Sub-Nanometer-Range Structural Effects From Mg2+ Incorporation in Na-Based Borosilicate Glasses Revealed by Heteronuclear NMR and MD Simulations

Magic-angle-spinning (MAS) nuclear magnetic resonance (NMR) experiments and molecular dynamics (MD) simulations were employed to investigate Na2O-B2O3-SiO2 and MgO-Na2O-B2O3-SiO2 glass structures up to ≈0.3 nm. This encompassed the {Na[p]}, {Mg[p]}, and {B[3], B[4]} speciations and the {Si, B[p], M[p]}-BO and {Si, B[p], M[p]}-NBO interatomic distances to the bridging oxygen (BO) and nonbridging oxygen (NBO) species, where the superscript indicates the coordination number. The MD simulations revealed the dominance of Mg[5] coordinations, as mirrored in average Mg2+ coordination numbers in the 5.2-5.5 range, which are slightly lower than those of the larger Na+ cation but with a narrower coordination distribution stemming from the higher cation field strength (CFS) of the smaller divalent Mg2+ ion. We particularly aimed to elucidate such Na+/Mg2+ CFS effects, which primarily govern the short-range structure but also the borosilicate (BS) glass network order, where both MD simulations and heteronuclear double-resonance 11B/29Si NMR experiments revealed a reduction of B[4]-O-Si linkages relative to B[3]-O-Si upon Mg2+-for-Na+ substitution. These effects were quantified and discussed in relation to previous literature on BS glasses, encompassing the implications for simplified structural models and descriptions thereof.

Quantum Dot-Siloxane Anchoring on Colloidal Quantum Dot Film for Flexible Photovoltaic Cell

Lead sulfide (PbS) colloidal quantum dots (CQDs) are promising materials for next-generation flexible solar cells because of near-infrared absorption, facile bandgap tunability, and superior air stability. However, CQD devices still lack enough flexibility to be applied to wearable devices owing to the poor mechanical properties of CQD films. In this study, a facile approach is proposed to improve the mechanical stability of CQDs solar cells without compromising the high power conversion efficiency (PCE) of the devices. (3-aminopropyl)triethoxysilane (APTS) is introduced on CQD films to strengthen the dot-to-dot bonding via QD-siloxane anchoring, and as a result, crack pattern analysis reveals that the treated devices become robust to mechanical stress. The device maintains 88% of the initial PCE under 12 000 cycles at a bending radius of 8.3 mm. In addition, APTS forms a dipole layer on CQD films, which improves the open circuit voltage (VOC ) of the device, achieving a PCE of 11.04%, one of the highest PCEs in flexible PbS CQD solar cells.

Co-doping studies to enhance the life and electro-chemo-mechanical properties of the LiMn2O4 cathode using multi-scale modeling and neuro-computing techniques

A number of engineered cathode materials with longer life cycles and better electro-chemo-mechanical properties can be obtained by partially replacing some of the elements with other relevant ones without compromising much with the structure. To design such superior cathode materials, in this work, we replace a small number (5% or 10%) of Mn³⁺, with one of the following elements: aluminium, nickel, magnesium, gallium, chromium, and yttrium. Additionally, S^2- and F^- were used to replace some (∼1%) of the O^2- ions (anion) in the crystal. In this work, we have used a combination of Quantum Mechanics (QM), Classical Molecular Dynamics (CMD), Neural Network (NN) and Computational Fluid Dynamics (CFD) modeling. QM has been used to validate the Classical Molecular Dynamics (CMD) simulation results for engineered structures where experimental data are not available. CMD simulations are used to obtain material properties such as lattice expansion, Young's modulus, and diffusion coefficients for un-doped, doped and co-doped structures. NN modeling was used to reduce the computational time to evaluate millions of possible crystal configurations. Finally, the impact of co-doping strategies at the macroscale has been studied using CFD simulations. As a first step, we employed neuro-computing techniques to identify the optimum ionic configuration for all crystal structures, saving ∼88% of the computational time. Next, molecular scale simulations were performed to study the material properties. Molecular dynamics (MD) modeling findings suggest that the relative volume expansion between the fully charged and discharged states of the battery can be reduced by ∼1.9% to ∼2.25%, indicating an improvement in the life of the cathode material by several hundreds of cycles. Findings from both QM and CMD simulations suggest that for these novel engineered materials, electro-chemo-mechanical properties, such as ionic mobility, chemical diffusion coefficient and elasticity, improved. Furthermore, CMD simulations showed that the inter-ionic space between doped metal ions and oxygen is smaller compared to the spacing between Mn³⁺-O^2- in the original LMO spinel, indicating an improvement in the material's structural strength along with the total number of the discharge cycle. Finally, macro scale computational modelling results show that chances of thermal runaway can be reduced significantly for some of the co-doped structures since the intercalation induced maximum stress is lower.

Laser-induced structural modification in calcium aluminosilicate glasses using molecular dynamic simulations

Glass structures of multicomponent oxide systems (CaO–Al₂O₃–SiO₂) are studied using a simulated pulsed laser with molecular dynamics. The short- and intermediate-range order structures revealed a direct correlation between the transformation of Al^(IV) to Al^(V), regions of increased density following laser processing, inherent reduction in the average T–O–T (T = Al, Si) angle, and associated elongation of the T–O bonding distance. Variable laser pulse energies were simulated across calcium aluminosilicate glasses with high silica content (50–80%) to identify densification trends attributed to composition and laser energy. High-intensity pulsed laser effects on fictive temperature and shockwave promotion are discussed in detail for their role in glass densification. Laser-induced structural changes are found to be highly dependent on pulse energy and glass chemistry.

Elucidating the formation of Al–NBO bonds, Al–O–Al linkages and clusters in alkaline-earth aluminosilicate glasses based on molecular dynamics simulations

Exploring the reasons for the initiation of Al–O–Al bond formation in alkali-earth alumino silicate glasses is a key topic in the glass-science community.

Structure of Strontium Aluminosilicate Glasses from Molecular Dynamics Simulation, Neutron Diffraction, and Nuclear Magnetic Resonance Studies

The structure of strontium glasses with the composition (SiO₂)_{1-2 x}(Al₂O₃) _x(SrO) _x ( R = [SrO]/[Al₂O₃] = 1) and (SiO₂)_{1-4 x}(Al₂O₃) _x(SrO)_{3 x} ( R = 3) has been explored experimentally over both short- and intermediate-length scales using neutron diffraction, ²⁷Al and ²⁹Si nuclear magnetic resonance, and classical molecular dynamics simulations in model systems containing around 10 000 atoms. We aim at understanding the structural role of aluminum and strontium as a function of the chemical composition of these glasses. The short- and medium-range structure such as aluminum coordination, bond angle distribution, Q^{( n)} distribution, and oxygen speciation have been systematically studied. Two potential forms of the repulsive short-range interactions have been investigated, namely, the Buckingham and Morse forms. The comparison of these forms allows us to derive general trends independent of the particular choice of the potential form. In both cases, it is found that aluminum ions are mainly fourfold coordinated and mix with the silicon network favoring the Al/Si mixing in terms of Al-O-Si linkages. For the R = 1 glass series, despite the full charge compensation ([SrO] = [Al₂O₃]), a small fraction of fivefold aluminum is observed both experimentally and in MD simulations, whereas the concentration of sixfold aluminum is negligible. MD shows that the fivefold aluminum units AlO₅ preferentially adopt a small ring configuration and link to tricoordinated oxygen atoms whose population increases with the aluminum content and are mainly found in OAl₃ and OAl₂Si configurations. The modeled Sr speciation mainly involves SrO₇ and SrO₈ polyhedra, giving a range of average Sr²⁺ coordination numbers between 7 and 8 slightly dependent on the short-range repulsive potential form. A detailed statistical analysis of T-O-T' (T, T' = Al,Si), accounting for the population of the various oxygen speciations, reveals that both potentials predict a nearly identical Al/Si mixing.

Direct 17O NMR experimental evidence for Al–NBO bonds in Si-rich and highly polymerized aluminosilicate glasses

Double-resonance ¹⁷O{²⁷Al} NMR unambiguously evidences Al–NBO bonds in rare-earth aluminosilicate glasses.