Temperature-assisted electrical poling of TeO2-Bi2O3-ZnO glasses for non-linear optical applications

The suitability for effective thermal poling of the ternary tellurite glasses with the compositions (100 − 2x)TeO₂-xBi₂O₃-xZnO (x = 5, 10 and 15, in molar percentage) for the second harmonic generation (SHG) was analyzed. The glass transitions and crystallization temperatures were studied via differential thermal analysis. The structural properties of the annealed glasses and furtherly heat-treated samples were probed by extended X-ray absorption fine structure (EXAFS) spectroscopy. Thermal poling of the glasses was undertaken conventionally at various temperatures close to the glass transition temperature under high vacuum and the second harmonic generated signals were compared. A new technique of two stage poling was tested for comparison. The non-linear second harmonic signal of the poled glasses was analyzed using the Maker-fringe technique and it was found that the two stage poling enhanced the non-linear efficiency when compared to the conventionally poled samples.     

Structural and physical properties of a novel TeO2-BaO-SrO-Ta2O5 glass system for photonic device applications

A detailed study on a novel TeO₂-BaO-SrO-Ta₂O₅ glass system developed for photonic device applications is reported in this paper. The glass transition and crystallization temperatures could be selected by varying the Ta₂O₅ content in this glass system. This glass system is found to have good thermal stability among tellurite glasses. Raman spectroscopy has been used as a tool to analyze the structural details of this technologically important glass system. In addition to the TeO₄ trigonal bipyramid and TeO₃ trigonal pyramid structural units, glasses in this system revealed the presence of an additional Raman band attributed to TaO₆ octahedra. The Raman bandwidth of the present glasses are broader compared to the conventional tellurite glasses by 35%. The influence of a gradual addition of the modifier oxides on the coordination geometry of tellurium atoms has been elucidated. Unlike the other tellurite glasses, even at higher modifier concentrations the TeO₄ structural units dominate in the glass network compared to TeO₃ trigonal pyramids. The ratio of TeO₄/TeO₃ structural units was discussed for different series of glass compositions.     

X-ray absorption and Raman characterizations of TeO2-Ga2O3 glasses

The thermodynamic properties of transparent glasses prepared in the TeO₂-Ga₂O₃ system were investigated by differential scanning calorimetry. The change of the thermal parameters as a function of the chemical composition is discussed. Raman and both Te L_III and Ga K edge X-ray absorption spectroscopies at room temperature were used to examine the short range order. Analyses of the spectra suggest that the addition of Ga₂O₃ content to the TeO₂ glass matrix induces the transformation of trigonal bipyramids (TeO₄E, E=lone electronic pair 5s² of Te) to trigonal pyramids (TeO₃E) with formation of Te-O-Ga bridging bonds. Furthermore, Ga K edge XANES and EXAFS studies show that Ga atoms exhibit both tetrahedral (GaO₄) and octahedral (GaO₆) environments.     

Structural investigations of copper doped B2O3-Bi2O3 glasses with high bismuth oxide content

Raman and infrared spectroscopy have been employed to investigate the 99.5%[xB₂O₃(1−x)Bi₂O₃]0.5%CuO glasses with different Bi/B nominal ratios (0.07?x?0.625) in order to obtain information about the competitive role of B₂O₃ and Bi₂O₃ in the formation of the glass network. The glass samples have been prepared by melting at 1100 °C and rapidly cooling at room temperature. In order to relax the structure, to improve the local order and to develop crystalline phases the glass samples were kept at 575 °C for 10 h. The influence of both Bi₂O₃ and CuO on the vitreous B₂O₃ network as well as the local order changes around bismuth and boron atoms in as prepared and heat treated samples was studied. Structural modifications occurring in heat treated samples compared to the untreated glasses have been observed.     

Structure and properties of Ge2.5PSx glasses

Ge_2.5PS_x glasses were studied with a combination of Raman spectroscopy, nuclear magnetic resonance, and neutron diffraction. From these experiments the distribution of bonding configurations was determined, and used to explain the compositional dependence of the index of refraction and the glass transition temperature. On reducing the sulfur content of these glasses below the stoichiometric amount, the sulfur deficit is accommodated by the progressive loss of the non-bridging sulfur of SPS_3/2 groups, followed by the conversion of the resultant PS_3/2 groups into species such as P₄S₃ characterized by P-P bonding. The presence of metal-metal bonds involving germanium, found in samples with the lowest sulfur content, was found to be the most important structural feature in determining the optical response.     

Molecular dynamics simulation of La2O3-Na2O-SiO2 glasses. II. The clustering of La cations

Clustering of high-field strength rare-earth ions in silicate glasses has been experimentally observed for a wide range of concentrations. Clustering has also been observed by molecular dynamics (MD) computer simulations over a range 1-10 mol% in soda silicate glasses. Although there have been numerous experimental studies, atomic-level details of the mechanisms that lead to clustering remain unclear. Coupling experiment with MD simulations is essential to uncovering the factors that lead to clustering. In this work, MD computer simulations are used to verify that clustering found in previous MD simulations is not an artifact of the simulation method. This work also provides clues as to the mechanism of atomic-level clustering.     

Sol-gel processing of TeO2-TiO2-PbO thin films

TeO₂-TiO₂-PbO thin films were prepared by sol-gel processing from tellurium(IV) isopropoxide precursor and their transmittance spectrum was measured, from which the refractive index was calculated. The hydrolysis of tellurium(IV) isopropoxide and the decomposition process of its hydrolysis product were investigated. The discrepancy between the observed hydrolysis behavior of tellurium(IV) isopropoxide and the partial charge model on the reactivity of metal alkoxides toward hydrolysis, being calculated with the Pauling electronegativity, is explained by a combination of the inductive and steric effects of isopropoxide groups and the electronic configuration of the tellurium atom with lone pair electrons.     

Structure and crystallization of potassium titanium phosphate glasses containing B2O3 and SiO2

Transparent glasses composition of which can be expressed by the formula: (100−x) · (K₂O · 2TiO₂ · P₂O₅) · x(K₂O · 2B₂O₃ · 7SiO₂), where x=5, 10, 15 and 20 mol% (KTP-xKBS), were obtained by melt quenching technique. The structure and crystallization behavior of these glasses have been examined by Fourier transform infrared spectroscopy, differential thermal analysis and X-ray diffraction. In spite of their nominal composition, the studied glasses exhibit a similar oxygen polyhedra distribution. However, significant differences were found in the trigonal BO₃ units amount. During DTA runs all the examined glasses devitrify in two steps. In the former, very small crystals of an unknown crystalline phase are produced. In KTP-5KBS and KTP-10KBS glasses anatase phase was also detected. Attempts were made in order to identify the unknown phase (UTP) for which a AB₃(XO₄)₂(OH)₆ Crandallite-type structure was proposed where the A, B and X sites were occupied by K, Ti and/or Al, and P, respectively. In the second devitrification step the crystallization of the KTiOPO₄ phase occurs while the UTP phase previously formed disappears. Isothermal heat treatments performed at temperature just above T_g have allowed one to obtain transparent crystal-glass nanocomposites, formed by crystalline nanostructure of the UTP phase uniformly dispersed in the amorphous matrix.     

Thermal and electrical properties of BaO-B2O3-ZnO glasses

Glasses in the BaO-ZnO-B₂O₃ system were examined as potential replacement for PbO glass frits with low firing temperature (500-600 °C) for the dielectric layer of a plasma display panel (PDP). The glasses were evaluated for glass transition temperature (T_g), thermal expansion coefficient (α) and dielectric constant ε. The electrical and the thermal properties were also compared with theoretical data calculated by a known empirical equation. T_g of the glasses varied between 480 and 560 °C, and α was in the range of 7-9×10⁻⁶ K⁻¹. The dielectric constant ranges from 14 to 19 and the theoretical data showed lower α and ε than the experimental data. The results suggest that BaO-ZnO-B₂O₃ glasses would be suitable as an alternative to Pb-based dielectric layer in PDPs.     

Sol-gel preparation and optical properties of SiO2-Ta2O5 glass

Tantalum-doped silica glass was fabricated by the sol-gel process in order to obtain a glass with a high refractive index for optical use. A crack-free, clear glass rod was successfully prepared from a low-density gel and used as the core material for fabricating optical fibers. Transmission loss in the fabricated fibers was high, in the range of 10³-10⁴ dB/km, which may be caused by coloration due to the multivalency of tantalum; however, the loss was reduced by nearly one order of magnitude by heat treatment at 800 °C, that is, to 75 dB/km at a wavelength of 0.8 μm.     

Structural investigation of sodium borate glasses and melts by Raman spectroscopy. II. Conversion between BO4 and BO2O units at high temperature

Raman scattering spectra were recorded for pure boron oxide and sodium borate glasses and their melts at the temperature ranging from room temperature to 1200 °C to investigate the structural changes occurring in the melts. The amounts of short-range order structures (SRO), BO₂O⁻ and BO₃, were estimated from the high frequency bands at 1100-1600 cm⁻¹. The ratio of 4-fold coordinated boron oxide BO₄, N₄, at high temperature could be derived for the glass melts as a function of Na₂O concentration. In Na₂O ?20 mol% region, N₄ showed a slight decrease while the remarkable decrease of N₄ was found in the region of Na₂O ?25 mol% with increasing temperature. The enthalpy of the equilibrium reaction,

     

Preparation and characterization of glasses in the Ag2S + B2S3 + GeS2 system

The glass forming range of the Ag₂S + B₂S₃ + GeS₂ ternary system was investigated for the first time and a wide range of ternary glasses were obtained. The Archimedes’ method was used to determine the densities of the Ag-B-Ge glasses. The thermal properties of these thioborogermanate glasses were studied by DSC and TMA. The Raman, IR and NMR spectroscopy were used to explore the short-range order structure of the binary (Ag-B) and (Ag-Ge) and ternary (Ag-B-Ge) glasses. The results show the presence of bridging sulfur tetrahedral units, GeS_4/2 and AgBS_4/2, and trigonal units, BS_3/2, in the ternary glasses. Non-bridging sulfur units, AgSGeS_3/2 and Ag₃B₃S₃S_3/2 six membered rings, are also observed in these glasses at higher Ag₂S modification levels because the further addition of Ag₂S results in the degradation of the bridging structures to form non-bridging structures. The NMR studies show that Ag₂S goes into the GeS₂ subnetwork to form Ag₃S₃GeS_1/2 groups before going to the B₂S₃ subnetwork. In doing so, it is suggested that B₁₀S₂₀ supertetrahedra exist in Ag₂S + B₂S₃ and Ag₂S + B₂S₃ + GeS₂ glasses. Significantly B-S-Ge bonds form in the B₂S₃ + GeS₂ glasses, whereas they appear to be absent in the ternary glasses. From these observations, a structural model for these glasses has been developed and proposed.     

Aggregation effects in non-linear absorption of CuPc-SiO2 sono-xerogels

It is known that aggregation effects in metallophthalocyanine/SiO₂ composites play an important role in the optical properties of these materials. With the aim to avoid phthalocyanine dimer and oligomer formation induced in aqueous solution, alternative processing methods for trapping the organic in the matrices have been tested. The combination of ultrasonic energy used to promote the reactions and the methanol used as solvent, makes it possible to obtain monolithic xerogels under extremely acid conditions, preserving their homogeneity and transparency. Textural parameters and pore size distribution of the composites and the optical absorption features have been evaluated. Finally, the effects of molecular self-association degree on the non-linear absorption of the samples have been analyzed. All the samples studied exhibit reverse saturable absorption behavior but the figure of merit is strongly determined by the aggregation state of the active phase in the composite.     

Structural investigation of SnO-B2O3 glasses by solid-state NMR and X-ray photoelectron spectroscopy

Local structure of the SnO-B₂O₃ glasses was investigated using several spectroscopic techniques. ¹¹B MAS-NMR spectra suggested that BO₄ tetrahedral units maximized at around the composition with 50 mol% SnO. The BO₄ units were still present at compositions with high SnO content (67 mol% SnO), suggesting that SnO acted not only as a network modifier but also as a network former. O1s photoelectron spectra revealed that the addition of small amounts of SnO formed non-bridging oxygens (NBO) (B-O?Sn) and the amounts of NBO increased with an increase in SnO content. ¹¹⁹Sn Mössbauer spectra indicated that Sn was present only as Sn(II) in the glasses. The structure of the SnO-B₂O₃ glasses was compared with that of conventional alkali borate glasses and lead borate glasses. The thermal and viscous properties of these glasses were discussed on the basis of the glass structure revealed in the present study.     

Preparation and characterization of ZrO2-SiO2 binary films for planar optical waveguides

ZrO₂-SiO₂ binary films for active optical waveguides were prepared by the sol-gel method with zirconium oxychloride and tetraethoxysilane as precursors. The main factors that influence the film thickness and refractive index have been found. The relationship between the film refractive index composition and heat treatment temperature has been determined. The continuous tuning of the thickness and refractive index of the thin films has also been achieved, which will open up new possibilities in the development of active optical waveguides.     

Processing and characterization of transparent TeO2-Bi2O3-ZnO glass ceramics

Fabrication of TeO₂-Bi₂O₃-ZnO glass ceramics with high transmittance in the near infrared (NIR) region is reported in the present work. Transparent tetragonal bipyramid crystals, tens of micrometers in size, with a refractive index closely matched to that of the glass matrix were formed using a two-step heat treatment. Nucleation- and growth-like curves for this crystal phase were determined using Differential Scanning Calorimetry (DSC). The crystalline phases present in the glass ceramics were identified via x-ray diffraction as a function of heat treatment. The lowest absorption coefficient of glass ceramic is approximately 0.5/cm in the near infrared region (1.2 to 2.8 μm).     

Thermal, chemical, optical properties and structure of Er-doped and Er/Yb-codoped P2O5-Al2O3-ZnO glasses

This study was explored in series of the optical, thermal, and structure properties based on 60P₂O₅-10Al₂O₃-30ZnO (PAZ) glasses system that doped with varied rare-earth (RE) elements Yb₂O₃/Er₂O₃. The glass transition temperature, softening temperature and chemical durability were increased with RE-doping concentrations increasing, whereas thermal expansion coefficient was decreased. In the optical properties, the absorption and emission intensities also increase with RE-doping concentrations increasing, When Er₂O₃ and Yb₂O₃ concentrations are over than 3 mol% in the Er³⁺-doped PAZ system and Yb³⁺-doped concentration is over than 3 mol% for Er³⁺/Yb³⁺-codoped PAZ system, the emission intensity significantly decreases presumably due to concentration quenching, formation of the ions clustering, and OH⁻ groups in the glasses network. It is suggested that the maximum emission cross-section (σ_e) is 7.64 × 10^− 21 cm² at 1535 nm is observed for 3 mol% Er³⁺-doped PAZ glasses. Moreover, the maximum σ_e × full-width-at-half-maximum is 327.8 for 5 mol% Er³⁺-doped PAZ glasses.     

DC conduvtivity of V2O5TeO2 glasses

The dc conductivity of semiconducting vanadium tellurite glasses of compositions in the range 50 to 80 mol% V₂O₅ has been measured in the temperature region 77 to 400 K. Measurements have been made on annealed samples at different annealing temperatures. Annealing the samples at temperature of about 250°C causes the appearance of a complex crystalline phase resulting in an increase of conductivity. Results are reported for amorphous samples of different compositions. The conductivity of tellurite glasses is slightly higher than the corresponding composition of phosphate glasses, but the general trend of the increase of conductivity and decrease of high temperature activation energy with increasing V₂O₅ content is similar in the two systems. The data have been analysed in the light of existing models of polaronic hopping conduction. A definite conclusion about the mechanics of conduction (adiabatic or nonadiabatic) is difficult in the absence of a precise knowledge of the characteristic phonon frequency v₀. Adiabatic hopping is indicated for v₀～10¹¹ Hz, however this value leads to unreasonably low value for the Debye temperature θ_D, and higher values for v₀～10¹³ hz satifiies the conditions for nonadiabatic hopping which appears to be the likely mechanism of conduction in V₂O₅TeO₂ glasses. The low temperature data (< 100 K) can be fitted to Mott's variable range hopping, which when combined with ac conductivity data gives reasonable values of α, but a high value for the disorder energy.     

The effect of alumina on the Sn/Sn redox equilibrium and the incorporation of tin in Na2O/Al2O3/SiO2 melts

Glasses with the basic compositions 10Na₂O · 10CaO · xAl₂O₃ · (80 − x)SiO₂ (x=0, 5, 15, 25) and 16Na₂O · 10CaO · xAl₂O₃ · (74 − x)SiO₂ (x=0, 5, 10, 15, 20) doped with 0.25-0.5 mol% SnO₂ were studied using square-wave-voltammetry at temperatures in the range from 1000 to 1600 °C. The voltammograms exhibit a maximum which increases linearly with increasing temperature. With increasing alumina concentration and decreasing Na₂O concentration the peak potentials get more negative. Mössbauer spectra showed two signals attributed to Sn²⁺ and Sn⁴⁺. Increasing alumina concentrations did not affect the isomer shift of Sn²⁺; however, they led to increasing quadrupole splitting, while in the case of Sn⁴⁺ both isomer shift and quadrupole splitting increased. A structural model is proposed which explains the effect of the composition on both the peak potentials and the Mössbauer parameters.