Exploration on nano-composite fumed silica-based composite polymer electrolytes with doping of ionic liquid

Fumed silica (SiO₂)-based composite polymer electrolytes were prepared by means of solution casing technique. Horizontal attenuated total reflectance-Fourier Transform Infrared (HATR-FTIR) study shows the complexation between polymer matrix and SiO₂. The highest ionic conductivity of (4.11 ± 0.01) × 10^? 3 Scm^? 1 is achieved upon inclusion of 8 wt.% of SiO₂. Three different regions have been observed in the frequency dependence–ionic conductivity study. The conductivity rises sharply with frequency at low frequency regime. It is followed by a frequency independent plateau region and sharp decrease in the conductivity at high frequency range. The dielectric permittivity (ε^') and dielectric loss (ε^") are decreased with increasing the frequency. This phenomenon is mainly attributed to the electrode polarization effect. The formation of electrical double layer has been proven in these dielectric permittivity studies. This indicates the non-Debye properties of the nano-composite polymer electrolytes.     

Forouhi–Bloomer analysis to study amorphization in Si

Single crystal Si (1 0 0) was irradiated with 120 keV Ar⁺ for fluences ranging from 6 × 10¹³ to 1 × 10¹⁶ ions/cm² and the real and imaginary parts of the dielectric function were measured using a spectroscopic ellipsometer in the energy range 1.5–5 eV. The pseudodielectric functions of the irradiated specimens were analyzed using Forouhi–Bloomer model for the first time. It was found that a minimum of four absorption terms is required to obtain ‘good’ fits to the experimental data. The parameters of the fit show distinct behavior above and below amorphization threshold. This paper demonstrates that Forouhi–Bloomer interband model for pseudodielectric functions can be used to follow structural changes too.     

Properties and structure of (1 − x)Li2O–xNa2O–Al2O3–4SiO2 glass systems

(1 − x)Li₂O–xNa₂O–Al₂O₃–4SiO₂ glasses were studied for the progressive percentage substitution of Na₂O for Li₂O at the constant mole of Al₂O₃ and SiO₂. The crystallization temperature at the exothermic peak increased from 898 to 939 °C when the Na₂O content increases from 0 to 0.6 mol. The coefficient of thermal expansion and density of these as-quenched glasses increase from 6.54 × 10⁻⁶ °C⁻¹ to 10.1 × 10⁻⁶ °C⁻¹ and 2.378 g cm⁻³ to 2.533 g cm⁻³ when the Na₂O content increases from 0 to 0.4 mol, respectively. The electrical resistivity has a maximum value at Na₂O · (Li₂O + Na₂O)⁻¹ = 0.4. The activation energy of crystallization decreases from 444 to 284 kJ mol⁻¹ when the Na₂O content increased from 0 to 0.4 mol. Moreover, the activation energy increases from 284 kJ mol⁻¹ to 446 kJ mol⁻¹ when the Na₂O content increased from 0.4 to 0.6 mol. The FT-IR spectra show that the symmetric stretching mode of the SiO₄ tetrahedra (1035–1054 cm⁻¹) and AlO₄ octahedra (713–763 cm⁻¹) exhibiting that the network structure is built by SiO₄ tetrahedra and AlO₄.     

Influence of manganese ions on spectroscopic and dielectric properties of LiF-SrO-B2O3 glasses

Transparent glasses, obtained through melt quenching technique, with composition 30LiF-10SrO-(60-x)B₂O₃-xMnO, with 0 ≤ x ≤ 3 mol% (x = 0, 1, 1.5, 2, 2.5 and 3), were characterized by X-ray diffraction (XRD) and then they were analyzed for physical, spectroscopic studies (optical absorption, electron spin resonance (ESR) and FTIR) and dielectric properties (dielectric constant ε′, loss tanδ ?and conductivity σ_ac etc.). The results were analyzed and correlated with each other in the light of local environment and oxidation states of manganese ion in the glass network. The increase in the area of optical absorption peak and ESR signal intensity indicate that both Mn²⁺ and Mn³⁺ ions exist in octahedral symmetry are increased with increasing MnO dopant in the glass matrix. The semi conducting nature of the glass network is found to increase due to the considerable increase in BO₃, MnO₆ structural units whenever B₂O₃ in the host glass is gradually replaced by MnO.     

Molecular dynamics in glass-forming poly(phenyl methyl siloxane) as investigated by broadband thermal,dielectric and neutron spectroscopy

The molecular dynamics of glass-forming poly(methyl phenyl siloxane) (PMPS) is studied by thermal (10⁻³–5 × 10² Hz), dielectric (10⁻³–10⁹ Hz) and neutron (5 × 10⁸–10¹² Hz) spectroscopy. Because of the broad frequency range of 15 orders of magnitude the study provides a precise determination of glassy dynamics in a wide temperature range using different probes. The relaxation rates extracted from the different methods agree quantitatively in both their absolute values and in their temperature dependencies. A detailed analysis of the temperature dependence of the relaxation rate f_p by a derivative technique shows that the α-relaxation of PMPS has to be characterized by a high and a low temperature branch separated by a crossover temperature T_B = 250 K. In both temperature ranges the temperature dependence of f_p has to be described by Vogel/Fulcher/Tammann laws with different Vogel temperatures. Also the analysis of the dielectric strength in its temperature dependence gives a crossover behavior from a low to a high temperature region with a similar value of T_B. T_B can be interpreted as onset of cooperative fluctuations and the formation of dynamical heterogeneities. The dependence of the relaxation rate on the scattering vector Q extracted from neutron scattering obeys a power law τ ∼ Q^−Slope, where the power Slope varies between Slope = 2 and Slope = 3.5 with increasing temperature. This anomalous dependence of the relaxation time on the momentum transfer is discussed in terms of dynamic heterogeneities in the underlying motional processes even at temperatures above T_B. Besides the segmental dynamics the fast Methyl group rotation is considered as well. The relaxation rates of this process have an activated temperature dependence with an activation energy of 8.3 kJ/mol. The data were discussed in the framework of the threefold jump model were the incoherent elastic scattering from ‘fixed’ atoms which are frozen on the time scale of the Methyl group rotation was taken into account.     

Optical properties and infrared-to-visible upconversion in Er3+-doped GeO2–Bi2O3 and GeO2–PbO–Bi2O3 glasses

Luminescence properties and upconversion studies of germanate glasses in ternary GeO₂–PbO–Bi₂O₃ and binary GeO₂–Bi₂O₃ systems containing Er₂O₃ (0.1–1.0 wt%) are presented for the first time. The Judd-Ofelt parameters found for these glasses are: Ω₂ = 4.50 × 10⁻²⁰ cm², Ω₄ = 1.55 × 10⁻²⁰ cm² and Ω₆ = 0.69 × 10⁻²⁰ cm² for binary glasses and Ω₂ = 4.44 × 10⁻²⁰ cm², Ω₄ = 1.82 × 10⁻²⁰ cm² and Ω₆ = 0.39 × 10⁻²⁰ cm² for ternary glasses. The refractive index of these glasses is found to be ∼2. The transition ⁴I_13/2 → ⁴I_15/2 is peaked at ∼1.53 μm and shows a radiative lifetime around 5 ms. Both systems exhibit similar emission cross-section at 1.53 μm around 0.8 × 10⁻²⁰ cm². Upconverted green emission at ∼530 nm (²H_11/2 → ⁴I_15/2) and ∼550 nm (⁴S_3/2 → ⁴I_15/2) and red emission at ∼668 nm (⁴F_9/2 → ⁴I_15/2) are observed under 980 nm cw excitation. Our results suggest that these glasses are promising candidates for applications in photonics.     

EPR and magnetic susceptibility studies of B2O3–Bi2O3–Gd2O3 glasses

Glasses of the xGd₂O₃ · (100 − x)[B₂O₃ · Bi₂O₃] system with 0.5 ⩽ x ⩽ 10 mol% were studied by electron paramagnetic resonance (EPR) and magnetic susceptibility measurements. Data obtained show that for low gadolinium oxide contents of the samples (x ⩽ 3 mol%) the Gd³⁺ ions are randomly distributed in the host glass matrix and are present as isolated and dipole–dipole coupled species. For higher gadolinium oxide contents of the samples (x > 3 mol%) the Gd³⁺ ions appear as both isolated and antiferromagnetically coupled species. The EPR spectra of the glasses reveal resonance sites with an unexpected high crystalline field in addition to the ‘U’ spectrum, typical for Gd³⁺ ions in disordered systems. This absorption line is due to Gd³⁺ ions that replace Bi³⁺ ions from the host glass matrix and could play the network unconventional former role in the studied glasses.     

Dielectric low-k composite films based on PMMA,PVC and methylsiloxane-silica: Synthesis,characterization and electrical properties

This report describes the preparation of low-k inorganic–organic hybrid dielectric films, based on a polymethylmethacrylate–polyvinylchloride (PMMA–PVC) blend and a silica powder functionalized on the surface with methylsiloxane groups (m-SiO₂). By dispersing m-SiO₂ into a [(PMMA)_x(PVC)_y] 50/50 (x/y) wt% polymer blend, six [(PMMA)_x(PVC)_y]/(m-SiO₂)_z hybrid inorganic–organic materials were obtained, with z ranging from 0 to 38.3 wt% and x = y = (100 − z)/2. The transparent, homogeneous, crack-free films were obtained by a solvent casting process from a THF solution. The morphology, thermal stability and transitions of hybrid materials were studied by environmental scanning electron microscopy (ESEM), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). ESEM revealed that hybrid dielectric films are very homogeneous materials. The electrical response of the dielectric films was studied by detailed broadband dielectric spectroscopy (BDS). BDS measurements were performed at frequencies of 40 Hz to 10 MHz and a temperature range of 0–130°C. In these temperature and frequency ranges the proposed materials have a dielectric constant of <3.5 and a tan δ of <0.05. BDS also revealed molecular relaxation events in [(PMMA)_x(PVC)_y]/(m-SiO₂)_z materials as a function of temperature and sample composition. Results showed that these films with z in the range 25–35 wt% are very promising low-k dielectrics for applications in organic thin film transistor (OTFT) devices.     

Luminescent materials consisting of Eu(III) ions complexed in heteropolyoxometalates incorporated into silica xerogels

Luminescent materials based on the energy transfer effect consist of heteropolyoxometalates of the type K₁₃[Eu(SiMo_xW_11−xO₃₉)₂] incorporated into xerogel matrices. Results of our experiments suggest that not only the composition parameter x (where x = 1, 3 and 5) of the salts with Eu(III) complex but also the type of the matrix influence the luminescent properties of these materials. The luminescent samples were characterized by such luminescence parameters as emission intensity, luminescence lifetime and quantum yield. The highest emission intensity of Eu(III) ions was exhibited by the salt with x = 1 incorporated into a silicate modified with 3-glycidoxypropyl groups. The longest lifetime was found in the material with a methylated silicate matrix with the same salt. For the complexed Eu(III) ions in these materials there is a correlation between emission intensity changes of the ⁵D₀ → ⁷F₂ band and the quantum yield. The materials with a high organic content in matrices such as the silicates with 3-glycidoxypropyl groups (either with closed or opened epoxy cycles) are more thermally unstable and they undergo larger photochemical degradation during exposure on UV radiation than the systems with limited organic content.     

Alkaline earth zinc borate glasses doped with Cu2+ ions studied by EPR,optical and IR techniques

Copper ions incorporated into alkaline earth zinc borate glasses 10RO + 30ZnO + 60B₂O₃ (R = Mg, Ca and Sr) and 10SrO + (30 ? x)ZnO + 60B₂O₃ + xCuO (x = 0, 0.1, 0.3, 0.5, and 0.7 wt.%) were characterized by electron paramagnetic resonance (EPR), optical absorption and FTIR techniques. The EPR spectra of all the glass samples exhibit resonance signals characteristic of Cu²⁺ ions. The values of spin-Hamiltonian parameters indicate that the Cu²⁺ ions in alkaline earth zinc borate glasses were present in octahedral sites with tetragonal distortion. The spin concentration (N) participating in resonance was calculated as a function of temperature for strontium zinc borate (SrZB) glass sample containing 0.7 wt.% of Cu²⁺ ions and the activation energy was calculated. From the EPR data, the paramagnetic susceptibility (χ) was calculated at different temperatures and the Curie constant was evaluated from the 1/χ-T graph. The optical absorption spectra of these samples show only one absorption band. The optical band gap energies (E_g) and Urbach energy (ΔE) are calculated from their ultraviolet edges. The FTIR studies show different stretching and bending vibrations of alkaline earth zinc borate glasses.     

Structural change of laser-irradiated Ge2Sb2Te5 films studied by electrical property measurement

Sheet resistance of laser-irradiated Ge₂Sb₂Te₅ thin films prepared by magnetron sputtering was measured by the four-point probe method. With increasing laser power the sheet resistance undergoes an abrupt drop from 10⁷ to 10³ Ω/□ at about 580 mW. The abrupt drop in resistance is due to the structural change from amorphous to crystalline state as revealed by X-ray diffraction (XRD) study of the samples around the abrupt change point. Crystallized dots were also formed in the amorphous Ge₂Sb₂Te₅ films by focused short pulse laser-irradiated, the resistivities at the crystallized dots and the non-crystallized area are 3.375 × 10^?3 and 2.725 Ω m, sheet resistance is 3.37 × 10⁴ and 2.725 × 10⁷ Ω/□ respectively, deduced from the I–V curves that is obtained by conductive atomic force microscope (C-AFM).     

Crystal growth and spectral properties of Nd3+:Ca9Gd(VO4)7 crystal

An Nd³⁺:Ca₉Gd(VO₄)₇ crystal with dimensions of ?25×30 mm³ was grown by the Czochralski method. The hardness, thermal expansion coefficient and thermal conductivity coefficient of the crystal were measured. The spectroscopic characteristics of Nd³⁺:Ca₉Gd(VO₄)₇ crystals were investigated. The absorption band at 810 nm has an FWHM of 10 nm, and absorption cross-sections are 5.81×10^?20 cm² for π-polarization and 7.47×10^?20 cm² for σ-polarization at 810 nm. The emission cross-sections at 1067 nm are 4.2×10^?20 and 6.5×10^?20 cm² for π- and σ-polarizations, respectively. The quantum efficiency η_c is equal to 94.3%. To sum up the above results, Nd³⁺:Ca₉Gd(VO₄)₇ crystal can be regarded as a highly efficient solid state laser material.     

Preparation and spectral properties of Nd3 +-doped transparent glass ceramic containing Ca5(PO4)3F nanocrystals

A Nd^3 +-doped transparent oxyfluoride glass ceramic containing Ca₅(PO₄)₃F nanocrystals was prepared by thermal treatment at the crystallization temperature for the precursor glass. The transmittances of the precursor glass and the glass ceramic with a thickness of about 2 mm are up to 84.7% and 77.4% in the visible range. The volume fraction of Ca₅(PO₄)₃F nanocrystals in the glass ceramic is about 19% and the ingress fraction of Nd^3 + ions into the Ca₅(PO₄)₃F nanocrystals is about 32%. The peak absorption cross-section increases to 224% at 807 nm and the full width at half maximum for the 807 nm band decreases from 17.5 to 3.5 nm after the crystallization process. The peak stimulated emission cross-section increases from 1.89 × 10^? 20 to 2.42 × 10^? 20 cm² at 1062 nm and the effective width of the emission line for the 1062 nm band decreases from 34 to 29 nm after the crystallization process. The improvement of spectroscopic properties indicates that the glass ceramic is potentially applicable as the 1.06 μm laser material.     

Preparation and characterization of CuO doped Bi2O3–B2O3–BaO–ZnO glass system for transparent dielectric layer

The electrical, thermal, optical, and morphological properties of CUO doped Bi₂O₃–B₂O₃–BaO–ZnO glasses were studied as a PbO-free, low firing transparent dielectric layer for plasma display panels (PDP). CuO improved the transmittance of Bi₂O₃–B₂O₃–BaO–ZnO by up to 84% in the visible region, eliminating a yellowish color typical of Bi₂O₃–B₂O₃–BaO–ZnO. A slight absorption within the near infrared (NIR) region was also observed. The glass transition temperature (T_g), thermal coefficient of expansion (TCE), and root-mean square (rms) roughness of 0.005 wt% CuO doped Bi₂O₃–B₂O₃–BaO–ZnO were found to be 455 °C, 81.4 × 10⁻⁷/K, respectively, and 162 ± 14 Å, which satisfied the requirements for a transparent dielectric layer for PDP application.     

Kerr studies of several tellurite glasses

Estimates of Kerr electrooptical sensitivity of several tellurite glasses are presented. The highest value of Kerr coefficient B ～ 190 × 10^?16 m V^?2 is registered for 0.6TeO₂–0.3TlO_0.5–0.1ZnO glass. This evidences the prospects of thallium–tellurite glass system for electrooptical applications. A gradual decrease of B from 41 × 10^?16 to 26 × 10^?16 m V^?2 in (1 ? x) TeO₂ – xNbO_2.5 system is revealed for x increasing from 0.1 to 0.15. No crystalline phase was found in that system, thus allowing attributing its Kerr sensitivity to the intrinsic properties of the glass matrix. The Kerr coefficient variation from 66 to 81 × 10^?16 m V^?2 was observed for 0.85TeO₂–0.15WO₃ glasses co-doped with small amounts of silver and cerium. The analysis of optical absorption spectra of several silver-containing tellurium–tungsten oxide glasses makes it possible to think that introducing cerium provokes formation of new mid-range orderings.     

Influence of TiO2 on proton conductivity in fuel cell electrolytes based on sol–gel derived P2O5–SiO2 glasses

P₂O₅–TiO₂–SiO₂ based glasses have been prepared by a sol–gel process. The glasses were characterized by structural, thermal, nitrogen adsorption–desorption and conductivity measurements. The structural formation has been confirmed by the FTIR and NMR analysis. The proton conductivity of the glasses increased linearly with increase in temperature. Glasses with an average pore size less than 2 nm showed higher values of proton conductivity in humid atmosphere. The conductivity value increased from 6.47 × 10⁻⁴ S/cm to 3.04 × 10⁻² S/cm at 70% RH in the temperature range 30–90 °C. We observed in fuel cell measurements that the performance of the E1 electrode is superior to that of the other electrodes at the same operating condition. The power density shows a similar pattern to current density.     

EPR and optical studies of Mn2+ ions in Li2O–Na2O–B2O3 glasses – An evidence of mixed alkali effect

EPR and optical absorption spectra of 0.5 mol% MnO₂ doped xLi₂O–(30 − x)Na₂O–69.5B₂O₃ (5 ⩽ x ⩽ 25) glasses have been studied. The EPR spectra exhibit resonance signals characteristic of Mn²⁺ ions. The resonance signal at g ≅ 2.0 is due to Mn²⁺ ions in an environment close to octahedral symmetry, whereas the resonances at g ≅ 4.3 and g ≅ 3.3 are attributed to the rhombic surroundings of the Mn²⁺ ions. The ionic character (A), the number of spins participating in resonance (N), optical band gap energies (E_opt) and Urbach energies (ΔE) show the mixed alkali effect (MAE) with composition. The present study gives an indication that the size of alkalis we choose, is also an important contributing factor in showing the MAE. The variation of N with temperature obeys the Boltzmann law. The optical absorption spectra show a single broad band at ∼21 000 cm⁻¹ corresponding to the transition ⁶A_1g(S) → ⁴T_1g(G) which exhibits a blue shift with x. The theoretical values of optical basicity (Λ_th) have also been evaluated.     

Structural impact of iron ions on BaBiBO4 glasses: Spectroscopic and dielectric investigations

Transparent glasses of composition 10BaO.20Bi₂O₃.(70 ? x)B₂O₃.xFe₂O₃ (wt.%) where 0 ≤ x ≤ 2.0, were characterized by XRD and SEM. Physical, spectroscopic and dielectric properties were investigated. At higher dopant of Fe₂O₃, EPR results revealed that, the number of Fe³⁺ ions participate in the resonance is decreased by forming a new signal at g ≈ 3.015 due to increase of antiferromagnetic interaction of Fe³⁺ ions and/or formation of low spin Fe³⁺ ions in the glass matrix. With initial 0.5 wt.% doping of Fe₂O₃, less dense glass is formed with colloids of metallic Bi⁰ atoms. The absorption bands at 604 and 712 nm in F5 glass are ascribed to Bi⁰ and Bi⁺ radicals respectively. No characteristic Fe³⁺ absorption bands (spin-forbidden) are found. Fe²⁺ ions are increased at higher concentration of Fe₂O₃. Higher concentration of Fe₂O₃ is favorable for BO₂O^?, BO₃, BiO₆ and FeO₆ symmetry unit leads to low band gap and high Urbach energy. By doping of Fe₂O₃ the dielectric parameters like dielectric constant (ε′), loss (tanδ and ac electrical conductivity (σ_ac) are found to increase.     

Spectroscopic properties of Tm3+ doped TeO2-R2O-La2O3 glasses for 1.47 μm optical amplifiers

Upon excitation at 808 nm laser diode, an intense 1.47 μm infrared fluorescence has been observed with a broad full width at half maximum (FWHM) of about 124 nm for the Tm³⁺-doped TeO₂-K₂O-La₂O₃ glass. The Judd–Ofelt parameters found for this glass are: Ω₂ = 5.26 × 10^?20 cm², Ω₄ = 1.57 × 10^?20 cm² and Ω₆ = 1.44 × 10^?20 cm². The calculated emission cross-sections of the 1.47 μm transition are 3.57 × 10^?21 cm², respectively. It is noted that the gain bandwidth, σ_e × FWHM, of the glass is about 440 × 10^?28 cm³, which is significantly higher than that in ZBLAN and Gallate glasses, a high gain of 35.5 dB at 1470 nm can be obtained in a TKL glass fiber. TeO₂-R₂O (R = Li, Na, K)-La₂O₃ glasses has been considered to be more useful as a host for broadband optical fiber amplifier.