Recent Advances in Corrosion Science Applicable To Disposal of High-Level Nuclear Waste.

High-level radioactive waste is accumulating at temporary storage locations around the world and will eventually be placed in deep geological repositories. The waste forms and containers will be constructed from glass, crystalline ceramic, and metallic materials, which will eventually come into contact with water, considering that the period of performance required to allow sufficient decay of dangerous radionuclides is on the order of 105-106 years. Corrosion of the containers and waste forms in the aqueous repository environment is therefore a concern. This Review describes the recent advances of the field of materials corrosion that are relevant to fundamental materials science issues associated with the long-term performance assessment and the design of materials with improved performance, where performance is defined as resistance to aqueous corrosion. Glass, crystalline ceramics, and metals are discussed separately, and the near-field interactions of these different material classes are also briefly addressed. Finally, recommendations for future directions of study are provided.

Self-accelerated corrosion of nuclear waste forms at material interfaces.

The US plan for high-level nuclear waste includes the immobilization of long-lived radionuclides in glass or ceramic waste forms in stainless-steel canisters for disposal in deep geological repositories. Here we report that, under simulated repository conditions, corrosion could be significantly accelerated at the interfaces of different barrier materials, which has not been considered in the current safety and performance assessment models. Severe localized corrosion was found at the interfaces between stainless steel and a model nuclear waste glass and between stainless steel and a ceramic waste form. The accelerated corrosion can be attributed to changes of solution chemistry and local acidity/alkalinity within a confined space, which significantly alter the corrosion of both the waste-form materials and the metallic canisters. The corrosion that is accelerated by the interface interaction between dissimilar materials could profoundly impact the service life of the nuclear waste packages, which, therefore, should be carefully considered when evaluating the performance of waste forms and their packages. Moreover, compatible barriers should be selected to further optimize the performance of the geological repository system.

Temperature dependent molecular fluorescence of [Agm]n+ quantum clusters stabilized by phosphate glass networks.

Molecule like silver quantum clusters ([Agm]n+ QCs) exhibit an ultrasmall size confinement resulting in efficient broadband fluorescence. However, free [Agm]n+ QCs are also chemically active, so their stabilization is required for practical applications. We report in this work a phosphate oxyfluoride glass network enabled stabilization strategy of [Agm]n+ QCs. A series of silver-doped P2O5-ZnF2-xAg glasses were prepared by a conventional melt-and-quench method. The NMR and XPS results reveal that two types of [P(O,F)4] tetrahedrons (Q1, Q2) form chain structures and Zn(iv) connects [P(O,F)4] chains into a 3-dimension network in the glasses. The frameworks with limited void spaces were designed to restrict the polymerization degree, m, of [Agm]n+ QCs; the negatively charged tetrahedrons were designed to restrict the charge, n, of [Agm]n+ QCs. Through optical and mass spectroscopy studies, silver quantum clusters, [Ag2]2+ and [Ag4]2+, were identified to be charge compensated by [ZnO4] tetrahedrons and surrounded with [P(O,F)4] complex anions. The fluorescence thus gives high quantum efficiencies of 55.2% and 83.4%, for P2O5-ZnF2-xAg glass stabilized [Ag2]2+ and [Ag4]2+ QCs, respectively. This further reveals that the peak fixed fluorescence of [Ag2]2+ and [Ag4]2+ can be described by molecular fluorescence mechanisms. These are parity-allowed singlet-singlet transitions (S1 → S0), parity-forbidden triplet-singlet transitions (T1 → S0) and intersystem crossings between singlets (S1) and triplets (T1). The phonon coupled intersystem crossing between singlets (S1) and triplets (T1) determines the phosphate stabilized [Ag4]2+ QCs to exhibit a series of temperature dependent fluorescence behaviors. These include fluorescence intensity (at 50-200 K), intensity ratio (FIR) (at 50-200 K), peak shift (at 100-300 K) and lifetime (at 300-450 K) with maximum sensitivities of 1.27% K-1, 0.94% K-1, 0.29% K-1 and 0.41% K-1, respectively. Therefore, phosphate stabilized [Ag4]2+ QCs can be applied as temperature sensing probes, especially at low temperatures (10-300 K) and for color-based visualized temperature sensors.

B2O3/SiO2 substitution effect on structure and properties of Na2O-CaO-SrO-P2O5-SiO2 bioactive glasses from molecular dynamics simulations.

The effect of B2O3/SiO2 substitution in SrO-containing 55S4.3 bioactive glasses on glass structure and properties, such as ionic diffusion and glass transition temperature, was investigated by combining experiments and molecular dynamics simulations with newly developed potentials. Both short-range (such as bond length and bond angle) and medium-range (such as polyhedral connection and ring size distribution) structures were determined as a function of glass composition. The simulation results were used to explain the experimental results for glass properties such as glass transition temperature and bioactivity. The fraction of bridging oxygen increased linearly with increasing B2O3 content, resulting in an increase in overall glass network connectivity. Ion diffusion behavior was found to be sensitive to changes in glass composition and the trend of the change with the level of substitution is also temperature dependent. The differential scanning calorimetry (DSC) results show a decrease in glass transition temperature (Tg) with increasing B2O3 content. This is explained by the increase in ion diffusion coefficient and decrease in ion diffusion energy barrier in glass melts, as suggested by high-temperature range (above Tg) ion diffusion calculations as B2O3/SiO2 substitution increases. In the low-temperature range (below Tg), the Ea for modifier ions increased with B2O3/SiO2 substitution, which can be explained by the increase in glass network connectivity. Vibrational density of states (VDOS) were calculated and show spectral feature changes as a result of the substitution. The change in bioactivity with B2O3/SiO2 substitution is discussed with the change in pH value and release of boric acid into the solution.

Effects of system size and cooling rate on the structure and properties of sodium borosilicate glasses from molecular dynamics simulations.

Borosilicate glasses form an important glass forming system in both glass science and technologies. The structure and property changes of borosilicate glasses as a function of thermal history in terms of cooling rate during glass formation and simulation system sizes used in classical molecular dynamics (MD) simulation were investigated with recently developed composition dependent partial charge potentials. Short and medium range structural features such as boron coordination, Si and B Qn distributions, and ring size distributions were analyzed to elucidate the effects of cooling rate and simulation system size on these structure features and selected glass properties such as glass transition temperature, vibration density of states, and mechanical properties. Neutron structure factors, neutron broadened pair distribution functions, and vibrational density of states were calculated and compared with results from experiments as well as ab initio calculations to validate the structure models. The results clearly indicate that both cooling rate and system size play an important role on the structures of these glasses, mainly by affecting the 3B and 4B distributions and consequently properties of the glasses. It was also found that different structure features and properties converge at different sizes or cooling rates; thus convergence tests are needed in simulations of the borosilicate glasses depending on the targeted properties. The results also shed light on the complex thermal history dependence on structure and properties in borosilicate glasses and the protocols in MD simulations of these and other glass materials.

The structural and electronic properties of reduced amorphous titania.

Crystalline titania has been extensively studied using experimental and theoretical tools. Amorphous titania, however, has received less attention in the literature, despite its importance for a number of applications, such as photocatalysis, batteries, and electronic devices. In this work we modeled amorphous titania using a combination of molecular dynamics and density functional theory with several stoichiometries (TiOx, 2 ≥ x ≥ 1.75). Our results show that oxygen atom removal from amorphous titania is much easier than from crystalline titania, indicating that reduced amorphous structures are likely common. Ti atoms in amorphous titania exhibit a distribution of coordination numbers (five to seven), but the average coordination number of oxygen increases upon reduction. We also identified that gap states arise in substoichiometric titania due to the formation of Ti3+ centers. Such gap states are highly localized and randomly distributed across different Ti atoms, although we do observe a slight preference for electron localization on seven-coordinated Ti atoms. We observe that band gaps increase with reduction of amorphous titania. We also analyzed a proposed hole hopping mechanism involving oxygen vacancies by calculating hole hopping distances. We found that such distances are large except in very reduced states, indicating likely slow hole diffusion through an oxygen vacancy mechanism. Our work is the first of its kind to thoroughly characterize the structural and electronic properties of amorphous titania in reduced states.

Stabilization of ultra-small [Ag2]2+ and [Agm]n+ nano-clusters through negatively charged tetrahedrons in oxyfluoride glass networks: To largely enhance the luminescence quantum yields.

Herein, three different silver species were stably formed in SiO2-Al2O3-B2O3-Na2O-ZnF2-CaF2 glasses and were identified by their characteristic luminescence bands: violet blue luminescence (Ag+: 4d95s1 → 4d10), green white molecular fluorescence (molecule-like [Agm]n+, named ML-Ag) and orange molecular fluorescence ([Ag2]2+ pairs). Due to the relatively low aggregation degrees of [Agm]n+ and [Ag2]2+, non-radiative transitions were highly suppressed, and the PL quantum yields (QYs) of ML-Ag and [Ag2]2+ pairs reached 73.7% and 89.7%, respectively. The substitution of 0.5B2O3-0.5Na2O with SiO2 promoted the partial reduction of Ag+ to Ag0 and the subsequent aggregation of Ag+ and Ag0 to form [Agm]n+ (ML-Ag). The absence of Na2O also resulted in an increasing amount of Ag+-Ag+ pairs with closing interionic distance to form [Ag2]2+ in glass. According to the X-ray photoelectron spectra (XPS) and magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectra, a solubility strategy and a charge compensation model were proposed to describe the transformations between different silver species. The formation of ML-Ag was further controlled via the solubility of Ag+ in glass, whereas [Ag2]2+ centers could be effectively produced by lowering the total amount of other competitive charge compensators, such as Na+, or by introducing negatively charged [BO4]-, [AlO4]-, and [ZnO4]2- tetrahedrons into the glass matrix.

Thermal conductivity of vitreous silica from molecular dynamics simulations: The effects of force field, heat flux and system size.

The thermal conductivity of vitreous silica is computed using the direct method in molecular dynamics simulations with three sets of empirical force fields, including the BKS, Teter, and ReaxFF, to investigate their performance in thermal characterization. Various heat flux and system sizes are used in the simulations to evaluate the statistical uncertainty and the finite-size effect. While all these potentials can reproduce realistic silica structures, the ReaxFF provides better agreement with experiments at 300 K than the BKS and Teter, which is due to its improved description of low-frequency vibrations. Increasing the heat flux and cross-sectional area tends to reduce the calculated standard deviation induced by thermal fluctuations, thus contributing to more accurate thermal conductivity predictions.

Three-dimensional structure determination from a single view.

The ability to determine the structure of matter in three dimensions has profoundly advanced our understanding of nature. Traditionally, the most widely used schemes for three-dimensional (3D) structure determination of an object are implemented by acquiring multiple measurements over various sample orientations, as in the case of crystallography and tomography, or by scanning a series of thin sections through the sample, as in confocal microscopy. Here we present a 3D imaging modality, termed ankylography (derived from the Greek words ankylos meaning 'curved' and graphein meaning 'writing'), which under certain circumstances enables complete 3D structure determination from a single exposure using a monochromatic incident beam. We demonstrate that when the diffraction pattern of a finite object is sampled at a sufficiently fine scale on the Ewald sphere, the 3D structure of the object is in principle determined by the 2D spherical pattern. We confirm the theoretical analysis by performing 3D numerical reconstructions of a sodium silicate glass structure at 2 A resolution, and a single poliovirus at 2-3 nm resolution, from 2D spherical diffraction patterns alone. Using diffraction data from a soft X-ray laser, we also provide a preliminary demonstration that ankylography is experimentally feasible by obtaining a 3D image of a test object from a single 2D diffraction pattern. With further development, this approach of obtaining complete 3D structure information from a single view could find broad applications in the physical and life sciences.

Local structure, composition, and crystallization mechanism of a model two-phase "composite nanoglass".

We report a detailed study of the local composition and structure of a model, bi-phasic nanoglass with nominal stoichiometry Cu55Nb45. Three dimensional atom probe data suggest a nanoscale-phase-separated glassy structure having well defined Cu-rich and Nb-rich regions with a characteristic length scale of ≈ 3 nm. However, extended x-ray absorption fine structure analysis indicates subtle differences in the local environments of Cu and Nb. While the Cu atoms displayed a strong tendency to cluster and negligible structural order beyond the first coordination shell, the Nb atoms had a larger fraction of unlike neighbors (higher chemical order) and a distinctly better-ordered structural environment (higher topological order). This provides the first experimental indication that metallic glass formation may occur due to frustration arising from the competition between chemical ordering and clustering. These observations are complemented by classical as well as ab initio molecular dynamics simulations. Our study indicates that these nanoscale phase-separated glasses are quite distinct from the single phase nanoglasses (studied by Gleiter and others) in the following three respects: (i) they contain at least two structurally and compositionally distinct, nanodispersed, glassy phases, (ii) these phases are separated by comparatively sharp inter-phase boundaries, and (iii) thermally induced crystallization occurs via a complex, multi-step mechanism. Such materials, therefore, appear to constitute a new class of disordered systems that may be called a composite nanoglass.

Synthesis and properties of anhydrous rare-earth phosphates, monazite and xenotime: a review.

The synthesis methods, crystal structures, and properties of anhydrous monazite and xenotime (REPO4) crystalline materials are summarized within this review. For both monazite and xenotime, currently available Inorganic Crystal Structure Database data were used to study the effects of incorporating different RE cations on the unit cell parameters, cell volumes, densities, and bond lengths. Domains of monazite-type and xenotime-type structures and other AXO4 compounds (A = RE; X = P, As, V) are discussed with respect to cation sizes. Reported chemical and radiation durabilities are summarized. Different synthesis conditions and chemicals used for single crystals and polycrystalline powders, as well as first-principles calculations of the structures and thermophysical properties of these minerals are also provided.

Structure and properties of sodium aluminosilicate glasses from molecular dynamics simulations.

Addition of alumina to sodium silicate glasses considerably improves the mechanical properties and chemical durability and changes other properties such as ionic conductivity and melt viscosity. As a result, aluminosilicate glasses find wide industrial and technological applications including the recent Corning(®) Gorilla(®) Glass. In this paper, the structures of sodium aluminosilicate glasses with a wide range of Al∕Na ratios (from 1.5 to 0.6) have been studied using classical molecular dynamics simulations in a system containing around 3000 atoms, with the aim to understand the structural role of aluminum as a function of chemical composition in these glasses. The short- and medium-range structures such as aluminum coordination, bond angle distribution around cations, Q(n) distribution (n bridging oxygen per network forming tetrahedron), and ring size distribution have been systematically studied. In addition, the mechanical properties including bulk, shear, and Young's moduli have been calculated and compared with experimental data. It is found that aluminum ions are mainly four-fold coordinated in peralkaline compositions (Al∕Na < 1) and form an integral part of the rigid silicon-oxygen glass network. In peraluminous compositions (Al∕Na > 1), small amounts of five-fold coordinated aluminum ions are present while the concentration of six-fold coordinated aluminum is negligible. Oxygen triclusters are also found to be present in peraluminous compositions, and their concentration increases with increasing Al∕Na ratio. The calculated bulk, shear, and Young's moduli were found to increase with increasing Al∕Na ratio, in good agreement with experimental data.

Effectiveness and safety of first-line immune checkpoint inhibitors for patients with extensive-stage small cell lung carcinoma: A systematic review and network meta-analysis.

Objective: In recent years, the introduction of immune checkpoint inhibitors (ICIs) has revolutionized the treatment of extensive-stage small cell lung carcinoma (ES-SCLC), but the optimal combination of ICI and standard chemotherapy strategy is yet to be established. The aim of this network meta-analysis (NMA) was to identify which first-line combination strategy is optimal for patients with ES-SCLC. Methods: PubMed, Embase, Cochrane Library, and the proceedings of international conferences, including American Society of Clinical Oncology and European Society for Medical Oncology meetings, were searched for randomized controlled trials (RCTs) published through October 31, 2022. The collected primary outcomes were overall survival (OS), progression-free survival (PFS), and grade 3-5 treatment-related adverse events (TRAEs). Results: Our NMA study included six phase 3 and three phase 2 RCTs including 4037 patients and 10 first-line regimens. Regarding effectiveness, the addition of programmed cell death 1 (PD-1) or programmed cell death ligand 1 (PD-L1) inhibitors to standard chemotherapy provided greater efficacy than chemotherapy alone. However, cytotoxic T lymphocyte-associated antigen-4 inhibitors were not associated with satisfactory prognoses. Serplulimab plus carboplatin-etoposide (vs. standard chemotherapy, hazard ratio [HR] = 0.63; 95% CI = 0.49-0.82) and nivolumab plus platinum-etoposide (HR = 0.65; 95% confidence interval [CI] = 0.46-0.91) displayed the greatest benefit regarding OS. In terms of PFS, serplulimab plus carboplatin-etoposide yielded the best benefit of all treatments (HR = 0.48; 95% CI = 0.39-0.6). The combination of ICIs and chemotherapy caused more toxicity in general, but durvalumab plus platinum-etoposide (odds ratio [OR] = 0.98; 95% CI = 0.68-1.4), atezolizumab plus carboplatin-etoposide (OR = 1.04; 95% CI = 0.68-1.6), and adebrelimab plus platinum-etoposide (OR = 1.02; 95% CI = 0.52-2) displayed similar safety as standard chemotherapy. Subgroup analysis by race illustrated that serplulimab plus carboplatin-etoposide was associated with the best OS in Asian patients. And in non-Asian patients, the combination of PD-1/PD-L1 inhibitors and chemotherapy (pembrolizumab plus platinum-etoposide, durvalumab plus platinum-etoposide, and durvalumab and tremelimumab plus platinum-etoposide) displayed superiority to standard chemotherapy. Conclusions: The results of our NMA study suggested that serplulimab plus carboplatin-etoposide and nivolumab plus platinum-etoposide are associated with the best OS as first-line treatments for patients with ES-SCLC. Serplulimab plus carboplatin-etoposide was associated with the best PFS. In Asian patients, serplulimab plus carboplatin-etoposide had the best OS. Systematic review registration: This study is registered with PROSPERO, number CRD42022345850.

Composition Effect on Interfacial Reactions of Sodium Aluminosilicate Glasses in Aqueous Solution.

Understanding the underlying reaction mechanisms responsible for aluminosilicate glass dissolution in aqueous environments is crucial for designing glasses for technological applications ranging from architecture windows and touch screens to nuclear waste disposal. This study investigated the glass composition effect on the interfacial reactions of sodium aluminosilicate (NAS) glasses using molecular dynamics (MD) simulations with recently developed reactive potentials. Glass-water interfacial models of six NAS glasses with varying Al2O3/Na2O ratios were investigated for up to 4 nanoseconds (ns) to elucidate the interfacial reaction mechanisms at ambient temperature. The results showed that the coordination defects, such as undercoordinated Si and Al, as well as non-bridging oxygens (NBOs) accumulated at the glass surfaces, play a crucial role in the initial hydration reaction process of the glasses. They promote the formation of silanol (Si-OH) and aluminol (Al-OH) species together with the Na+⇔ H+ ion-exchange reactions. The z-density profiles of H2O and H+ ions affirmed the water/H+ propagation into the glass up to 2 nanometers after 4 ns reactions. The penetration depth depends on the composition and shows a nonlinear dependence, suggesting that the subsequent water penetration, particularly into the bulk glass, is supported by the availability of random channels. Aluminol formations, including Al-OH or Al-OH2 near the surface, were found to form mainly through the hydrolysis of Al-O-Al bonds and hydration of Al+-NBO- units. While water molecules are involved in initial interfacial reactions, water penetration into the bulk glass region is primarily achieved by proton transfer. Compared to highly mobile proton transfer involving silanol groups, proton transfer associated with [AlO4]- species is much more limited, particularly in the bulk glass region. These new insights into the role of aluminum in interfacial reactions of the NAS glasses can help to understand the initial dissolution mechanisms and in designing more durable glasses.

87Sr solid-state NMR as a structurally sensitive tool for the investigation of materials: antiosteoporotic pharmaceuticals and bioactive glasses.

Strontium is an element of fundamental importance in biomedical science. Indeed, it has been demonstrated that Sr(2+) ions can promote bone growth and inhibit bone resorption. Thus, the oral administration of Sr-containing medications has been used clinically to prevent osteoporosis, and Sr-containing biomaterials have been developed for implant and tissue engineering applications. The bioavailability of strontium metal cations in the body and their kinetics of release from materials will depend on their local environment. It is thus crucial to be able to characterize, in detail, strontium environments in disordered phases such as bioactive glasses, to understand their structure and rationalize their properties. In this paper, we demonstrate that (87)Sr NMR spectroscopy can serve as a valuable tool of investigation. First, the implementation of high-sensitivity (87)Sr solid-state NMR experiments is presented using (87)Sr-labeled strontium malonate (with DFS (double field sweep), QCPMG (quadrupolar Carr-Purcell-Meiboom-Gill), and WURST (wideband, uniform rate, and smooth truncation) excitation). Then, it is shown that GIPAW DFT (gauge including projector augmented wave density functional theory) calculations can accurately compute (87)Sr NMR parameters. Last and most importantly, (87)Sr NMR is used for the study of a (Ca,Sr)-silicate bioactive glass of limited Sr content (only ~9 wt %). The spectrum is interpreted using structural models of the glass, which are generated through molecular dynamics (MD) simulations and relaxed by DFT, before performing GIPAW calculations of (87)Sr NMR parameters. Finally, changes in the (87)Sr NMR spectrum after immersion of the glass in simulated body fluid (SBF) are reported and discussed.

Origin of thermally induced second harmonic generation in PbO-B2O3 glasses.

Optical second harmonic generation (SHG) with second-order nonlinearity χ((2)) as high as 2.1 pm/V has been achieved in water quenched PbO-B(2)O(3) glasses. No nonlinear depletion layer or microcrystals were observed in these glasses and the mechanism for nonlinearity has been explored in this Letter. Our results show that the possible mechanism for SHG in these glasses can be attributed to their low thermal conductivity that led to a large surface stress gradient, which broke the inversion symmetry of the glasses and subsequently induced the nonlinear effect. These findings suggest that low thermal conductivity induced high stress gradients to lead to large SHG.

Atomistic Understanding of Ion Exchange Strengthening of Boroaluminosilicate Glasses: Insights from Molecular Dynamics Simulations and QSPR Analysis.

Ion exchange (IOX) is an effective and widely used method to enhance mechanical properties of various glass products ranging from the touch screen of consumer electronics to window shields of airplanes and spacecrafts. IOX or chemical strengthening is achieved through the creation of a compressive surface layer on the glass product. Although widely studied experimentally, the fundamental understanding of the IOX strengthening process is still limited. In this work, we have applied large-scale atomistic simulations to understand IOX-induced mechanical property changes and their relation to the glass composition and structural characteristics. Two series of borosilicate glasses are studied to elucidate the composition effect, with boron oxide for silica and alumina for silica substitutions, respectively, on the mechanical properties of different levels of K+ to Na+ ion exchanges by using molecular dynamics (MD) simulations with a set of recently developed effective partial charge potentials. The linear network dilation coefficient (LNDC), a common measure of IOX behaviors, was calculated for each of the glass compositions. Quantitative structural property relationship (QSPR) analysis based on the MD-generated structural features was used to establish the structure-property correlations of mechanical and other properties. The results show strong composition dependence of the LNDC, hence the suitability of IOX strengthening. This behavior is discussed based on glass structure features of the glasses. It was found that glass compositions with a higher amount of mixed glass formers, higher network connectivity, and less complex components tend to show higher calculated LNDC and higher surface compressive stress. MD simulations, in combination with QSPR analysis, can thus provide atomistic insights into how the glass composition and structural characteristics affect IOX behaviors.

Composition Dependence of the Atomic Structures and Properties of Sodium Aluminosilicate Glasses: Molecular Dynamics Simulations with Reactive and Nonreactive Potentials.

Understanding the composition-structure-property relations of glass materials is essential for their technological applications. In this study, the structures and properties of a series of sodium aluminosilicate glasses with varying Al2O3/Na2O ratios ((35 - x)Na2O-xAl2O3-65SiO2, x = 0, 5, 10, 15, 17.5, 20) covering peralkaline to peraluminous compositions, have been studied by using molecular dynamics simulations with two types of interatomic potentials: a fixed partial charge pairwise potential (Teter) and a reactive diffusive charge reactive potential (DCRP). The short and medium structural features such as bond lengths, coordination numbers, Qn distributions, and ring size distributions were obtained and compared with experimental data. It was found that silicon remained fourfold-coordinated throughout the compositional range, while a noticeable amount of fivefold-coordinated aluminum together with oxygen triclusters (TBO) are present in compositions with higher Al2O3 contents (RAl/Na > 1). In addition, the simulation results from both potentials show a certain level of violation of the Al avoidance rule by exhibiting a non-negligible amount of [AlOx]-[AlOx] polyhedral connections. Neutron and X-ray diffraction structure factors of the simulated glasses were calculated and compared with available experimental data. The mechanical properties, including Bulk, Shear, and Young's modulus, were calculated and found to increase with increasing RAl/Na, in good agreement with the experiments. Correlations of the properties with glass structures as a function of glass compositions and the advantages as well as potential issues of the two sets of potentials in modeling sodium aluminosilicate glasses are discussed in the context of features of glass structures and the prospect of future simulations of glass-water reactions.

A modified random network model for P2O5-Na2O-Al2O3-SiO2 glass studied by molecular dynamics simulations.

We investigated the short- and medium-range structural features of sodium aluminosilicate glasses with various P2O5 (0-7 mol%) content and Al/Na ratios ranging from 0.667 to 2.000 by using molecular dynamics simulations. The local environment evolution of network former cations (Si, Al, P) and the extent of clustering behavior of modifiers (Na+) is determined through pair distribution function (PDF), total correlation function (TDF), coordination number (CN), Q x n distribution and oxygen speciation analysis. We show that Al-O-P and Si-O-Al linkage is preferred over other connections as compared to a random model and that Si-O-Si linkage is promoted by the P2O5 addition, which is related to structural heterogeneity and generates well-separated silicon-rich and aluminum-phosphorus-rich regions. Meanwhile, due to the relatively high propensity of Al to both Si and P, heterogeneity can be partly overcome with high Al content. A small amount of Si-O-P linkages have been detected at the interface of separated regions. Clustering of Na+ is also observed and intensified with the addition of P2O5. Based on the simulated structural information, a modified random network model for P2O5-bearing sodium aluminosilicate glass has been proposed, which could be useful to optimize the mobility of sodium ions and design novel functional glass compositions.