Microstructure and electrical properties of La2O3-doped ZnO-based varistor thin films by sol-gel process简

Microstructure and electrical properties of La2O3-doped ZnO-Bi2O3 thin films prepared by sol-gel process have been investigated. X-ray diffraction shows that most diffraction peaks of ZnO are equal, and the crystals of ZnO grow well. Scanning electron microscopy and atomic force microscopy results indicate that the samples have a good structure and lower surface roughness. The nonlinear V-I characteristics of the films show that La2O3 develops the electrical properties largely and the best doped content is 0.3% lanthanum ion, with the leakage current of 0.25 mA, the threshold field of 150 V/mm and the nonlinear coefficient of 4.0 in detail.     

Influence of Ag doping on the microstructure and electrical properties of ZnO-Bi2O3-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 1.5mo1％.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 SiO_2 addition on the microstructure and electrical properties of ZnO-based varistors

The microstructure and electrical properties of ZnO-based varistors with the SiO 2 content in the range of 0-1.00mol% were prepared by a solid reaction route.The varistors were characterized by scanning electron microscopy,X-ray diffraction,energy-dispersive X-ray spectrometry,inductively coupled plasma-atomic emission spectrometry,and X-ray photoelectron spectroscopy.The results indicate that the average grain size of ZnO decreases with the SiO 2 content increasing.A new second phase (Zn 2 SiO 4) and a gla...     

高能振动球磨作用对纳米Al2O3相变温度的影响

为了探讨球磨作用对纳米A l2O3颗粒相变温度的影响,利用高能振动球磨机分别对纳米A l2O3进行不同时间的球磨,并将球磨作用后的A l2O3粉末在不同温度下进行退火处理。采用XRD、TEM、FT-IR及DTA等方法测定处理前后A l2O3粉末的结构、物相组成及相变温度。结果表明:随着球磨时间的增长,A l2O3的相变温度降低,当球磨时间达50 h时,-γA l2O3到θ-A l2O3相变以及-θA l2O3到-αA l2O3相变的温度均降低了100℃左右;球磨作用促进了A l2O3的晶化,同时可以造成纳米氧化铝的晶格缺陷,是导致相变温度降低的主要原因。     

反应高能球磨制备纳米WC/MgO复合粉末

将WO3、C和Mg粉末按摩尔比为1∶1∶3混合,在室温下用高能球磨法对其进行球磨,经XRD、SEM和TEM分析表明,在球磨到4.7 h时,WO3、石墨和镁之间发生氧化还原反应直接生成了WC和MgO粉末,之后随球磨时间的延长,粉末不断细化.球磨50 h后,得到WC晶粒度和颗粒度分别约为25 nm和100 nm的WC/MgO复合粉末.实验结果和热动力学分析表明,WC/MgO的合成是一个自蔓延反应过程,此反应可以在很短的时间内完成.     

Preparation of MgTiO3 Ceramics by High Energy Ball Milling

1 IntroductionMgTiO3ceramic is widely usedin manufacturing ce-ramic capacitors with a super thermal stability,due toitssmall dielectricloss and dielectric constant .However ,thesinteringtemperature of pure MgTiO3ceramicis as highas1 400-1 470 ℃even withfluxingagents .Inaddition,thesinteringrangeis much narrower withthe addition of flux-ing agents ,which makes it difficult to sinter[1].High-energy ball milling is an effective grindingmeans whichinduces a series of physicochemical changesto t…     

Microstructure and properties of Si3N4 ceramics obtained from addition of β-phase seeds and celsian

The silicon nitride based ceramics obtained by the addition of β-Si3N4 seeds was fabricated using celsian as the additive and by pressureless sintering. The microstructure of the material was observed and analyzed using XRD, SEM, and TEM and the mechanical response of this array microstructure was characterized for flexural strength and fracture behavior. The result shows that the growth of the larger aspect ratio grains initiate mainly from the seeds through the heterogeneous nucleation mechanism during the process of phase transformation, and the intergranular phase BaAl2Si20s services as good refractory materials. In contrast to conventional processing, a stable bimodal microstructure and complicated component with a lower cost can be achieved using the abovementioned process theoretically and practically.     

Microstructure and mechanical properties of 8YSZ ceramics by liquid-phase sintering with CuO-TiO2 addition

The 8% (mass fraction) yttrium-partially-stabilized zirconia (8YSZ) ceramic was fabricated via liquid phase sintering at 1 200–1 400 °C by adding different mass ratios of CuO-16.7%TiO₂ (molar fraction) as sintering aid. Relative density, microstructure, Vickers hardness and bending strength as a function of sintering temperature and additive content were investigated. The experiment results show that liquid phase sintering at low temperature can be realized through adding CuO-16.7% TiO₂ to 8YSZ. The Vickers hardness and bending strength of samples with sintering aid are generally much higher than those of samples without sintering aid for all sintering temperatures, and increase with the increase of sintering temperature. When the addition content of CuO-16.7% TiO₂ is beyond 0.5%, the relative density, Vickers hardness and bending strength decrease with the increase of the mass ratio of sintering aid. Low additions of sintering aid are beneficial to aiding densification; high additions of sintering aid are detrimental to the sintered properties mainly due to greater amounts of pores generated by the volatilization of oxygen with the eutectic reaction between copper oxide and titanium dioxide. It is found that the fine grain size and high relative density are two main reasons of the high bending strength and Vickers hardness of the materials.     

Microstructure and microwave dielectric properties of CaO-B2O3-SiO2 glass ceramics with various B2O3 contents

The effects of B2O3 addition on both the sintering behavior and microwave dielectric properties of CaO-B2O3-SiO2 (CBS) glass ceramics were investigated by Fourier transform infrared spectroscopy (FTIR),X-ray diffractometry (XRD) and scanning electron microscopy (SEM).The results show that the increasing amount of B2O3 causes the increase of the contents of [BO3],[BO4] and [SiO4],which deduces the increase of CaB2O4 and α-SiO2 and the decrease of CaSiO3 correspondingly.No new phase is observed throughout the...     

Microstructure and microwave dielectric properties of lead borosilicate glass ceramics with Al2O3

The effects of Al₂O₃ addition on both the sintering behavior and microwave dielectric properties of PbO-B₂O₃-SiO₂ glass ceramics were investigated by Fourier transform infrared spectroscope (FTIR), differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that with the increase of Al₂O₃ content the bands assigned to [SiO₄] nearly disappear. Aluminum replaces silicon in the glass network, which is helpful for the formation of boron-oxygen rings. The increase of the transition temperature T _g and softening temperature T _f of PbO-B₂O₃-SiO₂ glass ceramics leads to the increase of liquid phase precipitation temperature and promotes the structure stability in the glasses, and consequently contributes to the decreasing trend of crystallization. Densification and dielectric constants increase with the increase of Al₂O₃ content, but the dielectric loss is worsened. By contrast, the 3% (mass fraction) Al₂O₃-doped glass ceramics sintered at 725 °C have better properties of density ρ=2.72 g/cm³, dielectric constant ɛ _r =6.78, dielectric loss tan δ=2.6×10⁻³ (measured at 9.8 GHz), which suggest that the glass ceramics can be applied in multilayer microwave devices requiring low sintering temperatures.     

Effects of aluminum doping on the microstructure and electrical properties of ZnO-Pr6O11-Co3O4-MnCO3-Y2O3 varistor ceramics

The effect of Al2O3 doping on the microstructure and electrical properties of the ZnO-Pr6O11-Co3O4-MnCO3-Y2O3 system was investigated in the range of 0.0-0.1mol%. The results reveal that Al2O3 doping has slight influence on the densification process. The microstructure of the ceramics comprises of ZnO phase, ZnAl2O4 spine phase and Pr-rich phases. The addition of Al2O3 greatly affects the electrical properties. The varistor voltage(E1mA/cm2) of ZPCMYAl samples decreases over a wide range from 5 530 V/cm to 1 844 V/cm with the increasing Al2O3 content. The nonlinear exponent(α) increases with the increasing Al2O3 content to 0.01mol%, whereas it is decreased by the further doping. The ZPCMYAl-based varistor ceramics with 0.01mol% Al2O3 exhibit the best electrical properties, with the nonlinear exponent(α) attaining the highest value of 33.4 and the lowest leakage current of 2.7 μA. The capacitance-voltage(C-V) measurement shows that the donor density(N d) at the grain boundaries increase from 1.58×1018 to 3.15×1018 cm-3, the barrier height(j b) increases from 1.60 to 2.36 eV, and the depletion layer width(t) decreases from 24.9 to 21.6 nm.     

Low-temperature sintering and microwave dielectric properties of Li2MgTi3O8 ceramics doped with BaCu（B2O5）

The influences of BaCu(B₂O₅) (BCB) addition on sintering, microstructure and microwave dielectric properties of Li₂MgTi₃O₈ ceramics were investigated using X-ray diffractometry, scanning electron microscopy and microwave dielectric measurements. The experimental results show that a small amount of BaCu(B₂O₅) addition can effectively reduce the sintering temperature to 900 °C, and induce only a limited degradation of the microwave dielectric properties. Typically, the best microwave dielectric properties of ɛ _r=24.5, Q×f =24 622 GHz, τ _f=4.2×10⁻⁶ °C⁻¹ are obtained for 1.0% BCB-doped Li₂MgTi₃O₈ ceramics sintered at 900 °C for 3 h. The BCB-doped Li₂MgTi₃O₈ ceramics can be compatible with Ag electrode, which may be a strong candidate for low temperature co-fired ceramics applications.     

Influence of soaking time on nonlinear electrical behavior and dielectric properties of TiO2-based varistor ceramics

The influence of soaking time on the nonlinear electrical behavior and dielectric properties of TiO₂-based varistor ceramics was investigated. Based on single sintering process, six disk samples of (Sr, Bi, Si, Ta)-doped TiO₂-based varistor ceramics were fabricated by sintering at 1 250 °C for 0.5–5.0 h. The samples were characterized by X-ray diffraction, voltage-current characteristics, energy spectra, metallographs, breakdown voltages, and apparent dielectric constant. It is found that the breakdown electrical field intensity at a current density of 10 mA/cm² decreases from 5.5 to 4.1 V/mm first and then increases to 7.0 V/mm, the nonlinear coefficient increases from 2.39 to 2.62 first and then decreases to 2.42, and the apparent dielectric constant increases from 98 200 to 115 049 first and then decreases to 73 865 with the soaking time increasing from 0.5 to 5.0 h. These indicate that the optimal soaking time is 2.0–3.0 h considering both nonlinear electrical behavior and dielectric properties.     

Study on crystallization and microstructure of Li2O-Al2O3-SiO2 glass ceramics

Lithium aluminosilicate （LAS） glasses are generally difficult to prepare because of their high melting temperature. In this study, the preparation of LAS glasses was achieved at a relatively low melting temperature. The batch containing MgO-ZnO-LiEO- Al2O3-SiO2 was melted in a platinum crucible at 1550℃ for 2 h and was then followed by two- or three-step heat treatment processes for nucleation and crystal growth. The characterizations were carried out by differential thermal analysis, X-ray diffraction, infrared spectroscopy, scanning electron microscopy, and UV-Vis-NIR scanning spectrophotometry. The hexagonal stuffed β-eucryptite solid solution crystallized at 840-960℃. Most of the hexagonal β-eucryptite solid solution transformed into the tetragonal β-spodumene solid solution at 1100℃. Almost all the aluminum atoms entered into the tetrahedral sites in the aluminosilicate network of the 6- eucryptite/β-quartz solid solution. All of the Al atoms did not belong to the aluminosilicate network of the β-spodumene solid solution. The glass ceramic with a mean grain size of 10-20 nm is transparent, the transmittance reaches -85% in the visible light wavelength.     

Effect of sintering time on the electrochemical properties of spinel LiMn2O4 synthesized by solid-state reaction

LiMn2O4 powder as a cathode materials for rechargeable lithium-ion batteries was prepared by solid-state reaction from LitCO3 and electrolytic MnOz at different sintering periods （2, 6, 18, and 32 h）. X-ray diffraction （XRD） patterns of the prepared samples are identified as the spinel structure with a space group of Fd3 m. The lattice parameters almost remain the same as the sintering periods increase. The sample with a sintering period of 32 h shows good cycling performance at both low and nigh current densities, and also elevated temperature. It is believed that the excellent electrochemical behavior of this sample results from its good crystallinity and large grain size compared with other samples. Different electrochemical measurements were conducted to investigate the electrochemical properties of spinel LiMn204. 2008 University of Science and Technology Beijing. All rights reserved.     

水热法制备SrBi2Ta2O9陶瓷及其介电性能研究

采用水热法合成SrBi2Ta2O9(SBT)纳米粉体,成型后采用常规烧结法制备SBT陶瓷.利用XRD和SEM研究陶瓷的物相和微观形貌;利用介电温谱研究陶瓷的介电性能.结果表明:采用水热法能够制备出颗粒细小均匀、结构致密且物相纯净的SBT陶瓷;其居里温度为375℃,对应的介电常数为114.54.     

Ba2LaBiO6/ZnO复相材料的显微结构和电性能

采用固相烧结法制备了Ba2LaBiO6／ZnO复相材料,研究了Ba2LaBiO6／ZnO复相材料的组成和显微组织对材料电性能的影响：实验样品在较宽的温度范围内均显示了良好的NTC特性;烧结体中的相主要由六方结构的ZnO、立方结构的Ba2LaBiO6及含量很少的未知相组成,样品的平均晶粒尺寸随着材料中ZnO含量的增加有减小的趋势。在给定Ba2LaBiO6的组成下,随着材料中ZnO固溶体含量的增加,样品的室温电阻率减小,B25/125系数的值基本不变。     

Microstructure and mechanical properties of submicron-grained NiAl-Al2O3 composite prepared by pulse current auxiliary sintering

Dense and submicron-grained NiAl-Al2O3 composite was fabricated by pulse current auxiliary sintering(PCAS).Its microstructure was analyzed by XRD,SEM and TEM,and its mechanical behavior was evaluated through compression test and fracture toughness test.The average grain sizes of NiAl and Al2O3 are about 200 nm and 100 nm respectively.The Al2O3 particles dispersed in NiAl matrix,forming intergranular structure and intragranular structure.During sintering,Al2O3 particles were remarkably spherized due to the unique sintering mechanism of PCAS,which is beneficial to the improvement of toughness.The NiAl-Al2O3 composite exhibits high compressive yield strength,whether at room temperature or elevated temperature.Its room-temperature(23 ℃) and elevated-temperature(1 200 ℃) compressive yield strength are up to 2 050 MPa and 140 MPa,respectively.Meanwhile,its fracture toughness is significantly enhanced,which is up to 8.2 MPa?m1/2.It is suggested that the main strengthening-toughening mechanisms are grain refinement strengthening and Al2O3 dispersion strengthening.The fracture of larger NiAl grain is the transgranular cleavage and this is induced by crack tip deflection and grain boundary weakening which are caused by intergranular and intragranular Al2O3 particles,respectively.     

原位合成Al_2O_3/FeAl复合材料的组织与性能

利用Fe-Al-Fe2O3体系的放热反应,原位热压合成了Al2O3/FeAl复合材料.借助XRD和SEM等研究了复合材料的物相组成和显微结构,以及Al2O3生成量对复合材料显微结构和力学性能的影响.结果表明:经1 250℃保温1.5h热压烧结的块体材料主要由FeAl及少量Al2O3相构成,FeAl基体为片层结构,增强相Al2O3分散在基体和晶界处.随着Al2O3含量的增加,基体晶粒尺寸明显减小,同时对材料起增强增韧作用.在Al2O3含量为1.2wt%时,试样的抗弯强度达到最大值1 329.22MPa;在Al2O3含量为0.8wt%时,试样的断裂韧性达到最大值29.95MPa·m1/2.此值正好处于金属与陶瓷材料性能链的断缺处.因此,本研究结果对于完善材料性能体系具有重要意义.