Journal of Non-Crystalline Solids: X最新文献

In this work, the compositional series of sulfide and mixed oxysulfide (MOS) glasses 0.56Li₂S + 0.44[(0.33-x)PS_5/2 + xPO_5/2 + 0.67SiS₂] was prepared, where 0 ≤ x ≤ 0.33, and their short range order (SRO) structures and their thermal properties have been investigated. Powder x-ray diffraction (XRD) confirmed that the MOS glasses were free from crystallization, with only very minor diffraction peaks in the x = 0 glass being observed. Fourier transform infrared (FT-IR), Raman, and ²⁹Si and ³¹P magic angle spinning (MAS) NMR spectroscopies were used to identify the SRO structures present in these glasses. These spectra revealed oxygen migration from P to Si during synthesis. Although oxygen was introduced in the form of phosphorus oxide, the majority of the oxygen in these glasses ends up being bonded to silicon, thereby creating sulfur-rich SROs centered by phosphorus and MOS SROs centered by silicon. It was further found that the P-S SRO species were predominantly charged non-bridging sulfurs (NBS). The Si SRO species were comprised of neutral bridging oxygens (BOs) and charged non-bridging oxygens (NBOs) and neutral bridging sulfurs (BS) and charged non-bridging sulfurs with the neutral BO and BS species being larger in fraction than the NBO and NBS. These results suggest that the preponderance of the mobile Li⁺ cations in these glasses are located near the more negatively charged P centers and not near the more neutrally charged Si centers. The average negative charge of the P SRO structures was found to be ∼ − 3.0 with ∼97% of the phosphorous species in the P⁰ SRO while the average negative charge of the Si SRO structures was found to be −2.3. Consistent with the creation of the large numbers of NBS on the P and more BOs and BSs on the Si, these values are more negative and more positive, respectively, than the compositionally expected average value of −2.55. Differential scanning calorimetry (DSC) measurements of their glass transition (Tg) and crystallization (Tc) temperatures showed that the Tgs of these glasses are higher than 300 °C and their working ranges, ΔT ≡ Tc – Tg, are ∼100 °C.

In this review article, the impact of dissolved water on the viscous properties of soda lime silicate melts is addressed against the background of the upcoming switch from natural gas to hydrogen combustion. This change will lead to an increase in the total water content of the glasses by up to 0.4 mol%. In order to better define possible influences of water speciation, water-rich glasses were synthesised under increasing pressure up to the kbar range. It is shown that a distinction must be made between the influence of dissolved OH-groups and H₂O-molecules in order to accurately reflect the dependence of isokom temperatures on water content. In addition, an increase of one order of magnitude in the tolerance to higher deformation rates was observed for the range of expected increased water contents during isothermal deformation processes, which is based on the time-temperature superposition principle, i.e. congruent flow curves were determined under isokomal conditions.

During the manufacturing and in-service process, the water molecules from the humid or liquid environments are ubiquitous on glass surface, which can alter the various surface properties such as adhesion, stress corrosion, indentation, scratch, and wear behaviors when the stress is applied. In this brief review, the experimental techniques on measuring the adsorbed water molecules on glass surface are discussed and the effects of adsorbed water on mechanical and mechanochemical properties of silicate glass are discussed. In particular, recent advances on the effect of adsorbed water on the adhesion, indentation, scratch, and mechanochemical wear behaviors of silicate glass are discussed. Overall, the understanding on effect of adsorbed water on mechanical and mechanochemical properties of glasses are outlined in this review article, and thereby, some open questions are proposed to design next generation of tough functional glasses with improved both mechanical and mechanochemical properties.

Phase separation in the H₂O-SiO₂ system is examined in view of immiscibility in the alkali and alkaline earth silicates, critical parameters of which correlate with the charge and size of network modifier cations. Although the miscibility gaps of the H₂O-SiO₂ system have not been completely characterized, available data indicate a phase separation tendency greater than that of Li₂O-SiO₂, consistent with H⁺ being smaller than Li⁺. Extension of critical parameter correlations to H₂O-SiO₂ leads, however, to unrealistic predictions of critical composition due to neglect of cation/anion size asymmetry. To capture this effect, a new coulombic cell model is developed and combined with an asymmetric hard-sphere mixture model. The resulting equation of state predicts H₂O-SiO₂ critical parameters consistent with expected critical temperature and observed critical concentration. Suppression of the miscibility gap with pressure is explained as a consequence of silanol condensing into molecular H₂O and increasing the background dielectric constant.

Ortho-carborane condenses into a plastically crystalline state in which the icosahedrally shaped molecules perform various kinds of motion. Using ¹¹B nuclear magnetic resonance (NMR), the molecular motions and the phase transitions occurring in solid ortho-carborane are revisited. The motional narrowing of the ¹¹B spectra and the spin-relaxation times are monitored over wider temperature ranges than accessed previously. The spin-relaxation times are successfully described using an approach that takes second-order quadrupolar effects and a distribution of correlation times explicitly into account. Our work resolves a discrepancy previously noted for ortho-carborane when comparing activation energies from dielectric spectroscopy with those from NMR studies. In the temperature range between about 160 and 210 K a fast contribution to the longitudinal spin-lattice relaxation is observed which we interpret as a reporter of phase transitions occurring in ortho-carborane. Quantum chemical calculations are performed, not the least to assess possible effects of cross-correlated relaxation phenomena and to check whether or not the ¹¹B quadrupolar coupling constants display significant intermolecular contributions.

The power of X-ray photoelectron spectroscopy (XPS) measurements and analysis is demonstrated to establish the structure of network glasses using the examples of binary As-Se, As-S, Ge-Se and Ge-S series. Short-range chemical order in these materials is established, and main building blocks of their structurally-disordered glass network are identified throughout respective glass-forming compositional domains. The XPS fitting procedure is correlated with disproportionality analysis based on the conditions of chemically-ordered bond network model and uniform distribution of constituent chemical elements. The structure of binary As-based glasses (As-Se and As-S) is shown to be adequately described by the terms of ‘chain-crossing’ model, while ‘outrigger raft’ model has to be additionally used to build a network of Ge-based glasses (Ge-Se and Ge-S).

Understanding the atomic structure of amorphous solids or glasses is a perennial, and ultimately insoluble, challenge, since the randomness involved means that structural information can only ever be obtained, from either experiment or structural modelling, in a statistical form, unlike the case for crystalline materials. The particular atomic structure, in a glass or crystal, is dictated by the underlying chemical bonding between the atoms. The question arises therefore, conversely, to what extent can one infer anything about the nature of the bonding in amorphous/glassy solids from some knowledge of the atomic structure? In this focused perspective article, I discuss the case of telluride glassy materials, and show that they represent a special case of bonding in chalcogenide materials. The near-linear axial structural configurations characteristic of certain telluride crystals, also prevalent in the corresponding glasses, and giving rise to a particular degree of linear medium-range structural order, are shown to arise from hyperbonding (e.g. three-centre/four-electron) interactions, rather than being associated with conventional (two-centre/two-electron) covalent bonds, as in other chalcogenide materials. These structural configurations are responsible for the unique ‘phase-change memory’ behaviour exhibited by some telluride materials. An experimental technique is proposed which should be capable of detecting such linear-character, medium-range structural order in telluride glasses.