Microstructure and Electrical Properties of Er2O3-Doped ZnO-Based Varistor Ceramics Prepared by High-Energy Ball Milling

The microstructure, electrical properties and density of ZnO-based varistor ceramics with different Er2O3 content prepared by high-energy ball milling （HEBM） and sintered at 800℃ were investigated. With increasing Er2O3 content, the ZnO grain size decreases due to the Er-rich phases inhibiting grain growth ; and nonlinear coefficient （ α ） decreases because of the decrease of barrier height （φB） The breakdown voltage （Eb） and density increase, whereas leakage current （IL） decreases with increasing Er2O3 content. The barrier height （φB）, donor concentration （Nd）, density of interface states （Ns） decrease and barrier width （ω） increases with increasing Er2O3 content due to acceptor effect of Er2O3 in varistor ceramics.     

Effects of Rare-Earth La2O3 Addition on Microstructures and Electrical Properties of SrTiO3 Varistor-Capacitor Dual Functional Ceramics

Generally, metal oxide varistors used for the pro tection of electrical circuits are based on ZnO andTiO2[1,2]. ZnO varistor, which is widely used due toits high non linearity coefficient, is composed of ZnOceramics with minor oxide additive…     

Effect of CeO2 on Electrical Properties of （Nb, Mn）-Doped TiO2 Varistor Ceramics

Varistor ceramics are a class of semiconductor de-vices with high non-linearity in their current-voltage(V-I)characteristics.Among these,ZnO varistor isthe most typical material and is commercially used asvoltage suppressor to protect electronic componentsand power systems[1~4].However,ZnOis a kind ofpure resistance component and has low permittivity,high dielectric dissipation,lowresponse speed,andpoor ability to absorb high frequency noise and pulsesurge.Soits applicationis restrictedin el…     

合金粉末预氧化法制备Ag-SnO2-Y2O3电接触材料的研究

Ag-SnO2是各国电接触材料研究人员近年来新开发的一种无镉新型触头材料,它具有较好的导电导热性,优良的耐热性、抗电弧烧蚀性和抗熔焊性,是目前代替Ag-CdO的最理想材料。本文通过合金粉末预氧化法、复合粉体改性处理技术来制备Ag-SnO2-Y2O3电接触材料,添加稀土后合金粉末容易氧化,氧化粉体经改性处理后可有效改善氧化物颗粒与银基体间的润湿性、改善材料的后续加工性能,并且所制备的Ag-SnO2-Y2O3材料密度高、组织均匀、不存在宏观偏析,SnO2和Y2O3颗粒在材料中弥散均匀分布。     

Study on BaO-Sm2O3-TiO2 Microwave Dielectric Ceramics Doped with Bismuth and Zinc

BaO-Sm2O3-TiO2 microwave dielectric ceramics doped with Bi and Zn was studied. The experiment was based on BST microwave dielectric ceramics doped with Bi2O3, which is shown by Ba4(Sm1-yBiy)28/3Ti18O54. When y=0.15, ZnO was added and the effects of ZnO on this system were studied. The result shows that the dielectric characteristics of BST microwave dielectric ceramics are the most excellent when the content of ZnO is 3%, and the optimal sintering temperature is 1200 ℃.     

Effect of Rare Earths on Mechanical Properties and Microstructure of TiCN/Al2O3 Ceramics

The effects of Y on mechanical properties and microstructure of TiCN/Al2O3 ceramics were studied in details. The experimental results show that the mechanical properties and microstructure can be improved by adding rare earth in TiCN/Al2 O3 ceramics, flexural strength and fracture toughness of the composites increased when Y is doped by 18.99% and 18.58% than those of the matrix, respectively. Microstructure of cracks extension was observed through SEM and TEM. The mechanics of particles bridge, cracks branch and cracks deflection are enforced obviously during the processes of cracks extension because strong interfaces and weak interfaces coexist, so manifold mechanics of enforcement of toughness act upon together to increase fracture toughness of TiCN/Al2 O3 doped with Y.     

Upconversion properties of Y2O3：Er films prepared by sol-gel method

Y2O3:Er3+ films were prepared by a simple sol-gel process. The structural properties of Y2O3:Er3+ flints were characterized with X-ray diffraction, Fourier transform infrared spectroscopy and field emission scanning electron microscopy. The results indicated that the Y2O3:Er3+ f'rims might have high upconversion efficiency because of their low vibrational energy. Under 785 and 980 nm laser excitation, the samples showed green (2H11/2→4I15/2, 4S3/2→4I15/2) and red (4F9/2→4I15/2) upconversion emissions. The upconversion mechanisms were stud-led in detail through laser power dependence. Excited state absorption and energy transfer process were discussed as possible upconversion mechanisms. The cross relaxation process in Er3+ was also investigated.     

Properties of La2O3-Doped PNSZT Piezoelectric Ceramics Having Tetragonal and Rhombohedral Coexistent Phases

The relationship between composition and the electric mechanical properties for La2O3-doped lead niobium stibium zirconate titanate(La2O3-doped PNSZT) piezoelectric ceramics,in which there are tetragonal and rhombohedral coexistent phases, was studied. A series of piezoelectric ceramics with good properties was obtained, having dielectric constants(ε=1500～2500), plane electromechanical coupling factor(Kp=0.45～0.65), mechanical quality factor(Qm=500～1600). These materials are used for making ultrasonic sensor and filter, and marine acoustic launching and receiving device, and so on. It has been explored that the influence of composition on the lattice constant and phase composition of La2O3-doped PNSZT piezoelectric ceramics by XRD(X-ray diffraction). The character of dielectric constant changing of La2O3-doped PNSZT piezoelectric ceramics before polarization and after polarization was studied. The affecting mechanism about composition on the electric machine properties of phase coexistent La2O3-doped PNSZT piezoelectric ceramics was analyzed and discussed.     

Spectroscopic Properties of Er^3＋-Doped TeO2-WO3-ZnO-ZnF2 Glasses

The Er^3 -doped TeO2-WO3-ZnO-ZnF2(TWZOF) glasses were prepared. The absorption spectra, 1.5μm emission spectra and fluorescence lifetimes of Er^3 , excited at 970nm, were measured. The J-O parameters Ωt(t=2, 4, 6), absorption and emission cross-sections were calculated. The dependence of the 1.5μm emission intensity, fluorescence lifetime and bandwidth of the Er^3 emission upon the contents of ZnF2 in glass were investigated. In TWZOF glass, Er^3 ions had a broad emission profile around 1.5μm with the maximum FWHM of 83nm. With the increasing of the content of ZnF2, the emission intensity at peak wavelength and the fluorescence lifetime of Er^3 at 1.5μm increase.     

A comparative study on nano La2O3 suspension treated by ultrasonic and ball milling

This paper presented a scientific study of the effects of four dispersion methods on the dispersion capability of nano La2O3 suspensions, which are ball milling, ultrasonic, ultrasonic followed by ball milling and ball milling followed by ultrasonic. For the purposes of comparing their dispersion capability, sedimentation test, Zeta-potential measurement test, particles size measurement test and transmission electron microscopy (TEM) test were carried out. Suspension ability coefficient was also defined with expectation to estimate the stability of nano La2O3 suspension through granularity size, and their relationship curve was worked out. The results showed that ultrasonic followed by ball milling enjoyed an excellent capability of dispersion for nano La2O3 suspension. Its mechanism was discussed, and breakage models of nano La2O3 particles were developed. The study results indicated that ultrasonic followed by ball milling could break through both the limits of ultrasonic dispersion size range and thermo-effect, and thus was able to overcome the problem of the secondary aggregation of nanoparticles. Moreover, aggregations could be further de-agglomerated. As a result, dispersion capability of nano La2O3 suspension could be improved more greatly by ultrasonic followed by ball milling. And its suspension stability was the best with the highest suspension ability coefficient of the nanoparticles. It was found in the experiment that there was almost no obvious phenomenon of stratification for the suspension with a little sediment after being deposited for 8 d.     

Shape-Controlled Synthesis and Upconversion Luminescence of Y2O3:Yb, Er Microstructures

The Y2O3: Yb3 , Er3 microstructures were fabricated by a hydrothermal method without surfactants.The microstructures structure was characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM,KYKY 1000B).The up-conversion luminescence spectra were studied under 978 nm laser diode excitation.In Yb3 and Er3 codoped Y2 O3 microcrystals, the relative intensity of green emission became stronger as the morphology of sample changed from wires to films.     

Optical Spectroscopy of Er^3＋ and Er^3＋/Yb^3＋ Co-doped Bi2O3-GeO2-B2O3-ZnO Glasses

The （60 - x）Bi2O3 - xGeO2-30B2O3-10ZnO （x = 5, 10, 20, 30 molar percent） glasses doped with Er^3＋ and Er^3＋/Yb^3＋ were fabricated using the melting method. The thermal stability of the glasses was studied with their DTA curves. The results show that the difference between the glass transition temperature and the crystallization onset temperature increases with the increase of GeO2 content, indicating that the thermal stability of the glass has become better. The absorption spectra were recorded and the stimulated emission cross sections were calculated using the McCumber theory. The Ω2, O4, and Ω6 parameters,the transition probability, the radiative lifetime, and the fluorescence branch ratio of Er^3＋ for optical transition were calculated from their absorption spectra in terms of reduced matrix U^（t）（λ = 2, 4, 6） character for optical transitions. The infrared emission of Er^3＋ was measured upon excitation with 970 nm light and the full width at half-maximum （FWHM） was estimated from the emission spectra. The pumping efficiency and the intensity of the emission at the 1.54 μm band of Er^3＋ were enhanced considerably by co-doping Yb^3＋ .     

Preparation and Optical Properties of Er^3＋-Doped Gadolinium Borosilicate Glasses

Er3 -doped Gd2 O3 -SiO2 -B2 O3 -Na2O glasses were prepared, and formation range of glass of Gd2 O3 -SiO2 -B2O3 system was experimentally obtained. It is found that the glass phase can be formed only when the content of SiO2 is 0～50%(molar fraction), Gd2O3 is 0～30%(molar fraction) and B2 O3 is above 20%(molar fraction) in this glass system. The glass can also be obtained but becomes translucent at the contents of 60%(molar fraction) SiO2 and 30% Gd2O3 , or at the contents of 60%(molar fraction) SiO2 and 30%(molar fraction) B2O3. There is no glass phase formed in other glass components. Glass forming ability for Gd2O3 content of 10%, was characterized by the value of β, the parameter of crystallization tendency, which is 0.32～1.76, obtained from the differential thermal analysis. The absorption and emission cross section, the J-O parameters Ωt(2,4,6) and radiative transition probabilities were calculated by using the theory of McCumber and Judd-Ofelt. The emission properties at 1.5 μm of the samples are discussed with the product of full width at half maximum and stimulated emission cross section. It can be seen that the value of the FWHM×σepeak product in the prepared glass is more than those of germanate, silicate and phosphate glasses. Furthermore, the maximum value of the product among these glasses reported in this work is close to that of oxyfluoride silicate glass. Therefore, the Er3 -doped gadolinium borosilicate glass in this paper is a candidate for broadband erbium doped fiber amplifiers.     

Effect of Y2O3 on Dielectric Properties of BaTiO3 Ceramics

Tiny amount of rare earth Y2O3 can restrain the growth of grains and broaden the peak of BaTiO3 ceramics.Proper characteristics of capacitance change with temperature were obtained. Meanwhile, the insulation resistance increased with the increasing contents of Y2O3. In this system, the cooperation of Y2O3 with Ho2O3 was also discussed.It is concluded that the insulation resistivity reduces if the content of Y2 O3 is below 0.25 %. With the increasing content of additives, weak-binding electrons in grains will be compensated by V"8a so the insulation resistivity increased. The breakdown voltage is enhanced to 15 kV · mm-1.     

Structural and Electrochemical Characteristics of Mg0.94 La0.06 Ni AlloyPrepared by Ball Milling

The amorphous Mg0.94Lao.o6Ni alloy was synthesized by ball milling for different time at 400 r min^-1. Electrochemical performances of the alloy electrodes were investigated and the results show that the specimens would reach their maximum electrochemical discharge capacities at the first charge/discharge cycle. The cyclic tests and X-ray diffraction(XRD) results show that discharge capacities would decrease rapidly due to the crystallization of the amorphous and the oxidization of magnesium on the particle surface during the electrochemical charge/discharge cycling. In addition, the DTA and SEM results reveal that the thermal stabilities will be improved and the size of the alloy will be decreased with the ball-milling time. The amorphous Mgo.96Lao.04Ni alloy prepared by ball milling for 40 h at 400 r min^-1 shows the bestelectrochemical properties.     

Upconversion luminescence of Y2O3:Er3+, Yb3+ nanoparticles prepared by a homogeneous precipitation method

Y2O3: Er3 , Yb3 nanoparticles were synthesized by a homogeneous precipitation method without and with different concentrations of EDTA 2Na. Upconversion luminescence spectra of the samples were studied under 980 nm laser excitation. The results of XRD showed that the obtained Y2O3:Er3 ,Yb3 nanoparticles were of a cubic structure. The average crystallite sizes calculated were in the range of 28-40 nm. Green and red upconversion emission were observed, and attributed to 2H11/ 2,4S3/ 2→4I15/ 2 and 4F9/ 2→4I15/2 transitions of the Er3 ion, respectively. The ratio of the intensity of green emission to that of red emission drastically changed with a change in the EDTA 2Na concentration. In the sample synthesized without EDTA, the relative intensity of the green emission was weaker than that of the red emission. The relative intensities of green emission increased with the increased amount of EDTA 2Na used. The possible upconversion luminescence mechanisms were discussed.     

高能球磨对La_(2/3)Ca_(1/3)MnO_3晶体结构和磁性的影响

通过在传统的烧结工艺上加上球磨工艺制备了单相 L a2 / 3Ca1 / 3Mn O3氧化物 ,研究了球磨对氧化物的结构和磁性能的影响 ,发现晶格常数和晶胞体积增大 ,但晶体结构类型基本不变 ,仍为钙钛矿四方相结构 ,而交流磁化率、磁化强度、居里温度减小。球磨引起氧的欠缺、无序效应 ,对电阻有一定的影响     

Study on Mg PSZ Ceramics Doped with Y_2O_3 and CeO_2

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Doping Effects of Rare Earth on Dielectric Properties of Fine－Grained BaTiO3－Based Ceramics

The doping effects of rare earth oxides Ho2O3 and Er2O3 on dielectric properties of BaTiO3-based ceramics were studied. After adding rare earth elements, grain growth in this system was inhibited and the grain size was reduced evidently which realized the fine-grained effect. In this system, the trivalent oxides Ho2O3 and Er2O3 were added to BaTiO3 ceramics. The rare earth oxides do not enter into inner lattice totally to replace A or B sites.Some of additives can improve dielectric strength by forming nonferroelectric phases, and the rest maintained at grain boundaries controls overgrowth of grains. The dielectric constant at room temperature is increased up to 3000 and the curve of TCC becomes flat.Meanwhile, the dielectric strength Eb becomes higher.     

Effect of Y2O3, CeO2 on Sintering Properties of Si3N4 Ceramics

The effect of rare earth oxides Y203 or Ce02 on sintering properties of Si3N4 ceramics was studied and the mechanism of assisting action during sintering was analyzed. The results in dicate that the best sintering properties appear in Si3N4 ceramics with 5% Y203 or 8% CeO2. Secondary crystallites are formed at grain boundaries after heat treatment,which decreases the amount of glass phase and contributes to the improvement of high-temperature mechanical properties of silicon nitride.