Structural and optical properties of (100 − x)(Li2B4O7) − x(SrO–Bi2O3–0.7Nb2O5–0.3V2O5) glasses and glass nanocrystal composites

Glasses of various compositions in the system (100 − x)(Li₂B₄O₇) − x(SrO–Bi₂O₃–0.7Nb₂O₅–0.3V₂O₅) (10  x  60, in molar ratio) were prepared by splat quenching technique. The glassy nature of the as-quenched samples was established by differential thermal analyses (DTA). The amorphous nature of the as-quenched glasses and crystallinity of glass nanocrystal composites were confirmed by X-ray powder diffraction studies. Glass composites comprising strontium bismuth niobate doped with vanadium (SrBi₂(Nb_0.7V_0.3)₂O_9−δ (SBVN)) nanocrystallites were obtained by controlled heat-treatment of the as-quenched glasses at 783 K for 6 h. High resolution transmission electron microscopy (HRTEM) of the glass nanocrystal composites (heat-treated at 783 K/6 h) confirm the presence of rod shaped crystallites of SBVN embedded in Li₂B₄O₇ glass matrix. The optical transmission spectra of these glasses and glass nanocrystal composites of various compositions were recorded in the wavelength range 190–900 nm. Various optical parameters such as optical band gap (E_opt), Urbach energy (ΔE), refractive index (n), optical dielectric constant and ratio of carrier concentration to the effective mass (N/m^*) were determined. The effects of composition of the glasses and glass nanocrystal composites on these parameters were studied.     

高容量锂电池负极材料TiNb2O7的合成及其机理

将TiNb₂O₇的前驱体在不同温度(400℃、800℃、900℃、1000℃和1100℃)煅烧,用固相合成法制备TiNb₂O₇负极材料并对其样品进行了TG-DSC、XRD和SEM表征和电化学性能测试。结果表明：在900℃煅烧前驱体,锐钛矿与Nb₂O₅反应的主要产物为Ti₂Nb₁₀O₂₉。Ti₂Nb₁₀O₂₉与金红石反应生成了TiNb₂O₇,生成纯单斜相TiNb₂O₇的最佳条件为在1100℃煅烧6 h。TiNb₂O₇负极材料在0.2C电流密度时初始容量为278.4 mAh/g,初始库伦效率为82.9%。TiNb₂O₇具有良好的倍率容量,在1C循环100次后容量保持率为89%。     

Effect of La2O3 addition and O2 atmosphere on the electric properties of SnO2TiO2

The electric properties of (Sn, Ti)O₂ doped with 1.00 mol% CoO, 0.05 mol% Nb₂O₅ and x mol% La₂O₃ (0.25≤x≤1.00) have been studied. Sn_0.25Ti_0.75Co_0.01Nb_0.005 doped with 0.50 mol% La₂O₃ has a nonlinearity coefficient of 6. An increase in the concentration of La₂O₃ raised its resistivity, thereby altering the electric properties of the material. A thermal treatment in oxygen atmosphere increased the nonlinearity coefficient to a value of 9.     

Line-focus acoustic microscopy measurements ofNb2O5/MgO and BaTiO3/LaAlO3thin-film/substrate configurations

Line-focus acoustic microscopy has been used to measure the phase velocities of surface acoustic waves on bare MgO and bare LaAlO₃ , and on Nb₂O₅/MgO and BaTiO₃/LaAlO₃ thin-film/substrate configurations. The thin films are polycrystalline materials. The substrates are anisotropic single-crystals. The measured angular variation of the surface acoustic wave velocities has been used to determine the elastic constants of MgO substrate and Nb₂O₅ thin-film. It has been assumed that the Nb₂O₅ films may be considered as essentially isotropic. The measurements for LaAlO₃ and BaTiO₃/LaAlO₃ show anomalies which are attributed to twinning in the LaAlO₃ substrate     

Influence of the common varistor dopants (CoO, Cr2O3 and Nb2O5) on the structural properties of SnO2 ceramics

The influence of dopants commonly used in SnO₂ varistor ceramics, such as CoO, Cr₂O₃ or Nb₂O₅, on the structural properties of SnO₂ was investigated. Several SnO₂-based ceramics containing only one of the dopants were prepared and characterized. Spectroscopic investigations [visible, near infrared (IR) and IR region] were performed to obtain information about dopants valence states inside the ceramics, as well as about their influence on electronic structure of the material. Structural properties were investigated by X-ray diffraction analysis and mechanisms of dopant incorporation were proposed. Obtained results were confirmed with results of the electrical measurements. Microstructural changes in doped ceramics were investigated by scanning electron microscopy (SEM) analysis that showed great differences in densities, grain size, and morphology of the SnO₂ ceramics depending on type of dopants and their distribution.     

通过构筑嵌覆型碳结构提升Nb2O5的储锂性能

嵌入型过渡金属氧化物因具有安全的工作电压、高比容量和快速的嵌锂能力而受到广泛关注.但低本征电导率特性严重影响其作为锂电负极材料的寿命和性能.本文通过简便易行、可规模化放大的二氧化碳热处理方法构筑了具有新型嵌覆型碳结构的Nb₂O₅/C纳米杂化材料.在控制碳含量的前提下,实现了颗粒聚集体内部表面可控碳包覆.以嵌覆型碳结构的Nb₂O₅/C纳米杂化材料为负极组装的锂离子电池在40 mA g(-1)电流密度下容量可达387 mA hg(-1),而在200 mA g(-1)电流密度下循环500次后,容量保持率在92%以上.采用电化学滴定、差分电化学质谱(DEMS)等方法对嵌覆型五氧化二铌/碳纳米杂化材料脱嵌锂动力学过程以及产气行为进行了研究.本文提出的嵌覆型碳结构有望为高性能嵌入型过渡金属氧化物的结构设计提供参考.     

Nanocrystallization of SrBi2Nb2O9 from glasses in the system Li2B4O7---SrO---Bi2O3---Nb2O5

Transparent glasses in the system (100−x)Li₂B₄O₇–x(SrO---Bi₂O₃---Nb₂O₅) (10≤x≤60) (in molar ratio) were fabricated by a conventional melt-quenching technique. Amorphous and glassy characteristics of the as-quenched samples were established via X-ray powder diffraction (XRD) and differential thermal analyses (DTA) respectively. Glass–ceramics embedded with strontium bismuth niobate, SrBi₂Nb₂O₉ (SBN) nanocrystals were produced by heat-treating the as-quenched glasses at temperatures higher than 500 °C. Perovskite SBN phase formation through an intermediate fluorite phase in the glass matrix was confirmed by XRD and transmission electron microscopy (TEM). Infrared and Raman spectroscopic studies corroborate the observation of fluorite phase formation. The dielectric constant (_r) and the loss factor (D) for the lithium borate, Li₂B₄O₇ (LBO) glass comprising randomly oriented SBN nanocrystals were determined and compared with those predicted based on the various dielectric mixture rule formalism. The dielectric constant was found to increase with increasing SBN content in LBO glass matrix.     

Fabrication of β-Si3N4 whiskers by combustion synthesis with MgSiN2 as additives

β-Si₃N₄ whiskers with diameter of 0.5–2 μm and aspect ratio of 10–15 have been successfully prepared by combustion synthesis under 30–50 atm nitrogen pressure. The addition of MgSiN₂ powder plays a significant role in the growth of β-Si₃N₄ whiskers. The as-prepared products were characterized by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM).     

Preparation and characterization of LiAl0.23Mn1.77O4 for supercapacitor electrodes

LiAl_0.23Mn_1.77O₄ was synthesized by high temperature solid-state reaction. The structure and morphology of LiAl_0.23Mn_1.77O₄ were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS). The supercapacitive performances of LiAl_0.23Mn_1.77O₄ materials were studied using galvanostatic charge/discharge measurements, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) methods in 2 mol L⁻¹ (NH₄)₂SO₄ solution. The results show that the LiAl_0.23Mn_1.77O₄ electrode exhibits typical supercapacitive characteristics in aqueous (NH₄)₂SO₄ electrolyte. The specific capacitance is up to 185 F g⁻¹ at current density of 2 mA cm⁻². The ohmic resistance (R_sol) is only 0.22 Ω. Besides, the electrodes showed a stable cycle life in the potential range of 0–1.0 V and retained 93% of initial specific capacitance over 100 cycles.     

Preparation and photoluminescence of SrNb2O6 nanoparticles prepared by combustion method

Pure and Mn-doped SrNb₂O₆ nanoparticles have been prepared by sol–gel combustion method using citric acid as fuel and complexing agent and nitrates as oxidants at a relatively low temperature compared to solid-state reaction method. X-ray diffraction (XRD) patterns of the pure SrNb₂O₆ samples show that the SrNb₂O₆ nanoparticles exhibited orthorhombic phase. Photoluminescence (PL) properties of all the undoped and Mn-doped samples were studied in detail. For the pure SrNb₂O₆ samples, a strong blue emission band centered at 442 nm and two weak emission bands centered at 524 nm and 626 nm, respectively, can be observed. For the Mn-doped SrNb₂O₆ samples, no emission from Mn²⁺ was observed while the blue emission intensity of SrNb₂O₆ varied with the Mn-doping concentration. This novel PL characteristic of the doped samples was explained.     

Polyol method for the preparation of nanosized Gd2O3, boehmite and other oxides

A modified microwave-assisted polyol method was applied to prepare nanoparticulate ceramic powders of different oxides, i.e. Gd₂O₃, AlO(OH) (boehmite) and TiO₂. Due to the good dielectric properties of the utilised solvents, such as ethylene glycol, diethylene glycol and 1,4 butanediol, a significant decrease in reaction time was achieved under microwave heating. In the case of AlO(OH) and Gd₂O₃, <5 nm primary particle size were obtained. Boehmite was found to be intercalated with the solvent. The general applicability of the process is shown and the advantages in terms of properties and processibility are described. The powders thus prepared were investigated using X-ray diffractometry, electron microscopy and physisorption.     

Synthesis of amorphous Fe2O3 nanoparticles by microwave irradiation

Amorphous Fe₂O₃ nanoparticles of about 3–5 nm in size have been synthesized by microwave irradiation heating of an aqueous solution, containing ferric chloride, polyethylene glycol-2000 and urea. The Fe₂O₃ nanoparticles were characterized by the techniques of TEM, XRD, DSC, TGA and magnetization measurements.     

Synthesis, structure refinement and characterization of tetrahydrated acid gadolinium diphosphate HGdP2O7·4H2O

Synthesis and single crystal structure are reported for a new gadolinium acid diphosphate tetrahydrate HGdP₂O₇·4H₂O. This salt crystallizes in the monoclinic system, space group P2₁/n, with the following unit-cell parameters: a = 6.6137(2) Å, b = 11.4954(4) Å, c = 11.377(4) Å, β = 87.53(2)° and Z = 4. Its crystal structure was refined to R = 0.0333 using 1783 reflections. The corresponding atomic arrangement can be described as an alternation of corrugated layers of monohydrogendiphosphate groups and GdO₈ polyhedra parallel to the () plane. The cohesion between the different diphosphoric groups is provided by strong hydrogen bonding involving the W4 water molecule.

IR and Raman spectra of HGdP₂O₇·4H₂O confirm the existence of the characteristic bands of diphosphate group in 980–700 cm⁻¹ area. The IR spectrum reveals also the characteristic bands of water molecules vibration (3600–3230 cm⁻¹) and acidic hydrogen ones (2340 cm⁻¹). TG and DTA investigations show that the dehydration of this salt occurs between 79 and 900 °C. It decomposes after dehydration into an amorphous phase. Gadolinium diphosphate Gd₄(P₂O₇)₃ was obtained by heating HGdP₂O₇·4H₂O in a static air furnace at 850 °C for 48 h.     

Investigation of a new In2O3-based selective H2 gas sensor with low power consumption

The nanometer-size In₂O₃ was synthesized via a reverse microemulsion. A new catalytic combustion-type In₂O₃-based H₂ gas sensor was developed based on the technology for fabricating the direct-heating-type sensor and a surface-modifying process. A dense SiO₂ layer near the surface of the sensor was formed by chemical vapor deposition (CVD) of hexamethyldisiloxane (HMDS). The SiO₂ layer, which acted as a molecular sieve, reduced the penetration of large molecular, such as C₂H₅OH, CH₄, i-C₄H₁₀, into the sensing layer, resulting in the improvement of selectivity to H₂. The sensitive properties and the working mechanism of the sensor were presented. The In₂O₃ nanoparticles prepared by microemulsion were characterized by transmission electron microscopy and X-ray diffraction.     

Templated grain growth of SrBi2Ta2O9 ceramics: Mechanism of texture development

Textured SrBi₂Ta₂O₉ (SBT) ceramics were fabricated via templated grain growth (TGG) technique using platelet-like SBT single crystal templates. The templates (5 wt%) were embedded in a fine-grain SBT powder matrix containing 3 wt% of Bi₂O₃ excess that were subjected to uniaxial pressing and sintering at 1000–1250 °C for up to 24 h. Microstructural characterization by SEM was performed to establish the effect of sintering parameters on the grain growth and texture development. It was found that the ceramics developed a bimodal microstructure with notable concentration of large (longer than 90 μm) aligned grains with c-axis oriented parallel to the pressing direction. The mechanism controlling the texture development and grain growth in SBT ceramics is discussed.     

MnFe2O4/还原氧化石墨烯纳米复合材料的光学性能

由于纳米尺度的尖晶石结构金属氧化物独特的晶体结构和能带结构,使其具有广阔的应用前景。采用水热法合成了MnFe₂O₄复合还原氧化石墨烯(MnFe₂O₄/rGO)纳米复合材料,采用XRD、高分辨透射电子显微镜(HRTEM)、能量色散X射线光谱仪(EDX)、FTIR、XPS、拉曼光谱(Raman)、光致发光光谱(PL)和紫外-可见光谱漫反射(UV-vis DRS)对样品的晶体结构、形貌、元素分布、结合能和光学性能进行表征。结果表明,制备的MnFe₂O/rGO复合材料为立方尖晶石结构,形貌呈不规则的椭球形,颗粒大小比较均匀。rGO表面所负载的MnFe₂O₄纳米粒子被石墨烯部分包裹,颗粒尺寸小,分散性好。MnFe₂O₄/rGO复合材料的电子-空穴对的再结合效率降低,其中石墨烯具有较多缺陷,无序程度较高,含氧基团被聚乙烯吡咯烷酮(PVP)部分还原,数量大大减少。MnFe₂O₄/rGO复合材料的带隙小于纯MnFe₂O₄带隙,发生了红移现象。      

Influence of Mn doping on microstructure and DC-accelerated aging behaviors of ZnO–V2O5-based varistors

The microstructure, electrical properties, dielectric characteristics, and DC-accelerated aging behavior of the ZnO–V₂O₅–MnO₂ system sintered were investigated for MnO₂ content of 0.0–2.0 mol% by sintering at 900 °C. For all samples, the microstructure of the ZnO–V₂O₅–MnO₂ system consisted of mainly ZnO grain and secondary phase Zn₃(VO₄)₂. The incorporation of MnO₂ to the ZnO–V₂O₅ system was found to restrict the abnormal grain growth of ZnO. The nonlinear properties and stability against DC-accelerated aging stress improved with the increase of MnO₂ content. The ZnO–V₂O₅–MnO₂ system added with MnO₂ content of 2.0 mol% exhibited not only a high nonlinearity, in which the nonlinear coefficient is 27.2 and the leakage current density is 0.17 mA/cm², but also a good stability, in which %ΔE_1 mA = −0.6%, %Δ = −26.1%, and %Δtan δ = +22% for DC-accelerated aging stress of 0.85E_1 mA/85 °C/24 h.     

Crystal structure and characterization of [2,5-(CH3O)2C6H3NH3]4P4O12·2H2O

The preparation, crystal structure, TG–DTA analysis and spectroscopy investigation are reported for the 2,5-dimethoxy phenyl ammonium cyclotetraphosphate dihydrate [2,5-(CH₃O)₂C₆H₃NH₃]₄P₄O₁₂·2H₂O. This new compound is triclinic P with unit cell dimensions: a = 7.438(5) Å, b = 11.841(7) Å, c = 12.354(4) Å,  = 96.61(4)°, β = 98.35(4)°, γ = 102.60(6)°, Z = 1 and V = 1038.0(1) Å³. Its crystal structure has been determined and refined to R = 0.049, with 5128 independant reflections. The structure can be described by rows of P₄O₁₂ ring anions along the a axis; between these rows are located the organic groups, connected to them by hydrogen bonds.     

Influence of rare-earth oxides on structure and crystallization properties of Bi2O3–B2O3 glass

Bi₂O₃·B₂O₃ glasses doped with rare-earth oxides (RE₂O₃) (RE³⁺ = La³⁺, Pr³⁺, Sm³⁺, Gd³⁺, Er³⁺ and Yb³⁺) were prepared by the melting–quenching method. The relationships between composition and properties were demonstrated by IR, DSC, XRD and SEM analysis. The results show that the network structure resembles that of undoped Bi₂O₃·B₂O₃ glass, composing of [BO₃], [BO₄] and [BiO₆] units. RE₂O₃ stabilizes the glass structure as a modifier. Transition temperature (T_g) increases linearly with cationic field strength (CFS) of RE³⁺. La₂O₃, Pr₂O₃, Sm₂O₃ and Gd₂O₃ are benefit to promote the formation of BiBO₃ crystal. When Er₂O₃ and Yb₂O₃ are introduced, respectively, the main crystal phase changes to Bi₆B₁₀O₂₄. Transparent surface crystallized samples are obtained by reheating at 460–540 °C for 5 h. In this case, needle like BiBO₃ crystal or rare-earth-doped BiBO₃ crystal (Pr_xBi_1−xBO₃ and Gd_xBi_1−xBO₃) are observed, which is promising for non-linear optical application.     

CoFe2O4-Co3Fe7纳米粒子及CoFe2O4/多孔碳的制备及其电磁性能研究

在5% H₂+95% N₂气氛下,还原CoFe₂O₄纳米粒子制备了CoFe₂O₄-Co₃Fe₇纳米粒子;以焙烧黄麻纤维得到的多孔碳纤维为碳源用水热法将CoFe₂O₄纳米粒子负载到多孔碳中,制备出CoFe₂O₄/多孔碳。使用X射线衍射仪、扫描电子显微镜、透射电子显微镜、拉曼光谱仪、同步热分析仪等手段对材料进行表征,并使用矢量网络分析仪测量了复合材料的电磁参数和微波吸收性能。结果表明,CoFe₂O₄-Co₃Fe₇纳米粒子和CoFe₂O₄/多孔碳的微波吸收性能明显优于CoFe₂O₄纳米粒子。CoFe₂O₄-Co₃Fe₇纳米粒子的有效频宽(反射损耗<-10 dB的频率宽度)可达4.8 GHz。CoFe₂O₄/多孔碳的有效频宽可达6 GHz,覆盖了整个Ku波段(12~18 GHz)。这些材料优异的微波吸收性能,可归因于合适的介电常数、大的介电损耗、多孔结构以及介电损耗和磁损耗的协同作用。