Synthesis and characterization of LiCo0.3−xGaxNi0.7O2 (x = 0, 0.05) as a cathode material for lithium ion battery

The single phase of LiCo_0.3−xGa_xNi_0.7O₂ (x = 0, 0.05) was synthesized by a sol–gel method. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical performance. The powders are homogeneous and have a good-layered structure. The synthesized LiCo_0.25Ga_0.05Ni_0.7O₂ exhibits better electrochemical performance with an initial discharge capacity of 180.0 mAh g⁻¹ and a capacity retention of 95.2% after 50 cycles between 2.8 and 4.4 V at 0.2C rate. The study on the structural evolution of the material during the cycling shows that Ga-doping improves the structure stability of LiCo_0.3Ni_0.7O₂ at ambient temperature and 55 °C. Meanwhile, Ga-doping not only suppresses the alternating current (AC) impedance of LiCo_0.3Ni_0.7O₂ but also promotes the Li⁺ diffusion in LiCo_0.3Ni_0.7O₂. Furthermore, thermal stability of the charged LiCo_0.25Ga_0.05Ni_0.7O₂ is improved, which may be attributed to the retard of O₂ evolution in LiCo_0.3Ni_0.7O₂ and the suppression of electrolyte oxidation during cycling by Ga-doping_.     

Surface modification of LiCo1/3Ni1/3Mn1/3O2 with CoAl-MMO for lithium-ion batteries

Layered LiCo_1/3Ni_1/3Mn_1/3O₂ has been modified with Co–Al-mixed metal oxide (CoAl-MMO). The surface-modified materials were characterized by X-ray diffraction, field emission scanning electron microscopy, and galvanostatic charge–discharge cycling. The CoAl-MMO-coated LiCo_1/3Ni_1/3Mn_1/3O₂ had an initial discharge specific capacity of 178.1 mAh g⁻¹ within the potential range of 2.75–4.5 V (vs. Li⁺/Li), and its discharge specific capacity is 175.0 mAh g⁻¹ after 50 cycles, much higher than that of the pristine LiCo_1/3Ni_1/3Mn_1/3O₂ (148.4 mAh g⁻¹). The improvement could be attributed to the CoAl-MMO coating layer that would hinder interaction between LiCo_1/3Ni_1/3Mn_1/3O₂ and electrolyte and stabilize the structure of LiCo_1/3Ni_1/3Mn_1/3O₂. Moreover, DSC showed that the CoAl-MMO-coated LiCo_1/3Ni_1/3Mn_1/3O₂ had a higher thermal stability than the pristine LiCo_1/3Ni_1/3Mn_1/3O₂. Therefore, the CoAl-MMO-coated LiCo_1/3Ni_1/3Mn_1/3O₂ could be a high-performance cathode material for lithium-ion batteries.     

Influence of ZnO additive on the properties of Y-doped BaSnO3 proton conductor

The effects of ZnO additive on the phase formation, microstructure and electrical conduction of Y-doped BaSnO₃ have been investigated. The single-phase and dense BaSn_0.75Y_0.25O_3−δ compound with 4 mol% ZnO additive was successfully prepared after sintering at 1300 °C, which significantly reduces the sintering temperature. The conductivities measured under dry and wet air atmospheres reveal that the bulk conductivity of BaSn_0.71Y_0.25Zn_0.04O_3−δ is much lower than that of BaSn_0.75Y_0.25O_3−δ. However, ZnO as a sintering aid does not affect the bulk conductivity. The total conductivity of BaSn_0.75Y_0.25O_3−δ with ZnO as the sintering aid is slightly higher than that of unmodified BaSn_0.75Y_0.25O_3−δ, and reaches 2.4 × 10⁻³ S cm⁻¹ at 621 °C. Therefore, this material can be used as a proton-conducting electrolyte for intermediate temperature solid oxide fuel cells.     

Preparation and characterization of new visible-light-driven BaCo0.5Nb0.5O3 photocatalyst

A new type of visible-light-driven photocatalyst BaCo_0.5Nb_0.5O₃ was successfully synthesized via a sol-gel process in this study. After heating the precursors at 1000 °C, a pure perovskite phase was obtained. The particle size and crystallinity of BaCo_0.5Nb_0.5O₃ powders markedly increased with a rise in the calcination temperature. The band gap of BaCo_0.5Nb_0.5O₃ calculated from the UV-visible spectra was found to be less than that of titania. BaCo_0.5Nb_0.5O₃ was demonstrated to have photocatalytic activity under visible light irradiation and this activity significantly depended on the synthesis temperature. The sol-gel derived powders were found to have better photocatalytic activity than the solid-state derived powders because of the reduced particle size and increased surface area.     

Improvement in dielectric properties of Al2O3-doped Li0.30Cr0.02Ni0.68O ceramics

Li_0.30Cr_0.02Ni_0.68O giant dielectric ceramics doped with Al₂O₃ were prepared by solid-state reaction via sol-gel process. The sintered samples were characterized using X-ray powder diffraction and scanning electron microscopy, and dielectric properties were also investigated. All doped samples showed the single phase of cubic rock-salt structure NiO. With increasing Al₂O₃ content, the crystallite size and grain size decreased, possibly due to an occurrence of the secondary phases at grain boundaries which inhibit the grain growth. The sample with 0.2 wt.% Al₂O₃ showed nearly 7 times lower tanδ (2.37) and higher ε_r (7.25 × 10⁶) measured at 1 kHz and room temperature when compared to the pure sample.     

Structure and thermal conductivity of Gd2(TixZr1 − x)2O7 ceramics

The Gd₂(Ti_xZr_1 − x)₂O₇ (x = 0, 0.25, 0.50, 0.75, 1.00) ceramics were synthesized by solid state reaction at 1650 °C for 10 h in air. The relative density and structure of Gd₂(Ti_xZr_1 − x)₂O₇ were analyzed by the Archimedes method and X-ray diffraction. The thermal diffusivity of Gd₂(Ti_xZr_1 − x)₂O₇ from room temperature to 1400 °C was measured by a laser-flash method. The Gd₂Zr₂O₇ has a defect fluorite-type structure; however, Gd₂(Ti_xZr_1 − x)₂O₇ (0.25 ≤ x ≤ 1.00) compositions exhibit an ordered pyrochlore-type structure. Gd₂Zr₂O₇ and Gd₂Ti₂O₇ are infinitely soluable. The thermal conductivity of Gd₂(Ti_xZr_1 − x)₂O₇ increases with increasing Ti content under identical temperature conditions. The thermal conductivity of Gd₂(Ti_xZr_1 − x)₂O₇ first decreases gradually with the increase of temperature below 1000 °C and then increases slightly above 1000 °C. The thermal conductivity of Gd₂(Ti_xZr_1 − x)₂O₇ is within the range of 1.33 to 2.86 W m^− 1 K^− 1 from room temperature to 1400 °C.     

Transparent Ni-doped ZnO-Al2O3-SiO2 system glass-ceramics with broadband infrared luminescence

We report transparent Ni²⁺-doped ZnO-Al₂O₃-SiO₂ system glass-ceramics with broadband infrared luminescence. After heat-treatment, ZnAl₂O₄ crystallite was precipitated in the glasses, and its average size increased with increasing heat-treatment temperature. No infrared emission was detected in the as-prepared glass samples, while broadband infrared luminescence centered at 1310 nm with full width at half maximum (FWHM) of about 300 nm was observed from the glass-ceramics. The peak position of the infrared luminescence showed a blue-shift with increasing heat-treatment temperature, but a red-shift with an increase in NiO concentration. The mechanisms of the observed phenomena were discussed. These glass-ceramics are promising as materials for super broadband optical amplifier and tunable laser.     

Ferroelectric Bi3.25La0.75Ti3O12 thin films on a conductive Sr4Ru2O9 electrode obtained by pulsed laser deposition

Strontium ruthenate and Bi_3.25La_0.75Ti₃O₁₂ (BLT) layers were grown on Si(100) substrate using pulsed laser deposition technique. Starting from a Sr₂RuO₄ target, we obtained single phase films composed of Sr₄Ru₂O₉; on these strontium ruthenate electrodes, textured and non-textured BLT were grown at 700 °C. Structural characterizations of these double layers were done by X-ray diffraction, scanning electron microscopy, normal and high-resolution transmission electron microscopy. The Van der Pauw's resistivity measurements indicate that Sr₄Ru₂O₉ can be used as a back electrode. The temperature dependence of the resistivity at low temperatures is , which corresponds to a variable-range hopping mechanism.     

Effect of annealing on characteristics of Ni48Fe12Cr40/Ni80Fe20 bilayer films deposited on Si(1 0 0)/SiO2 by electron beam evaporation

Ni₄₈Fe₁₂Cr₄₀(7 nm)/Ni₈₀Fe₂₀(40 nm) bilayer films and Ni₈₀Fe₂₀(40 nm) monolayer films were deposited at ambient temperature on Si(1 0 0)/SiO₂ substrates by electron beam evaporation. The effect of annealing on the structure, composition, magnetization and magnetoresistance of the Ni₄₈Fe₁₂Cr₄₀/Ni₈₀Fe₂₀ bilayer films was investigated. The structure of the Ni₄₈Fe₁₂Cr₄₀/Ni₈₀Fe₂₀ bilayer films remains stable for annealing temperature up to 280 °C. For the as-deposited bilayer film the introducing of the Ni₄₈Fe₁₂Cr₄₀ underlayer promotes both the [1 1 1] texture and grain growth in the Ni₈₀Fe₂₀ layer. The annealing promotes the grain growth of the Ni₄₈Fe₁₂Cr₄₀/Ni₈₀Fe₂₀ bilayer films when the annealing temperature exceeds 280 °C. After annealing at a temperature over 280 °C, Cr atoms inside the Ni₄₈Fe₁₂Cr₄₀ layer diffuse into the Ni₈₀Fe₂₀ layer and segregate on the surface of the Ni₈₀Fe₂₀ layer. The Ni₄₈Fe₁₂Cr₄₀ underlayer as a seed layer can enhance the anisotropic magnetoresistance ratio of the Ni₈₀Fe₂₀ layer at a annealing temperature up to 280 °C compared with Ni₈₀Fe₂₀ monolayer film. After annealing at a temperature over 280 °C, however, the anisotropic magnetoresistance ratio of the Ni₈₀Fe₂₀ monolayer films exceeds that of the Ni₄₈Fe₁₂Cr₄₀/Ni₈₀Fe₂₀ bilayer films. For all annealing temperatures, the coercivities of the Ni₄₈Fe₁₂Cr₄₀/Ni₈₀Fe₂₀ bilayer films are smaller than those of the Ni₈₀Fe₂₀ monolayer films.     

Preparation and characterization of NiO, Fe2O3, Ni0.04Zn0.96O and Fe0.03Zn0.97O nanoparticles

Nickel oxide (NiO), iron (III) oxide (Fe₂O₃), and mixed oxide (Ni_0.04Zn_0.96O and Fe_0.03Zn_0.97O) nanoparticles were synthesized by modified sol–gel method. The nanoparticle structural and morphological properties were investigated by infrared spectroscopy (FTIR), X-ray powder diffractometry (XRD), scanning electron microscopy (SEM), and Mössbauer spectroscopy. The mixed oxides were characterized by energy-dispersive X-ray spectroscopy (EDX). The oxide precursor powders were analyzed by thermogravimetry (TG) and differential scanning calorimetry (DSC). The average sizes of the obtained NiO and Ni_0.04Zn_0.96O nanocrystallites were evaluated by X-ray line broadening using Scherrer's equation and were found to be 36 and 23 nm, respectively. Fe₂O₃ and Fe_0.03Zn_0.97O nanoparticles presented similar sizes, around 19 nm. EDX spectroscopy indicated that the calculated compositions of the mixed oxides were nearly consistent with their estimated molar ratios.     

Photoluminescence behaviors in ZnGa2O4 thin film phosphors deposited by a pulsed laser ablation

ZnGa₂O₄ thin film phosphors have been deposited using a pulsed laser deposition technique on Si (1 0 0) and Al₂O₃ (0 0 0 1) substrates at a substrate temperature of 550 °C with various oxygen pressures 100, 200 and 300 mTorr, and various substrate temperatures of 450, 550 and 650 °C with a fixed oxygen pressure of 100 mTorr. The films grown under different deposition conditions have been characterized using microstructural and luminescent measurements. Under the different substrate temperatures, ZnGa₂O₄ thin films show the different crystallinity and luminescent intensity. The crystallinity and photoluminescence (PL) of the ZnGa₂O₄ films are highly dependent on the deposition conditions, in particular, oxygen pressure, substrate temperature, a kind of substrates. The luminescent spectra show a broad band extending from 350 to 600 nm peaking at 460 nm. The PL brightness data obtained from the ZnGa₂O₄ films grown under optimized conditions have indicated that the sapphire is one of the most promised substrates for the growth of high quality ZnGa₂O₄ thin film phosphor.     

Effect of chromium substitution on structure and magnetic properties of Bi2Fe4O9

Orthorhombic Bi₂Fe_4 − xCr_xO₉ (x = 0.0, 0.25, and 0.75) nanoplatelets were synthesized by a simple hydrothermal method. The structure, morphology, and magnetic properties of the obtained powders have been characterized. Calculation of the lattice parameters of Bi₂Fe_4 − xCr_xO₉, as well as bond lengths and angles, was carried out by X-ray diffraction Rietveld refinement. The volumes of the metal-oxygen tetrahedra and octahedra were calculated to be sequentially increasing as the Cr doping level increases. The samples undergo an antiferromagnetic transition at 250 ± 5 K. The magnetic moments of the samples increase with higher Cr doping level. The 3d electron spin state for Fe³⁺ in the as-prepared samples is different, which is possibly due to the distortion of Fe-O tetrahedra and octahedra in the crystal structure after chromium substitution.     

Growth and properties of highly orientated Sr0.75Ba0.25Nb2O6 thin films on silicon substrates with MgO or TiN buffer layers

Sr_0.75Ba_0.25Nb₂O₆ (SBN75) thin films were deposited on silicon substrate with MgO (100) or TiN (100) buffer layer by radio-frequency magnetron sputtering technique. X-ray diffraction confirmed that a 900 °C annealed SBN self-buffer layer introduced before SBN deposition can lead to the highly c-axis orientation of SBN75 thin film on MgO buffer layer. Energy-dispersive spectrometry analysis showed that the SBN75 films had target-film composition transfer and the TiN buffer layer was partially oxidized during SBN growth. The refractive index of SBN films on both MgO/Si and TiN/Si substrates was determined by fitting the measured reflectance curves with Sellmeier dispersion model in the visible region and the micro-structures were studied by scanning electron microscopy. In this paper, the conditions for SBN/MgO/Si treated as waveguide structure were also discussed.     

Synthesis of porous NiFe2O4 microparticles and its catalytic properties for methane combustion

In this paper, we report the obtention of agglomerate porous NiFe₂O₄ microparticles type-spinel with uniform size of 1-2 μm by the oxalic acid co-precipitation method. The structure, morphology and surface of microparticles as-synthesized were characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy (XPS), respectively. Fixed bed reactor test confirmed that the NiFe₂O₄ microparticles exhibit a good catalytic activity for methane combustion with the methane light-off temperature below 350 °C. XPS spectrum revealed that the excellent catalytic activity may be attributed to the surface oxygen vacancies arising from the peculiar inverse spinel structure with octahedral (Oh) site occupied by Fe²⁺ and Ni²⁺ cations.     

Influence of SiO2 interlayer on the hydrophilicity of TiO2/SiO2/glass produced by RF-magnetron sputtering

The effect of silicon dioxide (SiO₂) on the hydrophilicity of the TiO₂ thin film is investigated. SiO₂ and TiO₂ films were deposited on the glass by RF-magnetron sputtering. Heat-treatment for 15 h at 573 K on TiO₂/glass and TiO₂/SiO₂/glass is carried out to make Na⁺-ion diffused from the glass to the TiO₂ thin film, which results in no band-gap change but instead the enhanced crystallinity of the anatase phase-TiO₂. This in turn leads to the improvement in hydrophilicity. Irrespective of the SiO₂ interlayer, the anatase phase-TiO₂ thin film with enhanced crystallinity shows outstanding super-hydrophilicity. Consequently, under the heat-treatment condition, the SiO₂ interlayer played an important role in improving the crystallinity of the anatase phase-TiO₂ rather than preventing Na⁺-ion diffusion.     

Syntheses of Mn3O4 and LiMn2O4 nanoparticles by a simple sonochemical method

Mn₃O₄ and LiMn₂O₄ nanoparticles were prepared by a simple sonochemical method which is environmentally benign. First, Mn₃O₄ nanoparticles were prepared by reacting MnCl₂ and NaOH in water at room temperature through a sonochemical method, operated at 20 kHz and 220 W for 20 min. Second, LiOH was coated onto the resulting Mn₃O₄ under the same sonochemical conditions as above. The thickness of coated LiOH on Mn₃O₄ obtained from the reaction ratio of 3:1 between LiOH and Mn₃O₄ was about 4.5–5.5 nm range. Then, by heating those LiOH-coated Mn₃O₄ particles at the relatively low temperature of 300–500 °C for 1 h, they were transformed into phase-pure LiMn₂O₄ nanoparticles of about 50 to 70 nm size in diameter.     

Co3O4负载rGO/g-C3N4臭氧光催化降解2,4-二氯苯氧乙酸活性研究

通过简单的水热法制备了Co₃O₄/rGO/g-C₃N₄催化剂,并在可见光照射下用于光催化臭氧氧化降解2,4-二氯苯氧乙酸(2,4-D)。利用XRD, SEM, TEM, XPS, UV-vis DRS, FT-IR和瞬态光电流对样品进行测试表征。研究表明,Co₃O₄, rGO和g-C₃N₄形成异质结后光生电子-空穴(e--h+)对的分离效率,e-的迁移能力以及光催化臭氧氧化活性都明显提升。此外,0.5Co₃O₄/0.25rGO/GCN对2,4-D具有100%的去除率,并具有最高反应速率(k=0.070 9 min^-1)。经过计算得出光催化臭氧氧化2,4-D的协同因子为3.91,表明光催化和臭氧氧化间具有较好的协同效应。活性组分的捕获实验结果表明h+和·OH是光催化臭氧氧化反应过程中的主要活性物种。此外,经过五次光催化臭氧氧化的循环实验,0.5Co₃O₄/0.25rGO/GCN样品表现处较好的稳定性,本文同时得出光催化臭氧氧化过程的反应机理。     

Conversion of V2O5·xH2O into orthorhombic V2O5 single-crystalline nanobelts

Orthorhombic V₂O₅ single-crystalline nanobelts have been synthesized by hydrothermal treating V₂O₅·xH₂O precipitate derived from aqueous solution of V₂O₅ and H₂O₂. The synthetic method is facile, fast, environmental friendly, and easy to scale up. The V₂O₅ single-crystalline nanobelts are 30-80 nm in width, 30-40 nm in thickness, and lengths up to several tens of micrometers. The V₂O₅·xH₂O precursor is crucial for the formation of orthorhombic V₂O₅ single-crystalline nanobelts. The influences of synthetic parameters, such as reaction time and reaction temperature, on the crystal structures and morphologies of the resulting products have been investigated. Time-dependent experiments show that V₂O₅·xH₂O are dehydrated gradually and converted into orthorhombic V₂O₅ single-crystalline nanobelts. High reaction temperature also favors the formation of orthorhombic V₂O₅ nanobelts.     

Influences of post-annealing on structural and electrical properties of Bi1.5Zn1.0Nb1.5O7 thin films prepared by pulsed laser deposition

Bi_1.5Zn_1.0Nb_1.5O₇ (BZN) thin films were prepared on Pt/TiO₂/SiO₂/Si(100) substrates at 650 °C under an oxygen pressure of 10 Pa by using pulsed laser deposition process. The crystallinity, microstructure and electrical properties of BZN thin films were investigated to verify the influences of post-annealing thermal process on them. The X-ray diffractometer (XRD) results indicate that all Bi_1.5Zn_1.0Nb_1.5O₇ thin films without post-annealing process or with post-annealing in situ vacuum chamber and in oxygen ambient exhibit a cubic pyrochlore structure. The improved crystallinity of BZN thin films through post-annealing was confirmed by XRD and scanning electron microscope (SEM) analysis. Dielectric constant and loss tangent of the as-deposited BZN thin films are 160 and 0.002 at 10 kHz, respectively. After annealing, dielectric properties of thin films are significantly improved. Dielectric constant and loss tangent of the in situ annealed films are 181 and 0.0005 at 10 kHz, respectively. But the films post-annealed in O₂ oven show the largest dielectric constant of 202 and the lowest loss tangent of 0.0002, which may attribute to the increase in grain size and the elimination of oxygen vacancies. Compared with the as-deposited BZN thin films, the post-annealed films also show the larger dielectric tunability and the lower leakage current density.     

High-performance Cu-doped vanadium oxide (CuxV2O5) prepared by rapid precipitation method for rechargeable batteries

Cu_xV₂O₅ (x = 0, 0.15, 0.25) was prepared by acidifying aqueous NaVO₃ with diluted H₂SO₄ followed by mixing Cu powder with V₂O₅ precipitate. The method is a rapid synthesis procedure, compared to the ion-exchange method. The effect of copper on the characteristics of V₂O₅ was also investigated. These materials maintained the layered structure typical of V₂O₅ xerogel. It was found that the copper-doped V₂O₅ material exhibits better cycle performance than the undoped V₂O₅. Cu_0.25V₂O₅ showed an initial discharge capacity of 259.2 mA h/g in the potential range of 1.5-4.0 V at 96 mA/g (C/3). After the 100 consecutive cycles, the specific capacity of the Cu_0.25V₂O₅ electrode maintained 219.5 mA h/g. The doped material prepared by the rapid method shows better a cycling performance, compared to the ion-exchange method.