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Luminescence of erbium ions in tellurite glasses

Optical characteristics of new generation of tellurite glasses having high stability against crystallization have been studied. As the initial reagents for the glasses synthesis on the base of tellurium oxide (TeO{sub 2}) there were used such oxides as WO{sub 3}, MoO{sub 3}, La{sub 2}O{sub 3}, Li{sub 2}CO{sub 3}, ZnO—Bi{sub 2}O{sub 2}CO{sub 3} and active components such as high purity Er{sub 2}O{sub 3}, Yb{sub 2}O{sub 3}, ErF{sub 3} and YbF{sub 3}. Intensities of luminescence at 1.53 µm of the erbium ions were determined after excitation at 975 nm. Experimental data obtained have shown the possibility to use the studied glasses doped by Er{sup 3+} and Yb{sup 3+} as active elements for fiber and integrated optics. - Graphical abstract: In contrast to the case of ZBLAN glass the TeO{sub 2}–WO{sub 3} (Er{sup 3+}) glass has bright intensity of luminescence at 1.53 µm for erbium ions that should be caused by excitation at 975 nm. Experimental data obtained have shown the possibility to use the studied glasses doped by Er{sup 3+} and Yb{sup 3+} as active elements for fiber and integrated optics. Display Omitted - Highlights: • We examined changes in growth of luminescence in doubly-doped tellurite glasses. • We found that luminescence grows in two orders by using Er{sup 3+} and Yb{sup 3+} at 1.53 μm. • We see possibility to use those glasses as active elements for integrated optics.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Structural features of silver-doped phosphate glasses in zone of femtosecond laser-induced modification

Femtosecond (fs) laser writing of two-dimensional microstructures (waveguides) is demonstrated in bulk phosphate glasses doped with silver ions. Silver-content phosphate and silver-content niobium–phosphate glasses with high concentration of silver oxide 55 mol% were used as samples for fs laser writing. The chemical network structure of the synthesized samples is analyzed through Raman spectroscopy and was found to be strongly sensitive to Nb incorporation. It was found that the direct laser writing process enables not only reorganization of glass network, but also formation of color centers and silver nanoparticles that are revealed in appearance of luminescence signal and plasmon absorption. The process of NPs' formation is more efficient for Nb-phosphate glass, while color centers are preferably formed in phosphate glass. - Graphical abstract: Formation of silver NPs on the surface of 0.5Ag{sub 2}O–0.4P{sub 2}O{sub 5}–0,1Nb{sub 2}O{sub 5} glass induced by CW laser irradiation. - Highlights: • The structure of 0.5Ag{sub 2}O–0.1Nb{sub 2}O{sub 5}–0.4P{sub 2}O{sub 5} and 0.55Ag{sub 2}O–0.45P{sub 2}O{sub 5} glasses was investigated by Raman spectroscopy. • Fs laser writing induces formation of silver NPs in investigated glasses. • Surface plasmon resonance in the absorption spectra confirms the formation of NP. • The possibility of CW laser induced formation of silver NPs on the surface of sample with niobium is shown.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Physical and absorption properties of titanium nanoparticles incorporated into zinc magnesium phosphate glass

We report the influences of Titania (TiO{sub 2}) nanoparticles (NPs) on the physical and optical properties of melt quench synthesized zinc magnesium phosphate glasses. Five glass samples with composition (42 − x)P{sub 2}O{sub 5}–50ZnO–8MgO–xTiO{sub 2}, where x = 0, 1, 2, 3, 4 mol% are prepared and characterized. XRD pattern verified the amorphous nature of all samples. TEM images manifested the growth of Ti NPs of average size ≈ 5.78 nm. TiO{sub 2} NP concentration dependent variation in the physical properties including glass density, molar volume, molar refractivity, electronic polarizability and ionic packing density are determined. The values of glass refractive indices, density and ionic packing density are increased with the increase of TiO{sub 2} NP contents. Conversely, the Urbach energy, direct and indirect optical band gap are found to decrease with the increase of TiO{sub 2} NP concentration. These glass compositions may be potential for various solid state devices including laser. - Highlights: • TiO{sub 2} NP embedded self-cleaning phosphate glass are synthesized for the first time. • Well dispersed and uniform sized TiO{sub 2} NPs are grown. • Absorption spectra revealed prominent peak in the UV region. • TiO{sub 2} NPs strongly influenced the physical and absorption features of synthesized glasses. • The effects of TiO{sub 2} NPs on the physical and optical properties of these glasses are determined.

36 MATERIALS SCIENCE↗

Influence of Sm2O3 addition on Judd-Ofelt parameters, thermal and optical properties of the TeO2-Li2O-ZnO-Nb2O5 glass system

Highlights: • Synthesis of Sm{sub 2}O{sub 3} doped TeO{sub 2}-Li{sub 2}O-ZnO-Nb{sub 2}O{sub 5} glass to be used in optical devices. • Area under the peak calculations of FTIR and Raman display higher presence of BOs. • DSC plots indicate high stability and high rigidity of prepared glass samples. • Judd-Ofelt analysis shows the ionic nature of Sm{sup 3+} ions with neighboring atoms. • Higher branching ratio values obtained from {sup 6}H{sub 5/2} → {sup 6}F{sub 5/2} emission transition. - Abstract: A series of transparent and light yellow color samples composed of Sm{sub 2}O{sub 3} doped tellurium oxide glasses with chemical composition 75TeO{sub 2}-5Li{sub 2}O-10ZnO-(10-X) Nb{sub 2}O{sub 5}-XSm{sub 2}O{sub 3} was prepared by conventional melt-quenching technique. Rare earth (Sm{sub 2}O{sub 3}) was added to improve all glass properties. From obtained radiative properties, the samples which prepared with above composition can be considered as a prospect application for laser design due to higher branching ratio. The physical properties including sample density, molar volume, and OPD were measured. The glassy nature is approved by XRD analysis. The structural modification of glass forming units with introducing Sm{sub 2}O{sub 3} was studied by FTIR and Raman spectra. The intensity ratio of TeO{sub 4}/TeO{sub 3} was measured to determine the ratio of bridging/non-bridging oxygen exists in glass network. Glass thermal stability, glass transition temperature, and melting temperature were obtained from DSC plots. The UV–vis-NIR absorption spectra display 9 peaks. Optical parameters including optical band gap E{sub Opt}, Urbach energy ΔE and refractive index n were determined. From absorption spectra, Judd-Ofelt intensity parameters (Ω{sub λ} and λ = 2, 4, 6) have been derived to study bonding nature. A spectroscopic quality factor was calculated. Branching ratio (β{sub r}) and lifetime (τ) have been calculated using JO parameters. Absorption and emission cross-sections were determined to measure the probability of an absorption or emission process. Finally, we propose that these prepared samples can be used in optical devices and other applications.

36 MATERIALS SCIENCE↗

ESR, optical absorption, IR and Raman studies of xTeO{sub 2} + (70 - x)B{sub 2}O{sub 3} + 5TiO{sub 2} + 24R{sub 2}O:1CuO (x = 10, 35 and 60 mol%; R = Li, Na and K) quaternary glass system

Highlights: Black-Right-Pointing-Pointer Peak of Cu{sup 2+} is found to be maximum at around 794 nm for lithium boro tellurite glasses. Black-Right-Pointing-Pointer Variation in g{sub ||} and A{sub ||} values is due to change in environment of Cu{sup 2+} ion due to the structural change in the glass. Black-Right-Pointing-Pointer BO{sub 3}-BO{sub 4}{sup -} ring structure is interconnected by TeO{sub 3}{sup -} and TeO{sub 4}{sup -} groups, where the BO{sub 4}{sup -} groups are neighbors of TeO{sub 3}{sup -}groups. Black-Right-Pointing-Pointer The structure comprising, isolate a BO{sub 3}{sup -}, B{sub 2}O{sub 5}, BO{sub 4}{sup -}, and metaborates, which enables glass forming for Borate rich glasses. Black-Right-Pointing-Pointer Distorted TeO{sub 4/2} network with BO{sub 3}{sup -}-BO{sub 4}{sup -} ring structure and TeO{sub 3}{sup -} group is enables glass forming for tellurite rich glasses. -- Abstract: xTeO{sub 2} + (70 - x)B{sub 2}O{sub 3} + 5TiO{sub 2} + 24R{sub 2}O:1CuO (x = 10, 35 and 60; R = Li, Na and K) glass system were studied by spectroscopic techniques such as ESR, optical absorption, Raman and IR. From ESR spectra, the spin Hamiltonian parameter values indicate that the ground state of Cu{sup 2+} is d{sub x{sup 2}-y{sup 2}} and the site symmetry around the Cu{sup 2+} ion is tetragonally distorted octahedral coordination. Bonding parameters calculated from optical absorption and ESR data are found to change with alkali oxide and TeO{sub 2} content. Bonding parameters indicate a slight covalency for the in-plane {sigma} bonding as compared to in-plane and out-of-plane {pi} bonds. Both Raman and IR results show that glass network consists of TeO{sub 3}, TeO{sub 4}, BO{sub 3}, BO{sub 4} and RiO{sub 4} group as basic structural groups. BO{sub 3}-BO{sub 4}{sup -} ring structure interconnected by TeO{sub 3}{sup -} and TeO{sub 4}{sup -} groups, where the BO{sub 4}{sup -} groups are neighbors of the TeO{sub 3}{sup -} groups. BO{sub 3} {yields} BO{sub 4} transition is also observed, which correlates with the transition of TeO{sub 4} {yields} TeO{sub 3} via TeO{sub 3+1}.

36 MATERIALS SCIENCE↗

Photocatalytic activity of glass ceramics containing Nasicon-type crystals

Graphical abstract: Display Omitted Highlights: ► Glass ceramics containing Nasicon-type crystals were prepared. ► The glass ceramics showed photocatalytic activity under UV irradiation. ► Higher activity was observed in the MgTi{sub 4}(PO{sub 4}){sub 6}- and CaTi{sub 4}(PO{sub 4}){sub 6}-containing glass ceramics. -- Abstract: Glass ceramics were prepared by heat-treating MO–TiO{sub 2}–P{sub 2}O{sub 5} (M = Mg, Ca, Sr and Ba) and R{sub 2}O–TiO{sub 2}–P{sub 2}O{sub 5}–SiO{sub 2} (R = Li, Na and K) glasses, and their photocatalytic activity was investigated. The crystalline phases precipitated in the glasses were only Nasicon-type crystals, MTi{sub 4}(PO{sub 4}){sub 6} or RTi{sub 2}(PO{sub 4}){sub 3}. Decomposition experiments of both methylene blue (MB) and acetaldehyde showed that the glass ceramics exhibited effective photocatalytic activity. The activity did not depend on the radius of the M{sup 2+} or R{sup +} ion, and higher activity was observed in the MgTi{sub 4}(PO{sub 4}){sub 6} and CaTi{sub 4}(PO{sub 4}){sub 6} precipitated glass ceramics.

36 MATERIALS SCIENCE↗

Influence of Ga{sup 3+} ions on spectroscopic and dielectric features of multi component lithium lead boro bismuth silicate glasses doped with manganese ions

Graphical abstract: The plots between ε″(ω)ω vs. ε′(ω) and ε″(ω)/ω vs. ε′(ω) yield straight lines with slope 1/τ and τ, respectively. Considerable deviation from the straight line is observed in the high frequency region. Such deviation suggests spreading of relaxation times and this is attributed to the presence of multiple type of dipoles in the glass matrix. Variation of the parameters ωε″(ω) and ε″(ω)/ω with ε′(ω) of glass Li{sub 2}O–PbO–B{sub 2}O{sub 3}–SiO{sub 2}–Bi{sub 2}O{sub 3}–MnO multi-component glasses mixed with 2.0 mol% of Ga{sub 2}O{sub 3} measured at 373 K. - Highlights: • A series of Li{sub 2}O–PbO–B{sub 2}O{sub 3}–SiO{sub 2}–Bi{sub 2}O{sub 3}–MnO:Ga{sub 2}O{sub 3} glasses have been synthesized. • A variety of spectroscopic and dielectric properties have been investigated. • Analysis of the results indicated that glasses with below 3.0 mol% Ga{sub 2}O{sub 3} are good conducting materials. - Abstract: Multi-component glasses of the chemical composition 19.5Li{sub 2}O–20PbO–20B{sub 2}O{sub 3}–30SiO–(10 − x)Bi{sub 2}O{sub 3}–0.5MnO:xGa{sub 2}O{sub 3} with 0 ≤ x ≤ 5.0 have been synthesized. Spectroscopic (optical absorption, IR, Raman and ESR) and dielectric properties were investigated. Optical absorption and ESR spectral studies have indicated that managanese ions do exist in Mn{sup 3+} state in addition to Mn{sup 2+} state in the samples containing low concentration of Ga{sub 2}O{sub 3}. The IR and Raman studies indicated increasing degree of disorder in the glass network with the concentration of Ga{sub 2}O{sub 3} up to 3.0 mol%. The dielectric constant, loss and ac conductivity are observed to increase with the concentration of Ga{sub 2}O{sub 3} up to 3.0 mol%. The quantitative analysis of the results of dielectric properties has indicated an increase in the insulating strength of the glasses as the concentration of Ga{sub 2}O{sub 3} is raised beyond 3.0 mol%. This has been attributed to adaption of gallium ions from octahedral to tetrahedral coordination.

36 MATERIALS SCIENCE↗

Sol–gel synthesis of silver nanocrystals embedded in sodium borosilicate monolithic transparent glass with giant third-order optical nonlinearities

Highlights: • We prepared Ag-doped sodium borosilicate monolithic glass. • The influence of temperature on the SPR absorption peak intensity was studied. • Nonlinear optical properties of the glass were investigated. • A mechanism for the formation of Ag quantum dots glass was proposed. - Abstract: We report the preparation of uniform spherical shape silver nanocrystals doped sodium borosilicate monolithic transparent glass by sol–gel method. The characterization of the resulting Ag nanocrystals was accomplished by using X-ray powder diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, and energy dispersive X-ray spectrum. Surface plasma resonance absorption peaks of the silver nanocrystals glass at about 406 nm have been obtained from ultraviolet–visible absorption spectrometer and their intensity is changed with different heat treatment temperatures. We have investigated the nonlinear optical properties of silver quantum dots doped glass using Z-scan technique. Third-order nonlinear optical susceptibility χ{sup (3)} of the glass was estimated to be 1.01 × 10{sup −11} esu. In particular, a mechanism for the formation of Ag quantum dots glass is proposed. This work will significantly promote the obtained material applications in optical devices.

36 MATERIALS SCIENCE↗

Erbium-doped borosilicate glasses containing various amounts of P{sub 2}O{sub 5} and Al{sub 2}O{sub 3}: Influence of the silica content on the structure and thermal, physical, optical and luminescence properties

Highlights: • Er{sup 3+} doped borosilicate glasses were processed with different compositions and characterizations. • An increase in the SiO{sub 2} content leads to a silicate-rich environment around the Er{sup 3+} site. • An increase in the SiO{sub 2} content decreases the Er{sup 3+} absorption cross-section at 980 nm. • Glasses with 60 mol% of SiO{sub 2} exhibit a stronger emission intensity at 1530 nm than glasses with x = 50. • Highest 1.5 μm emission intensity was achieved for the Al and P containing glass with 60 mol% of SiO{sub 2}. - Abstract: The influence of the silica content on several properties of Er-doped borosilicate glasses in the presence of various amounts of P{sub 2}O{sub 5} and Al{sub 2}O{sub 3} has been investigated. The introduction of P{sub 2}O{sub 5} and/or Al{sub 2}O{sub 3} are responsible for structural modifications in the glass network through a charge-compensation mechanism related to the formation of negatively-charged PO{sub 4} and AlO{sub 4} groups or through the formation of AlPO{sub 4}-like structural units. In this paper, we show that an increase in the SiO{sub 2} content leads to a silicate-rich environment around the Er{sup 3+} site, resulting in an increased dependence of the Er{sup 3+} ions optical and luminescence properties on the P{sub 2}O{sub 5} and/or Al{sub 2}O{sub 3} concentration. The highest emission intensity at 1.5 μm was achieved for the glass with an equal proportion of P and Al in the glass system with 60 mol% of SiO{sub 2}.

36 MATERIALS SCIENCE↗

Optical properties of bimetallic Au-Cu nanocrystals embedded in glass

Highlights: • Bimetallic Au-Cu/Au-Cu sosoloid nanocrystals embedded in glass have been synthesized. • We achieved good size control of the nanocrystals. • The glasses with bimetallic nanoparticles exhibit enhanced for NLO. • The mechanisms on the nonlinear effects of the obtained glasses are discussed. - Abstract: Bimetallic gold-copper and gold-copper solid solutions nanocrystals (NCs) with orthorhombic morphologies were successfully embedded in sodium borosilicate glass; these materials were fabricated via a facile and synthetic sol-gel technique. Microstructural investigations demonstrate that the Au-Cu intermetallic nanostructure is generated in the glass host. Z-scan technique was applied to reveal the third-order nonlinear optical properties of the as-obtained glasses at the wavelength of 800 nm. The as-synthesized glasses exhibit similar nonlinear behaviors with reverse saturation absorption effects and self-focusing performances. The third-order nonlinear susceptibility χ{sup (3)} values were optimized by tuning the sizes of the Au-Cu NCs. The χ{sup (3)} of Au-Cu(1), Au-Cu(2) and Au-Cu(3) measured to be 3.1 × 10{sup −12}, 5.4 × 10{sup −12}, and 4.4 × 10{sup −12} esu for the single-pulse energy of 1 μJ. We have discussed the nonlinear optical mechanism of Au-Cu sodium borosilicate glass that may be due to the quantum confinement effects and surface plasmon resonance effects.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

Spectroscopic studies of Dy3+ doped borate glasses for cool white light generation

Highlights: • BAZN glasses with Dy{sup 3+} ions were prepared using melt quench technique. • Under n-UV excitation the BAZN glasses show white light emission. • Energy transfer through cross-relaxation leads to concentration quenching. • Calculated CIE coordinates are close to the commercial w-LED. • 0.5 mol% of Dy{sup 3+} in these glasses are apt for cool white light generation. - Abstract: The Dy{sup 3+} ions doped Na{sub 2}O-ZnO-Al{sub 2}O{sub 3}-B{sub 2}O{sub 3} (BAZN) glasses with variable doping concentrations were synthesized by melt-quenching technique. The XRD pattern reveals amorphous nature of the as-synthesized glass. The FT-IR spectrum reveals various stretching and bending vibration of aluminates, borate and some other groups. The emission spectra exhibit two intense bands at around 482 nm (blue) and 575 nm (yellow) corresponding to the {sup 4}F{sub 9/2} → {sup 6}H{sub 15/2} and F{sub 9/2} → {sup 6}H{sub 13/2} transitions respectively. The CIE chromaticity coordinates of the as-synthesized glasses are lying in white region and in proximity to the coordinates for white light specified by National Television Standard Committee and commercial phosphor converted white light emitting devices. The decay profile of BAZN glasses showed bi-exponential behavior due to the energy transfer mechanism from excited donor ion to unexcited acceptor ion. The above-mentioned studies show potential of the as-synthesized Dy{sup 3+} doped BAZN glasses in solid state lighting applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

Preservation of higher Fe[II] content in borosilicate glass by microwave irradiation in air

Highlights: • Higher Fe[II] absorption within 1000–1200 nm in UV-vis-NIR spectra in microwave (MW) melted glass. • Spectrophotometric methods confirm higher Fe-redox ratio in MW melted glass. • Thermogravimetric analysis (TGA) recorded more weight gain signifying higher stabilisation of Fe[II] in MW melted glass. • Fe 2p{sub 3/2} peak in XPS demonstrates presence of higher FeO concentration in MW glass. • Slow conversation of Fe[II] to Fe[III] in MW heating influencing retention of higher Fe[II]. - Abstract: Existence of high Fe[II] content in glass is a perquisite for achieving high heat absorption property in glass. Present study investigates the capability of microwave (MW) irradiation in retention of higher Fe[II] in glass eliminating the stringent reducing atmosphere requirements in conventional heating. Stabilisation of higher Fe[II] in glass under influence of MW irradiation has been demonstrated, measuring absorbance at >1000 nm in UV–vis-NIR spectra, maintaining identical conditions in MW and in conventional heating. Spectrophotometric methods developing color complex of Fe{sup 2+} with ferrozine and 1, 10 ortho-phenanthroline are used to confirm higher content of Fe[II]. Further, more weight gain in thermo gravimetric analysis, higher isomer shift (>0.89 mm/s) with more relative absorption (% area) for Fe[II] in Mössbauer spectroscopy, and shifting of Fe 2p{sub 3/2} peak in X-ray photoelectron spectroscopy towards lower binding energy further confirm retention of higher FeO under MW irradiation.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

Nanoscale microstructure and chemistry of transparent gahnite glass-ceramics revealed by atom probe tomography

The nanoscale microstructure and chemistry of a transparent gahnite glass-ceramic and its precursor glass were investigated using atom probe tomography, transmission electron microscopy, and nuclear magnetic resonance spectroscopy. In the annealed precursor glass, statistically significant ZrO clustering was observed along with Si depletion within 2 nm of the ZrO clusters. This clustering is expected to be the first step in the nucleation and crystallization of the nucleating agent, ZrO 2 . In the glass-ceramic, gahnite (ZnAl 2 O 4 ) crystallites were found to exist in proximal locations to ZrO 2 and not in a core-shell arrangement. The residual glass composition was directly measured by atom probe, showing higher concentrations of Al, Zn, and Zr than previously expected. At the interfaces between the crystallites and residual glass, no enrichment or depletion zones were found. Our findings provide answers to outstanding questions surrounding the nucleation and elemental partitioning, microstructure, and the residual glass composition of transparent gahnite glass-ceramics.

36 MATERIALS SCIENCE↗

Surface Equilibration Mechanism Controls the Stability of a Model Codeposited Glass Mixture of Organic Semiconductors

While previous work has identified the conditions for preparing ultrastable single-component organic glasses by physical vapor deposition (PVD), little is known about the stability of codeposited mixtures. Here, we prepared binary PVD glasses of organic semiconductors, TPD (N,N'-Bis(3-methylphenyl)-N,N'-diphenylbenzidine) and m-MTDATA (4,4',4"-Tris[phenyl(m-tolyl)amino]triphenylamine), with a 50:50 mass concentration over a wide range of substrate temperatures (T sub ). The enthalpy and kinetic stability are evaluated with differential scanning calorimetry and spectroscopic ellipsometry. Binary organic semiconductor glasses with exceptional thermodynamic and kinetic stability comparable to the most stable single-component organic glasses are obtained when deposited at T sub = 0.78–0.90T g (where T g is the conventional glass transition temperature). When deposited at 0.94T g , the enthalpy of the m-MTDATA/TPD glass equals that expected for the equilibrium liquid at that temperature. Thus, the surface equilibration mechanism previously advanced for single-component PVD glasses is also applicable for these codeposited glasses. Furthermore, these results provide an avenue for designing high-performance organic electronic devices.

36 MATERIALS SCIENCE↗

Modeling Wavelength Dependent Mid-infrared (5.5–25 μm) Optical Constants of Silicate Glasses: A Genetic Algorithm Approach

Wavelength-dependent mid-infrared (400–1,800 cm -1 ; 5.56–25 μm) optical constants (real and imaginary indices of refraction; n and k) are determined using reflectance spectra at a spectral sampling of 4 cm -1 for several silicate glasses of varying SiO 2 wt% which include (a) basaltic volcanic glass from Kilauea, Hawaii, (b) synthetic andesite, (c) two synthetic dacites, (d) obsidian volcanic glass from Mount Lassen, California, (e) synthetic rhyodacite, and (f) rhyolitic volcanic glass from Mexico. Because glasses are optically isotropic, no specific orientation was required for spectral measurements, and polished glass samples were measured at random orientations using micro-FTIR spectrometer. Lorentz-Lorenz dispersion theory and Fresnel reflectance model for high symmetry materials were used to model the optical constants by optimizing oscillator parameters in modeled spectra to match laboratory spectra. A genetic algorithm (GA) approach automatically finds the natural oscillators and their parameters for each spectrum, and then uses these parameters in a non-linear least squares optimization routine. The study compared spectral parameters such as Christiansen feature, reststrahlen bands (RBs), and the peaks centered around 860–1,100 (peak 1) and 400–480 cm -1 (peak 2) of n and k to their respective SiO 2 wt% of the glasses. CF, RBs, peak 1 of n and k, and peak 2 of n shift to higher wavenumbers with increased SiO 2 wt%, whereas peak 2 of k shifts to lower wavenumbers with increased SiO 2 wt%. Derived optical constants of these glasses will improve quantitative abundance mapping of volcanic materials on the surfaces of silicate targets in the Solar System.

58 GEOSCIENCES↗

Insights into the mechanisms controlling the residual corrosion rate of borosilicate glasses

Borosilicate glasses are widely used to confine high-level radioactive wastes. The lifetime of these materials could reach hundreds of thousands of years if leaching of the glass into groundwater enables the formation of a passivating gel layer. Even in this regime, the glass will never stop corroding as thermodynamic equilibrium between glass and solution cannot be achieved. Therefore, accurate predictions of glass durability including passivation, require a deep understanding of the mechanisms controlling the so-called residual rate. However, despite tremendous efforts, these mechanisms remain poorly understood. Here, focusing on the behavior of the soluble elements of the International Simple Glass (B, Na, and Ca), we show that the residual rate is controlled by the behavior of B, a glass former supposed to dissolve instantaneously when in contact with water and thus widely considered as an ideal tracer. We then demonstrate that B release is controlled by multiple processes highly dependent on the pH. At the beginning of the passivating layer formation, the hydrolysis of B-O-Si linkages is rate-limiting and has an activation energy of ~60 kJ mol –1 , a value slightly lower than that for breaking Si-O-Si linkages. Once the fraction of closed pores resulting from gel restructuring is high enough, then diffusion of both reactants (water molecules) and some products (mainly B aq , Ca aq ) through the growing gel layer becomes rate-limiting. Consequently, B and Ca accumulate in an inner layer referred to as the active zone, with potential feedback on the B-O-Si hydrolysis. A new paradigm, including B as a key element of the system, is proposed to develop a comprehensive model for the corrosion of borosilicate glass.

36 MATERIALS SCIENCE↗

The corrosion behavior of borosilicate glass in the presence of cementitious waste forms

Borosilicate glasses are widely used for radioactive waste disposal due to their ability to incorporate a variety of contaminants and radionuclides while exhibiting high durability in various disposal scenarios. This research evaluated the dissolution of borosilicate glass using both single-pass-flow-through (ASTM C1662-18) and product consistency test (ASTM C1285-21) methods with different solutions, including a cementitious-contacted water (called grout-contacted, GC, from this point) and solutions with varying levels of dissolved cementitious species such as Si, Ca, Al. Here, the results indicated that the presence of Ca plays a crucial role in suppressing glass corrosion, as evidenced by the slower normalized dissolution rates, which were one order of magnitude lower for boron and two orders of magnitude lower for rhenium, observed in both Ca-amended and GC solutions compared to the pH 12 buffer solution. This effect is attributed to the formation of a dense, low-porosity, and strongly bonded calcium silicate hydrate (CSH) layer on the glass surface, which implies that a glass corrosion process is influenced by ion exchange involving alkali ions Na + , K + , Ca 2+ , and hydrogen-containing species. A small number of glass particles treated in the GC solution showed minor corrosion pits in the form of shallow craters with an average diameter of approximately 500 μm. This observation is correlated with a significant reduction, 2000 to 3000 times lower, in the cumulative volume of glass pores, indicating that smaller pore voids were “sealed” in the presence of Ca 2+ ions, likely attributed to the formation of CSH precipitation or other corrosion products such as calcium carbonate saturated from the grout solution. These findings suggest that the presence of dissolved Ca in the GC solution can slow down the dissolution of borosilicate glass, contrary to the expected trend of higher dissolution rates resulting from exposure to high alkaline and thus higher pH solutions.

36 MATERIALS SCIENCE↗

Deformation mechanisms during nanoindentation of sodium borosilicate glasses of nuclear interest

In this paper we analyze results of Molecular Dynamics simulations of Vickers nanoindentation, performed for sodium borosilicate glasses of interest in the nuclear industry. Three glasses have been studied in their pristine form, as well as a disordered one that is analogous to the real irradiated glass. We focused in the behavior of the glass during the nanoindentation in order to reveal the mechanisms of deformation and how they are affected by microstructural characteristics. Results have shown a strong dependence on the SiO{sub 2} content of the glass, which promotes densification due to the open structure of SiO{sub 4} tetrahedra and also due to the strength of Si-O bonds. Densification for the glasses is primarily expressed by the relative decrease of the Si-O-Si and Si-O-B angles, indicating rotation of the structural units and decrease of free volume. The increase of alkali content on the other hand results to higher plasticity of the matrix and increased shear flow. The most important effect on the deformation mechanism of the disordered glasses is that of the highly depolymerized network that will also induce shear flow and, in combination with the increased free volume, will result in the decreased hardness of these glasses, as has been previously observed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗