Influence of Ag doping on the microstructure and electrical properties of ZnO-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-based varistor ceramics

Silver in the form of AgNO₃ was added to ZnO-based varistor ceramics prepared by the solid-state reaction method. The effects of AgNO₃ on both the microstructure and electrical properties of the varistors were studied in detail. The optimum addition amount of AgNO₃ in ZnO-based varistors was also determined. The mechanism for grain growth inhibition by silver doping was also proposed. The results indicate that the varistor threshold voltage increases substantially along with the AgNO₃ content increasing from 0 to 1.5mol%. Also, the introduction of AgNO₃ can depress the mean grain size of ZnO, which is mainly responsible for the threshold voltage. Furthermore, the addition of AgNO₃ results in a slight decrease of donor density and a more severe fall in the density of interface states, which cause a decline in barrier height and an increase in the depletion layer.     

Dissolution of Al<Subscript>2</Subscript>TiO<Subscript>5</Subscript> inclusions in CaO-SiO<Subscript>2</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> slags at 1823 K

Al-Ti-O inclusions always clog submerged nozzles in Ti-bearing Al-killed steel. A typical synthesized Al₂TiO₅ inclusion was immersed in a CaO-SiO₂-Al₂O₃ molten slag for different durations at 1823 K. The Al₂TiO₅ dissolution paths and mechanism were revealed by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Decreased amounts of Ti and Al and increased amounts of Si and Ca at the dissolution boundary prove that inclusion dissolution and slag penetration simultaneously occur. SiO₂ diffuses or penetrates the inclusion more quickly than CaO, as indicated by the w(CaO)/w(SiO₂) value in the reaction region. A liquid product (containing 0.7–1.2 w(CaO)/w(SiO₂), 15wt%–20wt% Al₂O₃, and 5wt%–15wt% TiO₂) forms on the inclusion surface when Al₂TiO₅ is dissolved in the slag. Al₂TiO₅ initially dissolves faster than the diffusion rate of the liquid product toward the bulk slag. With increasing reaction time, the boundary reaches its largest distance, the Al₂TiO₅ dissolution rate equals the liquid product diffusion rate, and the dissolution process remains stable until the inclusion is completely dissolved.     

Microwave sintering of Ca<Subscript>0.6</Subscript>La<Subscript>0.2667</Subscript>TiO<Subscript>3</Subscript> microwave dielectric ceramics

Ca_0.6La_0.2667TiO₃ ceramics were prepared by conventional and microwave sintering techniques and their sinterability, microstructure, and microwave dielectric properties were investigated in detail for comparison. Densified Ca_0.6La_0.2667TiO₃ ceramics were obtained by microwave sintering at 1350°C for 30 min and by conventional sintering at 1450°C for 4 h. An unusual phenomenon was found that some larger grains (grain size range: 8–10 μm) inclined to assemble in one area but some smaller ones (grain size range: 2–4 μm) inclined to gather in another area in the microwave sintered ceramics. The microwave dielectric properties of Ca_0.6La_0.2667TiO₃ ceramics prepared by microwave sintering at 1350°C were as follows: dielectric constant (ɛ _r) = 119.6, quality factor (Qf) = 17858.5 GHz, and temperature coefficient of resonant frequency (τ _f) = 155.5 ppm/°C. In contrast, the microwave dielectric properties of the ceramics prepared by conventional sintering at 1450°C were ɛ _r = 117.4, Qf = 13375 GHz, and τ _f = 217.2 ppm/°C.     

Effects of Yb^3＋ codoping on visible and near infrared emissions of Er^3＋-Yb^3＋ codoped Al2O3 powders by the sol-gel method

The 0.1 mol% Er^3＋ and 0-2 mol% Yb^3＋ codoped Al2O3 powders were prepared by the sol-gel method, and the phase structure, including only two crystalline types of doped Al2O3 phase, γ-（Al,Er, Yb）2O3 and θ-（Al,Er, Yb）2O3, was detected at the sintering temperature of 1000℃. The visible and near infrared emissions properties depended strongly on the Yb^3＋ codoping, and the corresponding maximal peak intensities centered at about 523, 545, 660 and 1533 nm were obtained respectively for the 0.1 mol% Er^3＋ and 0.5 mol% Yb^3＋ codoped Al2O3 powders, which were composed of θ-（Al,Er,Yb）2O3 and a small amount of γ-（Al,Er, Yb）2O3 phases. The two-photon absorption process was responsible for the visible up-conversion emissions, and the one-photon absorption process was involved in the near infrared emissions of the Er^3＋-yb^3＋ codoped Al2O3 powders.     

Near-infrared to visible up-conversion emissions of Er^3＋ doped Al2O3 powders derived from the sol-gel method

The Er3 doped Al2O3 powders were prepared by the sol-gel method using the aluminium isopropoxide [Al(OC3H7)3]-derived Al2O3 sols with addition of the erbium nitrate [Er(NO3)3.5H2O]. The different phase structure, including three crystalline types of (Al,Er)2O3 phases, γ, θ, α, and two Er-Al-O phases, ErAlO3 and Al10Er6O24, was obtained with the 1 mol% Er3 doped Al2O3 powders at the different sintering temperatures of 600―1200℃. The green and red up-conversion emissions centered at about 523, 545 and 660 nm, corresponding respectively to the 2H11/2, 4S3/2→4I15/2 and 4F9/2→4I15/2 transitions of Er3 , were detected by a 978 nm semiconductor laser diodes excitation. The phase structure and OH content had evident influence on the up-conversion emissions intensity. The maximum intensities of both the green and red emissions were obtained respectively for the Er3 doped Al2O3 powders sintered at 1200 ℃, which was composed mainly of α-(Al,Er)2O3, less of ErAlO3 and Al10Er6O24 phases, and with the least OH content. The two-photon absorption up-conversion process was involved in the green and red up-conversion emissions of the Er3 doped Al2O3 powders.     

Electrodeposition and characterization of thermoelectric Bi<Subscript>2</Subscript>Se<Subscript>3</Subscript> thin films

Bi₂Se₃ thin films were electrochemically deposited on Ti and indium tin oxide-coated glass substrates, respectively, at room temperature, using Bi(NO₃)₃·5H₂O and SeO₂ as starting materials in diluted HNO₃ solution. A conventional three-electrode cell was used with a platinum sheet as a counter electrode, and a saturated calomel electrode was used as a reference electrode. The films were annealed in argon atmosphere. The influence of cold isostatic pressing before annealing on the microstructure and thermoelectric properties of the films was investigated. X-ray diffraction analysis indicates that the film grown on the indium tin oxide-coated glass substrate is pure rhombohedral Bi₂Se₃, and the film grown on the Ti substrate consists of both rhombohedral and orthorhombic Bi₂Se₃.     

Synthesis and characterization of wormhole-like mesoporous Ce0.6Zr0.35Y0.05O2 solid solutions

Nanoparticles of Ce0.6Zr0.35Y0.05O2 (CZY) solid solution have been prepared by the CTAB (hexadecyl-trimethyl ammonium bromide), CTAB-EG (ethylene glycol) templating, and CTAB-EG-NaCl (in which the pores of the precursor synthesized by the CTAB-EG method is filled by a certain amount of NaCl) method, respectively. The physical properties of these materials were characterized by means of tech-niques such as X-ray diffraction (XRD), high resolution scanning electron microscopy (HRSEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and N2 adsorp-tion-desorption measurements. The CZY samples synthesized by the above three methods display wormhole-like mesoporous morphology and cubic crystal structures. The materials are narrow in pore size distribution (averaged pore diameter = 5.3―7.1 nm), high in surface areas (95―119 m2/g), and large in pore volumes (0.16―0.18 cm3/g). It has been demonstrated that the introduction of NaCl is capable of retaining the pore structures of solid nanomaterials at high-temperature calcination.     

Fabrication and structural characterization of large-scale uniform SnO<Subscript>2</Subscript> nanotube arrays by sol-gel method

Semiconductor SnO2 nanotube arrays were fabricated by sol-gel method based on highly ordered nanoporous anodic alumina membrane. Their microstructures were characterized by scanning electron microscopy,transmission electron microscopy, selective electron diffraction spectroscopy and X-ray diffraction. Results indicated that SnO2 nanotubes have a thickness of about 20-30 nm,and a diameter of about 100-200 nm. The length of the nanotubes is about 1 μn, XRD and SEDS indicated that these SnO2 nanotubes are polycrystalline.     

Photoluminescence and cathodoluminescence properties of CaLaGa<Subscript>3</Subscript>O<Subscript>7</Subscript>:Eu<Superscript>3+</Superscript> phosphors

The CaLaGa₃O₇:Eu³⁺ phosphor was prepared by a chemical co-precipitation method. Field emission scanning electron microscopy (FE-SEM), laser particle size analysis, X-ray diffraction (XRD), photoluminescence (PL), and cathodoluminescence (CL) spectra were utilized to characterize the synthesized phosphor. The results revealed that the phosphor was composed of microspheres with a slight agglomerate phenomenon and was spherically shaped. The average grain size was about 1.0 μm. Eu³⁺ ions, as luminescent centers, substituted La³⁺ ions into the single crystal lattice of CaLaGa₃O₇ with the sites of C_s. Although the CL spectrum was greatly different from the PL spectrum, it had the strongest red emission corresponding to the ⁵D₀ →⁷F₂ transition of Eu³⁺. Under the excitation of UV light (287 nm) and electron beams (1.0–7.0 kV), the chromaticity coordinates of the phosphor were found to be in the nearly red and orange light regions, respectively.     

Synthesis, Characterization and Calorimetry of Ni（C4H8N2O3）2Cl2

A coordination complex was synthesized from NiCl2 and dipeptide glycylglycine（GG）. It was characterized by element analysis, NMR and TG methods, and then was determined to be Ni（C4HsN2O3）2Cl2. Using an isoperibolic reaction calorimeter, the standard molar enthalpy of formation of Ni（GG）2Cl2（solid） has been determined to be -（1 674.66±2.02） kJ · mol^-1 at 298.15 K.     

基于ANFIS方法的连续定向凝固BFe10-1-1合金的压缩流变应力模型

Silver in the form of AgNO3 was added to ZnO-based varistor ceramics prepared by the solid-state reaction method.The effects of AgNO3 on both the microstructure and electrical properties of the varistors were studied in detail.The optimum addition amount of AgNO3 in ZnO-based varistors was also determined.The mechanism for grain growth inhibition by silver doping was also proposed.The results indicate that the varistor threshold voltage increases substantially along with the AgNO3 content increasing from 0 to 1.5mol%.Also,the introduction of AgNO3 can depress the mean grain size of ZnO,which is mainly responsible for the threshold voltage.Furthermore,the addition of AgNO3 results in a slight decrease of donor density and a more severe fall in the density of interface states,which cause a decline in barrier height and an increase in the depletion layer.     

Effect of SiO2 addition on the dielectric properties and microstructure of BaTiO3-based ceramics in reducing sintering

The effect of SiO₂ doping on the sintering behavior, microstructure, and dielectric properties of BaTiO₃-based ceramics has been investigated. Silica was added to the BaTiO₃-based powder prepared by the solid state method with 0.075mol%, 0.15mol%, and 0.3mol%, respectively. The SiO₂-doped BaTiO₃-based ceramic with high density and uniform grain size were obtained, which were sintered in reducing atmosphere. A scanning electron microscope, X-ray diffraction, and LCR meter were used to determine the microstructure as well as the dielectric properties. SiO₂ can form a liquid phase belonging to the ternary system of BaO-TiO₂-SiO₂, leading to the formation of BaTiO₃ ceramics with high density at a lower sintering temperature. The SiO₂-doped BaTiO₃-based ceramics can be sintered to a theoretical density higher than 95% at 1220℃ with a soaking time of 2 h. The dielectric constants of the sample with 0.15mol% SiO₂ addition sintered at 1220℃ is about 9000. Doping with a small amount of silica can improve the sintering and dielectric properties of BaTiO₃-based ceramics.     

Preparation and upconversion luminescence of YVO<Subscript>4</Subscript>:Er<Subscript>3+</Subscript>, Yb<Subscript>3+</Subscript>

YVO₄:Er³⁺, Yb³⁺ with varying Yb³⁺ concentrations were prepared by a precipitation method. The results of X-ray diffraction (XRD) show that all the samples have a tetragonal zircon structure; the calculated average crystallite sizes are in the range of 14–22 nm. The lattice constants and cell volume of the samples decrease slightly with the increase in Yb³⁺ concentration. The upconversion luminescence spectra of all the samples were studied under 980 nm laser excitation. The strong green emission is observed, which is attributed to the ²H_11/2 → ⁴I_15/2 and ⁴S_3/2→⁴I_15/2 transitions of Er³⁺, and the red emission peaks in 650–675 nm can be ignored. The emission intensity for the sample depends on the Yb³⁺ concentration. These results reveal that the upconversion processes of YVO₄:Er³⁺, Yb³⁺ are related to the structure and the doping Yb³⁺ concentration of the sample.     

Preconcentration and Separation of Trace Copper in Water Samples with Nanometer-Size TiO2 Colloid and Determination by FAAS

A new absorbent of nanometer-size TiO2 colloid for Cu(Ⅱ) was studied in this work. The adsorption rate could reach above 99% when the pH values were at the range of 5-6. The adsorption balance time, adsorption capacities, and the eluent were investigated. A novel method of trace Cu(Ⅱ) preconcentration and separation with nanometer-size titanium dioxide colloid and determination by flame atomic absorption spectrometry (FAAS) was advanced. The detection limit (3σ) of the method was 1.15 μg· L~(-1) , and the relative standard deviation (R.S.D) was 1.53% (n=6). Environmental sample experiments were also conducted to test the feasibility of the method, and it came out that the recovery rates were between 95.9% and 97.8%.     

Electrochemical properties of LiNi<Subscript>0.5</Subscript>Mn<Subscript>1.3</Subscript>Ti<Subscript>0.2</Subscript>O<Subscript>4</Subscript>/Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript> cells

Spinel compounds LiNi_0.5Mn_1.3Ti_0.2O₄ (LNMTO) and Li₄Ti₅O₁₂ (LTO) were synthesized by different methods. The particle sizes of LNMTO and LTO are 0.5–2 and 0.5–0.8 μm, respectively. The LNMTO/LTO cell exhibits better electrochemical properties at both a low current rate of 0.2C and a high current rate of 1C. When the specific capacity was determined based on the mass of the LNMTO cathode, the LNMTO/LTO cell delivered 137 mA·h·g⁻¹ at 0.2C and 118.2 mA·h·g⁻¹ at 1C, and the corresponding capacity retentions after 30 cycles are 88.5% and 92.4%, respectively.     

Research on C<Subscript>3</Subscript>N<Subscript>4</Subscript> superhard compound thin film and its application

By combination of DC reactive magnetron sputtering with multiple arcplating, the alternating C₃N₄/TiN compound film is deposited onto HSS. The core level binding energy and the contents of carbon and nitrogen are characterized by X-ray photoelectron spectrum. X-ray diffraction (XRD) shows that compound thin film contains hard crystalline phases of α-C₃N₄ and β-C₃N₄. The Knoop microhardness in the load range of 50, 5–54, 1 GPa is measured. According to acoustic emission scratch test, the critical load values for the coatings on HSS substrates are in the range of 40–80 N. The metal coated with C₃N₄/TiN compound films has a great improvement in the resistance against corrosion. Many tests show that such a coating has a very high wearability. Compared with the uncoated and TiN coated tools, the C₃N₄/TiN coated tools have a much longer cutting life. Foundation item: Supported by the National Natural Science Foundation of China (19875037) Biography: Wu Da-we( (1941-), male, Professor, research direction; thin film and its application.     

Synthesis and Magnetic Properties of Spin-Liquid Tb2Ti2O7

Polycrystalline samples of a novel spin-liquid compound Tb2Ti2O7 were prepared by a standard solid-state reaction. X-ray diffraction at room temperature confirms that the synthesized compound of Tb2Ti2O7 is single phase with cubic unit cell constant a0 of 1.015 44 nm. Magnetic susceptibility measurements in the temperature range between 100 and 300 K give an effective moment of 9.44 μB and Curie-Weiss temperature of 12.68 K, respectively, indicating the dominance of antiferromagnetic interactions. However, below 50 K, the magnetic behavior of Tb2Ti2O7 deviates from Curie-Weiss law, whose origin remains suspicion.     

Preparation and characterization of γ-La<Subscript>2</Subscript>S<Subscript>3</Subscript> nanoparticles from thermal decomposition

To synthesize pure γ-La₂S₃ at lower temperature, lanthanide complex La(Et₂S₂CN)₃·phen, containing La-S bond, was chosen as the precursors to decompose. The obtained samples were characterized by X-ray power diffraction (XRD), field-emission scanning electron microscopy (FE-SEM) with an energy dispersive spectrometer and UV-Vis diffuse reflectance spectra. The decomposition mechanism of the lanthanide complex was studied by thermogravimetric analyses (TGA). The results show that the obtained samples are cubic phase particles with sizes among 20–50 nm and the band gap is 2.97 eV, which is bigger than that of its bulk crystal. TG/DTG results indicate that La(Et₂S₂CN)₃·phen decomposed to γ-La₂S₃ via La₄(Et₂S₂CN)₃ as an intermediate product.     

Immobilization of 12-phosphotungstic heteropolyacid on amine-functionalized SiO<Subscript>2</Subscript> for tetrahydrofuran polymerization

The 12-phosphotungstic heteropolyacid (HPW) was immobilized on the surface of a silica carrier modified by the amine groups of organosilane γ-aminopropyl triethoxysilane (APTES), and its catalytic performance was investigated for tetrahydrofuran (THF) ring-opening polymerization. This amine-functionalized catalyst exhibited better activity, and the polytetramethylene ether glycol (PTMG) yield was 63.7%. The 12-phosphotungstic heteropolyacid supported on aminopropyl-functionalized SiO₂ support (HPW/SiO₂-APTES) was reused four times and showed a good maintenance of activity which was better than that of the conven-tional catalyst HPW supported on SiO₂ (HPW/SiO₂). These results were obtained using infrared spectroscopy, nuclear magnetic resonance spectroscopy, nitrogen adsorption and X-ray diffraction. HPW on the HPW/SiO₂-APTES catalyst exhibited higher dispersed state and maintained a more stable structure than that of the HPW/SiO₂ sample.     

Effect of Ag addition on the thermal stability and glass-forming ability of Zr<Subscript>35</Subscript>Ti<Subscript>30</Subscript>Cu<Subscript>7.5</Subscript>Be<Subscript>27.5</Subscript> bulk metallic glass

The thermal stability and glass forming ability (GFA) of Zr35-xTi30Cu7.5Be27.5Agx (x = 0-10) alloys were studied by X-ray diffraction (XRD), differential scanning calorimetry (DSC) and ultrasonic techniques. We found that the addition of 1 at.% Ag can considerably enhance the GFA as indicated by an increase in the critical glass dimension from 15 mm in the Zr35Ti30Cu7.5Be27.5 alloy to 20 mm in the Zr34Ti30Cu7.5Be27.5Ag1 alloy. However, with the addition of more Ag the supercooled liquid region (△Tx) and y parameter (defined as Tx/(Tg+Tl)) drastically decreased from 155 K and 0.436 to 76 K and 0.363, respectively, resulting in a decrease in the GFA. Additionally, the elastic constant (the ratio of shear modulus to bulk modulus or Poisson’s ratio) was also used as a gauge to evaluate the GFA in Zr35-xTi30Cu7.5Be27.5Agx alloys.