AC Conductivity and Dielectric Behavior of Silicophosphate Glass Doped by Nd<Subscript>2</Subscript>O<Subscript>3</Subscript>

Silicophosphate glasses of nominal composition (P₂ O ₅ 50%-SiO₂ 30%-Na₂O 20%) and Nd₂ O ₃ additive (0.5 and 2 wt%) were prepared and dielectric behavior has been studied over a temperature range (302–483 K) in the frequency range (0.5 - 3243 kHz). Frequency dependence of AC conductivity (σ _ac), has been explored using the universal power law. Disparity of the frequency exponent (s) with temperature was examined in terms of diverse conduction mechanisms. The principal conduction mechanisms were found correlated to both barrier hopping (CBH) and quantum mechanical tunneling (QMT) models. Temperature dependence of σ _ac (ω) showed a linear increase with different frequencies. In addition, the capacitance, loss tangent, dielectric loss and dielectric constant were calculated over variable temperature ranges and frequencies.     

Effect of iron oxide (Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>) on the structural,optical, electrical,and dielectric properties of SrO–V<Subscript>2</Subscript>O<Subscript>5</Subscript> glasses

The oxide glass system of the composition (10 – x)SrO–xFe₂O₃–90V₂O₅, (x = 0, 2, 4, 6 and 8 mol %) were prepared by a standard melt quenching technique. The amorphous nature of the prepared glass was confirmed using X-ray diffraction technique. The infrared spectra of these glasses were recorded over a continuous spectral range (850–1500 cm^–1). The density of prepared sample was obtained by the Archimedes principle. The physical parameters of the glasses were also determined with respect to the composition. Density increases from 3.10 to 3.20 g/cm³, whereas the molar volume decreases with the increase in Fe₂O₃ concentration. In order to study optical properties, absorption spectra were measured at room temperature. Indirect optical energy band gap, optical dielectric constant, refractive index were calculated from optical energy band gap. The refractive index decreases gradually with the increase in Fe₂O₃ content due to increase of bridging oxygen’s. For temperatures from 300 to 500 K, the dc conductivity increased with the increasing Fe₂O₃ content. The dielectric properties like dielectric constant, dielectric loss factor and dielectric loss tangent investigated at the room temperature in the frequency range of 10 kHz to 1 MHz decreases with frequency. The dielectric behavior shows strong frequency as well as composition dependence.     

Electric Susceptibility and Energy Loss Functions of Carbon-Nickel Composite Films at Different Deposition Times

In this work, the optical properties of carbon–nickel films deposited at different deposition times from 50 to 600 sec were investigated. The obtained data of the refractive index n can be analyzed to obtain the high–frequency dielectric constant which describes free carriers and the lattice vibration modes of dispersion. The lattice dielectric constant ε _L and the plasma frequency ω _p at 180 sec have maximum values 10.68 and 79.92x10⁶ Hz, respectively. The free carrier electric susceptibility measurements in the wavelength range (300 – 1000 nm) are discussed according to the Spitzer–Fan model. It is shown that the electric susceptibility at 180 sec has a maximum value and with increasing wavelength it increases. The energy loss by the free charge carriers when traversing the bulk of the films at 180 sec has a maximum value and with increasing wavelength it decreases. The field emission scanning electronic microscopy (FESEM) images were used for estimation of particle size.     

Optical,Spectral, and Radiation-Shielding Properties of High-Lead Phosphate Glasses

The spectral, optical, physicochemical, radiative, and radiation-shielding properties of glasses in the PbO-P₂O₅-R _m O _n system (where R _m O _n stands for Group I–V element oxides) are investigated as a function of their composition. The composition of a colorless radiation-resistant high-lead glass suitable for production on a semicommercial scale is determined. The properties and optical quality parameters of the glass are studied. The new phosphate glass is a lead metaphosphate containing aluminum, alkali, and alkaline-earth oxides. This glass is resistant to radiation at doses up to 10⁷ R and has an optical transmission edge at 360 nm. The coefficient of absorption of gamma radiation for the new glass is larger than those of dense silicate flints. According to the optical parameters, the new glass lies between dense flints and dense barium flints in the Abbe diagram and compensates for the absence of the latter flints in catalogues of radiation-resistant glasses.     

EPR and optical studies on binary mixed alkali-alkaline earth oxide borate glasses doped with Cu<Superscript>2+</Superscript> ions

Mixed alkali alkaline earth oxide borate glasses of the composition (25 – x)Li₂O–xK₂O–12.5BaO–12.5MgO–49B₂O₃–1CuO (x = 0, 5, 10, 15 and 20 mol %) were prepared by the melt quenching technique. The X-ray diffractograms of all the glass samples were recorded at room temperature. Peak free X-ray spectra revealed the amorphous nature of all the prepared glasses. Modulated differential scanning calorimetry (MDSC) was used to determine the glass-transition temperature (T _g ). The probable mixed alkali effect was investigated using experimental techniques like density, molar volume, MDSC, electron paramagnetic resonance (EPR), and optical absorption studies. From the EPR spectra the spin-Hamiltonian parameters were evaluated. The spin-Hamiltonian parameter values indicated that the ground state of \(C{u^{2 + }}is{\kern 1pt} {d_{{x^2} - {y^2}}}\) orbital (²B_1g) and the site symmetry around Cu² is tetragonally distorted octahedral. The variation of g _|| and A _|| as a function of Li₂O content was found to be nonlinear. A broad optical absorption band was observed in all the glasses containing Cu² ions corresponding to ²B_1g → ²B_2g transition. From the optical absorption studies the values of the optical band gap (E _opt) for indirect, direct transitions and Urbarch energy (ΔE) have been evaluated. By co-relating the EPR and optical absorption data, bonding parameters α², β² and β ₁ ² were evaluated.     

Thermal,conductivity, and dielectric properties of poly(2-ethyl-2-oxazoline)-polyvinylpyrrolidone blends

Bio-compatible polymer blends of poly(2-ethyl-2-oxazoline) [PEOX] and polyvinylpyrro-lidone [PVP] were prepared at various compositions (80:20, 60:40, 40:60, and 20:80 wt%). These polymer blends were characterized by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The thermal stability of the blends was evaluated by thermogravimetry. The kinetic parameters such as activation enthalpy, ?H, activation entropy, ?S, and free energy of activation, ?G, were calculated using kinetic model given by Broido for all the blends. The thermal studies show that PEOX: PVP (20:80) blend has good thermal stability compared to other blends. The results show that thermal stability and decomposition temperature of PEOX was considerably improved by the addition of PVP. The electrical and dielectric properties of PEOX:PVP (80:20) blend were measured in the temperature range of 313 K - 353 K using an LCR meter for the frequency range 100 Hz - 8 MHz. The dielectric studies shows that dielectric constant, dielectric loss and electric modulus decreases with frequency and increases with temperature, whereas AC conductivity increases with frequency and temperature.     

Physical Properties,Optical band gaps and Radiation Shielding Parameters Exploration for Dy<Superscript>3+</Superscript>-doped Alkali/Mixed Alkali Multicomponent Borate Glasses

Six compositions of 1 mol % Dy³⁺-doped multicomponent borate glasses containing single Li₂O, Na₂O, K₂O and mixed Li₂O–Na₂O, Li₂O–K₂O, and Na₂O–K₂O oxides have been synthesized by well-known melt-quenching technique. Following the measured density and refractive index values, various physical parameters were estimated for all the glass samples and differences in them are correlated with structural changes. To explore optical properties like absorption edge (λ_cut-off), optical band gap energy (E_opt), and Urbach energy (ΔE), optical absorption spectra were recorded for all the glasses. The E_g has been calculated using Davis and Mott theory for direct allowed, and indirect allowed transitions and the results were reported. The E_g values are also estimated using absorption spectrum fitting (ASF) method. The optical parameters variations have also been associated with the structural changes occurring in the glasses with different alkali/mixed alkali oxides content presence. The shielding properties of the prepared glasses were studied in terms of effective atomic numbers (Z_eff), mean free path (MFP), half value layer (HVL) and macroscopic effective removal cross-section (Σ_R). From these results, it was found that Potassium (K) glass shows superior gamma ray shielding properties due to a higher value of Z_eff and lower values of both MFP and HVL. These results indicate that the prepared glasses might be utilized in place of some common shielding materials to shield γ-rays and neutrons.     

Phytofabrication,Characterization and Antibacterial Activity of <Emphasis Type="Italic">Cassia auriculata</Emphasis> Leaf Extract Derived CuO Nanoparticles

A simple, eco-friendly phytosynthesis of copper oxide nanoparticles (CuO NPs) using Cassia auriculata leaf extract was reported. The prepared CuO NPs was characterized by UV–vis spectroscopy which exhibited the surface plasmon resonance (SPR) band at 380–385 nm. TEM and EDX analysis confirmed that CuO NPs were spherical and in size range of 30–35 nm with identified elements Cu and O. X-ray diffraction (XRD) spectrum showed the crystalline nature of the prepared CuO NPs. FTIR spectrum confirmed the presence of Cu–O functional groups. CuO NPs showed significant antibacterial efficacy against all the tested bacterial strains, i.e., Bacillus subtilis, Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa. CuO NPs showed strong antibacterial action against B. subtilis and E. coli than P. aeruginosa and S. aureus. The results of this study revealed that C. auriculata leaf extract was found to be an effective bio-reducing agent for CuO NPs synthesis and also the antibacterial efficacy of phytofabricated CuO may be useful for its applications in medical and textile industries.     

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.     

Novel amphiphilic temperature responsive graft copolymers PCL-<Emphasis Type="Italic">g</Emphasis>-P(MEO<Subscript>2</Subscript>MA-<Emphasis Type="Italic">co</Emphasis>-OEGMA) via a combination of ROP and ATRP: synthesis,characterization, and sol-gel transition

A series of well-defined novel amphiphilic temperature-responsive graft copolymers containing PCL analogues P(αClεCL-co-εCL) as the hydrophobic backbone, and the hydrophilic side-chain PEG analogues P(MEO₂MA-co-OEGMA), designated as P(αClεCL-co-εCL)-g-P(MEO₂MA-co-OEGMA) have been prepared via a combination of ring-opening polymerization (ROP) and atom transfer radical polymerization (ATRP). The composition and structure of these copolymers were characterized by ¹H NMR and GPC analyses. The self-assembly behaviors of these amphiphilic graft copolymers were investigated by UV transmittance, a fluorescence probe method, dynamic light scattering (DLS) and transmission electron microscopy (TEM) analyses. The results showed that the graft copolymers exhibited the good solubility in water, and was given the low critical temperature (LCST) at 35(±1) °C, which closed to human physiological temperature. The critical micelle concentrations (CMC) of P(αClεCL-co-εCL)-g-P(MEO₂MA-co-OEGMA) in aqueous solution were investigated to be 2.0 × 10^?3, 9.1 × 10^?4 and 1.5 × 10^?3 mg·mL^?1, respectively. The copolymer could self-assemble into sphere-like aggregates in aqueous solution with diverse sizes when changing the environmental temperature. The vial inversion test demonstrated that the graft copolymers could trigger the sol-gel transition which also depended on the temperature.     

Density and microhardness of glasses in the SrO-B<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript> system

The density d at a temperature of 25°C is measured by the hydrostatic weighing method, the Vickers microhardness H _V is determined, and the fluctuation free volume fraction f _g is calculated for glasses in the SrO-B₂O₃-SiO₂ system with a constant strontium oxide content in the range from 35 to 45 mol %. It is demonstrated that the quantities H _V and f _g decrease and the density d increases with an increase in the SrO content.     

Synthesis and characterization of exfoliated polystyrene grafted hexagonal boron nitride nanosheets and their potential application in heat transfer nanofluids

Three different methods were used to develop surface-modified hexagonal boron nitride (h-BN) nanosheets, and polystyrene grafting was performed by an indirect covalent bond formation between modified h-BN nanosheets and styrene molecules through surface initiated atom transfer radical polymerization (SI-ATRP) approach. In all methods, an alkyl bromide as the ATRP-initiating site was first introduced on h-BN nanosheets and an SI-ATRP reaction of styrene from the initiator immobilized h-BN surface was achieved. The structure of synthesized PS grafted h-BN nanosheets (PS-g-h-BN) was identified and characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, field emission scanning electron microscopy, transmission electron microscopy, and atomic force microscopy methods. The functionalization promoted the exfoliation of h-BN layered structure into few layer sheets where the thickness of the sheets was dependent on the modification technique and the content of polymer grafted on nanosheets. The highest grafting content of PS-g-h-BN nanosheets was obtained around 20% which could enhance thermal conductivity of mineral oil-based nanofluids with the minimum concentration of the nanofiller (0.01 wt%). The electrical and physical properties of the nanofluid were also investigated. According to the results, the dielectric loss reduced by increase in nanofiller concentration was an indication of the enhanced dielectric nature of nanofluid. In addition, exfoliated PS-g-h-BN nanosheets dispersions were shown to be stable in mineral oil up to 2 months and this stability was linked to the presence of polymer chains followed by the formation of van der Walls interactions between the grafted polymer and the fluid.     

Problems of compatibility of the values of glass transition temperatures published in the world literature

The influence of different factors (primarily, the temperature-time conditions for preparation and measurement of samples) on the glass transition temperatures determined from the temperature dependences of properties is analyzed using the calculations performed in terms of the relaxation theory of glass transition. The most optimum conditions for measurement of the glass transition temperatures T _g that ensure the compatibility of the values of T _g obtained by different researchers are recommended. The validity of the assertion that the glass transition temperature T _g is a temperature at which the viscosity of glasses is equal to 10¹³ P is considered.     

Parameters of luminescence and the local structure of Eu<Superscript>3+</Superscript> centers in fluorogermanate glasses

The influence of the chemical nature of the local environment of Eu³⁺ ions on the parameters of luminescence of these centers in glasses of the (BaGeO₃)_{1 ? x ? y} (Al₂O₃) _x (0.45CaF₂ · 0.55MgF₂) _y (x = 0.25, y = 0; x = 0.17, y = 0.17; x = 0.15, y = 0.22; x = 0.07, y = 37.00; x = 0, y = 0.45) system is investigated. The oxidation state of europium atoms and the degree of homogeneity of their local environment in the glasses are determined using ¹⁵¹Eu Mössbauer spectroscopy.     

Dielectric properties of silver-doped nanoporous silicate glasses in the temperature range between –50 and +250°C

The results of measuring dielectric parameters of nanoporous silicate glasses with a nanopore size of 3.5 and 25.7 nm, either doped with silver or not, in the temperature range between–50 and +250°C and the frequency range of 0.1–10⁶ Hz are reported. It is demonstrated that when silver nanoparticles are formed in glass pores, some silver remains in the form of subnanosized molecular clusters Ag _n and molecular complexes Ag _n –(OH) _m . The key dielectric properties of the relaxation centers are determined for different temperature ranges.     

Effect of Gamma Radiation on Optical and EPR Absorption Spectra of Phosphate and Fluoride Glasses Containing Lead

The induced optical and EPR absorption spectra of phosphate and fluoride glasses containing lead are investigated. It is revealed that exposure to gamma radiation leads to the formation of radiation-induced defects responsible for the induced absorption band with a maximum at 12500–13500 cm⁻¹ and the EPR signal in the form of an almost symmetric line with a g factor of 1.999 and a linewidth of ≈26 Oe. Analysis of the intensities of the absorption bands and the EPR signals in the spectra of glasses with low terbium, tin, and carbon contents and the study of their thermal bleaching demonstrate that the color centers are electron traps, whereas the paramagnetic centers are hole-trapping centers. Examination of the change in the parameters of the absorption bands in the spectra of glasses with different R ₂O contents (R = Na, K, Rb, Cs) makes it possible to determine the location of the color centers associated with the Pb⁺ ions in the structure. It is established that the glasses under investigation are characterized by the nonlinear absorption of radiation at a wavelength of 1.06 μm. The mechanism of formation of radiation-induced defects is considered. Original Russian Text Copyright ? 2005 by Fizika i Khimiya Stekla, Bocharova, Karapetyan.     

On the critical displacement of excited kinetic units in liquids and glasses

The critical displacement of an atom (a group of atoms) in inorganic glasses Δr _m, which corresponds to the maximum of the interatomic attractive force, is calculated using available data on the surface tension and elastic constants. It is found that the critical atomic displacement Δr _m is close in order of magnitude to the linear dimension of the activation volume of atomic excitation v _h ^1/3 for glasses in the As-S and Ge-As-S systems with a chain structure and is considerably less than the value of v _h ^1/3 for alkali silicate glasses and glasses in the Cd-As system with a structure involving ionic sublattices. A relationship for calculating the activation volume of the atomic excitation from data on the glass transition temperature and elastic constants is derived within the model of an excited state.     

Glass formation in the ZrF<Subscript>4</Subscript>-BiF<Subscript>3</Subscript>-<Emphasis Type="Italic">Me</Emphasis>F (<Emphasis Type="Italic">Me</Emphasis> = Li,Na, K) fluoride systems

The glass formation in the ZrF₄-BiF₃-MeF (Me = Li, Na, K) systems is investigated. Bismuth fluorozirconate glasses are synthesized in this system, and their thermal and optical properties are described.     

Partition of <Emphasis Type="Italic">n</Emphasis>-Butanol Among Phases and Solubilization Ability of Winsor type III Microemulsions

The partition of n-butanol in Winsor type III (W-III) microemulsions was investigated in this work. Three kinds of anionic surfactants (sodium dodecyl sulfate (SDS), sodium dodecyl sulfonate (DSS), and sodium dodecyl benzene sulfonate (SDBS)) and two kinds of anionic/cationic surfactant mixtures (SDS/octadecyl trimethyl ammonium chloride (OTAC) mixtures and DSS/OTAC mixtures) were studied. Internal standard gas chromatography was employed in n-butanol content analysis. The results showed that no water exists in the excess oil (EO) phase and no oil exists in the excess water (EW) phase. For the W-III microemulsions obtained by salinity scanning, relatively constant n-butanol content in the EO (11–12 v%) and EW (1–4 v%) was found under different salinities. Accurate measurement of n-butanol content in each phase is important for those systems having low solubilization ability. For the W-III microemulsions prepared using SDS/OTAC surfactant mixture, the percentage of n-butanol distributed into the interfacial layer decreased while the fraction of n-butanol in the interfacial layer first increased sharply and then tended to be stable with the addition of n-butanol. For the different optimum W-III microemulsion systems tested, most of the surfactant-to-alcohol molar ratio data are near 1:3, but obvious deviation could be observed for some data. On the basis of the accurate measurement of n-butanol content in the EO and EW phases, the standard free energy, ΔG _o→in ^* (T = 298.15 K) of n-butanol transferring from the EO phase to the interfacial region was calculated. The results show negative ΔG _o→in ^* values. For microemulsions with the same components, n-butanol content is an important factor influencing the ΔG _o→in ^* value, and a high absolute value of ΔG _o→in ^* leads to high solubilization ability.     

Cadmium acetate as a ring opening polymerization catalyst for the polymerization of <Emphasis Type="Italic">rac</Emphasis>-lactide, <Emphasis Type="Italic">ε</Emphasis>-caprolactone and as a precatalyst for the polymerization of ethylene

In the present study, we have discussed the bulk ring opening polymerization (ROP) of rac-lactide (rac-LA) and ε-caprolactone (ε-CL) using Cd(OAc)₂. Cd(OAc)₂ appeared to be a good catalyst for the polymerization of rac-LA and ε-CL yielding high molecular weight (M _n) polymers with narrow molecular weight distributions (MWDs). The catalytic activity of the system can be increased markedly upon using catalytic amount of BnOH as external alcoholic initiator. There is a first order dependence of the rate constant with respect to monomer concentrations as understood from the kinetic studies. The rate was found to be faster in the presence of BnOH. The polymerization process was controlled. The polymerization proceeded via the coordination-insertion mechanism without BnOH as well as activated monomer mechanism in the presence of BnOH. In the absence of BnOH, the acetyl group initiated the polymerization as understood from the ¹H NMR and MALDI-TOF analysis. The benzyloxy group initiated the polymerization in the presence of BnOH. Moderate activity towards the polymerization of ethylene was observed using MAO as alkyl aluminum activator. The polymerization parameters towards the polymerization of ethylene were widely investigated.

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Graphical abstract The catalytic activity of Cd(OAc)₂ towards the ROP of rac-LA and ε-CL and precatalyst for the polymerization of ethylene were investigated.