Sb2O3掺杂对ZnO压敏陶瓷晶界特性和电性能的影响

制备了掺有Sb2O3不同掺杂量ZnO压敏陶瓷样品,采用扫描电镜对样品进行显微结构分析,研究了Sb2O3掺杂浓度对ZnO压缩电阻显微结构和性能的影响,测量了样品的电性能,由样品C－V特性的测量计算出晶界参数,并由此讨论了陶瓷性能与晶界特性的相关性。研究发现,在ZnO压敏陶瓷样品中掺杂适量的Sb2O3可以提高ZnO压敏陶瓷样品的非线性性能,但当Sb2O3的摩尔分数超过0．088％时,电性能反而优化,这是因为Sb2O3掺杂浓度不同会引起晶界势垒高度、施主浓度与陷阱密度的变化,因此Sb2O3掺杂量要控制在适当的范围内。     

Al_2O_3掺杂对Zn-Bi系压敏陶瓷性能的影响

采用Al_2O_3掺杂,通过固相法制备Zn-Bi系压敏陶瓷,研究了不同比例Al_2O_3对ZnO陶瓷的晶粒大小、显微结构以及电性能的影响。研究表明ZBSCCMY配方中掺杂少量Al_2O_3制备得到ZnO压敏陶瓷样品的晶粒大小愈加均匀,显微结构更加致密;陶瓷物相主要由Zn O相、少量的Bi_2O_3相和微量的Zn_7Sb_2O_7尖晶石物相构成;少量Al_2O_3的掺杂改进了晶粒和晶界结构和成分,活化了晶界,降低烧制压敏陶瓷的烧结温度,优化了压敏陶瓷的非线性特性。当掺杂浓度为0.05 wt%、烧结温度为1100℃、保温2 h得到性能良好的压敏陶瓷,其压敏电位梯度可达810 V/mm,非线性系数为68,漏电流为2.4μΑ。     

Fe2O3在ZnO压敏陶瓷中的作用

研究了Fe_2O_3对ZnO压敏陶瓷电性能的影响。试验表明,Fe_2O_3添加的摩尔含量小于0.1％能提高ZnO压敏陶瓷的非线性和压敏电压;但当其添加量大于0.1℃时,非线性急剧下降;Fe_2O_3添加量大于1％时,压敏电压下降。通过X射线衍射等微观分析,认为过量Fe_2O_3使ZnO压敏陶瓷非线性下降的原因主要是由于Fe_2O_3与ZnO在晶界处形成了具有低电阻率(ρ=10~2Ω·cm)的尖晶石相ZnFe_2O_4     

真空烧结对高压厚膜型ZnO压敏陶瓷的影响

采用真空烧结的方法制备出高电位梯度的厚膜型ZnO压敏陶瓷,并研究了多次真空烧结对高压厚膜型ZnO压敏陶瓷的影响。实验结果表明,多次真空烧结使试样的电学性能产生先劣化后优化的变化趋势。真空烧结5次后,试样的电位梯度为2890.9V/mm,漏电流为87.9μA,非线性系数为9.0,晶粒尺寸在2μm左右。晶粒中氧原子百分含量的降低表明真空烧结5次后,晶粒、晶界间发生了氧原子的转移,使试样宏观电学性能得到改善。     

ZnO压敏电阻的显微结构及其形成机理

用光学显微镜、X—射线、TEM、EPMA分析了典型ZnO压敏电阻(ZnO—MgO-Bi_2O_3-Sb_2O_3系统陶瓷)的显微结构、物相、晶界形貌、成分分布,ZnO是主晶相,添加剂是富集在颗粒边界中形成不连续的第二相。本文中,还讨论了该系统ZnO压敏陶瓷的形成机理。     

低温制备ZnO压敏陶瓷及其电性能研究

ZnO压敏陶瓷作为电压保护以及抗浪涌设备中电子元器件的核心材料,其高非线性系数,高通流容量,强浪涌吸收能力等性能研究以及低温烧结制备技术受到广泛关注。通过掺杂烧结助剂BST(Bi_2 O_3∶SiO_2∶TiO_2摩尔比为6∶4∶3),于875℃烧结制备了性能优异的ZnO压敏陶瓷。主要探究了烧结助剂的掺量对ZnO压敏陶瓷的物相组成、微观结构、体积密度以及压敏性能的影响。结果表明:BST掺杂会导致晶粒细化,有效地提高样品的致密度及压敏性能。当BST掺量摩尔分数为0.25%时,获得样品的综合性能最佳,体积密度为5.63 g/cm~3,相对密度为97.4%,非线性系数最大为38.9,电压梯度为最小值301.2 V/mm,漏电流密度为最小值0.028 A/mcm~2。     

Er2O3掺杂ZnO压敏陶瓷的制备及其电学性能

研究了Er₂O₃掺杂对ZnO–Bi₂O₃–Sb₂O₃–Co₂O₃–MnO₂–Cr₂O₃–SiO₂压敏陶瓷微观结构和电学性能的影响。Er₂O₃掺杂后，部分Er固溶于富Bi相中，对ZnO压敏陶瓷的晶界特性和电学性能产生了较大影响。随着Er₂O₃掺杂量从0.09%(质量分数)增大到0.35%，样品晶界电阻率不断减小，漏电流密度不断增大，双Schottky晶界势垒高度和非线性系数先增大后减小，击穿场强不断增大；当Er₂O₃掺杂量为0.27%时，所得ZnO压敏陶瓷非线性系数达到54.4±1.5，击穿场强为(470.1±2.8) V·mm^–1，漏电流密度为(1.9±0.1)μA·cm     

La2O3掺杂对Zn–Pr基压敏陶瓷电学特性的影响

利用固相烧结法制备出了ZnO–Pr₆O₁₁–Co₂O₃–Cr₂O₃–La₂O₃氧化锌压敏陶瓷。研究了La₂O₃掺杂对氧化锌压敏陶瓷微观结构、压敏特性以及介电性能等方面的影响。结果表明:在La₂O₃掺杂量为1.5%(摩尔分数)时,氧化锌压敏陶瓷的综合性能最好,其晶粒尺寸最小且较为均匀,击穿场强达到最高(752 V/mm),非线性系数较大(12),晶界电容达到最大(276 pF),介电损耗较小。     

掺杂TiO_2制备低压ZnO压敏陶瓷

主要研究了晶粒助长剂TiO2、烧成条件等对ZnO低压压敏陶瓷电性能的影响。结果表明:TiO2的掺入能显著促进晶粒生长,降低压敏电压V1mA,但掺入量超过一定值后一方面会生成阻止晶粒继续生长的晶界反应层,促使压敏电压又有所升高,另一方面会生成钛酸铋立方相而引起富铋晶界相含量的减少,导致非线性特性下降。提高烧成温度可以促进晶粒生长,降低压敏电压,但温度过高时由于铋的挥发加剧,利用提高烧成温度降低压敏电压会引起非线性特性和漏流等性能的劣化。     

掺杂对ZnO压敏陶瓷电性能的影响及其应用

ZnO压敏陶瓷具有优良的电流-电压非线性和冲击能量吸收能力、低漏电流和低成本,广泛用于电力系统和电子线路等领域。介绍了掺杂改性对ZnO压敏陶瓷电性能的影响,最后介绍了ZnO压敏陶瓷的应用。     

Effect of Ag on the microstructure and electrical properties of ZnO

Various amounts of silver particles, 0.08–7.7 mol%, are mixed with zinc oxide powder and subsequently co-fired at 800–1200 °C. The effects of Ag addition on the microstructural evolution and electrical properties of ZnO are investigated. A small Ag doping amount (<0.76 mol%) promotes the grain growth of ZnO; however, a reversed trend in grain growth is observed for a relatively larger Ag addition (>3.8 mol%). It is evident that a tiny amount of Ag (0.08 mol%) may dissolve into the ZnO lattice. High-resolution TEM observations give direct evidences on the segregation of Ag solutes at the ZnO grain boundaries. The grain boundary resistance of ZnO increases 35-fold with the presence of Ag solute segregates. The Ag-doped ZnO system exhibits a nonlinear electric current–voltage characteristic, confirming the presence of an electrostatic barrier at the grain boundaries. The barrier is approximately 2 V for a single grain boundary.     

Formation of Varistor Characteristics by the Grain-Boundary Penetration of ZnO-PrOx Liquid into ZnO Ceramics

Penetration of a liquid (ZnO-PrO _x ) into the grain boundaries of sintered, cobalt-doped ZnO pellets resulted in varistors with breakdown voltages per grain boundary in the 1-2 V range and nonlinearity coefficients of 22-37. The varistors were fabricated by spreading a thin layer of Pr₆O₁₁ powder paste on the surface of ZnO pellets and heating to various temperatures (1200°-1400°C) and times (0-60 min). Comparing the varistor properties per grain boundary (e.g., threshold voltage, donor concentration, and barrier height) of liquid penetration to those of conventional method indicated the individual grain boundaries were electrically activated when the samples were heat-treated above liquid-phase formation temperature.     

Enhanced Charge Transport in ZnO Nanocomposite Through Interface Control Using Multiwall Carbon Nanotubes

Hybrid strategy of ZnO with carbon nanotube (CNT) has been attempted, and synergistic effects have been demonstrated in ZnO‐CNT hybrid nanostructures owing to the advantageous effects of interface modification on the charge transport process. Here, we report the effects of interface control using multiwall CNTs (MWCNTs) on the charge transport properties in Al‐doped ZnO (AZO) nanocomposite. Although the AZO‐MWCNT nanocomposite is composed of numerous nanograins, it shows single crystalline charge transport behavior due to significantly weakened grain‐boundary scattering at room temperature. The dominant charge transport mechanism is converted from lattice vibration scattering to grain‐boundary scattering at 873 K due to the variation in the charge distribution at the grain boundary. The results demonstrate that interface control using carbon nanomaterials has a significant effect on the charge transport behavior in AZO nanocomposite.     

添加Nd2O3对氧化锌压敏阀片电性能与显微组织的影响

研究了微量Nd2O3添加剂对氧化锌压敏阀片的压敏电位梯度、漏电流和压比的影响,并对其显微组织进行了分析研究,从理论上探讨了Nd2O3对氧化锌压敏阀片电性能与组织的作用机理。研究结果表明:当Nd2O3的摩尔分数为0.04％时,氧化锌压敏阀片的压敏电位梯度最高,漏电流最小,压比最低,具有优良的综合电性能。其原因是Nd2O3加入到氧化锌压敏阀片中,使晶粒尺寸减小所致。     

Nondestructive characterization of grain boundary Z-directional lateral surface in ZnO using nanorobot combined with SEM

Different from focusing on grain boundary upper surface in plane X–Y, a unique approach of nanorobot-based nondestructive characterization of grain boundary Z-directional lateral surface within bulk ZnO ceramic can be creatively developed under scanning electron microscope (SEM). By rolling-over bulk ZnO, two-dimensional profiles and grain boundaries in Z-directional lateral surfaces have been imaged in plane Y–Z and individually electrically characterized nondestructively. Experiments demonstrate that it is feasible to realize nondestructive characterization of grain boundary Z-directional lateral surface structures and electrical properties using nanorobot combined with SEM. Relative height differences between grain boundaries within Z-directional lateral surface can characterize the relative position relationships. Z-directional lateral surface structures can further extend irregular grain boundary lengths in plane Y–Z to interpret surface effects of nonlinear electrical properties. Relative minor electrical reactive effects in grain indicate grain boundary dominate in nonlinear macroscopic electrical properties. Furtherly, it can be advanced to promote a nondestructive characterization of grain boundary.     

Sintering Temperature Dependence of Grain Boundary Resistivity in a Rare-Earth-Doped ZnO Varistor

We present a rare-earth-doped ZnO ceramic with nonohmic electrical properties. Analysis of the microstructure and composition indicates that the ceramic is composed of the main phase of ZnO and the second phase of rare-earth oxides (e.g., Dy₂O₃, Pr₆O₁₁, Pr₂O₃). The average grain size is markedly increased from 3 to 18 μm, with an increase in the sintering temperature from 1150° to 1350°C. The corresponding varistor voltage and nonlinear coefficient decrease from 1014 to 578 V/mm, and from 15.8 to 6.8, respectively. The resistivity of grain and grain boundary evaluated by the complex impedance spectrum indicates that the resistivity of the grain is approximately constant (∼10³Ω), and the resistivity of the grain boundary decreases. The relative dielectric permittivity of the sintered ceramic samples is much larger than that of pure ZnO ceramic, which should be ascribed to the internal boundary layer capacitance effect.     

Preparation and Electric Properties of Dense Nanocrystalline Zinc Oxide Ceramics

This communication reports on the preparation and electric properties of dense nanocrystalline ZnO ceramics. By spark plasma sintering, nanocrystalline (∼100 nm) ZnO ceramics with a high density of 98.5% were obtained at a very low temperature of 550°C. Electric property measurement revealed a novel conduction nonlinearity in the sample sintered at 500°C. This phenomenon is due to the nanometerization of ZnO crystal and the grain boundary layer with an amorphous interfacial layer.     

Direct measurements of voltage–Current characteristics of single grain boundary of ZnO varistors

In order to comprehend electrical properties of grain boundaries and other microscopic regions of electroceramics, an analytical apparatus based on scanning electron microscope (SEM) was newly developed. The apparatus was composed of SEM in which two micro probes made of Pt–Ir alloy were attached at the sample stage, an outer electric DC power supply and energy dispersion type X-ray analyzer (EDX), so that element analysis of specific area of samples was possible. Direct measurements of voltage–current (V–I) characteristics of single grain boundary of ZnO varistors having small grain size (≤10 μm) were attempted by the apparatus. As a result, nonlinear behavior of V–I characteristics of ZnO varistors was confirmed to take place at one grain boundary and, furthermore, inhomogeneity of the nonlinear V–I characteristics was observed.     

Microstructural, crystal structure and electrical characteristics of shock-consolidated Ga2O3 doped ZnO bulk

Ga₂O₃ (5 wt.%) doped zinc oxide (ZnO, 95 wt.%) bulk was fabricated by underwater shock compaction technique. The microstructural, crystal structure and electrical properties of shock-consolidated samples were investigated and compared to a commercially available sintered Ga₂O₃ (5 wt.%) doped ZnO (95 wt.%). The relative density of shock-consolidated sample was about 97% of the theoretical density, and no grain growth and lattice defects were confirmed. The grain boundary resistance was remarkably higher than that of commercial sintered Ga₂O₃ doped ZnO and nonlinear current-voltage (I-V) characteristics of shock-consolidated ZnO and Ga₂O₃ doped ZnO were very lower than that of commercial ZnO varistor.     

The transition from non-ohmic to ohmic characteristics in La2O3 doped ZnO–MgO–TiO2 linear resistance ceramics

La₂O₃ doped ZnO–MgO–TiO₂ based linear resistance ceramics were prepared by the solid phase sintering method. The doping content of La₂O₃ is from 0.0 wt% to 2.5 wt%. The solubility of La₂O₃ in ZnO is less than 0.06 mol% (0.5 wt%), La_0.66TiO_2.993 phases will be formed at grain boundary and change the distribution of spinel phase when La₂O₃ is excessive. For I–V test, undoped sample exhibits typical non-ohmic characteristics, but La-doped samples show excellent ohmic behaviors under low DC and high pulse current (PC). The complex impedance spectrum and the frequency dependent conductivity furtherly demonstrate that La-doped samples possess linear characteristics because there is no grain boundary effect which can affect the electron transmission at grain boundaries. Besides, the decrease of the grain boundary barrier from 0.2135eV for undoped sample to 0.0031eV for 0.5 wt% La doped samples can account for the elimination or reduction of grain boundary effect. In this work, the transition from non-ohmic to ohmic properties by doping La₂O₃ in ZnO–MgO–TiO₂ multiphase ceramics is realized.