氧化钐掺杂对氧化锌压敏陶瓷电学特性的影响

以氧化锌、氧化镨、氧化亚钴、氧化铬和氧化钐作为原料,经配料、球磨、造粒、压片和烧结等工序制得压敏电阻片,采用电流-电压特性测试、X射线衍射和扫描电子显微镜分别获得陶瓷的电性能参数,材料成分和微观结构图.实验结果表明:随着氧化钐含量的增加,氧化锌压敏陶瓷的非线性和压敏电压呈现先增大后降低的趋势.当氧化钐摩尔百分比低于0.3时,非线性系数和压敏电压随氧化钐含量的增加而增大.而氧化钐摩尔分数为0.3%时,压敏陶瓷具有最佳非线性电学特性,非线性系数为35,压敏电压为435伏/毫米;继续增加氧化钐至摩尔分数为0.5%时,非线性系数和压敏电压将会降低.氧化钐绝大多数聚集在晶界层,抑制晶粒生长,从而提高了压敏陶瓷的压敏电压.而极少数氧化钐与氧化锌发生置换反应,降低了氧化锌颗粒的电阻,从而提高了非线性.因此氧化锌压敏陶瓷因掺杂氧化钐提高了电性能而有望应用在高压领域.     

Relaxor behavior and electrical properties of high dielectric constant materials

Several typical high dielectric constant materials are reviewed to study the electrical properties and relaxation mechanism. It is found that a Lorenz-type law can be used to describe the dielectric permittivity of either the normal ferroelectrics with or without diffuse phase transitions (DPT) or the typical ferroelectric relaxors. The ferroelectric DPT can be well described by just one fitting process using the Lorenz-type law, while the relaxor ferroelectric transition needs two independent fitting processes. The Lorenz-type law fails at the low temperature side of the dielectric maximum of a first-order ferroelectric phase transition. Above the transition temperature, the dielectric curves of all the studied materials can be well described by a Lorenz-type law. Supported by the National Natural Science Foundation of China (Grant No. 50672075), New Century Excellent Talents (Grant No. 05-087), Natural Science Foundation of Northwestern Polytechnical University (Grant No. 200703), Xi’an Science & Technology Foundation (Grant No. CXY08006) and 111 Project (Grant No. B08040)     

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.     

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.     

Microstructure and electrical properties of Y2O3-doped ZnO-based varistor ceramics prepared by high-energy ball milling

Y2O3-doped ZnO-based varistor ceramics were prepared using high-energy ball milling （HEBM） and low-temperature sin- tering technique, with voltage-gradient of 1934-2197 V/mm, non-linear coefficients of 20.8-21.8, leakage currents of 0.59-1.04 μA, and densities of 5.46-5.57 g/cm3. With increasing Y2O3 content, the voltage-gradient increases because of the decrease of ZnO grain size; the non-linear coefficient and the leakage current improve but the density decreases because of more porosity; the donor con- centration and density of interface states decrease, whereas the barrier height and width increase because of the acceptor effect of Y2O3 in varistor ceramics.     

掺杂(Co,Nb,Pr)的SnO2介电与压敏性质

研究了（Co,Nb,Pr)掺杂的SnO2材料介电和压敏性质。当Pr6O11的量分数从0％增加到0.1%时,SnO2压敏电阻的相对介电常数从670降到280,击穿电压从827V/mm猛增到2150V/mm。微观结构分析发现：当Pr6O11的量分数从0％增加到0.1%时,SnO2的晶粒尺寸由4.50μm迅速减小到1.76μm。晶界势垒高度测量揭示SnO2的晶粒尺寸迅速减小是介电常数迅速减小及击穿电压急剧增高的原因。对Pr增加引起SnO2晶粒减小的根源也进行了解释。     

稀土Nd掺杂对Sr（Fe0.5Nb0.5）O3基介质陶瓷巨介电性能的影响

铁铌酸锶是一种重要的介质材料,具有复合钙钛矿结构,同其他介质材料相比,具有相对高的介电常数的优点,在高储能等领域有重要的应用潜力,是一种用途广泛的功能陶瓷材料．实验以Sr（Fe0.5Nb0.5）O3基陶瓷为研究对象,研究了稀土Nd掺杂对该系陶瓷巨介电性能的影响．结果表明：随着Nd抖掺杂量的增加,陶瓷样品的介电常数逐渐变大;随着温度的上升,陶瓷体系的介电常数也逐渐增大;Nd抖含量x≤0．10时,陶瓷样品有着良好的频率稳定性,x=0．10的陶瓷样品在100kHZ下有着良好的温度稳定性．     

The Effect of Bi2O3 on the Structure and Microwave Dielectric Properties of Ba6-3xNd8＋2xTi18O54 System（x=2/3）

The structures and dielectric properties of Ba6-3xNd8＋2xTi18O54 system（x=2/3） doped with different contents of Bi2O3, whose final molecular formula is Ba6-3x（Nd1-yBiy）8＋2xTi18O54 were investigated. It is indicated that the dielectric constant increases greatly whereas Q value（f0=4 GHz） decreases with the increase of Bi2O3 content. However, the temperature coefficient could be controlled below 0±30×10^-6/℃ in the experiment. These phenomena are related to the appearance of a new phase, Bi4Ti3O12, which has high dielectric constant. Also, that Bi^3＋（0.13 nm） substitutes for Nd^3＋（0.099 5 nm） will increase the unit cell volume, which will lead to the enlargement of the octahedron B site occupied by Ti^4＋. So the spontaneous polarization of Ti^4＋ ions will be strengthened. Besides, Bi^3＋ will fill up some vacancies which Ba^2＋ or Nd^3＋ ions leave in two A1 sites and four A2 sites. More positive ions polarize, which also contributes to higher dielectric constant. The samples got with the optimium properties are sintered at 1 200 ℃ for 4 h, when y=0.25, ε≈110, Q≈5 400（f0=4 GHz）, TCC=-4.7×10^-6/℃; When y=0.3, ε≈120, Q≈5 000（f0=4 GHz）, TCC=-24×10^-6/℃.     

Influence of grain size on distribution of temperature and thermal stress in ZnO varistor ceramics

The nonuniformity of temperature distribution within ZnO varistor ceramics would decrease its energy absorption capability. In this paper, the distributions of current, temperature and thermal stress within the microstructures of ZnO varistor ceramics are simulated using Voronoi diagram models. The results show that the current concentrates through a few paths in ZnO varistor due to the nonuniformity of ZnO grain size and the variety of electrical characteristics of grain boundaries, which induces local high temperature and great thermal stress when injecting impulse current into ZnO varistor, and leads to melting puncture or cracking failure. The influence of the ZnO grain size on the distributions of temperature and thermal stress within ZnO varistor ceramics is analyzed in detail. The energy absorption capability of ZnO varistor ceramics can be greatly improved by increasing the uniformity of ZnO grain size or decreasing the average size of ZnO grains.     

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...     

CCTO掺杂对BaTiO3-Nb2O5-Co3O4陶瓷系统介电性能的影响

以BaTiO3-Nb2O5-Co3O4(BTNC)系统陶瓷为研究对象,研究了掺杂CaCu3Ti4O12(CCTO)对该系统陶瓷介电性能的影响.结果表明,在20～85℃温度范围内,BT系统中CC-TO掺杂量为3.0%时,体系平均介电常数>2 600,温度稳定性△C/C≤4.7%;在20～125℃温度范围内,BTNC系统中CCTO掺杂量为2.0%时,体系的平均介电常数>2 700,温度稳定性△C/C≤10%;CCTO掺杂量为4.0%时,平均介电常数>2 200,温度稳定性△C/C≤4.7%.     

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.     

Sr/Zr掺杂以及抛光对BaTiO_3陶瓷结构和介电性能的影响

采用冷压陶瓷技术制备了(Ba0.75Sr0.25)TiO3、Ba(Ti0.8Zr0.2)O3、(Ba0.75Sr0.25)(Ti0.8Zr0.2)O3陶瓷.XRD结果表明,Sr和Zr在BaTiO3的Ba位、Ti位、及Ba/Ti双位并入均具有高固溶性,且为没有超结构特征的单相钙钛矿结构.Sr/Zr的双位并入加快介电峰向低温的移动.Sr掺杂对Ba(Ti0.8Zr0.2)O3介电峰移动率的贡献为-1.5℃/mol%Sr.抛光技术对介电温谱的影响研究表明,尽管水抛光导致(Ba0.75Sr0.25)(Ti0.8Zr0.2)O3陶瓷颜色变暗,但晶体结构不变、介电峰值降低.     

Effect of sintering aid CuO-MnO2 on dielectric properties of 0.5Ba(Mg1/3Nb2/3)O3-0.5Ba(Ni1/3Nb2/3)O3 ceramics

Microstructures and microwave dielectric properties of 0.5Ba(Mg_1/3Nb_2/3)O₃-0.5Ba(Ni_1/3Nb_2/3)O₃ ceramics with x wt% CuO−x wt% MnO₂ additions (x=0.25–1) prepared by conventional solid-state route were investigated. It is found that low level-doping of CuO-MnO₂ can significantly improve the density of the specimens and their microwave dielectric properties. The relative density of 0.5Ba(Mg_1/3Nb_2/3)O₃-0.5Ba(Ni_1/3Nb_2/3)O₃ ceramics can be increased by 95% sintering at 1 330 °C due to the liquid phase effect. The second phase is not observed in ceramics with CuO-MnO₂ addition. The parameter ε _r increases with increasing sintering temperature, and Q _f is effectively promoted by CuO-MnO₂ addition. Higher CuO-MnO₂ content would make τ_f value more positive. Meanwhile, ε _r value of 30.5, Q _f value of 63 200 GHz and τ _f value of 0.5 ppm/°C were obtained for 0.5Ba(Mg_1/3Nb_2/3)O₃-0.5Ba(Ni_1/3Nb_2/3)O₃ ceramics with 0.5 wt% CuO-0.5 wt% MnO₂ addition sintered at 1 330 °C for 4 h.     

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.     

La2O3、Cr2O3共掺杂的CCTO陶瓷介电性能研究

采用氧化物混合工艺制备了La2O3和Cr2O3共掺杂的CaCu3Ti4O12(CCTO)陶瓷材料。通过XRD、介电温度特性等测试手段,研究了掺杂不同浓度的La2O3和Cr2O3对CCTO体系陶瓷介电性能的影响,并对掺杂机理进行了分析.研究结果表明:分别掺杂La2O3和Cr2O3的CCTO陶瓷的介电损耗为～0.2,比纯的CCTO陶瓷样品低,而介电常数仍保持在～104;掺杂0.03at%La2O3和0.08at%Cr2O3的CCTO陶瓷材料的介电常数为4.4×104,介电损耗可降至0.15.因此,通过共掺杂的方法可以在有效降低CCTO陶瓷介质损耗的同时,仍维持高的介电常数.     

Coexistence of antiferromagnetic and ferromagnetic in Mn-doped anatase TiO2 nanowires

A series of Mn-doped TiO_2 nanowires (NWs) were prepared by hydrothermal method at the mole fraction of Mn changing from 0 to 12.0%. X-ray powder diffraction (XRD) analysis shows that all the samples have pure anatase structure. SEM and TEM studies show that the diameter and the length of the Mn-doped TiO_2 NWs are larger than those of the undoped TiO_2 NWs. Energy dispersive X-ray spectroscopy (EDX) reveals that the samples are composed of Ti, Mn and O. According to magnetization measurements, all samples show ferromagnetic behavior, but only the undopedTiO_2 NWs are completely ferromagnetic with a saturated magnetization about 1.0 mA·m~2/kg. Mn-doped TiO_2 samples exhibit antiferromagnetic and ferromagnetic (AF-FM) behaviors simultaneously. Photoluminescence (PL) spectra demonstrate the existence of MnO_2 sublattice. These observations indicate that an AF-WF crossover is induced by the coexistence of TiO_2 sublattice and MnO_2 sublattice.