纳米SiOx/聚乙烯复合材料强场电导特性的研究

用双溶液共混法制备了不同掺杂浓度的纳米SiOx/低密度聚乙烯(LDPE)复合材料,并利用动态机械谱(DMA)对复合材料的机械性能进行了测量.发现纳米SiOx/LDPE复合材料的玻璃化转变温度,储能模量和机械损耗模量随着纳米氧化硅掺杂浓度的增加先减小后增大,但均大于纯聚乙烯.研究了不同掺杂浓度的纳米SiOx/LDPE聚合物复合材料在293～353K的温度范围内的电导特性.结果表明纯聚乙烯和含有纳米SiOx的复合介质的强场电导不符合Schottky效应和Poole-Frenkel效应.进一步的分析表明,纯聚乙烯试样以空间电荷限制电流为主,而含纳米SiOx的复合介质的强场电导则以离子跳跃电导为主,并且通过实验数据计算了不同温度下载流子的跳跃距离.     

氧化硅掺杂对聚乙烯复合材料空间电荷分布的影响

用双溶液共混的方法制备了相同浓度的纳米SiOx/LDPE和微米SiO2/LDPE聚合物复合材料,利用傅立叶红外光谱对复合材料的分子间作用进行了测量。结果表明：聚乙烯分子链没有改变微米SiO2的谱峰,但对于纳米SiOx粒子,聚乙烯分子链使纳米SiOx的特征峰变宽、波数变小。采用PEA电声脉冲法对复合材料的空间电荷分布进行了测量,并对测试数据进行了分析。结果表明：纳米SiOx粒子的添加,使复合材料陷阱的能级变高,纳米SiOx/LDPE复合材料以异极性空间电荷为主,而微米SiO2/LDPE复合材料以同极性空间电荷为主。     

纳米SiO_x/LDPE复合材料中逾渗电导现象的研究

用双溶液共混的方法制备了不同质量分数的纳米SiOx/LDPE聚合物复合材料,利用X射线衍射对复合材料的结晶状态进行了研究。发现纳米SiOx的添加导致结晶度变大,晶粒的尺寸先变小后变大的现象。利用微电流计对不同质量分数的纳米SiOx/LDPE聚合物复合材料在293~353 K的温度范围内进行电导测量。试验结果表明:纳米SiOx/LDPE聚合物复合材料存在类似于掺杂导电粒子或半导电粒子的聚合物复合材料电导过程中的"逾渗"现象,即复合材料的电导随着纳米粒子质量分数的增加先减小后增加的现象,这与X射线衍射试验中的晶粒尺寸变化趋势相一致。最后结合纳米SiOx粒子对聚乙烯产生的微观结构的变化对强场电导的实验曲线进行了解释。     

纳米SiOx/聚乙烯复合介质强场电导的预电应力效应研究

测量纳米SiOx/低密度聚乙烯(LDPE)复合介质在强场下的电导特性时,发现这种介质具有预电应力效应,即复合e)dtysgye介质经相同极性的较高直流电场(8×107V/m)预压作用2h后,直流电导比预压前的小,并随着纳米SiOx浓度的增加,这种预电应力效应越明显。通过透射电子显微镜(TEM)研究了纳米SiOx与LDPE之间的界面状态及纳米SiOx在LDPE中的分散形态;X射线衍射(XRD)结果表明纳米SiOx影响LDPE的结晶形态;另外运用傅立叶红外光谱(FTIR)研究了纳米SiOx与LDPE分子链间的相互作用。文章最后结合上述微观测试结果解释了纳米SiOx的添加所引起的LDPE强场下的预电应力效应。     

PS/LDPE纳米复合材料介电性能研究

将一种高聚物纳米颗粒-聚苯乙烯(PS)纳米球加入到低密度聚乙烯(LDPE)中,通过熔融共混法制备了PS质量分数为2%的PS/LDPE纳米复合电介质,利用电声脉冲(PEA)法对40 k V/mm电场强度作用下试样内的空间电荷分布进行测试分析,并进行热刺激电流及电导测试。结果表明:PS/LDPE纳米复合材料内部的空间电荷量明显低于纯LDPE;PS/LDPE纳米复合材料在常温下的直流电导率也较纯LDPE小;热刺激电流(TSC)图谱显示PS纳米球的添加改变了材料的陷阱深度和密度,这有可能是抑制LDPE空间电荷累积和直流电导特性发生改变的原因。     

空间电荷与直流电导联合测试技术用于纳米MgO抑制XLPE中空间电荷的研究

粒径70nm的MgO以不同浓度与交联聚乙烯(XLPE)共混制成聚合物纳米复合介质。采用自主研发的四电极系统同时测量复合介质的高场电导特性和空间电荷分布。通过强场电导实验发现,在室温下,XLPE及纳米MgO/XLPE复合介质的电导机理不是单纯的空间电荷限制电流(SCLC)。此外,添加纳米MgO可以明显地提高空间电荷的注入阈值,并且在低于空间电荷注入阈值的电场下,复合介质的电导电流密度随纳米MgO浓度的增加,先减小后增大。最后从空间电荷的实验数据验证了纳米MgO能有效抑制XLPE中空间电荷,并进一步定性地认为纳米Mgo的添加提高了电子注入的电场强度阈值。     

低密度聚乙烯空间电荷与电导电流的联合测量

聚乙烯非常容易积累空间电荷,造成聚乙烯绝缘电缆用于高压直流输电时容易出现绝缘劣化和使用寿命减少的问题。为了研究绝缘材料在直流电场下的空间电荷特性与电导特性,考虑到由于外电流存在位移电流分量,对于同一块试样分别测量得到的结果并不能进行严格的联合分析,基于脉冲电声法（pulse electro acoustic, PEA）原理设计了一套能够对平板试样进行“同区分时”测量空间电荷和外电流的实验装置,联合测量了低密度聚乙烯（low density polyethylene, LDPE）在室温下的空间电荷和高场电导。实验结果表明：随着施加场强的升高,阳极异极性空间电荷逐渐增加,阴极由同极性注入转变为异极性空间电荷积累,这与材料内部的杂质解离以及不同电极材料的选取有关。低电场条件下位移电流在外电流中所占的比例大于电导电流,传导电流密度与电场强度的关系也符合空间电荷限制电流（space charge limited current）理论。     

制备工艺对SiO_2/LDPE纳米复合材料空间电荷特性和直流击穿强度的影响

采用平行双螺杆挤出机和转矩流变仪制备了Si O2/LDPE纳米复合材料,研究了两种工艺对纳米粒子分散情况和介电性能的影响。利用电声脉冲法(PEA)比较LDPE和Si O2/LDPE纳米复合材料的空间电荷抑制能力,并测量了其室温下的直流击穿特性。结果表明:Si O2/LDPE比LDPE具有更高的空间电荷抑制能力,且两种工艺制备的Si O2/LDPE直流击穿强度分别提高了21.8%和3%。扫描电镜(SEM)分析表明,平行双螺杆制备的Si O2/LDPE纳米复合材料中的纳米粒子分散性更好,其空间电荷的抑制能力更高,直流击穿强度比转矩流变仪制备的材料高18.22%。平行双螺杆比转矩流变仪具有较高的剪切力,可提高纳米粒子在聚合物中分散性,进一步提高了Si O2/LDPE纳米复合材料的介电性能。     

纳米氮化铝改性对芳纶1313绝缘纸介电特性的影响

聚合物纳米复合材料因其优良的介电性能在电介质绝缘领域得到了广泛的应用。为获得性能优良的绝缘纸,将纳米氮化铝(AlN)添加到芳纶1313中。将改性后的绝缘纸进行浸油处理,研究了AlN对油浸芳纶1313介电性能的影响。结果表明:纳米Al N能有效降低绝缘纸的电导电流,以及提升其交流击穿电场强度;同时Al N能够抑制空间电荷向介质内的注入、迁移和积聚,使绝缘纸内空间电荷分布更加均匀。另外聚合物纳米材料的界面特性使得改性后绝缘纸的相对介电常数和介电损耗值有所升高,介损松弛峰值也向低频段移动。芳纶1313/Al N油浸绝缘纸介电性能的变化归因于纳米粒子与聚合物之间的界面效应使界面区域陷阱浓度和深度增大,限制了电荷的运动。     

抗氧剂对聚乙烯电缆直流介电性能的影响

为研究抗氧剂对聚乙烯(LDPE)绝缘电缆直流介电性能的影响,通过熔融共混制备了4种质量分数为0.3%的抗氧剂聚乙烯复合材料,在恒定的场强下,测试电导率随温度的变化,利用电声脉冲法(PEA),测试各试样中空间电荷的分布,并测量室温直流击穿特性。结果表明,添加抗氧剂300的LDPE试样中空间电荷量较少;在低场强下,添加抗氧剂300的LDPE对温度的依赖性较小,表现出良好的电导特性,在场强较高时,抗氧剂1010聚乙烯复合材料表现出良好的电导特性;抗氧剂聚乙烯复合材料的直流击穿强度比聚乙烯的直流击穿强度高。     

Dielectric breakdown in high-ε films for ulsi DRAMs: III. Leakage current precursors and electrodes

Abstract

A somewhat qualitative review of leakage currents J(V,t) in perovskite oxides is presented. It is stressed that space-charge-limited currents (SCLCs) are not alternatives to ionic conduction, Schottky emission, Poole-Frenkel, or Fowler-Nordheim tunneling, but can occur whenever currents due to any of those mechanisms reach a certain threshold and are no longer limited by the details of the metal electrode-ferroelectric interface. Standard metal-semiconductor band models that exclude surface states fail qualitatively to account for the experimental dependences of leakage currents and breakdown voltages on electrode work function; the correct model is metal-n-p-n-metal, with surface donor-state trapping. A discussion of conduction properties in these materials is presented from an ionic conductor viewpoint.     

Current Instability, Permittivity Variation With Frequency, and Their Relationship in Ta2O5 Capacitor

In this paper, Ta₂O₅ current instability in MIM and MIS capacitors is studied over several sample thicknesses with a current-versus-time measurement and low-frequency dielectric spectroscopy. Three types of phenomena are identified. The first one is attributed to polarization current correlated to flat loss behavior. The second mechanism corresponds to the conduction current identified as a steady state: a unique mechanism, probably a Poole-Frenkel one, is observed on the whole investigated voltage range. Finally, a resistance degradation phenomenon occurs that has been attributed to ionic diffusion in dielectric and follows the space-charge-limited theory. According to physical characterization, a model based on oxygen vacancies migration in the dielectric is suggested. Moreover, according to low-frequency dielectric spectroscopy measurements, it has been identified that the low-frequency loss peak is created by the same defects and is well modeled by the Maxwell-Wagner approach.     

茂金属聚乙烯改性低密度聚乙烯中空间电荷的机理研究

针对高压,超高压直流塑料电缆中存在的空间电荷效应,文中选用与普通低密度聚乙烯(LDPE)化学结构相似的茂金属聚乙烯(MPE)作为成核剂与LDPE共混,用电声脉冲法(PEA)测量了共混物的空间电荷特性,以差示扫描量热法(DSC)研究了共混物的非等温结晶行为,用高阻计测量了共混物的体积电阻率的变化,结合聚合物的结晶和导电理论,讨论了共混物中空间电荷的形成和抑制机理。测试结果表明:1%的MPE与LDPE共混,能有效降低LDPE中空间电荷效应,提高结晶温度,降低体积电阻率。     

Electrical conduction of thin 1,4-cis-polybutadiene films

This work contains results on the internal structure and dc conduction of 1,4-cispolybutadiene. X-ray and thermally stimulated depolarization (TSD) studies have been a source of information on phase transitions in the investigated material. The conduction measurements have been performed on thin films of thickness varying from 1 to 10 μm. Gold and aluminum have been applied as electrodes. The temperature range changed from 13 to 325 K. The investigated material was 1,4-cis polybutadiene of the Philips Petroleum Co, It contained 96% cis and 4% of the trans form of polybutadiene. It was observed that the internal structure of the polymer had a strong influence on its electrical properties. Electric conduction resulted from non-activated or thermally activated hopping with some contribution of the Poole-Frenkel effect. Electrode contact phenomena, such as thermionic emission and field emission (tunneling), are very likely responsible for charge carrier injection into the investigated material. The obtained activation energies range from 0.002 to N 0.3 eV     

CB/LDPE纳米复合材料的空间电荷抑制特性

采用熔融共混法制备了纯低密度聚乙烯(LDPE)试样和纳米炭黑(CB)颗粒质量分数分别为0.01%、0.03%、0.05%、0.07%的CB/LDPE复合试样。采用扫描电子显微镜观察纳米CB颗粒在LDPE基体中的分散性,并利用电声脉冲法(PEA)测试各试样在常温和-40 kV/mm条件下的空间电荷积聚特性和陷阱特性,讨论纳米CB颗粒提升LDPE基体空间电荷抑制特性的机制。结果表明:相较于纯LDPE试样,CB/LDPE复合试样的空间电荷积聚特性得到了显著改善,其中CB质量分数为0.03%的CB/LDPE复合试样具有最佳的空间电荷抑制效果。纳米CB颗粒提高了复合试样内部的深陷阱密度,这是提高复合试样空间电荷抑制能力的关键。     

The effect of low-molecular-weight species on space charge andconduction in LDPE

We have investigated the effect of low-molecular mass species on the space charge behavior such as space charge distribution and electrical conduction of LDPE (low density polyethylene). We also attempted to explain the relationship between the space charge distribution and electrical conduction. The heterocharge, conduction current and effective charge mobility decreased when the low-molecular-mass species in LDPE was removed. It was found that the decrease in conduction current was related to the decrease of heterocharge in LDPE     

The effect of nano‐ZnO on corona aging and photo aging in low‐density polyethylene

In this paper, space charge distributions as well as dielectric properties, such as volume resistivity and AC breakdown strength, were studied in low‐density polyethylene (LDPE) and its composite obtained by adding nano‐ZnO nanofiller, before and after photo‐oxidation or corona aging for several days. It was found that a small amount of ZnO nanoparticles could effectively improve both the photostabilization and corona stabilization of the LDPE matrix. Fourier transform infrared (FTIR) spectra of the specimens were investigated to reveal the change of the microstructures. The results showed that a weaker carbonyl absorption peak appeared in LDPE/ZnO nanocomposite than in LDPE. A proper explanation is given according to the photodegradation and corona degradation theory of polyethylene. The results also showed that there was a certain similarity between photo aging and corona aging. IEEJ Trans 2010 DOI: 10.1002/tee.20600     

From LDPE to XLPE: investigating the change of electrical properties. Part I. space charge, conduction and lifetime

This paper discusses the results of space charge, conduction current and electrical lifetime measurements performed on widely-used materials for electrical insulation, that is, low density polyethylene (LDPE) and cross-linked polyethylene (XLPE). Space charge accumulation profiles were compared in LDPE, low density polyethylene plus antioxidant (LDPE+AO) and XLPE, with consideration of thermal treatment effects in LDPE and XLPE. Significant variation (decrease) of accumulated space charge and apparent mobility, as well as slight decrease of conduction current, can be seen going from LDPE to LDPE+AO and XLPE, which may be associated with formation of deeper trap levels (or an increase of their density). On the contrary, electrical life under AC voltage does not show significant differences from LDPE to XLPE. This latter result underlines that life under high AC electrical stress is mostly determined by defects (weak points) rather than material characteristics associated with charge injection and transport.     

LEAKAGE CURRENT MECHANISM OF POLYCRYSTALLINE BiFeO3 FILMS WITH PT ELECTRODE

ABSTRACT

Leakage current mechanism of the polycrystalline BiFeO₃ film annealing at 923 K with Pt electrodes was discussed based on Schottky-emission conduction, Poole-Frenkel trap limited conduction, Fowler-Nordheim tunneling conduction and space charge limited current (SCLC). The leakage current mechanism at room temperature is as follows; Schottky-emission or Poole-Frenkel was the candidate leakage current mechanism at low electric field and then leakage current mechanism was changed to the SCLC at high electric field. When decreasing the measuring temperature, the leakage current mechanism at low electric field was Poole-Frenkel trap limited conduction, though the electric field region of the PF trap limited conduction was much broader than that of the room temperature.