Influence of electro-mechanical stress on electrical properties of dielectric polymers

The influence of high electrical fields on water treeing, electrical treeing, relaxation, conductivity and charge mobility in various polymers is reviewed within the context of a molecular model. The real value of the AC field acting on water trees is questioned and it is shown that the strain induced by very large fields may affect the water tree growth in solutions with large dielectric constant. A model based on simple electrostatic and molecular parameters describes most water treeing results. Light emitted during electrical tree growth could be associated with the field-induced strain at the tip of the electrode. The strain in PET is also related to the Maxwell stress due to high DC field. The log of the charge stored in some polymers varies with the square of the field suggesting that there same phenomenon might influence charge formation under high fields. The significance of a constant mobility value is discussed in light of experiments showing that it is not constant at moderate fields in various polymers. It is shown that the only constant parameter under varying high fields is the activation volume typical of a given sample. Future work is pointed out, especially regarding the nature of the trapping sites and the influence of sample size on the activation volume.     

Effect of Ca co-dopant on the electrical conductivity of Gd-doped ceria

Co-doped ceria of Ce_0.8Gd_0.2?x Ca _x O_2-δ (x?=?0?0.2), were prepared by oxalate co-precipitation method. Their structures and conductivities were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and AC impedance spectroscopy (IS). All the electrolytes were found to be single phase with cubic fluorite structure. SEM cross-section image showed relatively uniform grains with distinct and clean grain boundaries. The chemical states of the surface of the prepared samples were analyzed by XPS. Though Gd and Ca were present in their characteristic chemical state, Ce was found in single Ce⁴⁺ state or in mixed Ce⁴⁺ and Ce³⁺ states. IS measurements indicated that the conductivities for Ce_0.8Gd_0.2–x Ca _x O_2-δ pellets increased with increasing the sintering temperature. Moreover, co-doping with appropriate ratio of gadolinium and calcium was found to effectively enhance the conductivity in comparison to the singly doped ceria. The isothermal conductivity plots showed that sample Ce_0.8Gd_0.1Ca_0.1O_2-δ had the maximum conductivity with minimum activation energy (σ _700°C?=?0.0742?S/cm, Ea?=?0.58?eV), which is much higher compared to the conductivity exhibited by most of the reported codoped ceria compositions.     

Effect of re-oxidation on dielectric properties in Ni-MLCC

The effect of re-oxidation treatment on the solubility of dopants and the dielectric properties of rare-earths (La, Ho) and V-substituted BaTiO₃ solid solutions, assuming the shell phase of X7R dielectrics, was investigated. Ho-V-substituted samples showed larger increase of the lattice parameter and T _c by re-oxidation treatment compared with La-V-substituted samples. Electron spin resonance measurements revealed that the oxidation of V³⁺ to V⁴⁺ or V⁵⁺ appeared in the range in which the increase of lattice parameter by re-oxidation treatment was observed. This suggests that the increase of T _c is due to the change of preferential occupational site of Ho ion from A-site to B-site, being accompanied with the oxidation of V³⁺. We also investigated the effect of re-oxidation treatment on the electrical properties and microstructure in Ni-MLCC samples, using rare-earths (La, Ho, Yb) and acceptors (Mn, V) doped BaTiO₃ based X7R dielectrics. The change in temperature characteristic of the dielectric constant by re-oxidation treatment was observed for the MLCC samples containing V with smaller content. In the case of Ho-V- and Yb-V-doped samples showed larger increase of the dielectric constant at around 120 °C compared with La-V-doped samples. The relationship between the microstructure and electrical properties of the MLCC sample was investigated by impedance measurement at elevated temperature.     

Effect of tacticity on the dielectric properties of polystyrene

Dielectric properties of polystyrene (PS) were investigated by measuring electrical conduction current and frequency spectra of complex permittivity at temperatures from 20 to 199 °C. To clarify the effects of tacticity, the properties were compared among two kinds of syndiotactic PS (SPS) with different crystallinity values and one atactic PS (APS). Experimental results indicate that the two SPS samples show a high melting point of about 250 °C. The conductivity is lowest in SPS with the low crystallinity in the whole temperature range from 20 to 199 °C, while APS had a breakdown at 140 °C. Moreover, the low‐crystallinity SPS shows the smallest permittivity values and the smallest increase in dielectric loss factor toward low frequencies among the three samples. The high‐crystallinity SPS has α crystals. Since the density of α crystals is lower than the amorphous region, the charge transport and polarization are easier in the high‐crystallinity SPS than in the low‐crystallinity SPS. © 2011 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Relationship between the dielectric properties and the conductivity of Ba2FeNbO6

In the present work, we performed detailed investigation on the relationship between the dielectric properties and the conductivity of Ba₂FeNbO₆. Our results revealed that (1) the colossal dielectric behavior of the sample can be well understood based on the framework of universal dielectric response, (2) the observed relaxation shows a distinct deviation from the Arrhenius behavior, and (3) the peak intensity of dielectric loss can be well expressed by a relation similar to the Fermi?CDirac distribution function rather than a thermally activation relation. These are the typical features for the hopping motions of polaronic carriers demonstrating that the dielectric properties and the conductivity of Ba₂FeNbO₆ are closely linked.     

Effect of heat treatment on electrical properties of zinc oxides

The electrical properties of ZnO ceramics were studied from their voltage-current characteristics, thermally stimulated current (TSC), and heat-treatment effects. ZnO ceramic samples with a few mol% of insulating oxide components were prepared. After sintering at 1200°C in air, some of the sample were heat treated at various temperatures between 450 and 900°C in air. On the voltage-current curves, the current varies as a function of applied dc voltage according to the relation I = CV^α, where α is the nonlinear exponent. The nonlinear exponent α decreased with the heat-treatment temperature in the low-temperature region, became the lowest around 600–750°C, and almost recovered at 900°C. Three TSC peaks (designated by P₁, P₂ and P₃ from the low-temperature side) were observed in the nonheat-treated samples. The samples heat treated at 600 and 750°C showed only the P₁ and P₂ peaks; the P₃ peak increased in magnitude with the increase of biasing temperature t_b, and it shifted toward the high-temperature side. These results suggest that the electrical properties of ZnO ceramics will be associated with the phase transition of the Bi₂O₃- rich intergranular layers by heat treatment.     

Basic electrical processes in dielectric liquids

The basic processes of electrical conduction in dielectric liquids are reviewed, attention being drawn to the similarities between conductive electrolytes and insulating liquids. The concepts of the electronic amorphous solid state are employed to provide a framework for the review. The conditions at metal electrodes can be incorporated naturally into the scheme, and it is known that the space charge layers occurring on them can control conduction. Although electrical breakdown itself is not considered, the underlying electronic processes which will develop when breakdown electrical fields exist in the liquid are considered     

Effect of Ca substitution on structure and dielectric properties of bismuth-based microwave ceramics

The effect of the chemical substitution of Ca cation on the microstructure and microwave dielectric properties of bismuth-based pyrochlores has been investigated. Broad ranges of solid solutions based on (Bi_3x Zn_2?3x )(Zn _x Nb_2?x )O₇ (x?=?0.56–0.64) were obtained with Ca cation substitution of Zn at A site. The XRD patterns revealed that the substitution of Ca for Zn led to the α–β pyrochlore phase transformation and pure β pyrochlore structure were obtained. The dielectric constants (? _r ) varied slightly with x increasing. The quality factor Q was significantly improved by Ca substitution. The temperature coefficient of resonant frequency (τ _f ) was negative and increased with x increasing. (Bi_3x Ca_2?3x )(Zn _x Nb_2?x )O₇(x?=?0.58) ceramic, sintered at 960 °C, exhibits the optimal microwave dielectric properties of ? _r ?～?74, Qf value ～6,457 (at 4.8 GHz), and τ _f ?～??143 ppm/°C.     

中频变压器用环氧树脂/纳米BN复合介质的导热和电气性能研究

为了研究中频变压器用环氧树脂复合材料的导热和电气特性,本文选取高导热纳米氮化硼(BN)颗粒作为填料,利用盐酸多巴胺对其进行表面修饰,采用溶液法制备了环氧树脂/纳米BN复合材料试样(BN质量分数分别为1％、2％和5％),通过扫描电子显微镜对试样的微观形貌进行分析,测试了试样的热导率、体积电导率、中频击穿场强和表面电位衰减特性.结果表明:纳米BN的添加提高了环氧树脂的热导率;1 wt％和2 wt％纳米BN的添加降低了环氧树脂的电导率和载流子迁移率;随着电压频率的升高,试样的击穿场强降低;随着纳米BN浓度的增加,击穿场强呈现出先升高后降低的趋势;纳米BN能够缓解环氧树脂击穿场强随频率升高的影响,降低环氧树脂的表面电位衰减速度.上述结果表明,适量添加1 wt％和2 wt％的纳米BN能够提高中频变压器用环氧树脂复合材料的导热和电气性能.     

Effect of B-site doping on electrical conductivity of YAlO3 based electrolytes for solid oxide fuel cells

Journal of Electroceramics - Solid oxide fuel cells (SOFCs) have emerged as high temperature fuel cell technology operating at temperatures around 1000 °C. Lowering the operating...     

Effect of doped Ni2+ on the dielectric properties of NiO-BaTiO3 composites

NiO-BaTiO₃ composites were prepared by sintering BaTiO₃ together with NiO in air at 1300°C. Microstructure and morphology of the composites were detected by XRD and SEM, and the dielectric properties were measured by LCZ meter. The results indicate that the perovskite phase is formed in fact in status of solid solution doped with Ni²⁺, although only a small amount of Ni ions can dissolve into the perovskite phase. Ni doping decreases the formation temperature of the composite without inhibiting the grain growth of the crystalline phase. The dielectric constant decreases sharply and the dielectric loss decreases smoothly with increasing Ni²⁺ below NiO addition of 0.5 wt.%. When NiO addition increases above 0.5 wt.%, the dielectric constant and loss correlate with mixing rule of the two phases. Meanwhile, the replacement of Ni²⁺ for Ti⁴⁺ decreases the Curie temperature of perovskite phase by 30°C.     

不同比例NiO对硫正极材料导电性能的影响

单质硫的导电性一直是需要解决的关键问题。为了有效抑制一些多硫化物的产生,现在有效的措施是碳的复合、金属氧化物的混合填充,以及电解液的改善。在碳硫复合材料中"填充"过渡金属氧化物,这些氧化物通常具有离子选择性。这样的复合材料,能够抑制多硫化物的溶解,改善电池的循环性能。纳米氧化物利用其吸附性可以有效抑制硫及其还原产物在电解液中的溶解,提高正极反应的表面积,并对电池的氧化还原反应起到催化作用。通过对锂硫电池正极材料单质硫的导电特性进行研究,研究"填充"Ni O对单质硫电化学性能的影响,并采用XRD、SEM、粒度分析仪对电池材料物相、颗粒形貌和粒度分布进行表征。利用高精度电池性能分析测试系统等对正极材料、电池进行电性分析。     

Structures and electrical conductivity of CaNdFeO4 ceramics

CaNdFeO₄ ceramics were prepared using a solid-state process, and their crystal structure was identified by Rietveld method, while the electrical conductivity was evaluated as a function of sintering and testing temperatures. CaNdFeO₄ ceramics had an orthorhombic K₂NiF₄ structure, and a secondary perovskite phase (Ca,Nd) ${\text{FeO}}_{{3 \pm \delta }} $ was observed in the samples. The DC electrical conductivity of CaNdFeO₄ ceramics increased firstly to a maximum value, 0.065 Scm^?1, and then decreased with increasing sintering temperature. The relationship between electrical conductivity of CaNdFeO₄ ceramics and testing temperature obeyed the Arrhenius law.     

Effect of BiAlO3 concentration on the dielectric and piezoelectric properties of lead-free (Bi0.5Na0.5)0.94Ba0.06TiO3 piezoelectric ceramics

In this paper, lead-free (1-x)(Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃-xBiAlO₃ (BNBT-BA, x?=?0, 0.010, 0.015, 0.020, 0.025, and 0.030) piezoelectric ceramics were synthesized using a conventional solid-state reaction method. The effect of BiAlO₃ concentration on dielectric, ferroelectric and piezoelectric properties were investigated. The ferroelectric and piezoelectric properties of BNBT ceramics are significantly influenced by the presence of BA. In the composition range studied, X-ray diffraction revealed a perovskite phase with the coexistence of rhombohedral and tetragonal phases. The temperature dependence of dielectric properties showed that the depolarization temperature (T _d) shifted towards lower temperatures and that the degree of diffuseness of the phase transition around T _d and T _m became more obvious with increasing BiAlO₃ content. The remanent polarization increased with increasing BA, and reached a maximum value of 30 μC/cm² at x?=?0.020. As a result, at x?=?0.020, the piezoelectric constant (d ₃₃) and the electromechanical coupling factor (k _p) of the ceramics attained maximum values of 188 pC/N and 34.4 %, respectively. These results indicate that BNBT-BA ceramics is a promising candidate for lead-free piezoelectric materials.     

Influence of switching on dielectric properties of vacuuminterrupters

This paper deals with the influence of switching operations `closing without current/breaking without current', `closing without current/breaking with rated current', and `closing without current/breaking of rated short-circuit current' on vacuum interrupter dielectric strength. Two types of commercially available vacuum interrupter with transverse magnetic field CuCr contacts were tested. Breakdown voltages and emission currents, which appear before and after switching operations, were determined experimentally. The corresponding characteristics were determined after conditioning. The voltage shapes, dc, lightning impulse voltage (1.2/50 μs), and 50 Hz ac were applied. The obtained results were statistically treated. After taking into account theoretical considerations, it was concluded which physical mechanisms determine the influence of switching operations on the dielectric strength. It was found that in interrupters with poor contact material, the dielectric strength can deteriorate below the limits required by standards