Increase in the refractive index of alkali titanium-hafnium silicate glass upon Na+ (glass)-Li+ (melt) ion exchange

An increase in the refractive index upon ion exchange in the Li₂SO₄ + Li₂MoO₄ salt melt has been studied for glasses of composition (mol %)xLi₂O-(25 -x)Na₂O-15TiO₂-6HfO₂-54SiO₂, wherex = 0, 5, 10, 15, 20, and 25. The ordinary transparent single-layer and two-layer diffusion zones are obtained. In the latter zone, the optically opaque near-surface layer gives way to a deeper optically transparent layer with the refractive index gradient. The opaque layer produced by the low-temperature exchange exhibits a unique structure, which is permeable to melt. An increase in the refractive index as large as 0.055 is achieved for the first time without fracture and crystallization of glass.     

Effect of Li<Subscript>2</Subscript>O on the Refractive Index and Optical Band Gap of Cadmium Phosphate Glasses

A series of lithium cadmium phosphate glasses having composition (mol %) xLi₂O-(50 ? x)CdO-50P₂O₅ were prepared in a platinum crucible by the melt quenching technique. The quantity x varies in the range 0–40. The mass density and refractive index of these glasses were found in the ranges 3.95–2.89 g/cm₃ and 1.55–1.40, respectively. The optical absorbance studies were also carried out on these glasses to measure their energy gaps. The absorption spectra of these glasses were recorded in the UV-visible range. No sharp edges were found in the optical spectra, which verifies the amorphous nature of these glasses. The optical band gap energies for these glasses were found to be in the range 2.58–3.5 eV. It was observed that the density, the refractive index, and the optical band gap energy decrease with increasing amount of lithium oxide. The band tailing, worked out from the Urbach plots, shows an increase with increasing Li₂O content and lies in the range 0.47–0.78 eV. The absorption coefficient is observed to show an exponential dependence on the photon energy.     

Enhanced up-conversion luminescence of Tb3+-Yb3+ doped glass ceramics by doping Li+

Tb³⁺-Yb³⁺ co-doped transparent glass ceramics (GCs) containing Y₂Ti₂O₇ crystal phases were synthesized by the melt crystallization. The light transmittance of GCs in the visible region reached 78%, and the average grain size was 278 nm under the optimal heat treatment conditions (720 °C/2 h). The GCs exhibited greater up-conversion luminescence intensity than precursor glass, and the reason for this result was explained in accordance with the Judd-Ofelt theory. Moreover, the introduction of Li⁺ did not change the crystalline phase of GCs. The emission intensity of the green light of the 8% Li ⁺ doped GCs was significantly enhanced by nearly 4.48 times under 980 nm excitation. The XRD refinement results suggest that the enhanced luminescence intensity is correlated with the change of the Y₂Ti₂O₇ crystal lattice caused by Li⁺ doping. The relevant luminescence mechanism was elucidated. The results suggest that Li⁺ doped transparent GCs open novel avenues for green UC applications.     

Microstructure and electrochemical properties of LBO-coated Li-excess Li1+xMn2O4 cathode material at elevated temperature for Li-ion battery

An amorphous glass film, Li₂O-2B₂O₃ (LBO) glass, was coated on the surface of the cathode material by solution method. The Li-excess cathode powder Li_1+xMn₂O₄ derived from co-precipitation method was calcined with various weight percentage of the surface modified lithium boron glass. Fine powders with distinct particle size, size distribution and morphology were fabricated. The electron probe microanalyzer (EPMA) was employed to evaluate the composition of LBO-coated Li_1+xMn₂O₄. The morphology was observed with a field emission scanning electron microscope (FE-SEM), and the particle size in the range of several microns measured by laser scattering. The electrochemical behavior of the cathode powder was examined by using two-electrode test cells consisted of a cathode, metallic lithium as anode, and an electrolyte of 1 M lithium hexafluorophosphate (LiPF₆). Cyclic charge/discharge testing of the coin cells, fabricated by both LBO-coated and base Li_1+xMn₂O₄ material were conducted. The LBO-coated cathode powder with the fading rate of only 7% after 25 cycles showed better cycleability than the base one with the fading rate of 17% after 25 cycles, particularly at higher temperature. It is demonstrated that the employment of LBO glass coated Li_1+xMn₂O₄ cathode material exhibited higher discharge capacity and significantly reduced the fading rate after cyclic test.     

An Increase in the Refractive Index of a Multicomponent Silicate Glass by Six-Hundredths upon the Na+glass–Li+meltIon Exchange

An increase in the refractive index of the glass surface by n= 0.06 after the Na⁺ _glass–Li⁺ _meltion exchange is obtained for the first time.     

Y3NbO7 transparent ceramic series for high refractive index optical lenses

A₂B₂O₇ and A₃BO₇ transparent ceramic families are potential materials for optical lenses because of their high refractive index. Although nonstoichiometry is widely present in these material families, its effect on refractive index and optical properties has not yet been fully studied. In this study, optical properties are reported for the Y₃NbO₇ transparent ceramic series, Y_1−xNb_xO_1.5+x (x = 0.20, 0.22, 0.24, 0.25, 0.26), which were fabricated by a pressureless pre-sintering and a hot isostatic pressing post-sintering treatment. The refractive index increases from 2.04 to 2.10 (at 587.6 nm) as the Nb content x increases, which is mainly attributed to the variation in the oxygen ion/vacancy ratio. The Abbe number is larger than 40, showing a decreasing trend as the Nb content x increases. The specimen with x = 0.24 has the highest inline transmittance, which were 62% and 76% at 587.6 and 2000 nm, respectively, for a 1-mm-thick specimen. Through the approach of nonstoichiometry, Y_1−xNb_xO_1.5+x series exhibit balanced properties of refractive index, Abbe number, and transmittance, which can be considered as a promising candidate for high refractive index optical lenses.     

Phase separation and crystallization in glasses of the lithium silicate system xLi2O · (100 ? x)SiO2 (x = 23.4, 26.0, 33.5)

The phase separation in ultimately homogenized glasses of the lithium silicate system xLi₂O · (100 − x)SiO₂ (where x = 23.4, 26.0, and 33.5 mol % Li₂O) has been investigated. The glasses of these compositions have been homogenized using the previously established special temperature-time conditions, which provide the maximum dehydration and the removal of bubbles from the glass melt. The parameters of nucleation and growth of phase_separated inhomogeneities and homogeneous crystal nucleation have been determined. The absolute values of the stationary nucleation rates I _st of lithium disilicate crystals in the 23.4Li₂O · 76.6SiO₂ and 26Li₂O · 74SiO₂ glasses with the compositions lying in the metastable phase separation region have been compared with the corresponding rates I _st for the glass of the stoichiometric lithium disilicate composition. It has been established that the crystal growth rate have a tendency toward a monotonic increase with an increase in the temperature, whereas the dependences of the crystal growth rate on the time of low-temperature heat treatment exhibit an oscillatory behavior with a monotonic decrease in the absolute value of oscillations. The character of crystallization in glasses with the compositions lying in the phase separation region of the Li₂O-SiO₂ system is compared with that in the glass of the stoichiometric lithium disilicate composition. The inference has been made that the phase separation weakly affects the nucleation parameters of lithium disilicate and has a strong effect on the crystal growth.     

Impact of TeO2–B2O3 manipulation on physical,structural, optical and radiation shielding properties of Ho/Yb codoped mixed glass former borotellurite glass

In this work, (75-x)B₂O₃-xTeO₂-11Bi₂O₃–10Li₂O-1Ho₂O₃-3Yb₂O₃ (x = 10–60 mol%) mixed glass former (MGF) glasses were prepared by using the melt-quenching method to investigate the effect of mixed glass former between B₂O₃ and TeO₂ on the structural, optical and radiation shielding properties of glass. The amorphous nature of the glass samples was confirmed through XRD measurement. Optical ultraviolet–visible light (UV–Vis) spectroscopy revealed that the direct and indirect optical band gap (E_opt) decreased as TeO₂ content increased except for the anomaly at x = 30 mol% due to the interchanging dominance of bridging oxygen (BO) and non-bridging oxygen (NBO) in the glass network. Both direct and indirect refractive indices, n posted an increment except for x = 30 mol% due to polarizability influence of BO and NBO. Urbach energy, E_u declined thus indicating lesser disorder and less defects on the glass structure. The radiation shielding properties of the glass samples were determined for 15 keV–15 MeV photon energy range by using Phy-X/PSD software. Atomic number-dependent parameters such as mass attenuation coefficient (MAC) and effective atomic number (Z_eff) demonstrated an enhanced performances caused by higher Z of Te over B. Meanwhile, density-dependent parameters such as linear attenuation coefficient (LAC), mean-free path (MFP), half-value layer (HVL) and tenth-value layer (TVL) all exhibited an improvement over TeO₂ concentration due to higher density data obtained.     

Energy storage properties and transparency in (Ba0.6Sr0.4)1-1.5xBixTi1-x(Mg1/3Nb2/3)xO3 ceramics

Fully densified (transparent) ceramic with small grain size is highly desired to improve the field breakdown strength (BDS) and its scattering. Sintering behavior, microstructural evolution, electric, dielectric, and energy storage properties of (Ba_0.6Sr_0.4)_1-1.5xBi_xTi_1-x(Mg_1/3Nb_2/3)_xO₃ (x = .04–.10) ceramics have been studied in this paper. Phase pure cubic perovskite is observed for the x = .04 composition. Nb-rich tungsten bronze type and Ti-rich barium titanate secondary phases are present in the x > .05 compositions. A multiphasic transparent ferroelectric ceramic with ∼74.2% (780 nm) transmittance and a high refractive index of ∼2.3 within the visible region could be successfully obtained for the x = .10 composition by traditional ceramic process. The x = .09 composition demonstrates good energy storage performance (recoverable energy density W_rec = 3.74J/cm³, efficiency η = 77% and BDS = 390kV/cm) with extremely low scattering in BDS, suggesting potential application in large sized energy storage capacitor.     

Optical properties,thermal stability,and forming region of high refractive index La2O3–TiO2–Nb2O5 glasses

The high refractive index La₂O₃–TiO₂–Nb₂O₅ glasses were prepared by containerless processing, and the glass‐forming region was determined. The refractive index showed the range from 2.20 to 2.32, and the values were much higher than those of most optical glasses. The completely miscible 30LaO_3/2–(70?x)TiO₂–xNbO_5/2 (0 ≤ x ≤70) system was fabricated to study the compositional dependence of refractive index and optical transmittance. The crucial determinants of the refractive index of oxide glasses, oxygen molar volume, and electronic polarizability of oxygen ions were calculated. The principle of additivity of glass properties was suitable for the calculation of refractive index between glass and compositional oxides. All the glasses were colorless and transparent in the visible to 6.5 μm middle infrared (MIR) region. These results are useful for designing new optical glasses with high refractive index and low wavelength dispersion in wide optical window.     

Nanostructured high‐energy xLi2MnO3·(1‐x)LiNi0.5Mn0.5O2 (0.3 ≤ x ≤ 0.6) cathode materials

Nanostructured lithium‐manganese‐rich nickel‐manganese‐oxide xLi₂MnO₃·(1‐x)LiNi_0.5Mn_0.5O₂ (0.3 ≤ x ≤ 0.6) composite materials were synthesized via spray pyrolysis using mixed nitrate precursors. All the materials showed a composite structure consisting of Li₂MnO₃ (C2/m) and LiNi_0.5Mn_0.5O₂ components, and the amount of Li₂MnO₃‐phase appeared to increase with x, as observed from XRD analysis. These composite materials showed a high‐discharge capacity of about 250 mAhg^?1. In the range of x considered, the layered 0.5Li₂MnO₃·0.5LiNi_0.5Mn_0.5O₂ materials displayed the highest capacity and superior cycle stability. Nonetheless, voltage suppression from a layered‐spinel phase transition was observed for all the composites produced. This voltage suppression was dependent of the amount of Li₂MnO₃ phase present in the composite structure. © 2013 American Institute of Chemical Engineers AIChE J 60: 443–450, 2014     

Preparation and properties of optically transparent,pressure-cured poly(methacrylate) composites

The objective of this work was to develop optically transparent glass fiber reinforced poly(methyl methacrylate) (PMMA) composites by matching the refractive index of the glass fiber reinforcement to that of the PMM, A matrix, thereby minimizing the quantity of light which is normally scattered and reflected at the interface of dissimilar materials. A pressure curing process is described for preparing composites 10 by 15 by 0.6 cm thick and containing up to ∼ 35% glass fiber. By curing at 65°C under 6.9 MPa N₂ for 18 H, composites have been produced with optical quality surfaces and flexural strengths more than seven times that of commercial PMMA of the same thickness. A transparent composite containing 10.4 vol% of 13 μm diameter fiber had an 84% optical transmission (92% maximum for PMMA) at 600 nm and 25°C.     

Structure and microwave dielectric properties of the Li2/3(1−x)Sn1/3(1−x)MgxO systems (x = 0‐4/7)

In this paper, the Li_2/3(1?x)Sn_1/3(1?x)Mg_xO (LSMxO) ceramic systems were prepared by solid‐state reaction using novel atmosphere‐controlled sintering (x = 0‐4/7). Pure Li₂SnO₃ was observed for x = 0, the Li₂Mg₃SnO₆ and Li₂SnO₃ coexisted for x = 1/7, and the coexistence of three kinds of phases was detected for x = 1/5 and 1/4, including Li₄MgSn₂O₇ impurity phase. Pure Li₂Mg₃SnO₆‐like phase with cubic rock salt structure in Fm‐3m space group was obtained in the range of 1/3‐4/7. All samples showed well‐dense and smooth microstructures. The microwave dielectric properties highly depended on the phase composition, bond valence, FWHM of Raman spectrum, Raman shift, average grain sizes, and octahedral distortion. The LSMxO ceramics sintered at 1250°C for 5 hours possessed excellent comprehensive properties of ε_r = 15.43, Q×f = 80 902 GHz and τ_f = +5.61 ppm/°C for x = 1/7. Typically, the LSMxO ceramics sintered at 1350°C for 5 hours showed a maximum Q × f of 168 330 GHz for x = 1/2.     

Fabrication of transparent electro-optic (K0.5Na0.5)1−xLixNb1−xBixO3 lead-free ceramics

Lead-free transparent electro-optic ceramics (K_0.5Na_0.5)_1?xLi_xNb_1?xBi_xO₃ have been fabricated by hot-press sintering. Owing to the effective suppression of grain growth, the Li and Bi co-modified ceramics generally possess a dense and fine-grained structure. The co-modification also causes the ceramics to transform into a nearly cubic structure with minimal optical anisotropy. A diffuse phase transformation is also induced, causing the ceramics to become more relaxor-like and contain more polar nano-regions. These would reduce the light scattering by the grains, at the grain boundaries and at the domain walls, respectively, and thus making the ceramics become optically transparent. For the ceramic modified with 5 mol% Li⁺ and Bi⁵⁺, the optical transmittance reaches a high value of 60% in the near-IR region. The ceramics also exhibit a strong linear EO response, giving a large effective linear EO coefficient in the range of 120–200 pm/V.     

Diffusion Properties of Tm3+ in Congruent LiNbO3 Crystal

Diffusion properties of Tm³⁺ in congruent LiNbO₃ crystal have been investigated, together with other two related issues, i.e., Tm³⁺‐doping contribution to refractive index of LiNbO₃ substrate and Li out‐diffusion. Four X‐cut and four Z‐cut congruent LiNbO₃ substrates locally coated with 15–31 nm‐thick Tm‐metal films were annealed in surrounding air under different temperatures of 1030°C–1130°C for different durations of 20–70 h. After anneal, refractive index at Tm³⁺‐doped and Tm³⁺‐free parts of crystal surface was measured at the wavelengths of 1311 and 1553 nm and surface Li₂O contents were evaluated from measured refractive index. The results show that Tm³⁺ doping has a weak effect on substrate index and a small contribution to index increment in waveguide layer in comparison with Ti⁴⁺‐ or Zn²⁺ doping. The Li₂O content at the Tm³⁺‐doped surface equals that at the Tm³⁺‐free surface. The Li out‐diffusion depends mainly on the diffusion temperature. Below 1100°C, the Li out‐diffusion is not measurable. At 1130°C, a 30‐h diffusion procedure may cause 0.2–0.3 mol% slight loss of Li₂O content. Secondary ion mass spectrometry was used to study the Tm³⁺ diffusion properties. The results show that the diffused Tm³⁺ ions in all samples follow a complementary error function profile. From measured Tm³⁺ profiles, characteristic diffusion parameters such as diffusivity, diffusion constant, activation energy, solubility, solubility constant, and heat of solution were obtained and discussed in comparison with the case of Er³⁺ diffusion. In comparison with Er³⁺ diffusion, the Tm³⁺ diffusion shows similar anisotropy and temperature dependence of solubility. In the aspect of diffusivity, under lower temperature the Tm³⁺ has a lower diffusivity than the Er³⁺, and their diffusivity difference reduces with the increased temperature and becomes null at 1130°C.     

Crystal structure,densification, and microwave dielectric properties of Li3Mg2(Nb(1−x)Mox)O6+x/2 (0 ≤ x ≤ 0.08) ceramics

A novel system Li₃Mg₂(Nb_(1−x)Mo_x)O_6+x/2 (0 ≤ x ≤ 0.08) microwave dielectric ceramics were fabricated by the solid-state method. The charge compensation of Mo⁶⁺ ions substitution for Nb⁵⁺ ions was performed by introducing oxygen ions. The X-ray diffraction patterns and Rietveld refinements indicated Li₃Mg₂(Nb_(1−x)Mo_x)O_6+x/2 ceramics with single phase and orthorhombic structure. Micro-structure and density confirmed that the grain of Li₃Mg₂(Nb_(1-x)Mo_x)O_6+x/2 ceramics grew well. In addition, the permittivity of Li₃Mg₂(Nb_(1−x)Mo_x)O_6+x/2 ceramics with the same trend as density decreased slightly with increasing Mo⁶⁺ ions content. However, the Q*f and τ_f were obviously improved with an appropriate amount of Mo⁶⁺ ions. When x ≤ 0.04, the Q*f was closely related to the bond valence of samples, while when x ≥ 0.06, the Q*f was closely related to the density of samples. The variations of τ_f and oxygen octahedral distortion were the opposite. In conclusions, the Li₃Mg₂(Nb_0.98Mo_0.02)O_6.01 ceramic sintered at 1200°C for 6 hours exhibited outstanding properties: ε_r ~ 15.18, Q*f ~ 116 266 GHz, τ_f ~ −15.71 ppm/^oC.     

Potentiometric measurements and impedance characteristics of Li0.30La0.57TiO3 membrane in lithium anhydrous solutions

The potentiometric response of the Li⁺ ion-selective electrode based on the fast ion conductor Li_3xLa_2/3−xTiO₃ (x = 0.10) membrane (named LLTO) as well as the impedance of the LLTO membrane/Li⁺ solution in either anhydrous or hydrated PC solvent have been carried out. A four-electrode configuration has been used for the investigation of the interfacial phenomenon. It has been shown that the LLTO membrane can be used to detect the Li⁺ activity in anhydrous solutions through a Li⁺ ion exchange mechanism. The potentiometric response shows a Nernstian behavior with a Li⁺ sensitivity of −72 mV/decade at 25 °C. This high sensitivity can be correlated to a localised hydroxylation of the oxide surface with the residual water present in the solution in combination to the Li⁺ exchange reaction. An apparent standard current density of 12 μA/cm² and a charge-transfer coefficient of 0.29 have been determined. However, as water content in the electrolyte increases, the activity domain of the detection decreases to lead to the disappearance of the Li⁺ ion exchange mechanism in Li⁺ aqueous solution. This annihilation of the exchange process may be due to the predominant catalytic reaction of [Ti-O]⁻ with H₂O and/or to the formation of a water layer on the oxide surface.     

Uncommon potential hysteresis in the Li/Li2xVO(H2−xPO4)2 (0 ≤ x ≤ 2) system

Physical and electrochemical investigations of vanadium phosphates, Li_2xVO(H_2−xPO₄)₂ (0 < x < 2), have been undertaken. H⁺/Li⁺ ionic exchange from VO(H₂PO₄)₂ to Li₂VO(HPO₄)₂ leads to grain decrepitation. Further ionic exchange toward formation of Li₄VO(PO₄)₂ lowers the symmetry. As inferred from potentiodynamic cycling correlated to ex situ and in situ X-ray diffraction (XRD), the system Li/Li₄VO(PO₄)₂ shows several phase transformations that are associated with thermodynamical potential hysteresis that span from roughly 15 mV to more than 1.8 V. Small hysteresis are associated with topotactic reactions and with V^V/V^IV and V^III/V^II redox couples. Large potential hysteresis values (>1 V) were observed when oxidation of V^III to V^IV is involved.     

Synthesis and Properties of Glasses in the (Sb2S3)1 – x(TlI)x System

The glass formation region, density, glass transition temperature, optical transmission, and refractive index are investigated for glasses in the (Sb₂S₃)_{1 – x} (TlI) _x system.     

Structural dependence of crystallization in glasses along the nepheline (NaAlSiO4) ‐ eucryptite (LiAlSiO4) join

Lithium and sodium aluminosilicates are important glass‐forming systems for commercial glass‐ceramics, as well as being important model systems for ion transport in battery studies. In addition, uncontrolled crystallization of LiAlSiO₄ (eucryptite) in high‐Li₂O compositions, analogous to the more well‐known problem of NaAlSiO₄ (nepheline) crystallization, can cause concerns for long‐term chemical durability in nuclear waste glasses. To study the relationships between glass structure and crystallization, nine glasses were synthesized in the Li_xNa_1‐xAlSiO₄ series, from x = 0 to x = 1. Raman spectra, nuclear magnetic resonance (NMR) spectroscopy (Li‐7, Na‐23, Al‐27, Si‐29), and X‐ray diffraction were used to study the quenched and heat‐treated glasses. It was found that different LiAlSiO₄ and NaAlSiO₄ crystal phases crystallize from the glass depending on the Li/Na ratio. Raman and NMR spectra of quenched glasses suggest similar structures regardless of alkali substitution. Li‐7 and Na‐23 NMR spectra of the glass‐ceramics near the endmember compositions show evidence of several differentiable sites distinct from known Li_xNa_1‐xAlSiO₄ crystalline phases, suggesting that these measurements can reveal subtle chemical environment differences in mixed‐alkali systems, similar to what has been observed for zeolites.