Study on nonlinear conductivity and breakdown characteristics of zinc oxide–hexagonal boron nitride/EPDM composites

The ethylene–propylene–diene monomer (EPDM) has been widely used in HVDC cables accessories. The nonlinear conductivity of EPDM-based composites plays an important role on relieving the distortion of electric field. In this study, the zinc oxide (ZnO) particles are selected as fillers for improving the nonlinear conductivity of EPDM. The result shows that nonlinear conductivity characteristics of ZnO/EPDM becomes more and more pronounced with the increase of ZnO doping content, however, the breakdown strength of ZnO/EPDM composites has been seriously deteriorated with the increase of ZnO doping content. The excellent breakdown strength of composites is very important for ensuring the safe operation of cable accessories, so the hexagonal boron nitride (h-BN) with good electrical insulation has been employed for improving the breakdown strength of ZnO/EPDM. The results indicate that both of non-linear conductivity and good breakdown strength have been obtained in ZnO–h composite-BN/EPDM composites. This work provides a novel way for constructing the composites with excellent electrical performances which are used for cable accessories.     

p-Type ZnO nanowire arrays

Well-aligned ZnO nanowire (NW) arrays with durable and reproducible p-type conductivity were synthesized on alpha-sapphire substrates by using N2O as a dopant source via vapor-liquid-solid growth. The nitrogen-doped ZnO NWs are single-crystalline and grown predominantly along the [110] direction, in contrast to the [001] direction of undoped ZnO NWs. Electrical transport measurements reveal that the nondoped ZnO NWs exhibit n-type conductivity, whereas the nitrogen-doped ZnO NWs show compensated highly resistive n-type and finally p-type conductivity upon increasing N2O ratio in the reaction atmosphere. The electrical properties of p-type ZnO NWs are stable and reproducible with a hole concentration of (1-2) x 10(18) cm(-3) and a field-effect mobility of 10-17 cm2 V(-2) s(-1). Surface adsorptions have a significant effect on the transport properties of NWs. Temperature-dependent PL spectra of N-doped ZnO NWs show acceptor-bound-exciton emission, which corroborates the p-type conductivity. The realization of p-type ZnO NWs with durable and controlled transport properties is important for fabrication of nanoscale electronic and optoelectronic devices.     

Sb掺杂对ZnO厚膜的电导和气敏性能的影响

用共沉淀的方法,制备了纤锌矿结构的ZnO及其掺Sb的ZnO纳米粉.X射线衍射(XRD)分析表明,当锑掺量小于5wt%时没有新相生成.纯ZnO和掺Sb的ZnO器件的气敏和电阻测试结果发现:不同的厚膜烧结工艺对气体的敏感性影响较大,并且掺Sb后ZnO的气敏性能有所提高,电导峰消失.从缺陷角度、XPS分析的结果进行了讨论,初步解释了锑的掺入导致电导变化和气敏性能提高的原因.     

Effect of MWCNTs/ZnO inorganic fillers on the electrical,mechanical and thermal properties of SiR-based composites

Rubber insulation materials were widely used in the fields of electrical and electronic engineering, especially, which have excellent nonlinear electrical conductivity and can be employed to homogenize the electric field distribution of cable accessories. To enable the rubber materials, such as silicon rubber (SiR), to possess excellent nonlinear electrical conductivity has been a hot issue. In this paper, MWCNTs/ZnO inorganic fillers were prepared by mixing a small amount of multi-wall carbon nanotubes (MWCNTs) with zinc oxide (ZnO) nanosheets, and MWCNTs/ZnO/SiR composites were prepared. The macroscopical properties results show that the nonlinear electrical conductivity characteristics can be induced by filling appropriate content of MWCNTs/ZnO fillers, and the threshold field strength corresponding to the nonlinear conductivity gradually decreases with the increase of MWCNTs filling content, which further decreases with the increase of measured temperature. The COMSOL simulation results also verify that MWCNTs/ZnO/SiR composite with nonlinear conductivity can effectively reduce the electric field strength at the stress cone of cable accessories. In addition, the thermal conductivity and tensile strength for MWCNTs/ZnO/SiR composite are also improved comparing to pristine SiR. This work demonstrates MWCNTs/ZnO/SiR composites possess outstanding overall properties and have good potential to be used in the cable accessory.

     

Conductivity relaxation in lodomolybdate glass-nanocomposites embedded with znO nanoparticles and alpha-AgI nanocrystals

We have reported the conductivity relaxation of the 0.70AgI-0.15Ag20-0.15(xZnO-(1-x)MoO3), glass-nanocomposites embedded with ZnO nanoparticles and alpha-Agl nanocrystals. Formation of ZnO nanoparticles and alpha-AgI nanocrystals was confirmed from field emission scanning electron microscopy (FE-SEM) and high-resolution transmission electron microscopy (HR-TEM). It is observed that the conductivity relaxation process depends upon the size of the ZnO nanoparticles embedded in the host glass matrix. The variation of conductivity relaxation time and stretched exponent is correlated with their structure. The scaling of the modulus spectra reveals that the relaxation dynamics of Ag+ ions is independent of temperature but depends on composition.     

纳米ZnO/低密度聚乙烯复合材料的介电特性

为探讨纳米ZnO/低密度聚乙烯（LDPE）复合材料的介电特性,首先,采用硅烷偶联剂和钛酸酯偶联剂对纳米ZnO进行改性,并利用两步法制备了不同纳米ZnO质量分数、不同纳米ZnO粒径、不同纳米ZnO表面修饰方式和不同冷却方式的纳米ZnO/LDPE复合材料;然后,通过FTIR、SEM、DSC和热激电流（TSC）测试了纳米ZnO在基体中的分散情况、复合材料的等温结晶过程参数变化及陷阱密度;最后,在不同实验温度下分别进行了交流击穿、绝缘电导率、介电常数和空间电荷实验。结果表明:纳米ZnO的加入使纳米ZnO/LDPE复合材料内部陷阱深度和密度均有所增加;当纳米ZnO的粒径为40 nm且质量分数为3%时,复合材料的结晶速度最快,纳米ZnO在基体中的分散性较好,击穿场强达到最高值133.3 kV/mm,电导率及介电常数也相对较低,加压时复合材料内部空间电荷少,短路时释放电荷速度快,介电性能较好;由于纳米粒子增加了材料内部的热传导速率,降低了复合材料随着温度升高而降解的速度,因而相对于纯LDPE,随着实验温度的提高,纳米ZnO/LDPE复合材料的击穿场强下降幅度及电导率上升幅度均较小。      

La,Pr改性ZnO导电粉的制备

为了提高ZnO的导电性,采用稀土气相扩渗法对ZnO粉体进行了La,Pr改性.采用X射线衍射分析、扫描电子显微镜、差热分析和电阻测试仪,对改性前后ZnO组成、结构及电性能的变化进行了研究.XRD测试结果表明:La扩渗后,在29.5°出现了一个与La有关的特征峰,Pr扩渗后,在30.5°出现了一个与Pr有关的特征峰,证明La,Pr已渗入ZnO粉体.SEM测试结果表明:ZnO粉体经La,Pr扩渗后晶粒明显细化,团聚现象减弱.热重分析表明:经稀土扩渗后的ZnO粉体具有较好的热稳定性.La,Pr扩渗后ZnO粉体的室温电阻率由1014Ω.cm分别下降到1.6×106Ω.cm和1.9×106Ω.cm,说明La,Pr扩渗可明显改善ZnO粉体的导电性能和应用性能.     

Thermal conductivity of the vitreous system (ZnO) x −(P2O5)1−x

Glasses of the system (ZnO)_x–(P₂O₅)_1–x have been prepared by melting ZnO with anhydrous P₂O₅ in open crucibles. These glasses had compositions ranging from 20 to 70 mol % ZnO (chemically analysed ZnO mol %). Measurements of the thermal conductivity for the present glass system have been made in the temperature range 305 to 630 K. The thermal conductivity of this glass system is mainly due to lattice thermal vibrations. The thermal conductivity data are found to be fairly sensitive to the ZnO mol % content. It is observed from these data that the present glass system can be divided into three compositional regions. This behaviour is qualitatively explained in terms of changes in glass structure.     

Synthesis,Crystal Structural and Electrical Conductivity Properties of Fe-Doped Zinc Oxide Powders at High Temperatures

The synthesis,crystal structure and electrical conductivity properties of Fe-doped ZnO powders(in the range of 0.25-15 mol%) were reported in this paper.I-phase samples,which were indexed as single phase with a hexagonal(wurtzite) structure in the Fe-doped ZnO binary system,were determined by X-ray diffraction(XRD).The solubility limit of Fe in the ZnO lattice is 3 mol% at 950℃.The above mixed phase was observed.And the impurity phase was determined as the cubic-ZnFe 2 O 4 phase when compared with standard XRD data using the PDF program.This study focused on single I-phase ZnO samples which were synthesized at 950℃ because the limit of the solubility range is the widest at this temperature.The lattice parameters a and c of the I-phase decreased with Fe-doping concentration.The morphology of the I-phase samples was analyzed with a scanning electron microscope.The grain size of the I-phase samples increased with heat treatment and doping concentration.The electrical conductivity of the pure ZnO and single I-phase samples was investigated using the four-probe dc method at 100-950℃ in air atmosphere.The electrical conductivity values of pure ZnO,0.25 and 3 mol% Fe-doped ZnO samples at 100℃ were 2×10-6,1.7×10-3 and 6.3×10-4 S.cm-1,and at 950℃ they were 3.4,8.5 and 4 S.cm-1,respectively.     

Influence of interfacial modification on the thermal conductivity of polymer composites

In this study, the influence of modifying ZnO filler with surface-treating agents on the thermal conductivity of the ethylene-vinyl acetate copolymer (EVA) composites was reported. Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) were applied to analyze the surface modification of ZnO filler and the fractured surface morphology of the EVA–ZnO composites. The test results indicated that surface-treating ZnO filler with the valid modifying agents (stearic acid, OL-AT16, KH-560, or NDZ-132) at right dosage and treating temperature, the thermal conductivity of the EVA–ZnO composites can be enhanced effectively on account of reducing the interfacial phonon scattering; while the dosage of modifying agents exceed a right amount, the thermal conductivity of EVA–ZnO composites modified with the small-molecule treating agents (F-1, n-Octylic acid, or stearic acid) descend more evidently with the dosage increase.     

Numerical evaluation on heat transport characteristics between Al2O3 and ZnO materials in nanoscale situation

The aim of this article is to provide a systematic method to perform numerical evaluation on the cross-plane thermal conductivity of Al(2)O(3)/ZnO film interface. The Equilibrium Molecular Dynamics (EMD) simulations method is used to investigate the cross-plane thermal conductivity of Al(2)O(3)/ZnO film interface along the direction of Z axis at different equilibrium temperature and film interface thickness. The Buckingham two-body potential function and Green-Kubo linear response theory are used for modeling and calculation. The results show that the size effect is obvious. It implies the film interface thickness is 23.4-52 ? and the equilibrium temperature is 300-600 K. The cross section thermal conductivity of Al(2)O(3)/ZnO film interface increases with the increase of interface thickness, and decreases with the increase in equilibrium temperature.     

Effect of ZnO nanoparticles on the structure and ionic relaxation of poly(ethylene oxide)-LiI polymer electrolyte nanocomposites

The effect of ZnO nanoparticles on the structure and ionic relaxation of LiI salt doped poly(ethylene oxide) (PEO) polymer electrolytes has been investigated. X-ray diffraction, high resolution transmission electron microscopy and field emission scanning electron microscopy show that ZnO nanoparticles dispersed in the PEO-LiI polymer electrolyte reduce the crystallinity of PEO and increase relative smoothness of the surface morphology of the nanocomposite electrolyte. The electrical conductivity of the nanocomposites is found to increase due to incorporation of ZnO nanoparticles. We have shown that the structural modification due to insertion of ZnO nanoparticles results in the enhancement of the mobility i.e., the hopping rate of mobile Li+ ions and hence the ionic conductivity of PEO-LiI-ZnO nanocomposite electrolyte.     

Sn doping effects on properties of ZnO thin films deposited by RF magnetron sputtering using a powder target

In the present study, tin doped ZnO thin films (ZnO:Sn) at different contents (0–3 wt%) were deposited onto glass substrates by RF magnetron sputtering using a powder compacted target at room temperature. The effect of Sn concentration on the structural, optical and electrical properties of the ZnO:Sn thin films were investigated. The X-ray diffraction analysis shows that the pure ZnO thin film exhibits a strong intensity of the (002) peak indicating a preferential orientation along the c-axis. For Sn doped ZnO thin films, there is a change in the orientation from the (002) plane to the (101) one. The undoped ZnO thin films have transmittance 85% in the visible range and slightly increased for 0.5 wt% of Sn, while it get decreased with further increasing the Sn doping concentration. The optical band gap energy get increased with increasing the doping concentration. Moreover, the electrical conductivity and conduction mechanism are also studied by impedance spectroscopy in the frequency range of 1KHz–13 MHz at various temperatures (633–743 K). The AC conductivity in ZnO thin films increased with angular frequency. The frequency exponent S decreases with increasing temperature. Such behavior suggests that the correlated barrier hopping (CBH) model may be suitable to explain the conduction mechanism in ZnO thin films. The activation energy values calculated from angular frequency and DC conductivity are in good agreement confirming that the conduction mechanism is thermally activated by hopping between localized states.     

Self-compensation in ZnO thin films: An insight from X-ray photoelectron spectroscopy, Raman spectroscopy and time-of-flight secondary ion mass spectroscopy analyses

As-grown ZnO typically exhibits n-type conductivity and the difficulty of synthesizing p-type ZnO for the realization of ZnO-based optoelectronic devices is mainly due to the compensation effect of a large background n-type carrier concentration. The cause of this self-compensation effect has not been conclusively identified although oxygen vacancies, zinc interstitials and hydrogen have been suggested. In this work, typical n-type ZnO thin films were prepared by sputtering and investigated using X-ray photoelectron spectroscopy, Raman spectroscopy and time-of-flight secondary ion mass spectroscopy to gain an insight on the possible cause of the self-compensation effect. The analyses found that the native defect that most likely behaved as the donor was zinc interstitial but some contribution of n-type conductivity could also come from the electronegative carbonates or hydrogen carbonates incorporated in the ZnO thin films.     

ZnO的点缺陷结构与p型化转变的研究进展

ZnO是一种典型的直带隙宽禁带半导体材料,是下一代光电材料的代表.但由于P型化转变困难,使ZnO在光电领域的应用受到了极大限制.系统分析了ZnO的本征点缺陷结构和P型化转变方面的理论和实验研究成果,认为ZnO的n型电导应起源于本征点缺陷Zn或Vo.通过V族元素实现P型化转变的关键在于其稳定性,因此通过亚稳的点缺陷之间的相互作用实现相对较稳定的p-ZnO是V族元素掺杂实现P型化转变的研究方向.考虑到I族元素在ZnO中的固溶度较高且受主能级较浅,通过I族元素的掺杂实现高电导p-ZnO也是实现P型化转变的思路;但是Ⅰ族元素的掺杂会引起严重的自补偿,因此实现I族元素在ZnO晶格中的定位是Ⅰ族元素掺杂实现P型化转变的研究方向.     

氧化钇掺杂锆铈酸钡质子导体的制备及性能研究

采用高温固相法制备了钇掺杂锆铈酸钡(BaZr_0.90-xCe_xY_0.10O_3-δ, x=0.09、0.18、0.27)(即BZCY系列)前驱体粉末, 研究了烧结性能和电导率. 结果表明, 在所研究的组成范围内, x=0.27(即C3)试样为最佳. 再进一步通过优化烧结助剂ZnO添加量以提高试样的烧结性能及电化学性能. 实验表明, ZnO能够与前驱体发生固溶取代反应, 有效地提高了样品烧结性能. 随着ZnO添加量的增加, 试样烧结致密度提高, 但直流电导率先增大后减小. 当ZnO添加量为2mol%(C3-Z2)时, 试样具有最高的直流电导率, 800℃在湿H₂中电导率可达9.27 mS/cm. C3-Z2试样的XRD衍射峰与BaCeO₃、BaZrO₃标准衍射峰相比出现一定角度的偏移, 而与BaCe_0.4Zr_0.6O₃的标准图谱相对吻合较好.     

氧化锌晶须/环氧树脂导热绝缘复合材料的制备与性能

以环氧树脂(E-44)为聚合物基体,四针状氧化锌晶须(ZnOw)为填充材料,制备了氧化锌晶须/环氧树脂导热绝缘复合材料,研究了ZnOw含量对复合材料的导热性能、电性能的影响,并用扫描电子显微镜对断口形貌进行了观察。结果表明,较少量ZnOw的加入(体积分数<10%),复合材料的导热性能得到有效改善,但仍维持了聚合物材料所具有的电绝缘和低介电常数、低介电损耗的特点。其中当ZnOw体积分数为10%时,ZnOw/EP复合材料的热导率达到0.68W/(m·K),相比纯环氧树脂提高了3倍。     

Novel Transparent and Self‐Powered UV Photodetector Based on Crossed ZnO Nanofiber Array Homojunction

A novel self‐powered UV photodetector based on electrospun ZnO nanofiber arrays is introduced. Aligned pure ZnO nanofibers and Ag‐doped p‐type ZnO nanofibers are processed perpendicular to each other, and p–n junction arrays of ZnO nanofibers are fabricated as a result. Owing to the intrinsic intervals between nanofibers, the device is fully transparent on quartz substrate. Various characterization methods including TEM, XRD, and XPS are used to testify the existence form of Ag element in ZnO nanofibers, and a field effect transistor is constructed to judge their conductivity. It is discovered that the Ag doping process not only transforms ZnO to p‐type conductivity, making it possible to build this self‐powered photodetector, but also forms Ag nanoparticles in ZnO nanofibers and thus helps reduce the response time. Benefiting from the abovementioned dual effects, this UV detector is found to have an enhanced performance, with the on–off ratio up to 10⁴ at zero bias and a rather short rise/decay time of 3.90 s/4.71 s.     

Transparent conducting zinc oxide thin film prepared by off-axis rf magnetron sputtering

Highly conducting and transparent ZnO : Al thin films were grown by off-axis rf magnetron sputtering on amorphous silica substrates without any post-deposition annealing. The electrical and optical properties of the films deposited at various substrate temperatures and target to substrate distances were investigated in detail. Optimized ZnO : Al films have conductivity of 2200 S cm^-1 and average transmission in the visible range is higher than 85%. The conductivity and mobility show very little temperature dependence.     

Sensitivity to Combustible Gas for ZnO Thin Films

A fine polycrystalline ZnO thin film with 0.3～0.6 μm grain size was obtained by sol-gel process and a consequential heat treatment at 500℃. The process of preparing ZnO thin film was analysed. The sensitivity and conductivity of ZnO thin films as combustible gas (CO, CH4,H2) sensor as well as the influence of catalyst and pH value of the precursor on its sensitivity were studied in detail. The structure characteristics of ZnO thin film by different process were irlvestigated by X-ray diffraction, thermal analysis and photoelectron spectrometer. The atomic ratio of Zn to O on the surface of ZnO thin film was found to be 1.14:1 measured from XPS result. The conductivity of the thin film increases greatly when doped with Al3+ ion but decreases while doped with Na+ ion