Evolution of MgAl<Subscript>2</Subscript>O<Subscript>4</Subscript> crystals in Al-Mg-SiO<Subscript>2</Subscript> composites

The present study analyzes the morphological transformations of reaction products i.e., MgO, MgAl₂O₄ occurring during the reaction between SiO₂ and Al-Mg alloy in Al-Mg-SiO₂ composite processed by the liquid metallurgy technique. Different phases of platelet and hexagonal morphologies are detected and their composition analysis by EDS has confirmed them as being transition phases existing between MgO, MgAl₂O₄ and Al₂O₃. This study has also revealed the gradual transformation of (i) MgO needles to octahedral MgAl₂O₄ through Mg-Al-Si-O and Mg-Al-O transition phases having platelet morphologies and (ii) MgAl₂O₄ to Al₂O₃ through hexagonal transition phases on holding of Al-5Mg-SiO₂ and Al-1Mg-SiO₂ composites respectively at 1023K. Fully developed α-Al₂O₃ crystals are not observed under the present experimental conditions, wherein the Mg content is well above the equilibrium Mg content required for the formation of stable Al₂O₃ (<0.05 wt. %). PACS 05.70.Np     

UV-protection properties of electrospun polyacrylonitrile nanofibrous mats embedded with MgO and Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticles

This article describes the ultraviolet (UV) protection of MgO and Al₂O₃ nanoparticles embedded electrospun polyacrylonitrile (PAN) nanofibrous mats. UV radiation is a harmful part of sunlight and prolonged exposure to it can cause serious skin damages. In this research, nanofibrous mats consisting of nanofibers with different diameters containing different amounts of MgO, Al₂O₃, MgO Plus, and Al₂O₃ Plus nanoparticles were produced, and their UV-protection was measured. The specific surface area of MgO, MgO Plus, Al₂O₃, and Al₂O₃ Plus nanoparticles was 230, 600, 275, and 550 m²/g, respectively. The mean diameter of electrospun PAN nanofibers embedded with metal oxide nanoparticles was in the range of 665–337 nm. The results showed that the UV-protection (shielding) capability of the mats strongly depends on fiber diameter; in fact a thin mat of nanofibers has a much stronger UV-protection in comparison to a thicker mat composed of regular fibers. UV transmission is reduced as a result of embedding MgO and Al₂O₃ nanoparticles in the electrospun PAN nanofibrous mats. MgO Plus and Al₂O₃ Plus show higher UV-protection than MgO and Al₂O₃.     

Synthesis and characterization of mono-dispersed Y<Subscript>3</Subscript>Al<Subscript>5</Subscript>O<Subscript>12</Subscript>:Er<Superscript>3+</Superscript>-coated SiO<Subscript>2</Subscript> nanoparticles by co-precipitation process

In this paper, a facile co-precipitation process for preparing mono-dispersed core–shell structure nanoparticles is reported. The 110 nm SiO₂ cores coated with an yttrium aluminum garnet (Y₃Al₅O₁₂) layer doped with Er³⁺ were synthesized and the influence of the concentration ratio of [urea]/[metal ions] on the final product was investigated. The structure and morphology of samples were characterized by the X-ray powder diffraction, Fourier transform IR spectroscopy and transmission electron microscopy, respectively. The results indicate that a layer of well-crystallized garnet Y₃Al₅O₁₂:Er³⁺ were successfully coated on the silica particles with the thickness of 20 nm. The near infrared and upconversion luminescent spectra of the SiO₂@Y₃Al₅O₁₂:Er³⁺ powders further confirm that a Y₃Al₅O₁₂:Er³⁺ coating layer has formed on the surface of silica spherical particles.     

Investigation on structural characteristics of PVDF–AgCF<Subscript>3</Subscript>SO<Subscript>3</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanocomposite solid polymer electrolyte system

There has been an increasing interest towards the incorporation of nanosize ceramic fillers in polymer electrolytes. Solid polymer electrolytes based on polyvinylidene fluoride (PVDF), silver triflate (AgCF₃SO₃), and x wt% of aluminum oxide (Al₂O₃) nanopowders (where x = 1, 3, 5, and 10, respectively) have been prepared using solution casting technique. The structural characteristics of these thin film specimens were studied using Fourier transform infrared (FTIR) and X-ray diffraction (XRD) patterns at room temperature. The appearance of new absorption bands and gradual shifts observed in some characteristic peaks confirmed the complex formation between polyvinylidene fluoride and silver triflate. Furthermore, the addition of nanosized filler Al₂O₃ has also indicated the interaction of the filler with the polymer salt complex. The XRD patterns obtained for all these samples in the 2θ range 10° to 70° showed the amorphous nature of these samples. Paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamilnadu, India, December 7–9, 2006.     

The influence of Fe,Cu, SiO<Subscript>2</Subscript>, TiO<Subscript>2</Subscript>, and Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticles in aqueous solution on proton relaxation times

Measurements of proton nuclear spin-spin and spin-lattice relaxation times are applied for determining the concentration of solid-phase nanoparticles in nanofluids. This approach is tested for metal oxides SiO₂, TiO₂, Al₂O₃ and metal-carbon nanoparticles of 3d-metals Fe and Cu. It is shown that the sensitivity of the method for determining concentrations of 3d-metals is much higher than for oxides (by 2–4 orders of magnitude). It is revealed that measurement of the proton spin-spin relaxation time allows one to determine the concentration of Cu nanoparticles to 0.0001 mg/ml and that of Fe nanoparticles to 0.00001 mg/ml.     

Magnetic properties of LiNi<Subscript>0.5</Subscript>Mn<Subscript>0.47</Subscript>Al<Subscript>0.03</Subscript>O<Subscript>2</Subscript> as positive electrode for Li-ion batteries

The layered LiNi_0.5Mn_0.47Al_0.03O₂ was synthesized by wet chemical method and characterized by X-ray diffraction and analysis of magnetic measurements. The powders adopted the α-NaFeO₂ structure. This substitution of Al for Mn promotes the formation of Li(Ni_0.47²⁺Ni_0.03³⁺Mn_0.47⁴⁺Al_0.03³⁺)O₂ structures and induces an increase in the average oxidation state of Ni, thereby leading to the shrinkage of the lattice unit cell. The concentration of antisite defects in which Ni²⁺ occupies the (3a) Li lattice sites in the Wyckoff notation has been estimated from the ferromagnetic Ni²⁺(3a)–Mn⁴⁺(3b) pairing observed below 140 K. The substitution of 3% Al for Mn reduces the amount of antisite defects from 7% to 6.4–6.5%. The analysis of the magnetic properties in the paramagnetic phase in the framework of the Curie–Weiss law agrees well with the combination of Ni²⁺ (S = 1), Ni³⁺ (S = 1/2) and Mn⁴⁺ (S = 3/2) spin-only values. Delithiation has been made by the use of K₂S₂O₈. According to this process, known to be softer than the electrochemical one, the nickel ions in the (3b) sites are converted into Ni⁴⁺ in the high spin configuration, while Ni²⁺(3a)–Mn⁴⁺(3b) ferromagnetic pairs remain, as the Li⁺(3b) ions linked to the Ni²⁺(3a) ions in the antisite defects are not removed. The results show that the antisite defect is surrounded by Mn⁴⁺ ions, implying the nonuniform distribution of the cations in agreement with previous NMR and neutron experiments.     

Synthesis and luminescent properties of Eu<Superscript>3+</Superscript>- and Eu<Superscript>2+</Superscript>-activated sodium pyrophosphate Na<Subscript>4</Subscript>P<Subscript>2</Subscript>O<Subscript>7</Subscript>

The luminescent properties of Eu³⁺ and Eu²⁺ ions in sodium pyrophosphate, Na₄P₂O₇, have been studied. The excitation spectrum of the Eu³⁺ emission in Na₄P₂O₇ consists of several sets of bands in the range 280–535 nm due to 4f–4f transitions of Eu³⁺ ions and a broad band with a maximum at about 240 nm interpreted to be due to a charge transfer (CT) transition from oxygen 2p states to empty states of the Eu³⁺ 4f⁶-configuration. Although the CT band energy is large enough, the quantum efficiency (η) of the Eu³⁺ emission in Na₄P₂O₇ under CT excitation was estimated to be very low (η ≤ 0.01). In terms of a configurational coordinate model, this fact is interpreted as a result of the high efficiency of a radiationless relaxation from the CT state to the ⁷F₀ ground state of Eu³⁺ ions occupying sodium sites in Na₄P₂O₇. A strong reducing agent is required in order to stabilize Eu²⁺ ions in Na₄P₂O₇ during the synthesis. Several nonequivalent Eu²⁺ luminescence centers in Na₄P₂O₇ were found.     

Silver Nanoparticle-Enhanced Chemiluminescence Method for Determining Naproxen Based on Europium(III)-Sensitized Ce(IV)-Na<Subscript>2</Subscript>S<Subscript>2</Subscript>O<Subscript>4</Subscript> Reaction

A simple and sensitive chemiluminescence (CL) method coupled with flow-injection technique is proposed to determine naproxen (NAP). The method is based upon the enhancement of the weak CL signal arising from the reaction of Ce(IV) and Na₂S₂O₄ with Eu³⁺ to form the Eu³⁺-Ce(IV)-Na₂S₂O₄ system. The CL intensity was significantly increased by the introduction of NAP into this system in the presence of silver nanoparticles (Ag NPs). Examination of the recorded UV–vis spectra and fluorescence spectra indicated that the energy of the intermediate SO₂*, which originated from the redox reaction of Ce(IV) and Na₂S₂O₄, was transferred to Eu³⁺ via NAP and that the process was accelerated by Ag NPs due to their catalytic activity. Under the optimum conditions, the CL intensity was increased with increasing NAP concentration and the correlation was linear (r = 0.9992) over the NAP concentration range of 1–420 ng mL⁻¹. The limit of detection (LOD) was 0.11 ng mL⁻¹ with a relative standard deviation (RSD) of 1.15% for 5 replicate determinations of 200 ng mL⁻¹ NAP. The method was successfully applied to determine NAP in pharmaceutical and biological samples.     

Tunable optical parametric oscillator based on a KTP crystal,pumped by a pulsed Ti<Superscript>3+</Superscript>:Al<Subscript>2</Subscript>O<Subscript>3</Subscript> laser

We present the characteristics of an optical parametric oscillator based on a KTP crystal, pumped with noncritical phase matching by a pulsed Ti³⁺:Al₂O₃ laser, tunable in the range 677–970 nm. Tunable generation of signal and idler waves is obtained in the ranges 1030–1390 nm and 2690–3050 nm respectively. The efficiency of conversion of the pump to the signal wave is ≈23%, which for pulses of duration ≈8 nsec ensures an energy in the range 1.0–11.5 mJ. The width of the emission spectrum for the signal wave is within the range 0.8–1.8 nm and is predominantly determined by the linewidth of the Ti³⁺:Al₂O₃ pump laser. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 3, pp. 351–356, May–June, 2007.     

Tunable bluish green to yellowish green Ca<Subscript>2(1-x)</Subscript>Sr<Subscript>2x</Subscript>Al<Subscript>2</Subscript>SiO<Subscript>7</Subscript>:Eu<Superscript>2+</Superscript> phosphors for potential LED application

A series of solid solutions with a general formula of Ca_2(1-x)Sr_2xAl₂SiO₇:Eu²⁺ were synthesized by a high temperature solid state reaction. The structure, diffuse reflection spectra, photoluminescence spectra, color-coordinate parameters and lifetimes of phosphors were investigated. XRD results show that Ca₂Al₂SiO₇ is totally miscible with Sr₂Al₂SiO₇. These solid solution phosphors show a broad excitation band of 350–450 nm that matches well with the output lights of near-UV LEDs and tunable emission from bluish green to yellowish green. These optical properties originate from the 4f⁷–4f⁶5d transition of Eu²⁺ ions. The crystal field strength was considered to be tailed by controlling the host composition, which leads to the shift of absorption band and emission band, and the varying of color coordinates. PACS  78.55.-m; 42.70.-a; 61.05.C-     

Preparation and investigation of composite SiO<Subscript>2</Subscript>-TiO<Subscript>2</Subscript> films

SiO₂-TiO₂ films [Si:Ti = 1:(0.06–2.3)] are obtained by the sol-gel method. The structural and photoluminescent properties of the films and powders heat-treated at different temperatures are studied. It is shown that after 700°C the composite consists of TiO₂ crystallites that are structurally similar to anatase and distributed in an amorphous SiO₂ matrix. The photoluminescence spectra have maxima at 450–500 nm. The photoluminescence intensity depends on the treatment temperature and TiO₂ content. __________ Translated from Zhurnal Prikladnoi Spektroskopii Vol. 74, No. 3, pp. 357–361, May–June, 2007.     

Tunneling conductivity in lithiated transition metal oxide cathode Li<Subscript>0.9</Subscript>[Ni<Subscript>1/3</Subscript>Mn<Subscript>1/3</Subscript>Co<Subscript>1/3</Subscript>]O<Subscript>1.95</Subscript>

Electrical complex ac conductivity of the compound Li_0.9[Ni_1/3Mn_1/3Co_1/3]O_1.95 has been studied in the frequency range 10 Hz–2 MHz and in the temperature range 93–373 K. It has been observed that the frequency dependence of the ac conductivity obeys a power law and the temperature dependence of the ac conductivity is quite weak. The experimental data have been analyzed in the framework of several theoretical models based on quantum mechanical tunneling and classical hopping over barriers. It has been observed that the electron tunneling is dominant in the temperature range from 93 K to 193 K. A crossover of relaxation mechanism from electron tunneling to polaron tunneling is observed at 193 K. Out of the several models discussed, the electron tunneling and the polaron tunneling models are quite consistent with the experimental data for the complex ac conductivity. The various parameters obtained from the fits of the experimental results for the real and imaginary parts of the conductivity to the predictions of these models are quite reasonable.     

Microstructure,dielectric and piezoelectric properties of (K<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>)NbO<Subscript>3</Subscript>-Ba(Ti<Subscript>0.95</Subscript>Zr<Subscript>0.05</Subscript>)O<Subscript>3</Subscript> lead-free ceramics with CuO sintering aid

Using an ordinary ceramic fabrication technique, we fabricated lead-free (1-x)(K_0.5Na_0.5)NbO₃-xBa(Ti_0.95Zr_0.05)O₃ ceramics with CuO sintering aid . Ba(Ti_0.95Zr_0.05)O₃ diffuses into (K_0.5Na_0.5)NbO₃ to form a new solid solution. The ceramics with perovskite structure possess orthorhombic phase at x≤0.04 and become tetragonal phase at x≥0.06. Both the paraelectric cubic–ferroelectric tetragonal and the ferroelectric tetragonal–ferroelectric orthorhombic phase transition temperatures decrease with increasing the concentration of Ba(Ti_0.95Zr_0.05)O₃. The doping of CuO effectively promotes the densification of the ceramics. The coexistence of the orthorhombic and tetragonal phases at 0.04<x<0.06 and the improvement in sintering performances of the ceramics significantly enhance the piezoelectric and dielectric properties at room temperature. The ceramics with x=0.04–0.06 and y=0.75–1.50 possess excellent properties: d₃₃=119–185 pC/N, k_P=37–44%, k_t=35–49%, ε=341–1129, cosδ=0.7–4.4% and T_c=312–346 °C. PACS 77.65.-j; 77.84.Dy; 77.84.-s     

Thermal conductivity,heat capacity,and thermodynamic functions of the Bi<Subscript>4</Subscript>Ge<Subscript>3</Subscript>O<Subscript>12</Subscript> single crystal

The thermal conductivity and the heat capacity of a single crystal of bismuth orthogermanate Bi₄Ge₃O₁₂ have been experimentally investigated in the temperature ranges 50–300 and 56–300 K, respectively. The temperature dependences of the phonon mean free path, the characteristic Debye temperature, and the changes in the entropy and enthalpy have been calculated.     

RETRACTED ARTICLE: Refractive-index tailoring and morphological evolutions in Gd<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript> and ZrO<Subscript>2</Subscript>–SiO<Subscript>2</Subscript> composite thin films

Refractive-index tailoring and morphological evolutions in two different thin film composite systems of gadolinia–silica (Gd₂O₃:SiO₂) and zirconia–silica (ZrO₂:SiO₂) deposited through reactive electron-beam codeposition processes are discussed in this research paper. For Gd₂O₃:SiO₂ the refractive-index tuning has been achieved from 1.45 to 2.18, whereas in the case of ZrO₂:SiO₂ the achieved tunable range is from 1.45 to 2.45 in the ultraviolet region. Under certain compositional mixings with lower silica fractions both the systems demonstrated relative microstructural and morphological densifications. Such evolutions were very successfully derived through phase-modulated ellipsometry and atomic force microscopy. The composition-dependent refractive-index tailoring and microstructural densifications have been investigated by adopting Tauc–Lorentz and single-effective-oscillator models. The morphological correlation functions have also very aptly supported such evolutions in these composite films. These experimental results indicate their favourable properties and applicability down to the extreme ultraviolet wavelength region of the electromagnetic spectrum. PACS 42.79.Wc; 78.66.-w; 78.20.Ci; 61.16.Ch; 42.70.-a;68.55.-a; 68.35.Bs; 81.15.Ef     

Enhanced photoluminescence of Ca<Subscript>2</Subscript>Al<Subscript>2</Subscript>SiO<Subscript>7</Subscript>:Eu<Superscript>3+</Superscript> by charge compensation method

The effect of compensator on optical properties of Ca₂Al₂SiO₇:Eu³⁺ is systematically investigated by the X-ray powder diffraction, photo-luminescence (PL) properties and lifetime. It is obviously observed that the PL intensity of Eu³⁺ under 394 nm excitation increases in the order of Ca_1.86Eu_0.14Al₂SiO₇ (CAS), Ca_1.72Na_0.14Eu_0.14Al₂SiO₇ (CASNa) and Ca_1.86Eu_0.14Al_2.14Si_0.86O₇ (CASAl), the intensity of Eu³⁺ are 100%, 134%, 184%, and the lifetime of Eu³⁺ are 0.75 ms, 1.28 ms and 1.39 ms, respectively. A charge compensation model is proposed to explain the changes in the emission intensity and lifetime of Eu³⁺ in Ca₂Al₂SiO₇ with different compensation methods. PACS 78.55.-m; 61.72.Ji; 61.43.Gt; 42.70.-a; 74.62.Dh     

Synthesis and nanostructural investigation of TiO<Subscript>2</Subscript> nanorods doped by SiO<Subscript>2</Subscript>

TiO₂ Nano rods can be used as dye-sensitized solar cells, various sensors and photocatalysts. These nanorods are synthesized by a hydrothermal corrosion process in NaOH solution at 200°C using TiO₂ powder as the source material. In the present work, the synthesis of TiO₂ nanorods in anatase, rutile and Ti₇O₁₃ phases and synthesis of TiO₂ nanorods by incorporating SiO₂ dopant, using the sol–gel method and alkaline corrosion are reported. The morphologies and crystal structures of the TiO₂ nanorods are characterized using field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM) and X-ray diffraction (XRD) study. The obtained results show not only an aggregation structure at high calcination temperatures with spherical particles but also Ti–O–Si bonds having four-fold coordination with oxygen in SiO^4 −.     

Solid polymeric electrolyte of PVC–ENR–LiClO<Subscript>4</Subscript>

The ionic conductivity of PVC–ENR–LiClO₄ (PVC, polyvinyl chloride; ENR, epoxidized natural rubber) as a function of LiClO₄ concentration, ENR concentration, temperature, and radiation dose of electron beam cross-linking has been studied. The electrolyte samples were prepared by solution casting technique. Their ionic conductivities were measured using the impedance spectroscopy technique. It was observed that the relationship between the concentration of salt, as well as temperature, and conductivity were linear. The electrolyte conductivity increases with ENR concentration. This relationship was discussed using the number of charge carrier theory. The conductivity–temperature behaviour of the electrolyte is Arrhenian. The conductivity also varies with the radiation dose of the electron beam cross-linking. The highest room temperature conductivity of the electrolyte of 8.5 × 10⁻⁷ S/cm was obtained at 30% by weight of LiClO₄. The activation energy, E _a and pre-exponential factor, σ _o, are 1.4 × 10⁻² eV and 1.5 × 10⁻¹¹ S/cm, respectively.     

Electrical characterization of the [N(CH<Subscript>3</Subscript>)<Subscript>4</Subscript>][N(C<Subscript>2</Subscript>H<Subscript>5</Subscript>)<Subscript>4</Subscript>]ZnCl<Subscript>4</Subscript> compound

The [N(CH₃)₄][N(C₂H₅)₄]ZnCl₄ compound has been synthesized by a solution-based chemical method. The X-ray diffraction study at room temperature revealed an orthorhombic system with P2₁2₁2 space group. The complex impedance has been investigated in the temperature and frequency ranges 420–520 K and 200 Hz–5 MHz, respectively. The grain interior and grain boundary contribution to the electrical response in the material have been identified. Dielectric data were analyzed using the complex electrical modulus M ^* for the sample at various temperature. The modulus plots can be characterized by full width at half height or in terms of a non-exponential decay function ϕ(t) = exp[(−t/τ) ^β ]. The detailed conductivity study indicated that the electrical conduction in the material is a thermally activated process. The variation of the AC conductivity with frequency at different temperatures obeys the Almond and West universal law.     

The transport and thermal properties of glassy LiPO<Subscript>3</Subscript>/crystalline Al<Subscript>2</Subscript>O<Subscript>3</Subscript> (ZrO<Subscript>2</Subscript>) composite electrolytes

Glassy LiPO₃/crystalline Al₂O₃ and glassy LiPO₃/crystalline ZrO₂ (0–12.5 vol.% of oxide fillers) composite solid electrolytes have been prepared by glass matrix softening. Their thermal and transport properties have been investigated by differential scanning calorimetry (DSC) and impedance spectroscopy methods. The addition of ZrO₂ leads to a decrease in the crystallization temperature of LiPO₃ glass. It was found that the conductivity behavior depends on the nature of the dispersed addition. In the case of the Al₂O₃ addition, the increase in the electrical conductivity is observed. The ionic conductivity of the LiPO₃/10% Al₂O₃ composite reaches 5.8 × 10^?8 S/cm at room temperature. In contrast, the conductivity in the LiPO₃/ZrO₂ composite system decreases.