Non-bridging Oxygen Research Articles

Influence of the substitution of CaO by SrO on the structure, degradation and in vitro apatite formation of sol–gel derived SiO2–CaO–SrO–P2O5system bioactive glasses

The present study investigates the influence of the substitution of CaO by SrO on the structure, degradation and in vitro apatite formation of sol–gel-derived bioactive glasses with composition of 58SiO2–(38-x)CaO–xSrO–4P2O5, where x varies between 0 and 10 mol.%. The IV-type nitrogen adsorption/desorption isotherms and pore size values (ranging from 5.41 to 12.56 nm) confirmed the mesoporous structure of the synthesized glasses. The detailed structural analysis was carried out by X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR). As network modifiers, the addition of Ca and Sr oxides disrupted the bonds of bridging oxygens (BOs) and resulted in the formation of non-bridging oxygens (NBOs), where the substitution of Ca with Sr led to an increase in Q1 units and a decrease in Q3 units. The effects of the addition of Sr on sample degradation and apatite formation were assessed using an assay in tris-(hydroxymethyl)-aminomethane and hydrochloric acid (Tris–HCl) and simulated body fluid (SBF). The results demonstrated that the substitution of CaO by SrO in the CaO–SiO2–P2O5 bioglass system altered the glass structure, resulting in reduced sample degradation and delayed apatite formation. This suggests that the incorporation of Sr into bioactive glasses may serve as a promising strategy to regulate the structure, dissolution behavior and apatite formation of silicate-based glasses, particularly concerning their long-term applications within the human body.

Phase and microstructural characterization of swat soapstone (Mg3Si4O10(OH)2)

Abstract This study focuses on the comprehensive exploration of Swat soapstone, employing a range of analytical techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) spectroscopy, Fourier-transform infrared (FTIR) spectroscopy, and X-ray fluorescence (XRF) spectroscopy. XRD was used to identify the phase and lattice parameters of the soapstone. SEM further scrutinizes the dispersed soapstone particles, revealing different structural characteristics such as a slightly elongated, cubic-like structure, a straight rod-like formation, and a rough, textured surface. EDX spectroscopy was utilized for studying the elemental composition of the soapstone. The analysis identifies talc as the primary mineral in Swat soapstone, with iron, an element, also contributing notably to its composition. This underscores the complexity of Swat soapstone’s internal structure. XRF analysis further contributes to the elemental characterization, revealing a dominant composition of silicon (Si) at 48.567 wt% and a notable contribution from iron (Fe) at 16.108 wt%. FTIR analysis confirmed the absorption of infrared radiation at the non-bridging oxygen (Si–O–) within the silicate network and the Si–O–Si bending vibration. This work investigates the chemical and morphological details of the Swat soapstone.

Crystallization Behavior and Structure of CaO–SiO2–Al2O3 Melts Representing the Oxide Inclusions in Si‐Mn Deoxidized Steel

For further optimization of the inclusion plasticization control process of Si‐Mn deoxidized steel, the crystallization behavior and structure of CaO–SiO2–Al2O3 system inclusions are investigated. The crystallization behavior of four typical low melting point CaO–SiO2–Al2O3 inclusions at 1000 to 1250 °C is studied by steel crucible isothermal heating experiment. The obtained results reveal that the glassy stability of the inclusions is high when the composition of low melting point inclusion is located in the eutectic region of tridymite, pseudowollastonite, and anorthite in the ternary phase diagram. However, when the composition of the inclusion is located in the eutectic region of melilite, pseudowollastonite, and anorthite, it is easy to undergo glass‐crystallization transformation and precipitate wollastonite and anorthite crystalline phases when isothermal heating at 1100 to 1200 °C. In addition, the crystallization mode of these inclusions is mainly surface crystallization, and the crystallization degree of inclusions increases with the increase of heat treatment temperature and time. The activation energy of crystallization and the content of nonbridging oxygen in the silicate structure NBO/T can be used to predict the crystallization ability of inclusions. The greater the activation energy of crystallization and the smaller the NBO/T value, the higher the glassy stability of the inclusions.

Enhanced optical and structural traits of irradiated lead borate glasses via Ce3+ and Dy3+ ions with studying Radiation shielding performance

Lead borate glass is the best radiation shielding glass when lead is in high concentration. However, it has low transparency after radiation exposure. Radiation decreases transparency due to chemical and physical changes in the glass matrix, such as creating or healing defects in the glass network. The addition of rare earth elements like cerium and dysprosium oxides to lead borate glasses can improve their transparency and durability as radiation shielding barriers. The newly manufactured glasses’ optical absorption, structural, and radiation shielding properties were measured. The optical characteristics of the generated samples were examined to determine the effect of the cerium/dysprosium ratio on the structural alterations, specifically in the presence of bridging oxygen (BO) and non-bridging oxygen (NBO). Incorporating Ce3+ results in peaks at 195 nm for borate units, 225 nm for Ce3+, and a broadened peak at 393 nm due to overlapping peaks for Ce3+ and Ce4+ in the UV region. By adding Dy, multiple peaks are observed at 825, 902, 1095, 1275, and 1684 nm, corresponding to the transition from 6H15/2 ground state to 6F5/2, 6F7/2, 6F9/2, 6F11/2, and 6H11/2. The samples were also tested before and after exposure to gamma irradiation from a 60Co source at a dose of 75 kGy to assess their stability against radiation. The energy gap value during irradiation shows decreased non-bridging oxygen. The energy gap difference before and after irradiation for the M4 sample shows higher NBO to BO conversion, reducing radiation damage and improving structural stability. Furthermore, X-ray photoelectron spectroscopy was utilized to get insight into the coordination chemistry of the created glass samples. The half-value layer (HVL), radiation protection efficiency (RPE), neutron removal cross-section (FRNCS), mean free path (MFP), mass attenuation coefficients (MAC), and effective atomic numbers (Zef) of the glassy structure were calculated theoretically to assess its radiation shielding qualities. The linear attenuation coefficient order for the prepared samples was M1 > M2 > M3 > M4. The FRNCS values were 0.090, 0.083, 0.081, and 0.079 cm−1 for samples M1, M2, M3, and M4, respectively.

Fluidity and structure of aluminate slags for smelting high-alumina iron ores: Effect of CaO/SiO2 mass ratio

Slag regulation is crucial for achieving smelting of high-alumina iron ore in blast furnaces. This study investigated the fluidity and structure of CaO-SiO2–10 wt.%MgO-30 wt.%Al2O3 slag by varying the CaO/SiO2 ratio (1.0–2.0). The results revealed that viscosity decreased with increasing CaO/SiO2 ratio, while the free running temperature, defined as the temperature at which the slag can flow freely, initially increased and then decreased, peaking at the range of 1.2–1.6. Interestingly, the free running temperature of slag at basicity 2.0 (1392 °C) was lower than that at basicity 1.0 (1398 °C). Spectroscopic analysis demonstrated that increasing basicity facilitated greater charge compensation of Al3+ ions, resulting in an increased amount of [AlO4] tetrahedra. Moreover, increasing free oxygen promoted the depolymerization of [SiO4] and [AlO4] tetrahedra, reducing bridging oxygen and increasing non-bridging oxygen. Consequently, the slag's overall polymerization degree decreased. Furthermore, MD simulations identified two distinct fracture mechanisms of bridging oxygen within the Si-O-Si structure.

Blue Na2O - CoO - P2O5 glasses: Structural, physico-chemical, thermal and optical characterizations

Two blue phosphate glasses series, (50-x/2)Na2O - xCoO - (50-x/2)P2O5 (0 ≤ x ≤ 35) and (50-x)Na2O - xCoO - 50P2O5 (0 ≤ x ≤ 50) labelled NaCoPO(I) and NaCoPO(II), were synthesized by the melt quenching route and characterized by diverse techniques. Introduction of cobalt oxide CoO in vitreous NaPO3 metaphosphate induces an increase in the glass transition temperature, a decrease in the molar volume and the dissolution rate of the glasses in distilled water, and therefore a strengthening of the glass network. Raman spectra of NaCoPO(I) series, where O/P ratio varies from 3 to 3.54, show that Co2+ ions breakdown the infinite metaphosphate chains and provoke remarkable structural modifications. In contrast, no significant change was observed in the glassy network of NaCoPO(II) series, where O/P ratio is constant and equal to 3. Optical study results show that Co2+ ions have both octahedral and tetrahedral environments with predominance of tetrahedral coordination. The reduction in band gap energy when CoO content rises is due to the increase of non-bridging oxygen number in the vitreous network. The values of CIE L∗a∗b∗ parameters are consistent with the blue color, sought for commercial pigments. The physical parameters deduced from optical spectra suggest that the studied glasses are promising materials for several applications such as pigments and nonlinear optical materials.

Electrical conduction and optical characteristics of Li2O and Bi2O3 Co-doped zinc-phosphate glassy nanocomposites: A critical observation of mixed ionic electronic effect

In the present report, the combined effects of the co-doping of metal oxide (Bi2O3) and Lithium oxide (Li2O) into the glassy matrix with chemical composition xLi2O-(0.45-x)Bi2O3-(0.15ZnO-0.40P2O5) (x = 0.05, 0.15, 025, and 0.35 mol%) are investigated thoroughly. The FESEM and X-ray diffraction data affirm the crystalline nature of the studied glassy composites. The obtained band gap energy values are declined from (3.68–3.17) eV, while the Urbach energy values are declined from (0.38–0.27) eV. Moreover, the mechanism responsible for AC conductivity has been analyzed using Almond–West formalism and Jonscher's universal power law. The observed rise in both AC and DC conductivity in the glass samples is attributed to the mixed ionic electronic effect. In the ionic diffusion model, an increased defect site concentration improves Li+ ion migration through percolation channels. The reduction in both electrostatic binding energy and strain energy lowers the Anderson-Stuart activation energy, facilitating Li+ ion migration and enhancing conductivity. Additionally, in the small polaron hopping model, an increase in the density of defect states suggests more defect sites that facilitate electronic hopping, creating deep localized states and transitions between localized and extended states. Replacing a Bismuth atom with a Lithium atom increases the number of non-bridging oxygen, enhancing the conduction band tail, reducing the energy needed for hopping conductivity, and increasing conductivity.

Improving the impermeability of cement/epoxy coating interface by g-C3N5: A molecular dynamics study

The accumulation of chloride that penetrates through the concrete cover from the ambient environment is the primary factor contributing to the interfacial degradation between concrete and epoxy-coated steel rebar. In this study, a nitrogen-rich carbon nitride (g-C3N5) modified epoxy (EP) coating is proposed to enhance the impermeability of the concrete/epoxy interface. The local structure, dynamic characteristics, and impermeability mechanism of g-C3N5 inserted into the interface of concrete/epoxy coating during the penetration of NaCl solution are studied using the molecular dynamics method. It is found that the insertion of g-C3N5 at the concrete/epoxy interface effectively slows down the penetration of NaCl solution. The g-C3N5 nanosheets block the C-S-H channel, and the water molecules form hydrogen bonds with the nitrogen and oxygen-containing groups in the g-C3N5 grafted with oxygen-containing functional groups (g-C3N5-COOH), significantly inhibiting the movement of water molecules. The oxygen-containing functional groups on g-C3N5-COOH form hydrogen bonds with the non-bridging oxygen on the surface of C-S-H and the oxygen in EP, respectively. This enhances the interaction of the C-S-H/epoxy interface and reduces the degree of interfacial peeling. The impermeability mechanism of the C-S-H/epoxy interface and the capture of corrosive particles can offer molecular insights into the interface design of cement/organic coatings.

Effect of lithium concentration on the network connectivity of nuclear waste glasses

Structure of borosilicate glasses with varying Li2O contents were investigated using Magic Angle Spinning (MAS) Nuclear Magnetic Resonance (NMR), employing 6Li, 11B, 23Na, 27Al and 29Si nuclei. 11B MAS NMR revealed that increasing Li2O contents result in formation of [BO4]− sites at the expense of BO3. 11B{6Li} and 27Al{6Li} dipolar heteronuclear multiple quantum correlation (D-HMQC) NMR revealed Li as a charge compensator for anionic tetrahedral sites with increased Li. 11B{6Li} J-coupling mediated HMQC NMR suggested the possible association of Li with non-bridging oxygens on Q2 and Q3 sites, indicating its dual role in the glass network. 29Si and 23Na MAS NMR spectra showed depolymerisation of the silicate network and shortening of Na-O bond lengths with increased Li. NMR results are supported by Raman spectroscopy and thermal analysis that indicate depolymerisation of the silicate network and a reduction in glass transition temperature at higher Li content.

The effect of Sb2O3 on optical, scintillation and service performance of Ce3+-ion doped gadolinium aluminosilicate glasses

Ce3+-doped gadolinium aluminosilicate glass has great potential as a scintillator in neutron detection and high-energy physics. Ce3+-doped gadolinium aluminosilicate glasses with different concentrations of clarifier Sb2O3 were prepared by high temperature feeding method, combined with crucible interlocking technology. Ce4+ ions were reduced to be Ce3+ ions by CO atmosphere in an interlocking crucible. The properties of glass with 0.7 mol% content of Sb2O3 are the best. The glass has a high density (>6.0 g/cm3) and high refractive index (nd > 1.74). Compared with the sample without clarifier Sb2O3, the light yield of the glass increased to about 2 times. From XPS results, it is concluded that the proportion of bridge and non-bridge oxygen in the glass is 58.83 % and 41.67 % respectively. The composition of bridge oxygen in the glass is high, so there are many silicon-oxygen polyhedrons, and the structure in the glass system is stable, which is beneficial to the light yield. It can be seen from the Ce3d spectrum that there is no third characteristic peak of Ce4+ at ∼916 eV, indicating that the content of Ce3+ is more than that of Ce4+. The presence of Ce3+ in the glass is excellent for scintillation properties.

Effect of Bi2O3 in Bi2O3-SrO-ZnO-B2O3 glass: structural, mechanical, optical, and gamma ray shielding modifications

The effect of Bi2O3 in Bi2O3-SrO-ZnO-B2O3 glasses has been evaluated in this study. The density of the glasses increased from 5.127 g/cm³ to 6.214 g/cm³ as Bi2O3 concentration increased from 35% to 50%. The rise in molar mass and molar volumes points towards the opening of the network. The structural modifications increased the elastic moduli from 30.110 to 30.944 GPa for Young modulus; 17.653 to 17.860 GPa for bulk modulus; 13.242 to 13.662 GPa for shear modulus and 35.309 to 36.077 GPa for longitudinal modulus, respectively. The FTIR spectra indicate the conversion of BO4 to BO3 with increasing Bi2O3 concentration which accounts for the increase of the non-bridgingoxygens (NBOs). The band gap energy decreases from 3.165 to 3.020 eV with increasing Bi2O3 content. The transmission factors (TF) and other relevant parameters were evaluated for four different thicknesses of the glasses (0.5, 1, 1.4 and 2 cm). The 0.5 cm thick glass retained the highest TF when compared to other thicknesses. The TF for 0.5cm thick glass is about 70%, and drops to about 20% for 2 cm thickness, which confirms that at 2 cm thickness, the glass materials shield better than 0.5, 1 and 1.4 cm. Furthermore, the addition of Bi2O3 causes a decrease in TF, so the glass with a high Bi2O3 content shields gamma radiation better than those with a low Bi2O3 content. The half value layer (HVL) values reduce as the Bi2O3 content is increased at all examined energies, confirming that the glass sample with highest Bi2O3 content has the superior shielding capability compared to the remaining examine glasses.

The structural and electronic configuration of an amorphous silica surface, from its liquid to glassy state

Through classical molecular dynamics computational simulations, the surface of amorphous silica (vitreous silica) was generated for a system comprising 64 SiO2 molecules (192 atoms) via the classical three-body glass potential. Starting from the liquid state of silica at 3400 K, it was cooled in three different ways at intervals of 200, 400, and 2000 K, with a cooling rate of 4.4 K/ps and establishing relaxation at intermediate temperatures, yielding three groups of surfaces from 3400 to 1400 K. Subsequently, these systems underwent sudden cooling from 1400 to 300 K via the Andersen and Nosé‒Hoover thermostats, followed by relaxation at 300 K via a microcanonical ensemble (NVE constant). Each surface that underwent relaxation was analyzed through ab initio molecular dynamics for the following three physical properties, which are temperature dependent. The average electric charges of oxygen and silicon. Microstructures on the outermost part of the surface were observed and comprised nonbridging oxygen atoms, undercoordinated silicon, and N-membered rings (3 ≤ N ≤ 5). The radial distribution functions were analyzed for all surfaces. Below 2000 K, a type of freezing is observed in all the structures because of the glass transition. All analyses were performed at zero pressure.

Evaluation of crack initiation load of silica glass surfaces formed during subcritical crack growth

AbstractThe crack initiation load of freshly fractured surfaces for silica glass was evaluated with ball indentation. The fracture surfaces were formed during subcritical crack growth in the regions I, II, and III of the stress intensity factor (KI)—crack velocity (V) curve. From the KI–V curve, we linked the obtained fracture surfaces with the ones in the regions I, II, and III. It was found that the crack‐forming probability was the lowest for the fracture surface formed in the region III of the KI–V curve. In order to understand the controlling factors of the crack formation, some properties which are topography, relative nonbridging oxygens (NBO), hydrogen concentrations, and Si–O three‐ or four‐membered ring structures, of the fracture surfaces were measured by atomic force microscopy, X‐ray photoelectron spectroscopy, dynamic secondary ion mass spectroscopy, and Raman spectroscopy, respectively. No distinct difference in NBO and hydrogen concentrations nor the ring structures were found among the fracture surfaces formed in different regions in the KI–V curve. The peak‐to‐valley height of the fracture surface, however, decreased with increasing crack velocity. It is concluded that the roughness or topography of the freshly fractured surface is one of the controlling factors which reduce the intrinsic strength of silica glass.

The beauty of symmetry: siRNA phosphorodithioate modifications reduce stereocomplexity, ease analysis, and can improve in vivo potency

Phosphorothioates (PS) can be essential in stabilizing therapeutic oligonucleotides against enzymatic degradation. However, unless synthesis is performed with stereo-defined amidites, each PS introduces a chemically undefined stereocenter, resulting in 2n unique molecules in the final product and affecting downstream analytics and purification. Replacing the second non-bridging oxygen with sulfur results in phosphorodithioate (PS2) linkages, thereby removing the stereocenter. We describe synthesis and analytical data for GalNAc-conjugated siRNAs with PS2 in the GalNAc cluster and at the siRNA termini. All siRNA conjugates with PS2 internucleotide linkages were produced with good yield and showed improved analytical properties. PS2 in the GalNAc cluster had no, or only minor, effect on in vitro and in vivo activity. Except for the 5′-antisense position, PS2 modifications were well tolerated at the siRNA termini, and a single PS2 internucleotide linkage gave similar or improved stabilization and in vitro activity as the two PS typically used for end stabilization. Surprisingly, several of the PS2-containing siRNA conjugates resulted in increased in vivo activity and duration of action compared to the same siRNA sequence stabilized with PS linkages, suggesting PS2 linkages as interesting options for siRNA strand design with reduced number of undefined stereocenters.

Exploring the impact of CuCl2 modification on structural variations and dielectric constant in bismuth borate tellurite glasses

Copper chloride doped boro-tellurite-based glass series with compositions 60TeO2-(25-x) Bi2O3–15B2O3-xCuCl2 (x = 0, 5, 10, 15, and 20) were synthesized using the traditional melt-quench procedure. The X-ray diffraction patterns of the examined glasses reveal their amorphous nature. The effect of CuCl2 addition on the glass network/structural units was studied using vibrational (FTIR/Raman) spectroscopy, and CuCl2 inclusion in the glass matrix resulted in a transformation from compact TeO4 to TeO3 structural units This shows that copper chloride acts as a modifier in the examined glass series, resulting in the creation of non-bridging oxygen (NBOs), meaning that the loosening of the glass network is further supported by a decrease in the glass transition temperature as CuCl2 content increases. UV–Vis DRS spectra of examined glasses reveal an absorption band corresponding to the typical transition of Cu2+ ions from 2B1g → 2B2g, situated in deformed octahedral sites in absorption spectra. As Cu+ concentration rises, the indirect optical band gap values drop from 2.94 eV to 1.75 eV. The metallization criterion values lie between 0.383 and 0.300 suggesting that these glasses are potential candidates for nonlinear optical applications. With an increase in Cu+ concentration, the values of molar refractive index (Rm) and molar electronic polarizability αm increases from 22.412 to 26.205 and 8.894 to 10.398 respectively, which correlate with increasing dielectric constant (ε′) values as the Cu+ amount increases. Further dielectric studies reveal non-Debye-type relaxation behaviour.

On the Relationship between Water Adsorption and Surface Chemistry in Soda-lime Silicate Glasses.

Understanding how the surface structure affects the bioactivity and degradation rate of the glass is one of the primary challenges in developing new bioactive materials. Here, classical and reactive molecular dynamics simulations are used to investigate the relationship between local surface chemistry and local adsorption energies of water on three soda-lime silicate glasses. The compositions of the glasses, (SiO2)65-x(CaO)35(Na2O)x with x=5, 10, and 15, were chosen for their bioactive properties. Analysis of the glass surface structure, compared to the bulk structure, showed that the surface is rich in modifiers and non-bridging oxygen atoms, which were correlated with local adsorption energies. The reactivity of the glasses is found to increase with higher Na2O content, attributed to elevated Na cations and undercoordinated species at the glass surfaces. The current work provides insights into the relationship between the surface structure, chemistry, and properties in these bioactive glasses and offers a step toward their rational design.

Reassessment of Electrical and Dielectric Properties in the Borophosphate Glass System: A Promising Solid Electrolyte for High-Temperature Batteries.

This study investigates the conduction mechanism of ternary sodium borophosphate glass 30Na2O-(70 - x)B2O3-xP2O5 with 0 ≤ x ≤ 35 mol % from a different perspective, focusing on previously unreported high-temperature electrical and dielectric properties for potential solid electrolytes in high-temperature batteries. The glass composition with B2O3/P2O5 = 1 exhibits a conductivity of approximately 10-4 S/cm at 250 °C. Dielectric analysis supports this improved conduction, showing higher dielectric values and minimal energy dissipation during storage, indicating promising conductivity and favorable dielectric properties. This enhancement is attributed to the large-polaron (QMT) model, deduced from the power law exponent, due to the creation and spreading of lattice distortion of a long-range order with interconnected B4-O-P1 and B4-O-P2 linkages. Contrary to previous results, the glass transition temperature does not vary coherently with the conductivity and activation energy, displaying a discontinuity at 14 mol %. This discontinuity is caused by the initial extreme depolymerization of P2O5, leading to an increase in nonbridging oxygens (NBOs) within the glass network and forming B4-O-P0 linkages. Despite this, the ionic mobility of Na+ is continuously enhanced, correlated with the increase in the molar volume. This new perspective highlights the significant impact of both free volume expansion and reduced Coulombic effects on conduction improvement.

Compositional impacts of high CdO content on the structure and radiation shielding efficiency of CoO–Na2O–B2O3 glass system

Here, this study investigated the structural changes and radiation shielding efficiency of a borate glass host modified by varying cadmium oxide (CdO) concentrations. The glass composition consisted of boron oxide (B2O3; 80:56 mol%), sodium oxide (Na2O; 19.6 mol%), and cobalt oxide (CoO; 0.4 mol%), with cadmium oxide (CdO; 0:24 mol%). The glass structure was analyzed utilizing mass density and FT-infrared spectroscopy (FTIR) in the 400 to 1600 cm−1 range, while radiation shielding properties were investigated utilizing the online Phy-X software in the 0.284–1.333 MeV energy window. Notably, the addition of CdO significantly impacted the glass density, increasing it by approximately 93 % as the added CdO concentration rose from 0 to 24 mol% (i.e., from 2.507 g/cm3 to 4.849 g/cm3). FTIR analysis revealed a concurrent increase in BO4 structural units with increasing CdO/B2O3 ratios. This observation was supported by the calculated N4BO4/(BO3+BO4) ratio, which increased from 40.73% for the CdO-free sample to 52.00% for the highest CdO content. This increase in BO4 units, denser than BO3 units, explains the observed density increase. Conversely, the concentration of non-bridging oxygens decreased from 10.14% to 4.34% with increasing CdO contents, indicating a more tightly packed glass network. Radiation shielding studies demonstrated that increasing CdO concentration from 0 to 24 mol% enhanced the shielding efficiency, evidenced by a decrease in the half-value layer parameter (HVL). The radiation protection efficacy (RPE) also increased from 0.214 to 0.426 for the CdO-free sample to the sample containing 24 mol% CdO at the investigated energy level. This finding highlights the superior shielding capability of the CdO-rich sample. Furthermore, the transmission factor (TF) was investigated for a constant thickness of 0.75 cm for glasses. The CdO-rich sample exhibited a lower TF compared to the CdO-free sample, particularly at lower energies. This finding confirms that, for a given thickness and energy, raising the cadmium oxide content in the current composition leads to an observed mitigation in the transmitted radiation.

Transformations to the aluminum coordination environment and network polymerization in amorphous aluminosilicates under pressure.

The structure of calcium aluminosilicate glasses (CaO)x(Al2O3)y(SiO2)1-x-y with the near tectosilicate compositions x ≃ 0.19 and 1 - x - y ≃ 0.61 or x ≃ 0.26 and 1 - x - y ≃ 0.49 was investigated by in situ high-pressure neutron diffraction and 27Al nuclear magnetic resonance (NMR) spectroscopy. The results show three distinct pressure regimes for the transformation of the aluminum coordination environment from tetrahedral to octahedral, which map onto the deformations observed in the production of permanently densified materials. The oxygen packing fraction serves as a marker for signaling a change to the coordination number of the network forming motifs. For a wide variety of permanently densified aluminosilicates, the aluminum speciation shares a common dependence on the reduced density ρ' = ρ/ρ0, where ρ is the density and ρ0 is its value for the uncompressed material. The observed increase in the Al-O coordination number with ρ' originates primarily from the formation of six-coordinated aluminum Al(VI) species, the fraction of which increases rapidly beyond a threshold ρthr'∼ 1.1. The findings are combined to produce a self-consistent model for pressure-induced structural change. Provided the glass network is depolymerized, one-coordinated non-bridging oxygen atoms are consumed to produce two-coordinated bridging oxygen atoms, thus increasing the network connectivity in accordance with the results from 17O NMR experiments. Otherwise, three-coordinated oxygen atoms or triclusters appear, and their fraction is quantified by reference to the mean coordination number of the silicon plus aluminum species. The impact of treating Al(VI) as a network modifier is discussed.

Influence of La3+ ions on the structural, elastic, optical, and radiation shielding properties of Cr2O3-Doped heavy metal glasses

This study investigates the effect of La³⁺ rare earth ions on the structural, elastic, optical, and radiation shielding features of heavy metal borate glass (B₂O₃-PbO) doped with Cr₂O₃. Density measurements and FT-IR spectra analysis revealed the role of La3+ ions as a network modifier, where successive additions of La2O3 content led to a gradual increase in the density and an increase in the non-bridging oxygen content resulting from the structural transformation between the BO4 and BO3 units. The significant improvement in the elastic modulus and microhardness factor moduli was confirmed by calculating the change in ultrasonic velocities through the glassy system. The structural modifications induced by La³⁺ ions narrowed the band gap and increased the Urbach energy, indicating higher disorder within the glass network. The linear refractive indices increased due to increased optical basicity and electronic polarization. Optical absorption results showed that Cr⁶⁺/Cr³⁺ ions occupy octahedral/tetrahedral sites, with the tendency for Cr³⁺ cations to occupy more octahedral sites with increasing La₂O₃ content. The produced samples showed a greenish-yellow color caused by the absorption band centered at ∼415 nm associated with the electronic transition ⁴A₂g(F)→2Eg(G). The ligand field effect highlighted the significance of La³⁺ cations in increasing the crystalline field intensity surrounding Cr³⁺ cations and reducing the nephelauxetic ratio, signifying enhanced covalent character between Cr³⁺ cations and neighboring ions. Moreover, the radiation shielding capabilities of the glassy system were analyzed and compared with standard shielding materials, confirming superior shielding performance in samples with the highest La₂O₃ content.