D.c. conductivity of V2O5–MnO–TeO2 glasses

Semiconductive oxide glasses in the system V2O5–MnO–TeO2 were prepared, and the mechanism of d.c. conduction was studied. The Seebeck coefficient measurements at temperatures from 375–475 K indicated the glasses to be n-type semiconducting. The d.c. conductivity ranged from 5×10–5 to 1.9×10–6 S cm–1 at 405 K for V2O5=60 mol% and MnO=0–20 mol%, and decreased with increasing MnO content. The conduction was confirmed to obey the adiabatic small polaron hopping model, and was due to mainly hopping between V-ions in the glasses. The polaron band width J was estimated to be J=0.10–0.20 eV. The electron–phonon interaction coefficient p was very large (21–26). The hopping mobility evaluated as 2.3×10–7–2.7×10–6 cm2 V–1 s–1 increased with increasing V2O5 content. The estimated carrier concentration was the order of 1019 cm–3. The principal factor determining conductivity was the polaron hopping mobility in these glasses. © 1998 Chapman & Hall     

Effect of NiO content on the optical band gap, refractive index, and density of TeO2–V2O5–NiO glasses

Amorphous layers and bulk glasses of 40TeO₂–(60 ? x)V₂O₅–xNiO compositions with 0 ≤ x ≤ 30 (in mol%) have been prepared using the usual blowing technique and press-melt quenching method, respectively. The optical absorption spectra of the layers have been recorded in the wavelength range 400–800 nm. The fundamental absorption edge has been identified from the optical absorption spectra. The optical band gap, width of the tail of the localized states, and refractive index have been evaluated using available theories. Results show that the values of optical band gap decrease from 2.02 to 1.64 eV as the contribution of NiO increases. The refractive index dispersion is fitted to the single oscillator model, and results show that the static refractive index increase from 1.309 to 1.673 as the NiO content increases. The glass transition temperature, density, and molar volume have been studied, indicating act of NiO as network modifier. Values of theoretical optical basicity are also reported.     

Synthesis and characterization of Cu2O·TeO2 and CuI·Cu2O·TeO2 glasses

Cu₂O·TeO₂ and CuI·Cu₂O·TeO₂ glasses were synthesized and characterized by complex impedance measurement, Raman spectroscopy, X-ray photoelectron spectroscopy, and atomic force microscopy techniques. Samples of the binary and the ternary systems are found to have both Cu⁺ and Cu²⁺ with their relative concentration being composition dependent. Bonds like -O-Cu²⁺-O-, leading to the formation of bridging oxygen are found to form in the binary system. Structural units like (Te₃O₈ ^4–)_n are also found to form when Cu₂O content is high in the binary system. Phase separation is observed in the ternary system. The glass structure and hence the ionic conduction behavior are found to depend upon chemical composition. When CuI content exceeds 60 mol%, the crystalline phase of -Cul gets stabilized at room temperature, thus causing the enhancement in conductivity.     

Synthesis,structural, thermal and optical properties of TeO2–Bi2O3–GeO2–Li2O glasses

In this study, synthesis and characterization of novel quaternary tellurite glass system TeO₂–Bi₂O₃–GeO₂–Li₂O is presented. The compositions include TeO₂ and GeO₂ as glass formers while different proportion of Bi₂O₃ and Li₂O act as network modifiers. Differential thermal analysis, X-ray diffraction, scanning electron microscopy energy dispersive X-ray spectroscopy, laser ablation inductively coupled plasma mass spectrometry, UV–Vis and Raman spectroscopy are applied to study the structural, thermal and optical properties of the studied glasses. Obtained glasses possess a relatively low glass transition temperature (around 300 °C) if compared to other tellurite glasses, show good thermal transparency in the visible and near infra-red (from 2.4 to 0.4 μm) and can double the frequency of laser light from its original wavelength of 1064 nm to its second-harmonic at 532 nm (i.e. second harmonic generation).     

Preparation and structural studies in the (70 − x)TeO2–20WO3–10Li2O–xLn2O3 glasses

Quaternary tellurite glass systems (70 ? x)TeO₂–20WO₃–10Li₂O–xLn₂O₃ where x = 0, 1, 3 and 5 mol% and Ln are La, Pr, Nd, Sm, Er and Yb, respectively, have been prepared by the melt quenching technique. Densities of the obtained glasses were measured and the molar volume was calculated. IR absorption spectra of the present glass systems were determined at room temperature over the range of wavenumbers from 400–1,600 cm^?1. Raman spectra of the present glass samples were measured in the range of 30–1,030 cm^?1. Density, molar volume, IR and Raman spectra of the glasses were discussed by calculating average cross-link density, packing density, theoretically calculated Poisson’s ratio and number of bonds per unit volume of the studied glasses. Also, the quantitative interpretations were based on concentration of ions per unit volume of Te, Ln and O, short distance in nanometre between ions for (Te–O) of TeO₄ and TeO₃ groups, (W–O) of WO₄, WO₆ groups and calculated wavenumber, $ \bar{\upsilon } $ , for TeO₄ and TeO₃, respectively. The average stretching force constant that present in these quaternary glasses has been calculated in order to interpret the data obtained.     

Thermodynamic properties of TeO2-ZnO glasses in the range 0–650 K

The heat capacity C _p ⁰ of (TeO₂)_n(ZnO)_{1 ? n} (n = 0.65, 0.70, 0.80) tellurite glasses has been determined by precision adiabatic (6–350 K) and dynamic scanning (320–650 K) calorimetry. The thermodynamic characteristics of their devitrification and glassy state have been determined. The experimental data have been used to calculate the standard thermodynamic functions of samples in the glassy and “supercooled liquid” states (0–650 K): heat capacity C _p ⁰ (T), enthalpy H ⁰(T) ? H ⁰(0), entropy S ⁰(T) ? S ⁰(0), and Gibbs function G ⁰(T) ? H ⁰(0). Multifractal processing of the low-temperature heat capacity data has been used to assess the character of structural heterodynamicity of the tellurite glasses. The heat capacity of the glasses has been analyzed in comparison with that of their constituent oxides. The composition dependences of the glass transition temperature, crystallization onset temperature, and thermodynamic functions at 298.15 and 600 K have been obtained.     

EPR study of V2O5–P2O5–Li2O glass system

glass system, with 0 < x 50 mol%, was prepared and investigated by EPR method. For low content of V₂O₅ all the spectra present a hyperfine structure typical for isolated V⁴⁺ ions. With the increasing of V₂O₅ content, the EPR absorption signal showing hyperfine structure is superposed by a broad line without hyperfine structure characteristic for clustered ions. At high V₂O₅ content, the vanadium hyperfine structure disappears and only the broad line can be observed in the spectra. Spin Hamiltonian parameters g , g , A , A , dipolar hyperfine coupling parameters, P, and Fermi contact interaction parameters, K, have been calculated.The composition dependence of line widths of the first two absorptions from the parallel band and of the broad line characteristic to the cluster formations was also discussed.     

Optical properties of Nd3+ and Er3+ ions in TeO2–WO3–PbO–La2O3 glasses

Multicomponent telluride-tungstate glasses containing Nd³⁺ and Er³⁺ ions were studied experimentally at 77 and 293 K using spectroscopic methods. The Judd–Ofelt intensity parameters were derived from the absorption spectra and used to calculate the radiative lifetimes and branching ratios. The quantum efficiency η = 0.95 of the ⁴F_3/2 level of Nd³⁺ ion is higher than the typical value of other tellurite-based glasses. For low concentration of Er³⁺ ions, the luminescence decay of the ⁴S_3/2 and ⁴I_11/2 levels is governed by radiative transitions and multiphonon relaxation involving the Te-O highest energy vibrations.     

Nanocrystallization as a method of improvement of electrical properties of Fe2O3–PbO2–TeO2 glasses

Selected glasses of Fe₂O₃–PbO₂–TeO₂ system have been transformed into nanomaterials by annealing at a temperature close to the crystallization temperature (T_c). The effects of the annealing of the present samples on the structural and electrical properties were studied by transmission electron micrograph (TEM), X-ray diffraction (XRD), differential scanning calorimeter, density (d) and dc conductivity (σ). TEM and XRD of glass–ceramic naocrystals indicated nanocrystals embedded in the glassy matrix with average particle size of 20–35 nm. The glass–ceramic naocrystals obtained by annealing at T_c exhibit improvement of electrical conductivity up to four orders of magnitude than the starting glasses. This considerable improvement of electrical conductivity after nanocrystallization is attributed to formation of extensive and dense network of electronic conduction paths which are situated between Fe₂O₃ nanocrystals and on their surface. The conduction is attributed to non-adiabatic hopping of small polaron.     

Ti K-edge XANES study of the local environment of titanium in bioresorbable TiO2–CaO–Na2O–P2O5 glasses

Ti K-edge XANES (X-ray absorption near edge structure) spectroscopy has been used to study the local coordination of titanium in biocompatible and bioresorbable TiO₂–CaO–Na₂O–P₂O₅ glasses. Both conventional melt-quenched glasses of composition (TiO₂) _x (CaO)_0.30(Na₂O)_(0.20−x)(P₂O₅)_0.50, where x = 0.01, 0.03 and 0.05, and sol–gel derived (TiO₂)_0.25(CaO)_0.25(P₂O₅)_0.50 glass have been studied. The results show that in all the materials studied, titanium is surrounded by an octahedron of oxygen atoms. Further analysis reveals that the TiO₆ site in the amorphous samples is not heavily distorted relative to that in rutile, anatase or CaSiTiO₅. The spectra from the (TiO₂)_0.25(CaO)_0.25(P₂O₅)_0.50 sol–gel samples reveal greater distortion in the TiO₆ site in the dried gel compared to the heat-treated sol–gel glass. The XANES spectra from melt-quenched glass samples soaked in distilled water for various times do not shown any evidence of degradation of the titanium site over periods of up to 14 days.     

Photoluminescence and scintillation properties of Eu2O3–BaO–Nb2O5–TeO2 glass and glass ceramics

Journal of Materials Science: Materials in Electronics - 1Eu2O3–3BaO–20Nb2O5–76TeO2 glass and the corresponding glass-ceramics were synthesized with the aim to investigate the...     

Microwave dielectric properties of 3Li2O–Nb2O5–3TiO2 ceramics with Li2O–V2O5 additions

A new Li₂O–Nb₂O₅–TiO₂ (LNT) ceramic with the Li₂O:Nb₂O₅:TiO₂ mole ratio of 3:1:3 has been investigated. The compound is composed of two phases, the Li₂TiO₃ and “M-phase” solid solution phase. The microwave dielectric ceramic has low sintering temperature (∼1100 °C) and good microwave dielectric properties of a relatively high permittivity (∼51), high Q × f value up to 8700, and small temperature coefficient (∼37 ppm/°C). The low-amount doping of 0.83Li₂O–0.17V₂O₅ (LV) can effectively lower the sintering temperature from 1100 to 900 °C and induce no obvious degradation of the microwave dielectric properties. Typically, the 1 wt.% LV-doped ceramic sintered at 900 °C has better microwave dielectric properties of ε_r = 51.3, Q × f = 7235 GHz, τ _f  = 22 ppm/°C, which suggests that the ceramics can be applied in microwave LTCC devices.     

Effect of borosilicate glasses on the microwave dielectric properties of ZnO–Nb2O5–Ta2O5 system

(1 ? y)[0.5ZnNb₂O₆–0.5Zn₃Nb₂O₈]–yZnTa₂O₆ with y = 0.91 (ZNT) ceramic have been prepared by conventional solid state ceramic route. The effect of glass additives on the microstructure, densification, and microwave dielectric properties of the ZNT ceramic for low temperature co-fired ceramic applications was investigated. Different weight percentages of quenched glass such as ZnO–B₂O₃–SiO₂, BaO–B₂O₃–SiO₂, LiO–B₂O₃–SiO₂ and MgO–B₂O₃–SiO₂ were added to ZNT powder. The crystal structure of the ceramic–glass composites was studied by X-ray diffraction and microstructure by scanning electron microscopy. The microwave dielectric properties such as relative permittivity (ε_r), quality factor (Q_uxf) and co-efficient of temperature variation of resonant frequency (τ_f) of the ceramics have been measured in the frequency range 4–6 GHz. The 5 wt% ZnO–B₂O₃–SiO₂ added ZNT ceramic sintered at 900 °C showed: ε_r = 28.1, Q_uxf = 32820 GHz (at 4.92 GHz), and τ_f = ?7.7 ppm/^oC respectively.     

Surface crystallization and second-order optical non-linearity in Gd2O3–Bi2O3–B2O3 glasses

Some ternary Gd₂O₃–Bi₂O₃–B₂O₃ glasses are prepared, and crystallization behavior and second harmonic intensity are examined to develop new non-linear optical crystallized glasses. The glasses with Gd₂O₃ contents of 8–14 mol% have large densities of over 6 g/cm³ and large refractive indices of ∼1.9. Transparent surface crystallized glasses consisting of two kinds of crystalline phases with different morphologies, i.e. plate shape and needle shape crystals, are fabricated by heat-treatment at temperatures between glass transition and crystallization temperatures. From second harmonic generation microscope observations, micro-Raman scattering spectra and XRD analyses, plate shape crystals are determined to be non-linear optical Gd_xBi_1−xBO₃ and needle shape crystals are Bi₃B₅O₁₂ having no second-order optical non-linearity. Since crystallized glasses consisting of Gd_xBi_1−xBO₃ crystals exhibit relatively strong SHGs, they have a high potential for application to light control devices.     

Surface crystallization and second-order optical non-linearity in Gd2O3–Bi2O3–B2O3 glasses

Some ternary Gd₂O₃–Bi₂O₃–B₂O₃ glasses are prepared, and crystallization behavior and second harmonic intensity are examined to develop new non-linear optical crystallized glasses. The glasses with Gd₂O₃ contents of 8–14 mol% have large densities of over 6 g/cm³ and large refractive indices of ～ 1.9. Transparent surface crystallized glasses consisting of two kinds of crystalline phases with different morphologies, i.e. plate shape and needle shape crystals, are fabricated by heat-treatment at temperatures between glass transition and crystallization temperatures. From second harmonic generation microscope observations, micro-Raman scattering spectra and XRD analyses, plate shape crystals are determined to be non-linear optical Gd_xBi_1KxBO₃ and needle shape crystals are Bi₃B₅O₁₂ having no second-order optical non-linearity. Since crystallized glasses consisting of Gd_xBi_1KxBO₃ crystals exhibit relatively strong SHGs, they have a high potential for application to light control devices.     

Phase Relations in the Li–V2O5–Cu System at 600°C and Cathodic Properties of Cu x V2O5

The phase relations in the Li–V₂O₅–Cu system at 600°C are studied by x-ray diffraction. The existence of the known vanadium bronzes M _x V₂O₅ (M = Li, Cu) is confirmed, and the composition ranges of the related solid solutions are determined. -Li _x V₂O₅ (0.22 x 0.49) and -Li _x V₂O₅ (0.88 x 1.0) are shown to dissolve Cu, forming Li _x Cu _y V₂O₅ solid solutions with y = 0.72 – 1.48x and y = 0.58 – 0.18x, respectively. Cu _x Li _y V₂O₅ solid solutions (y= 0.51 – 0.76 x) are only obtained from -Cu _x V₂O₅ (0.24 x 0.67). -Li _x V₂O₅ and -Cu _x V₂O₅ form a continuous series of solid solutions. The cathodic properties of Li–V₂O₅–Cu materials in high-temperature pulsed lithium batteries are investigated.     

Phase Relations in the Na2O–Al2O3–Nb2O5and CaO–Al2O3–Nb2O5Systems

Phase relations in the Na₂O–Al₂O₃–Nb₂O₅and CaO–Al₂O₃–Nb₂O₅systems were studied. The Na₂O system was found to contain neither ternary compounds nor niobate–aluminate solid solutions. In the CaO system, a ternary compound of composition 4CaO · Al₂O₃·Nb₂O₅was identified (cubic structure, a= 7.628 Å, Z= 2, _meas= _x= 4.43 g/cm³).     

Microwave synthesis and properties of NaPO3–SnO–Nb2O5 glasses

Tin niobiophosphate glasses were produced using a domestic microwave oven under a nitrogen flow. The fast microwave melting method and the protective atmosphere prevent the oxidation of SnO. After 10 min of heating, the NaPO₃, SnO, and Nb₂O₅ mixtures are homogeneous and permit to obtain transparent glasses. Three series of glasses with different Sn/Nb ratio were studied to determine the influence of each oxide. The glass transition temperature increases linearly with the amount of Nb₂O₅ and SnO. These variations are more important for compositions with high metallic cation proportions and with a low Sn/Nb ratio. The same evolutions were observed for the density, Vickers hardness, and elastic modulus while the thermal expansion coefficient decreases monotonously. The simultaneous insertion of SnO and Nb₂O₅ in phosphate glass matrix leads to a progressive strengthening of the glass network. The chemical durability of the glasses also increases as a function of the amount of metal oxides. We prepared a bulk glass sample with a dissolution rate of about 3.3 × 10⁻⁸ g cm⁻² min⁻¹ in renewed water conditions at 95 °C. This durability is equivalent to those of the window glass whereas the glass transition temperature remains lower than 485 °C.     

Characterisation of Ga2O3–Na2O–CaO–ZnO–SiO2 bioactive glasses

The structural role of Gallium (Ga) is investigated when substituted for Zinc (Zn) in a 0.42SiO₂–0.40–xZnO–0.10Na₂O–0.08CaO glass series, (where x = 0.08). Each starting material was amorphous, and the network connectivity (NC) was calculated assuming Ga acts as both a network modifier (1.23), and also as a network former. Assuming a network forming role for Ga the NC increased with increasing Ga concentration throughout the glass series (Control 1.23, TGa-1 2.32 and TGa-2 3.00). X-ray photoelectron spectroscopy confirmed both composition and correlated NC predictions. Raman spectroscopy was employed to investigate Q-structure and found that a shift in wavenumbers occurred as the Ga concentration increased through the glass series, from 933, 951 to 960 cm^?1. Magic angle spinning nuclear magnetic resonance determined a chemical shift from ?73, ?75 to ?77 ppm as the Ga concentration increased, supporting Raman data. These results suggest that Ga acts predominantly as a network former in this particular Zn-silicate system.