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The growth and partial discharge (PD) characteristics of electrical tree in crosslinked polyethylene (XLPE) needle-plate electrode samples are investigated under constant dc voltage at different temperatures. The results reveal that under the experimental conditions, the electrical trees are all branch trees, and the discharge intensity fluctuates with time. The increase in temperature promotes the growth of electrical tree as well as the intensity of PD. Five texture features of PD ${q}$ - ${t}$ histogram are extracted and used as the elements to evaluate the insulation status of XLPE needle-plate electrode under dc voltage based on the gray correlation degree. The area ratio and lateral tree ratio of electrical tree is extracted based on the gray histogram. The lateral tree ratio increases with the increase in temperature, which is closely related to the intensity of PD. Gray correlation theory is used to evaluate the status of XLPE insulation. The results reveal that the evaluated insulation statuses based on the gray correlation degree are the same as those based on experience, which indicates that the proposed diagnosis method of XLPE insulation status based on the gray correlation degree with ${q}$ - ${t}$ histogram texture features as elements has a high accuracy. [ABSTRACT FROM AUTHOR]

Space charge problems have been widely acknowledged for solid insulation such as polyethylene for high-voltage dc cable insulation. However, the effect of space charge on the reliability of high-voltage power module packaging insulation has not been systematically investigated. In this article, a simultaneous measurement of space-charge and isothermal relaxation current (IRC) is performed on silicone packaging insulation. An iterative algorithm based on the nonnegative least-square method is introduced to estimate multilevel trap energy distribution in silicone insulation. It is found that homocharges are accumulated around the electrodes, and more charges are accumulated with the increase in applied electric field and temperature. The local electrical field is distorted, and the threshold of the external applied electric field for charge accumulation decreases with increasing temperature. The trapped charges tend to be trapped in deep traps as the temperature increases. Furthermore, to investigate the charge dynamics in the complex power module package structure, a 2-D space-charge simulation model based on the combination of the bipolar charge transport model and finite-element method (FEM) is proposed with the parameters derived from the simultaneous measurement. According to the simulation results, the maximum electric field is located at the triple-junction position of the high-voltage power module package. With the accumulation of homocharges and the increase in temperature, the electric field decreases at the triple-point position but increases between the injected positive and negative charges. Space-charge behavior affects the local electric field of power module packaging insulation and should be thoroughly investigated in the future. [ABSTRACT FROM AUTHOR]

A bistable electrochromic (EC) device which can reversibly transform between transparent, mirror, and black states based on reversible metal Ag electrodeposition is achieved by introducing 1) a (3‐mercaptopropyl) trimethoxysilane (MPTMS)‐treated indium‐tin‐oxide (ITO) glass electrode modified with WO3 nanoislands (WNs) as the rough surface and 2) ionic liquids (IL) into electrolyte to form an anion‐blocking layer, toward achieving long‐term memory performance. Typically, the EC cell is packaged by sandwiching gel electrolyte between the flat and WNs‐modified ITO electrodes. Under opposite voltages, this smart device can transfer from transparent to black (+2.5 V/9.4 s) or mirror (−2.5 V/8.3 s) state by depositing Ag on the WNs‐modified or flat ITO electrode surface, respectively. The assembled device exhibits over 80% mirror reflectance and below 10% transmittance of black state. After power off, both the black and mirror states remain bistability for a long time (>30 min) when IL are introduced into electrolyte for the EC device. The electrical double layer in the highly viscous electrolyte with IL contributes to form a barrier to bromide ions, which protects the Ag layer from dissolution at open circuit. This multifunctional energy‐efficient EC device has shown great potential and competitiveness for numerous applications compared to conventional EC devices. [ABSTRACT FROM AUTHOR]

To explore dc flashover characteristics and evaluate the dc flashover resistance of epoxy resin, an online surface potential measurement is proposed and verified in this article. Rising positive and negative dc high voltages (HVs) with a step of 0.5 kV per 5 min are applied to epoxy resin until the intensive flashover occurs, and the surface potential at the triple junction point is measured during flashover. It is found that the surface potential profile appears as the recurrence of flashover units during intensive flashover. A three-point peak-finding algorithm with threshold judgment is proposed to determine the interval between adjacent flashover units. Both appropriate surface potential difference threshold (SPDT) and flashover interval (FI) are used to evaluate the severity of flashover (i.e., the opposite of flashover resistance). It is interesting to find positive and negative flashover has different surface potential evolution characteristics. Positive flashover exhibits larger fluctuation, higher SPDT, and shorter FI, which may result from severe positive charge accumulation before every single flashover due to the low surface mobility of the positive charge. The results manifest positive flashover is more serious than negative flashover for the investigated epoxy resin. [ABSTRACT FROM AUTHOR]

In this study, a pulsed electroacoustic (PEA) system, which can measure the space charge distribution of polymer films from low to high temperatures, is introduced. The space charge behavior of direct current (DC) stressed low density polyethylene (LDPE) film is investigated at temperatures from −40 to 70 °C. The space charge results show that homocharges accumulate in the vicinity of electrodes at low temperatures (−40 to 0 °C), whereas heterocharges that appear during short circuit at the ambient temperature (30 °C), and negative charges gradually dominate the distribution with the increase of temperature. Moreover, the accumulated space charge density at −20 °C reaches the maximum within the investigated temperature range, which may be related to the traps formed by the polyethylene molecular chain branches. This finding coincides with the dynamic mechanical analysis (DMA) result and the thermally stimulated current (TSC) of LDPE reported by other researchers. Besides, the apparent mobilities of carriers at various temperatures calculated based on space charge decaying data indicates that the mobility decreases first and then increases with the increase of temperature from −40 to 70 °C. The variation of the apparent mobility can be explained by the hopping model. In addition, with the help of atomic force microscope (AFM) with Kelvin probe, the contact mode of aluminum/ LDPE/semiconductor was found to be the main reason that resulted in the slower decay of injected holes around the anode, as compared to the injected electrons around the cathode. [ABSTRACT FROM AUTHOR]

To estimate arbitrary electron and hole trap energy distribution of cross-linked polyethylene (XLPE), a modified method based on the combination of relaxation current and space charge measurement is proposed. This method is on the premise that homocharges are injected at the shallow depth of dielectrics and then detrap and flow away from electrodes. During depolarization, space charge and relaxation current are measured simultaneously by a specialized pulsed electro-acoustic (PEA) equipment. Furthermore, the decrease rates of positive and negative space charge are separately calculated and the ratio between them are employed to differentiate the contribution of electrons and holes to relaxation current. Thus, the relaxation current can be divided into two components to calculate energy distribution of electron and hole traps. Besides, simulation based on a modified bipolar charge transport model with calculated energy distribution were performed to simulate the dynamics of space charge. The experiment results of XLPE show that more hole traps than electron traps exist at energy levels above 0.86 eV. The energy distribution corroborates the decay pattern of space charge. In addition, the simulation results show the same qualitative characters as experiment results. Therefore, this method could be employed to estimate arbitrary trap energy distribution and the simulation may help give an insight of trap properties as well as space charge dynamics. [ABSTRACT FROM AUTHOR]

The simplest space charge measurement system is introduced for the direct space charge observation under arbitrary periodic stresses. An essential component of the system is the frequency allocation strategy for periodic stress fa and detection source fp. This strategy is based on the modified automatic equal phase shift (AEPS) principle, in which the relationship between fa and fp can be an integral multiple and a non-integral multiple. The phase detection in the range of 0??360? can be completed during Na cycles of periodic stress with Np detected excitation to realize phase resolution ?' = 2?/Np. Two different allocation strategies, namely, Na = 1 for the integral multiple between fa and fp and Na > 1 for the non-integral multiple between fa and fp, can be used to realize a high-phase resolution with consideration of the available frequency range for the detected source. Phase monitoring can be realized with the discrete voltage Va(i) of periodic stress at the detection phase and with the peak voltage Vg(i) of the raw signal representing the space charge density of the ground electrode. Phase delay is also introduced between the monitoring signal and real phase to avoid phase errors, especially at a high frequency and electric field. The detection phase of the space charge can be accurately identified through the monitoring signal via the data fitting or the Hilbert transform using the base wave component acquired with the Fourier transform. However, the data processing is complex for both methods. Thus, a simple and fast identification method is presented on the basis of the characteristic sequence of the AEPS principle. Finally, the feasibility and accuracy of the proposed system are successfully verified through the direct detection of the space charge within low-density polyethylene under several practical periodic stresses, namely, AC wave at 0.01 Hz, square wave at 1 kHz, and harmonic wave at 10 kHz. [ABSTRACT FROM AUTHOR]

In this paper, trap distribution variation in low density polyethylene (LDPE) after filled with 1 wt% nanosilica is investigated through the charge decay after corona charging with a needle-plane electrodes system. The LDPE and LDPE/SiO2 nanocomposite were firstly polarized under needle-plane electrodes system. The electrons and holes are injected through the variation of polarization of the needle. Then the surface space charge behavior and relaxation current were measured with a simultaneous measuring equipment, which overcomes the poor correlation of separate measurement. Lastly, the apparent mobility and trap distribution are evaluated based on the decay of surface space charge and relaxation current decay. It is found that the observed surface space charge and current are associated with trap distribution from 0.855 eV to 1.000 eV during decay process from 10 s to 3600 s. In LDPE/SiO2 nanocomposite, the estimated trap density of electrons and holes is more than that of LDPE in a relatively low energy range from 0.855 eV to 0.925 eV. These traps with low energy levels as transport media for carriers may be the main reason for the higher mobility of carriers in LDPE/SiO2 than LDPE, which is testified by surface space charge decay. It is also worth noting that according to the relaxation current decay, the estimated density of the relatively deep hole traps (>0.990 eV) is more than that of electron traps in LDPE, which is not observed in LDPE/SiO2. This is in accord with other scholar's molecular simulation result that most hole traps exist in intra-chain areas and electron traps exist in inter-chain areas, reflecting the different transportation characteristics of electrons and holes. [ABSTRACT FROM AUTHOR]

Cobalt-free perovskite oxide La 0.5 Sr 0.5 Fe 0.8 Cu 0.2 O 3 − δ (LSFC) was applied as both anode and cathode for symmetrical solid oxide fuel cells (SSOFCs). The LSFC shows a reversible transition between a cubic perovskite phase in air and a mixture of SrFeLaO 4 , a K 2 NiF 4 -type layered perovskite oxide, metallic Cu and LaFeO 3 in reducing atmosphere at elevated temperature. The average thermal expansion coefficient of LSFC in air is 17.7 × 10 − 6 K − 1 at 25 °C to 900 °C. By adopting LSFC as initial electrodes to fabricate electrolyte supported SSOFCs, the cells generate maximum power output of 1054, 795 and 577 mW cm − 2 with humidified H 2 fuel (~ 3% H 2 O) and 895, 721 and 482 mW cm − 2 with humidified syngas fuel (H 2 :CO = 1:1) at 900, 850 and 800 °C, respectively. Moreover, the cell with humidified H 2 fuel demonstrates a reasonable stability at 800 °C under 0.7 V for 100 h. [ABSTRACT FROM AUTHOR]

In recent years, the multilayered polyimide films have been widely used in flexible Print- Circuit Board in order to reduce the thickness of the combination of the flexible Print- Circuit Board. The existence of space charge as a main reason for dielectric breakdown, has a great effect on breakdown characteristic. So it is important to study the space charge characteristics of the multilayered polyimide films. Fluorination can change the chemical component in surface layer of polymers and therefore can influence the charge injection from electrodes and affect the electrical properties of the surface layer. This paper presents a study aimed at clarifying the effect of fluorination on space charge behavior in multilayered polyimide films. Samples were fluorinated in a laboratory vessel at 328 K (55 °C) using a F2/N2 mixture with 20% F2 by volume and 0.05 MPa (500 mbar) for respectively 15, 30, 45 and 60 minutes. The surface chemical compositions of the films were characterized by attenuated total reflection infrared analysis. The space charge distributions in multilayered polyimide films were measured by using the pulsed electroacoustic (PEA) method. Obtained results showed that the space charge distribution of multilayered film stacking with five fluorinated samples was quite different from that of multilayered film stacking with five untreated samples. It is also suggested that the fluorination can significantly suppress the injection of space charge. [ABSTRACT FROM AUTHOR]

This paper presented the measurement results of space charge distribution and high field conduction in cross-linked polyethylene (XLPE) plate sample at various electric fields for a broad temperature range from 30 to 90 °C. The temperature effect on charge trapping and transport mechanism is discussed based on estimation of threshold characteristic and apparent mobility. It is shown that the threshold field for space charge accumulation apparently decreased with the temperature, probably associated with acceleration of charge injection and ionic dissociation. The apparent mobility of charges showed an exponential dependence on temperature, which indicates enhancement of charge detrapping and transfer rate at higher temperature. The field dependence of the space charge decreases with the temperature, results in more space charge accumulate at room temperature than at high temperature at certain high field. This behavior indicates that the space charge formation rate increases slower than the charge detrapping rate as the temperature increases. Besides, negative charge is always dominant in the sample at the measuring field and temperature range. This is probably due to stronger electron injection at XLPE-aluminum interface or more negative ion formed by dissociation of chemical species. [ABSTRACT FROM AUTHOR]

Abstract: This paper describes the preparation and characterization of unimorph actuators for deformable mirrors, based on Pb(Zr0.52Ti0.48)O3 (PZT52) thin film. As comparison, two different designs, where the PZT layer in the unimorph actuators was driven by either interdigitated electrodes (IDT-mode) or parallel plate electrodes (d31-mode), were investigated. The actuators utilize a unimorph membrane (diaphragm) structure consisting of an active PZT piezoelectric layer and a passive SiO2/Si composite layer. To fabricate the diaphragm structures, n-type (100) silicon-on-insulator (SOI) wafers with 1μm thermal SiO2 were used as substrates (for d31-mode actuators, the upper Si part of SOI need to be heavily doped and used as bottom electrodes simultaneously). Sol–gel derived PZT piezoelectric layers with PbTiO3 (PT) bufferlayer in total of 0.86μm were then fabricated on them, and 0.15μm Al reflective layers were deposited and patterned into top electrode geometries, subsequently. The diaphragms were released using orientation-dependent wet etching (ODE) with 5–10μm residual silicon layers. The complete unimorph actuators comprise 4×4 discrete units (4mm2 in size) with patterned PZT films for parallel plate configuration or 3×3 individual pixels (2mm in IDT diameter) with continuous PZT films in graphic region for IDT configuration. The measurement results indicated that both of the two configurations can generate considerable deflections at low voltage. The measured maximum central deflections at 15V were approximately 2.5μm and 2.8μm, respectively. The intrinsic strain conditions shaping the deflection profiles for the diaphragm actuators were also analyzed. In this paper, the behaviors of clamped parallel plate configuration without a diaphragm were also evaluated. [Copyright &y& Elsevier]

Abstract: A systematic study and evaluation were performed on the effect of scandium doping at the B site of Pr0.6Sr0.4Co0.2Fe0.8O3−δ (PSCF) on key material properties as cathode for intermediate temperature solid oxide fuel cells (IT-SOFC). The doped products Pr0.6Sr0.4(Co0.2Fe0.8)(1−x)Sc x O3−δ (PSCFS x , x=0.0–0.2) retained perovskite structure confirmed by X-ray diffraction, and their particles were smaller than the non-doped materials as evidenced by TEM. The electrical conductivity (EC) of PSCFS x decreased with increasing Sc3+ content, but EC values were still larger than 100 S cm−1 in temperature range of 300–800 °C as x ≤ 0.1. The thermal expansion coefficients (TEC) of PSCFS x were observed to generally decrease with increasing x especially at lower temperature range of 50–600 °C. In addition, the AC impedance revealed better electrochemical performance of PSCFS x cathode as x ≤ 0.1 than that of the undoped sample PSCF. Therefore, PSCFS x (x ≤ 0.1) shows some potential as cathode electrode for IT-SOFC. The function of Sc3+ dopant was tentatively elucidated and discussed. [Copyright &y& Elsevier]