composite structure, and the current state of research into the use of a femtosecond laser to induce PNCs in glass. We also discuss the recent progress in the use of perovskite nanocrystals-glass composite structure for stereo-holographic computing, micro-LEDs and optical storage.

Telluride glasses such as Ge-As-Te, Ge-Te, and As-Te are of much interest due to their extensive infrared transparency. The structure of these glasses has also been broadly investigated, but Raman studies are rare and current literature data shows a significant level of disagreements and discrepancies. Here we show that the source of this disparity is two-fold, first the low damage threshold of these glasses requires low photon energy and low power to obtain reliable spectra, and second the unusual surface oxidation of telluride glasses leads to strong Raman artefact in relatively short time. Overall, high resolution spectra of freshly polished glasses obtained at low power with a near infrared source reveal that only four main modes are required to consistently interpret all Raman spectral features. Analysis of these Raman spectra confirm the presence of large chemical disorder in Ge-As-Te and As-Te glasses, consistent with previously reported spectroscopic studies.

Molecular dynamics simulations were used to evaluate the fracture strength of pre-stressed silica glass exposed to water molecules, with and without heating. The pre-stressed wet glasses had a strength enhancement of 5–7% in comparison to the original dry glasses. Heating the glasses while pre-stressed with included water resulted in an even greater strength enhancement. The glasses with a higher concentration of structural defects in the dry glass have an expected lower dry-glass strength in comparison to the glass with fewer defects. However, the weaker dry glass shows a greater strength enhancement after pre-stressed water exposure caused by the increase in the silanol concentration in the more defective glass that offsets the otherwise weakened glass. Increased silanol concentration has been shown to increase the expansion of silica glass, creating an increased compressive stress on the pre-stressed-wet glass relaxed to original dimensions, allowing for an increased strength enhancement.

The oxygen speciation in (Na₂O)_x(GeO₂)_100-x glasses with 4 ≤ x ≤ 28 is studied using high-resolution ¹⁷O NMR spectroscopy at ultra-high field (35.2 T). The structure of glasses with x ≤ 18 consists of oxygen atoms bridging either two four-coordinated Ge^IV atoms (O⁴⁴) or a Ge^IV and another six-coordinated Ge^VI atom (O⁴⁶). The O⁴⁶: O⁴⁴ ratio monotonically increases with increasing Na₂O content in this composition range. Further addition of Na₂O results in a lowering of O⁴⁶ and in a concomitant rise in the concentration of non-bridging oxygen (NBO) atoms. The resulting compositional variation in the average coordination number of Ge atoms is associated with the non-monotonic evolution of density and the germanate anomaly in these glasses. On the other hand, increasing fictive temperature results in a net conversion of Ge^VI → Ge^IV + NBO in these glasses, which is argued to be a source of temperature dependent configurational entropy in germanate liquids.