Infrared absorption spectra and structure of TiO2-SiO2 composites

The composites xTiO₂-(1−x)SiO₂ (x = 0.1, 0.5, 0.9) were obtained by coprecipitation from solutions of alkoxides: tetraethoxysilane (TEOS) and titanium tetraisopropoxide (TIPT). Intermolecular interaction of the components of the composite is apparent in the IR absorption spectra in the 928–952 cm⁻¹ region, and is connected with bending vibrations of the Si-O-Ti bond. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 5, pp. 724–728, September–October, 2008.     

Tuning X/(TiO2)x–(SiO2)100 – x (0 < x < 40) xerogel photocatalysts

Microporous (TiO₂) _x –(SiO₂)_{100 − x} (0 < x < 40) xerogels have been produced by sol–gel methods either by partial pre-hydrolysis or reflux of tetraethoxysilane and titanium isopropoxide. These have been characterised by ²⁹Si nuclear magnetic resonance, X-ray diffraction, EXAFS at the Ti–K edge, X-ray photoelectron spectroscopy, temperature-programmed reduction, FT infrared, N₂ adsorption at 78 K (BET), transmission electron microscopy and dynamic light scattering (DLS). These were dip coated onto fused silica and characterised by atomic force microscopy and UV–visible absorption. Their photoactivity in removal of alkylphenol ethoxylate TX100 from water was less than for less porous titania. The advantages of including thermally removable PEG or PPG templates in terms of increasing surface, meso-porosity and photon absorbance at visible wavelengths to give nanoengineered photocatalytic films are described.     

Synthesis of Cr-based mixed oxides by reactive ion beam mixing of Cr/X interfaces (X=Al or Si)

The 3 keV O₂⁺\mathrm{O}_{2}^{+} reactive ion beam mixing of Cr/X interfaces (X=Al or Si) has been used to synthesize Cr-based mixed oxide thin films. The kinetics of growth, composition, and electronic structure of those films has been studied using X-ray photoelectron spectroscopy, Auger electron spectroscopy, ultraviolet photoelectron spectroscopy, and factor analysis. Initially, for low ion doses, Cr₂O₃ species are formed. Later, with increasing the ion dose, Cr₂O₃ species are first transformed into Cr³⁺–O–X species, and subsequently, those Cr³⁺–O–X species are transformed into Cr⁶⁺–O–X species. This sequential transformation, Cr₂O₃→Cr³⁺–O–X→Cr⁶⁺–O–X, is accompanied by a slight increase of the oxygen concentration and a decrease of the Cr/X ratio in the films formed leading to the synthesis of custom designed Cr-based mixed oxides. The changes observed in the valence band and Auger parameters further support the formation of Cr–X mixed oxide species. Angle resolved X-ray photoelectron spectroscopy shows that for low ion doses, when only Cr₂O₃ and Cr³⁺–O–X species coexist, Cr³⁺–O–X species are located nearer the surface than Cr₂O₃ species, whereas for higher ion doses, when only Cr³⁺–O–X and Cr⁶⁺–O–X species coexist, the Cr⁶⁺–O–X species are those located nearer the surface.     

Structural phase changes in a titanium-silicon system modified by high-current electron beams and compression plasma flows

Structural phase changes in a titanium-silicon system treated by low-energy high-current electron beams (HCEBs) and compression plasma flows (CPFs) with the duration 100 μs and the energy density 12–15 J/cm² are studied. Scanning electron microscopy, X-ray diffraction and electron microprobe analysis are used in this work. The formation of a titanium-doped silicon layer 10–25 μm thick, titanium silicides (TiSi₂ under HCEBs and Ti₅Si₃ under CPF treatment), silicon dendrites, and needle-like eutectics (typical size of precipitates is about 50 nm) is revealed. It is shown via the results of numerical simulation that the thickness of the metal-doped layer is mainly controlled by the power density value and the surface nonuniformity of the heat flow over the target surface. The thermodynamic regularities of phase formation are discussed, taking into account heat transfer between the silicide nuclei and solid silicon.     

Core–shell nanostructures and nanocomposites of Ag@TiO2: effect of capping agent and shell thickness on the optical properties

Two different shell-forming reagents viz. titanium isopropoxide and titanium hydroxyacylate, have been employed to obtain core–shell nanostructures of Ag@TiO₂. However, nanocomposites were formed when the shell-forming agent, titanium isopropoxide, was added before breaking the micelles. Titanium hydroxyacylate has been used for the first time as a shell-forming agent which resulted in uniform core–shell structures of Ag@TiO₂ with core diameter ranging from 10 to 40 nm and a shell thickness of 10–50 nm. The low rate of hydrolysis of titanium hydroxyacylate than titanium isopropoxide (used in other methods) appears to be responsible for the uniform shell thickness. The presence of capping agent (2-mercaptoethanol) disrupts the formation of a uniform shell structure of Ag@TiO₂. HRTEM, IR, and XPS studies of Ag@TiO₂ synthesized using capping agent show the formation of Ag₂S coated with an amorphous layer of TiO₂. A red shift of 25 and 10 nm was observed in the surface plasmon band of silver for Ag@TiO₂ core–shell structures (compared with that of silver nanoparticles) synthesized using titanium hydroxyacylate and titanium isopropoxide, respectively. The presence of capping agent (2-mercaptoethanol) masks the surface plasmon peak. Photoluminescence studies show an increase in the emission intensity for the core–shell structures when compared to that of TiO₂ nanoparticles.     

Electrical characterization of highly Titania doped YSZ

The defect fluorite region of the ternary system ZrO₂-Y₂O₃-TiO₂ encompasses compositions which offer both, good electronic and oxygen ion conductivity which enable good catalytic activity for the direct oxidation of methane in a solid oxide fuel cell (SOFC). The electrical properties of compositions Y_xTi_yZr_1−(x+y)O_2−x/2 (with x=0.15, 0.2, 0.25 and y=0.15, 0.18) were characterised in order to find the composition with highest ionic and electronic conductivity. High titanium dopant concentrations (Y) of 15 and 18 atom%, near the solubility limit of Ti⁴⁺ in the fluorite structure, have been introduced to achieve a high electronic conductivity at low oxygen partial pressure. The yttrium content x has been varied between 15 and 25 atom% to find the fluorite composition with the highest ionic conductivity for each titanium level. In the pO₂-range from 0.21 to 10⁻¹³ atm the conductivity is predominantly ionic and constant over that range. The maximum ionic conductivity is 0.01 Scm⁻¹ for the compositions, which contain 15 atom% yttrium. Substantial electronic conductivity is introduced into the system at low oxygen pressures below 10⁻¹³ atm via reduction of Ti⁴⁺ ions to Ti³⁺. The maximum electronic conductivity of 0.2 Scm⁻¹ at 930 °C has been measured for a sample with 18 atom% titanium. The slope of all log(σ) vs. log(pO₂) plots follows a pO ₂ ^−1/4 -dependence. Paper presented at the 5th Euroconference on Solid State Ionics, Benalmádena, Spain, Sept. 13–20, 1998.     

Intense formation of intermetallic phases during implantation of aluminum ions in titanium

The results from microstructure and phase composition investigations of titanium in different structural states (with average grain sizes of 0.3 μm, 1.5 μm, and 17 μm) are presented following Al ion implantation using the Mevva-V.RU source (irradiating dose, 10¹⁸ ion/cm²). The implanted multiphase layers are found to form on the base of α-Ti grains. The size, shape, and localization of the formed phases (TiO₂, Ti₂O, TiC, Ti₃Al, Al₃Ti) depend strongly on the grain size of titanium target. It is shown that the nanostructural particles of TiO₂ phase are located mainly on dislocations in the body of target grains. A Ti₂O surface layer is found to arise in titanium with a grain size of 17 μm. It is established that an ordered Ti₃Al phase is located at a depth of more than 200 nm in the implanted layer along the bounaries of the titanium grains.     

Vibrational spectra of thin eulytine films

This is a study of IR reflection spectra of systems of a thin Bi₄X₃O₁₂(X=Si, Ge) film and a substrate of fused quartz v-SiO₂ in the range 400–1600 cm⁻¹ at T=295 K. Bands assigned to Bi₄X₃O₁₂ are interpreted. It is found that single-photon processes are exhibited in the range 400–800 cm⁻¹, while biphonon processes, in the range 800–1600 cm⁻¹. I. Franko State University of Lvov, 50 Dragomanov St., 290005, Lvov, Ukraine. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 4, pp. 494–498, July–August, 1997.     

Comparison of optical properties and mechanical/electrical degradation of some low density polyethylene-and polypropylene-based polymer blends

In this study, the optical properties as well as mechanical and electrical degradation of low-density polyethylene (LDPE)/polypropylene fiber (PP fiber) (10–50% PP fiber), polypropylene (PP)/PP fiber (10–50% PP fiber), and LDPE/diamond (0.1–3% diamond) blends, which are prepared by hot pressing method, with changing thicknesses ranging from 30 to 225 μm, are compared. The spectra, in the wavelength range 200–2500 nm, are examined. Based on optical absorption spectra obtained, Tauc graphs are plotted. Determined values of the direct optical energy gap (E _d ^opt ), the indirect optical energy gap (E _i ^opt ), the width of the band (ΔE), and ultraviolet transmittance (T_UV) are listed. The direct E _d ^opt and indirect E _i ^opt values for organic blends are in the range of 3.10–3.17 eV and 1.52–2.99 eV; for inorganic blends they are 1.80–4.13 eV and 1.55–4.7 eV respectively. The electrical strength (ε) and the mechanical tension (σ) have been investigated, and graphs (the dependence of the electrical life time log τ_ε on ε) are given. The experimental results are analyzed from the viewpoint of the validity of the thermofluctuation theory. LDPE and LDPE/0.5% diamond composite parameters consecutively changed: σ from 68 to 82 MPa, ε from 60·10⁶ to 85·10⁶ V/m, mechanical lifetime τ_σ from 10 to 1.5·10⁵ sec, electrical lifetime τ_ε from 2· 10³ to 2·10⁵ sec, and structure-sensitive parameters γ and χ — from 1.48 to 1.18 (J)MPa/mole and from 0.97 to 0.70 (J)Vm⁻¹/mole respectively. The values of mechanical and electrical durability were observed to increase by 20 and 41%, respectively, for LDPE/0.5% diamond composite. Published in Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 5, pp. 677–683, September–October, 2007.     

Characterization and antibacterial functions of Ag–TiO<Subscript>2</Subscript> and W–TiO<Subscript>2</Subscript> nanostructured thin films prepared by sol-gel/laser-induced technique

A novel sol-gel/laser-induced technique (SGLIT) has been developed to form nanocrystalline titanium dioxide (TiO₂) based thin films with an improved antibacterial performance. TiO₂ precursor films loaded with W⁺⁶ and Ag⁺² ions (W–TiO₂, Ag–TiO₂) were prepared separately by sol-gel method and spin-coated on microscopic glass slides. As-dried films were subjected to KrF excimer laser pulses at optimized parameters to generate mesoporous anatase and rutile phases at room temperature. The anatase phase was obtained after irradiation with 10 laser pulses only at 75–85 mJ/cm² fluence in W–TiO₂ films. However, higher number of laser pulses and higher W⁺⁶ content favored the formation of rutile. Whereas Ag–TiO₂ films exhibited anatase up to 200 laser pulses at the same fluence. The films were characterized by using XRD, FEG-SEM, TEM and UV-Vis spectrophotometer to investigate the crystallographic structure, phase transformation, surface morphology, film thickness and the optical properties. A crystallite size of approximately 20 nm was achieved from the anatase prepared by SGLIT. The films exhibited an enhanced antibacterial function against E-Coli cells under the UV excitation.     

ESR of V4+ in α-RbTiOPO4 single crystals

We have recorded and investigated the ESR spectrum of vanadium-doped α-RbTiOPO₄ single crystals in the temperature interval 77–300 K. Two types of structurally distinct centers, V1 and V2, with a 4:1 ratio of the peak intensities were observed. The angular dependences of the resonance magnetic fields are described by a spin Hamiltonian corresponding to axial symmetry with the parameters g _∥1=1.9305, g _⊥1=1.9565, A _∥1=−168.2×10⁻⁴cm⁻¹, and A _⊥1=−54.3×10⁻⁴cm⁻¹ for V1 centers and g _∥2=1.9340, g _⊥2=1.9523, A _∥2=−169.0×10⁻⁴cm⁻¹, and A _⊥2=−55.2×10⁻⁴cm⁻¹ for V2 centers. A model of a paramagnetic center is proposed: The vanadium ions replace titanium ions in two structurally distinct positions Ti1 and Ti2 (V1 and V2 centers, respectively). The possibility that a VO²⁺ ion forms when α-RbTiOPO₄ crystals and crystals of the KTP group (KTiOPO₄, NaTiOPO₄, α-and β-LiTiOPO₄), studied earlier, are doped with vanadium is discussed. Fiz. Tverd. Tela (St. Petersburg) 40, 534–536 (March 1998)     

Titanium K-edge absorption structure in Ti1−x NbxO2

The fine structure in the titanium x-ray K-edge absorption has been measured in Ti_1−x Nb_xO₂ mixed dioxides (x=0–0.1) with rutile structure in a laboratory-type spectrometer by total electron quantum-yield measurement. The position of the XANES lines is shown to be in good agreement with classical x-ray absorption spectra obtained in transmission. The structure and main features of the XANES spectra, including the effects of impurities and manyelectron excitations, are discussed. It is suggested that the intensity of the B peak characteristic of the titanium K edge depends on the Nb concentration and correlates with the charge state of titanium ions. Fiz. Tverd. Tela (St. Petersburg) 41, 894–896 (May 1999)     

Spectroscopic investigation of the plasma of a high-current diffuse discharge in He/Ar/CF2Cl2(CCl4) mixtures

Survey emission spectra in the region of 190–600 nm and time and service-life characteristics of a transverse nanosecond discharge in He/Ar/CF₂Cl₂(CCl₄) mixtures at a pressure of 10–100 kPa are investigated. In the emission spectra, excited products of the decomposition of freons—C₂(A−X), CN(B−X), Cl ₂ ^* , C^*, Cl^*, and Cl^+*— and the emission of ArF at λ=193 nm are revealed. The emissions of Cl ₂ ^* at λ=258 nm and ArF at λ=193 nm were the most intense. The discharge in the He/Ar/CF₂Cl₂ mixture is a multiwave emission source with λ=258 nm Cl ₂ ^* 193 nm ArF, and probably, 175 nm Arcl. It is of interest for applications in UV-VUV-range pulse photometry. The duration of the emission on Cl ₂ ^* , ArF, ArI, ClI, and ClII transitions in the discharge in the Ar/CF₂Cl₂ mixture (P=10–20 kPa) was 200–300 nsec. With adding He and increasing pressure to 100 kPa the duration of the emission decreased by a factor of 1.5–2. The basic mechanisms of the formation of Cl₂, ArF, and CN(B) molecules in the transverse-discharge plasma are considered. Uzhgorod State University, 46, Pidgirna Str., Uzhgorod, 294000, Ukraine. Translated from Zhurnal. Prikladnoi Spektroskopii, Vol. 66, No. 2, pp. 241–246, March–April, 1999.     

Spectral-luminescent properties of condensation products of 8-aminoquinoline,aromatic aldehydes,and dimedone

Hydrobenzophenanthrolinone derivatives were synthesized by three-component condensation of 8-aminoquinoline, aromatic aldehydes, and dimedone. The structures of the obtained substances were confirmed by NMR and IR spectroscopy and mass spectrometry. Spectral-luminescent investigations of the synthesized compounds showed that they were characterized by high oscillator strengths for allowed electronic transitions S _n ← S ₀ (n = 1–3). Low fluorescence quantum yields in EtOH (Φ_fl ~ 10^–4–10^–3) and an increase of the Φfl values in toluene (~10^–2) at room temperature and with lowering the temperature to 77 K (Φ_fl ~ 10^–1) for a number of the compounds under study were satisfactorily explained within the framework of Marcus theory.     

Spectral and kinetic characteristics of CdI<Subscript>2</Subscript> and CdI<Subscript>2</Subscript>:Pb scintillators

We have studied the effect of lead dopant on the optical absorption, photoluminescence, and x-ray luminescence spectra, and the scintillation characteristics of CdI₂ at room temperature. The crystals for the study were grown by the Stockbarger-Bridgman method. Activation of CdI₂ from the melt by the compound PbI₂ leads to the appearance in the absorption spectra in the near-edge region of an activator band at 395–405 nm, which is interpreted as an A band connected with electronic transitions from the ¹S₀ state to the ³P₁ levels in the Pb²⁺ ion. For x-ray excitation, CdI₂:Pb²⁺ crystals with optimal dopant concentration (∼1.0 mol%) are characterized by a light yield with maximum in the 570–580 nm region that is an order of magnitude higher than for CdI₂ crystals in the 490–500 nm band. For α excitation, the radioluminescence kinetics for cadmium iodide is characterized by a very short (∼0.3 nsec) rise time and fast decay of luminescence, with τ₁ ≈ 4 nsec and τ₂ = 10–76 nsec. Depending on the conditions under which the crystals were obtained, the fast component fraction is 95%–99%. The crystal is characterized by a similar scintillation pulse in the case of excitation by x-ray pulses. The radioluminescence pulse shape for CdI₂:Pb in the decay stage is predominantly exponential, with luminescence decay time constants τ₁ ≈ 10 nsec and τ₂ = 200–250 nsec. This system is characterized by low afterglow, at the level for the Bi₄G₃O₁₂ scintillator. We have demonstrated the feasibility of using CdI₂:Pb as a scintillator for detecting α particles. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 6, pp. 825–830, November–December, 2008.     

Studying the electronic structure of Cr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Ti<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Se<Subscript>2</Subscript> by X-ray resonance and absorption spectroscopy

Cr _x Ti_{1 − x} Se₂ (x = 0–0.83) solid solutions have been synthesized. Single crystals have been grown in the range of concentrations x = 0–0.83. Structural studies of samples have revealed that chromium atoms substitute titanium in the TiSe₂ matrix. The X-ray photoelectron spectra of the core levels, the resonance spectra of the valence bands in 1T-Cr _x Ti_{1 − x} Se₂, and the X-ray absorption spectra of titanium and chromium are studied. The titanium and chromium atoms are shown to have oxidation numbers of +4 and +3, respectively, in an identical octahedral environment. The local density of chromium states has been calculated. The results of the calculation agree well with the experimental data and indicate that the electronic 3d states of chromium substituting titanium in the matrix are spin-polarized and the density of chromium states is halfmetal magnet in behavior.     

Light intensity and temperature dependence on performance of a photoelectrochemical cells of ITO/TiO<Subscript>2</Subscript>/PVC-LiClO<Subscript>4</Subscript>/graphite

The photovoltaic characteristics of a photoelectrochemical cell of ITO/TiO₂/PVC-LiClO₄/graphite are reported. This paper is concerned with the influence of light intensity and temperature on short-circuit current density, J_sc and open-circuit voltage, V_oc of the device. The photoelectrochemical cell material was a screen-printed layer of titanium dioxide onto an ITO-covered glass substrate, which was used as a working electrode of the cell. The solid electrolyte was polivinylchloride-lithium perchlorate. The graphite film serves as a counter electrode of the cell. The current density–voltage characteristics of the device under an illumination of 20, 40, 60, 80 and 100 mW cm⁻² light from a tungsten halogen lamp were recorded at 40 °C as well as under an illumination of 100 mW cm⁻² at 30, 35, 40, 45 and 50 °C, respectively. It was found that the short-circuit current density, J_sc of the device increases with both light intensity and temperature. The J_sc obtained at 100 mW cm⁻² was 1.0 μAcm⁻² and that at 50 °C was 0.7 μAcm⁻².     

Pseudo-capacitive properties of LiCoO<Subscript>2</Subscript>/AC electrochemical capacitor in various aqueous electrolytes

LiCoO₂ particles were synthesized by a sol-gel process. X-ray diffraction analysis reveals that the prepared sample is a single phase with layered structure. A hybrid electrochemical capacitor was fabricated with LiCoO₂ as a positive electrode and activated carbon (AC) as a negative electrode in various aqueous electrolytes. Pseudo-capacitive properties of the LiCoO₂/AC electrochemical capacitor were determined by cyclic voltammetry, charge–discharge test, and electrochemical impedance measurement. The charge storage mechanism of the LiCoO₂-positive electrode in aqueous electrolyte was discussed, too. The results showed that the potential range, scan rate, species of aqueous electrolyte, and current density had great effect on capacitive properties of the hybrid capacitor. In the potential range of 0–1.4 V, it delivered a discharge specific capacitance of 45.9 Fg^–1 (based on the active mass of the two electrodes) at a current density of 100 mAg^–1 in 1 molL^–1 Li₂SO₄ aqueous electrolyte. The specific capacitance remained 41.7 Fg^–1 after 600 cycles.     

Effect of alkali-metal doping on photoluminescence of CdS films

It is established that doping of CdS polycrystalline films with alkaline metals (Li, Na, K, Cs) results in an increase of luminescence intensity by 3–5 times compared with pure films. This increase is accounted for by the placement of alkaline-metal ions in V _Cd ²⁻ cation vacancies, which are nonradiative recombination centers in these films. From the dependences of the luminsecence intensity of the doped films on the synthesis conditions (deposition temperature, concentration of doping impurities, type of doping metal), the parameters that ensure the maximum luminescence intensity of the films are determined as T_dep ≈ 450°C and C_Me = 1·10⁻⁵ at %. The luminescence intensity decreases by 1–3% upon exposure of the films to UV light (λ_max = 365 nm, I = 10²¹ quanta·sec·cm⁻¹) for several hours. This is indicative of the stability of these films against UV radiation. __________ Translated from Zhurnal Prikladnoi Spektroskopii Vol. 74, No. 3, pp. 362–366, May–June, 2007.     

Grafted natural rubber-based polymer electrolytes: ATR-FTIR and conductivity studies

Attenuated total reflectance–Fourier transformed infrared spectroscopy measurement is employed to study the interactions between the components of 30% methyl-grafted natural rubber (MG30), lithium trifluromethanesulfonate (LiCF₃SO₃ or LiTF), and propylene carbonate (PC). Vibrational spectra data of LiTF reveals that the ν_s(SO₃) at 1,045 cm⁻¹, δ_s(CF₃) at 777 cm⁻¹, and C=O stretching mode at 1,728 cm⁻¹ for MG30 have shifted to lower wave numbers in MG30–LiTF complexes indicating that complexation has occurred between MG30 and LiTF. The solvation of lithium ion is manifested in Li⁺ ← O=C interaction as shown by the downshifting and upshifting of C=O mode at 1,788 to 1,775 cm⁻¹ and ν_as(SO₃) at 1,250 to 1258 cm⁻¹, respectively, in LiTF–PC electrolytes. There is no experimental evidence of the interaction between MG30 and PC. Competition between MG30 and PC on associating with lithium ion is studied, and the studies show that the interaction between MG30–LiTF is stronger than that of the PC–LiTF in plasticized polymer–salt complexes. The effect of PC on the ionic conductivity of the MG30–LiTF system is explained in terms of the polymer, plasticizer, and salt interactions. The temperature dependence of conductivity of the polymer films obeys the Vogel–Tamman–Fulcher relation. Values of conductivity and activation energy of the MG30-based polymer electrolyte systems are presented and discussed.