Dielectric Breakdown Field Strength Research Articles

BaTiO3-based lead-free relaxor ferroelectric ceramics for high energy storage

Barium titanate (BaTiO3, BT) is widely used in capacitors because of its excellent dielectric properties. However, owing to its high remanent polarisation (Pr) and low dielectric breakdown field strength (Eb), achievement of high energy storage performance is challenging. Herein, a systematic strategy was proposed to reduce Pr and elevate Eb of BT via: (i) modification of the relaxor behavior by alloying it with Bi(Mg2/3Ta1/3)O3 (BMT) and (ii) heightening Eb by introducing NaTaO3 (NT) with high band gap. Consequently, the energy storage efficiency (η) of 90 % and high Eb of 780 kV cm−1 were achieved simultaneously for the BT-BMT-xNT system, which facilitated the recoverable energy density (Wrec) of 6.02 J cm−3. At 300 kV cm−1, its temperature (20–120 °C) and frequency (1–500 Hz) stabilities were found to be good. Moreover, the BT-BMT-0.15NT possessed ultrafast discharge rate (t0.9 < 51 ns) and ultrahigh power density (PD > 94 MW cm−3). This study offers an effective strategy for the design of novel high-performance dielectric energy storage materials.

Mechanism of the effect of Al and Sr substitution on the electrical resistance in CaCu3Ti4O12 ceramics

To investigate the mechanism of Al and Sr substitution on grain resistance (Rg) and grain boundary resistance (Rgb) in CaCu3Ti4O12 (CCTO) ceramics, various compositions of Ca1-xSrxCu3Ti4-yAlyO12 (x = y = 0; x = 0, y = 0.04; x = 0.6, y = 0; x = 0.6, y = 0.04) ceramics were synthesized. All samples exhibited excellent dielectric loss and breakdown field strength performance. These improvements can be attributed to the substantial rise in Rgb and an unconventional boost in Rg. Activation energy tests and X-ray photoelectron spectroscopy analysis indicate that both Rgb and Rg are strongly influenced by oxygen vacancies (V•• O) and the mixed structures of Cu+/Cu2+ and Ti3+/Ti4+. This study explains the mechanism of Al and Sr substitution based on atomic electronegativity, with Al inhibiting the formation of Cu+ and Ti3+ but promoting the generation of V•• O, while Sr inhibiting the formation of Ti3+ and V•• O but promoting the generation of Cu+. This research offers valuable theoretical instructive for the design of high-resistivity CCTO ceramics.

Improving the electric energy storage performance of multilayer ceramic capacitors by refining grains through a two-step sintering process

Dielectric materials for multilayer ceramic capacitors (MLCCs) have been widely used in the field of pulse power supply due to their high-power density, high-temperature resistance and fatigue resistance. However, the low energy storage density is one of most critical issues hindering their miniaturization and integration development in cutting-edge technologies. In this manuscript, Na0.5Bi0.5TiO3-based MLCCs with improved energy storage properties were fabricated via composition modification and sintering process improvement. The introduction of BiMg0.5Hf0.5O3 weakens the ferroelectricity of 0.94Na0.5Bi0.5TiO3-0.06BaTiO3, while ensures high saturation polarization, delays polarization saturation, and low residual polarization, improving energy storage efficiency. Specifically, we adopted a two-step sintering process, by which the grain size of MLCCs sintered reduces by 60 %, the dielectric breakdown field strength increases by 33 %. The energy storage density reaches 7.8 J cm−3, 77 % higher than the MLCCs fabricated by traditional one-step sintering method. Moreover, the energy storage density changes by less than 10 % in a wide temperature range of 10 ∼ 180 °C. This study confirms that two-step sintering can also be applied to the preparation of Na0.5Bi0.5TiO3-based MLCCs and provides a way to improve the energy storage performance of lead-free MLCCs, and benefits to the application of MLCCs as high voltage capacitors.

A series of formic acid MOFs/polylactic acid blending composites with the improved dielectric performance in Co(II) systems

In order to improve the limited compatibility of existing polymer/ceramic dielectric composites and further enhance the energy storage density, MOF/polymer composite dielectrics have been explored, which exhibit good compatibility to the polymer matrix from abundant organic groups of the inorganic–organic hybrid metal-organic framework (MOF) fillers. However, they still lack a clear composition–structure–property rule, and the precise design of MOF fillers and polymer matrix becomes a prominent problem in these composites due to the diversity of the metal ions and the organic groups. Thus, in this paper, we present a series of formic acid MOFs/polylactic acid dielectric composites in which ferroelectric formic acid MOFs, namely PDLLA/[NH[Formula: see text](CH[Formula: see text])[Formula: see text]NH[Formula: see text]][M[Formula: see text](HCOO)[Formula: see text]][Formula: see text] and PDLLA/[CH[Formula: see text]NH[Formula: see text]][M[Formula: see text](HCOO)[Formula: see text]][Formula: see text], in which the formic acid MOFs are with different structures and different metal ions as fillers, including [NH3(CH[Formula: see text]NH3][MII(HCOO)3]2 (namely MOF–Co (M [Formula: see text] Co), MOF–Mg(M [Formula: see text] Mg), MOF–Mn (M [Formula: see text] Mn), with 1, 4-butanediamine ion as guest) and [CH3NH3][M[Formula: see text](HCOO)3]2 (namely MOF–Co[Formula: see text] (M = Co), MOF–Ni[Formula: see text] (Ni), with methylamine ion as guest). The composition and morphology of composite films were characterized by XRD, IR, SEM, DSC and UV, respectively, while the dielectric characterizations of the composites including the dielectric permittivity, the dielectric loss, the breakdown field strength and the energy density were also performed. The composition–structure–property relationships were also investigated including the influence of MOF content and MOF category. With the introduction of MOFs, the dielectric constant of the polylactic acid substrate was improved slightly while the breakdown field strength can be improved in some systems. Interestingly, the Co(II)-containing formic acid MOF has advantages over other formic acid MOFs with similar structure for the enhancement of the dielectric constant and breakdown field strength. Also, in some composite films with methylamine ion guest MOF fillers and low-MOF content (MOF–Co[Formula: see text] (1 vol.%) and MOF–Ni[Formula: see text] (1 vol.%)), the breakdown electric field enhanced significantly and further led to improved energy storage density which was about 43% higher than that of the polylactic acid matrix. The possible reason is that in these composites, the orientation of C–H bonds of MOFs seems more beneficial to the formation of hydrogen bonds between the carboxyl group of formic acid and the polylactic acid matrix. These relationships obtained from formic acid MOFs/polylactic acid composites are valuable to the design of high-performance polymer/MOF energy storage composites and may be a new perspective to the practical use of ferroelectric MOFs.

The Lifetime Prediction and Insulation Failure Mechanism of XLPE for High-Voltage Cable

The performance parameters and service life of the insulation layer of high-voltage cables are the key to ensure safe cable operation. Through extracting the mechanical parameters of high voltage cable insulation layer under different thermal aging temperatures, a normal linear regression model is established to predict the service life of high voltage cables. Meanwhile, the physicochemical characteristics such as microscopic morphology and molecular structure changes of the cable insulation layer are analyzed, the dielectric properties and breakdown field strength under ac condition are tested and the macroscopic electrical properties of the insulation layer are studied, and the insulation failure mechanism is further analyzed. The experimental results show that the elongation at break retention rate of cross-linked polyethylene (XLPE) increases slowly with the aging time, and then decreases rapidly when it reaches 50% of the initial elongation at break retention rate. The normal linear regression prediction model is established based on the Arrhenius formula, and it can be obtained the life endpoint of XLPE high voltage cable about 65 years at an operating temperature of 70 °C. Further analysis, under the action of heat and oxygen, the crystal zone structure of cable insulation is seriously damaged, and the carbonyl index is significantly increased. Accordingly, when the aging failure point is reached, the dielectric permittivity and dielectric loss of insulation are significantly increased, and the breakdown performance is significantly decreased. The work has an important guiding significance for insulation condition assessment and life prediction of high voltage cable.

Effect of silicon dioxide and organized montmorillonite on the crystalline morphology and dielectric properties of polypropylene‐based composites

AbstractPolypropylene (PP), a thermoplastic material that can be recycled by melting, is viewed as a potential alternative to cross‐linked polyethylene for insulation. In this work, PP‐based composites were fabricated with surface‐modified silicon dioxide (SiO2), organized montmorillonite (OMMT), and polyolefin elastomer (POE) as fillers via a two‐step melt blending method. The dispersion states of SiO2 nanoparticles, OMMT, and POE in PP and their effects on PP crystallization were investigated. Moreover, the elongation at break, yield stress, energy storage modulus, damping loss factor, broadband dielectric spectrum, bulk resistivity, and alternating current (AC) breakdown strength of the specimens were tested. POE significantly increased the composite toughness, whereas the AC breakdown field strength and volume resistivity of POE/PP were lower. The homogeneously dispersed SiO2 and OMMT in the matrix acted as heterogeneous nucleation sites and reduced the grain size. To varying degrees, they effectively improved the dielectric properties, volume resistivity, and breakdown field strength of the composites. Hence, the composites simultaneously had excellent mechanical and dielectric properties. The volume resistivity of SiO2‐OMMT‐POE/PP with higher crystallinity was 15.4 times higher than that of POE/PP, and the breakdown field strength increased by 16.4%.

Blending Modification of Alicyclic Resin and Bisphenol A Epoxy Resin to Enhance Salt Aging Resistance for Composite Core Rods.

In order to promote the application of composite insulators in coastal areas with high temperature, high humidity and high salt, it is of great importance to develop matrix resin with salt corrosion resistance for composite core rods. In this study, bisphenol A epoxy resin was modified by blending with alicyclic epoxy resin (2021P). Three different proportions of 2021P/DGEBA blend resins (0% 2021P/DGEBA, 10% 2021P/DGEBA and 20% 2021P/DGEBA) were prepared, and the high salt medium corrosion test was carried out. The physicochemical (FTIR, DMA, TGA) and electrical properties (dielectric loss, leakage current and breakdown field strength) of the blend resin before and after aging were tested and analyzed, and the optimal blend proportion was determined. The results showed that after salt aging, the Tg of 0% 2021P/DGEBA decreased to 122.99 °C, while the Tg of 10% 2021P/DGEBA reached 134.89 °C; The leakage current of 0% 2021P/DGEBA increased to 48.994 μA, while that of 10% 2021P/DGEBA only increased to 44.549 μA; The breakdown field strength of 0% 2021P/DGEBA dropped to 40.36 kv/mm, while that of 10% 2021P/DGEBA only dropped to 43.63 kv/mm. The introduction of 2021P enhanced the salt corrosion resistance of the blend resin, which could hinder the penetration, diffusion and erosion of external media (such as Na+, Cl−, H2O, etc.) to the matrix resin. The comprehensive properties of 10% 2021P/DGEBA blend system reached the best, which was better than other blending resins, showing great application potential.

The positive effect of A-site nonstoichiometry on the electrical properties of Sr2Nb2O7 ceramics for high temperature piezoelectric sensor application

The structure and electrical properties of A-site nonstoichiometric perovskite layered structured (PLS) Sr2-xNb2O7-x piezoelectric ceramics prepared by the traditional solid-state reaction method are studied. The piezoelectric constant increases from 1.0 pC/N to 2.1 pC/N. Through XRD refinement and Raman analysis, the enhancement of the piezoelectric performance is mainly achieved by enhancing the distortion and/or rotation of the oxygen octahedron. The dielectric breakdown field strength at room temperature increases from 206 kV/cm to 435 kV/cm. The mechanism of dielectric breakdown enhancement has been explored by intrinsic factors such as dielectric constant and band gap. The resistivity at 700 °C increases from 6.7 × 105 Ω cm to 1.1 × 107 Ω cm which meets the requirements of high temperature vibration sensors at 650 °C. The improvement of high temperature resistance may be related to the inversion of oxygen vacancies. This work provides promising PLS piezoelectric ceramics for potential applications in high-temperature piezoelectric vibration sensors which uses a simple synthesis method without doping any elements.

Ultra-fast charge-discharge and high energy storage density realized in NaNbO3–La(Mn0.5Ni0.5)O3 ceramics

Lead-free antiferroelectric (AFE) NaNbO3 (NN) is one of promising materials for dielectric capacitors, but the recoverable energy-storage density and efficiency get restrained owing to huge remanent polarization and limited dielectric breakdown field strength. In this work, a variety of NN based lead-free bulk (1-x)NaNbO3-xLa(Mn0.5Ni0.5)O3 (abbreviated as (1-x)NN-xLMN, x = 0, 0.05, 0.10, 0.15, 0.20) ceramics were designed using a solid-state synthesis method. Remarkably, an ultra-fast charge-discharge speed 47 ns and an acceptable recoverable energy-storage density Wrec ~1.77 J/cm3 with a high efficiency η = 77% were obtained under the Eb of 200 kV/cm at x = 0.05. The superior energy storage performance is attributed to the regulation of domain size and voltage resistance by special ions substitution of A and B sites. This work not only proposes an efficient strategy to realize high recoverable energy-storage density and efficiency, but also provide an candidate material for application of advanced pulsed power capacitors.

Piezoelectric response of energetic composites under an electrostatic excitation

Several high-explosive (HE) crystals are known to be piezoelectric. However, no systematic study has been carried out on how this effect can be utilized. In this paper, we report the results of an analysis on the response of composites consisting of HE crystals and a polymeric binder under electrostatic excitation. The HE crystals considered are 1,3,5-trinitroperhydro-1,3,5-triazine, octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine, pentaerythritol tetranitrate, and ammonium perchlorate. To explore avenues for enhancing the piezoelectric effect, the binder of the composites is taken to be piezoelectric polyvinylidene fluoride. The focus is on the distributions of induced electric field vector and mechanical stress in the microstructures. The effects of crystal–binder volume fraction, HE crystal size, and dielectric constants of the HE crystals are investigated. To further explore the effect, microparticles of lead zirconate titanate piezoelectric ceramic are introduced to some microstructures. For the HE crystals considered here, a coupled electromechanical analysis shows that the microstructural heterogeneities can enhance the local electric fields to as high as 1.34 times the applied E-field, causing the dielectric breakdown field strength of the overall composite to be much lower than the breakdown strengths of the constituents in the microstructure. In addition, the induced stress levels just prior to dielectric breakdown are well below the yield strengths of the respective constituents. As such, controlled dielectric breakdown, rather than mechanical damage, should primarily be used to facilitate hotspot formation, ignition, and chemical reaction. The likelihood of local dielectric breakdown within the HE crystals is systematically quantified as a function of applied electric field, microstructural attributes, and constituent behavior. To gauge the effect of the direct piezoelectric effect, one material case is also subjected to mechanical excitation in the form of compression. Under an applied external stress, the results show that the direct piezoelectric effect can lead to local yielding and thereby serve as a hotspot generation mechanism. On the other hand, the induced E-field is weak and unlikely to serve as a practical or efficient means of effecting hotspots within an energetic material. The analysis points out that simultaneous application of electrostatic excitation and mechanical excitation can also be considered.

Preparation of BT/GNP/PS/PVDF composites with controllable phase structure and dielectric properties

The composite system composed of polymer, conductive and dielectric filler has excellent dielectric properties. Herein, by studying the effect of filler distribution on the composite system's performance, the graphene nanoplatelets/Polystyrene (GNP/PS)/Barium titanate/Polyvinylidene Fluoride (BT/PVDF) selective composite system is prepared. When the conductivity and dielectric loss change little, the dielectric constant and breakdown field strength of the selective composite system are improved obviously. In the selective composite system, as the dielectric constant is between 12 and 13, the characteristic breakdown field strength is as high as 25.8 kV/mm, which is over three times higher than it of the pure composite system. It is because the addition of BT and GNP particles enhances the establishment of polarization. Besides, the blending of PVDF and PS improves the breakdown field strength of the material. Comprehensive properties of the material are enhanced. Therefore, this study provides a basis for the subsequent study of dielectric materials.

Energy storage performance of BaTiO3-based relaxor ferroelectric ceramics prepared through a two-step process

As the industrial pillar of electronic ceramics, BaTiO3 ceramic is difficult to achieve large energy storing performance due to its high Pr and low dielectric breakdown field strength, making it difficult to satisfy their development requirements of miniaturization and lightweight of power electronic equipment. Therefore, a two-step strategy including adjusting the ratio of chemical elements to modify the microstructures and optimizing the preparation process to enhance electric breakdown strength has been proposed to greatly enhance the energy storing performance of lead-free ferroelectric ceramics, whose effectiveness has been proved within this investigation. Especially, the (Ba0.65Sr0.245Bi0.07)0.99Nd0.01TiO3 (BT-SBT-NdVPP) ceramic prepared by this strategy obtains a superhigh energy storage density of 4.2 J/cm3 under 460 kV/cm, and its temperature (30 ~ 100 °C) and frequency (10 ~ 400 Hz) stabilities under 300 kV/cm are pretty good. In addition, this ceramic has excellent pulse performance under 350 kV/cm between 30 and 150 °C. Therefore, this two-step strategy put forward within this investigation not only significantly improves the energy storage performance of BT-based ceramics but also provides a reference for the preparation of dielectric ceramics with high quality, which could has great potential for the practical industrial application.

Modified polybutene-1 film with high dielectric constant based on low doping amount of fluorine-based compound

In this paper, a C8 perfluoroacrylate/polybutene-1 composite film was prepared by solution casting method. Analysis by FTIR, XRD and SEM shows that C8 perfluoroacrylate has been successfully and uniformly integrated into the matrix polybutene-1, and the crystal structure of the matrix polybutene-1 remains intact without any change. When the content of the filler is very low, local structural changes can occur, resulting in an increase in dielectric constant and breakdown field strength, and can reduce conduction losses at high frequencies. Therefore, at room temperature, when f = 1kHz and the filler content is 0.2wt%, the dielectric constant of the composite film ε = 12.81, which is nearly 620 % higher than that of the pure PB-1 film (ε = 1.78), and the dielectric loss still remains in tanσ = 0.011, and the composite film storage performance as well as the most excellent Ue = 8.65 J/cm3, which is 8.5 times the energy storage density of the pure PB-1 material (Ue = 1.02 J/cm3). The composite materials in this work show excellent properties such as high dielectric constant, low dielectric loss, and high breakdown field strength, which are prospective in the application of capacitors.

Gate engineering in metal insulator semiconductor capacitors on native gallium nitride substrates for applications with high lifetime requirements

Planar metal-insulator-semiconductor capacitors are fabricated on native gallium nitride substrates with different gate dielectrics, namely, silicon dioxide, silicon nitride, and aluminum oxide. The leakage current was measured to determine their robustness regarding electrical breakdown. Hysteresis effects were evaluated for the different gate dielectrics and for the substrate and the epitaxial surface. A gate-first process with a gate contact made from poly-crystalline silicon was compared to a gate-last process with a sputtered aluminum gate. The former showed superior robustness against electrical breakdown with a dielectric breakdown field strength of ≈ 9 MV/cm, which was found to be mostly independent of temperature in the range of 250–450 K. Furthermore, gate oxide traps were estimated by means of stress/recovery gate current transient measurements to confirm field strength limits for high lifetime requirements. Based on the various measurements, silicon dioxide emerged as the best choice regarding breakdown robustness and hysteresis effects. A limit for the dielectric field strength of 3–4 MV/cm is proposed to avoid short- and long-term damage of the dielectric layer.

Influence of simultaneous Cr2O3 and TiO2 additions on the microstructure and properties of APS alumina coatings

Alumina is an important material for thermal spray coating solutions. For improving the coating properties, additions of TiO2 or Cr2O3 are common, but their simultaneous addition has not been studied so far. One alumina-rich ternary feedstock powder composition (81 wt% Al2O3−12.5 wt% Cr2O3–6.5 wt% TiO2) was prepared in three different ways: 1) blending of commercial fused and crushed plain oxide powders; 2) blending of two commercial binary jointly fused and crushed feedstock powders (Al2O3–13 wt% TiO2 and Al2O3–25 wt% Cr2O3); 3) preparing an experimental agglomerated and sintered powder. Plain oxide powders and the two binary powders were used for comparison. The feedstock powders were studied by a standard procedure, including particle size distribution by laser diffraction, the morphology and microstructure by SEM and EDS, and phase composition by XRD. Coatings were prepared by APS with an Ar-H2 plasma gas mixture, using a single spray parameter set optimized for the plain Al2O3 powder. The influence of the feedstock powder properties on coating deposition was evaluated by the average thickness per layer and coating roughness. The coating microstructures were studied by optical microscopy and SEM, including the investigation of local compositions by EDS. The phase compositions and lattice parameters of the alumina phases in the powders and coatings were investigated by XRD. The coatings were characterized for their microhardness HV0.3, and tribological (unidirectional dry sliding wear resistance), corrosion (exposure testing against H2SO4) and electrical (resistivity, dielectric breakdown field strength and impedance) properties. Chromia additions, existing as a (Al,Cr)2O3 solid solution in the feedstock powder, were found to have a positive effect on the stabilization of the corundum phase for APS coatings, while titania additions were found to have no influence on the corundum phase stability. The corrosion resistance was found to be positively influenced by the joint addition of chromia and titania compared to plain alumina-

Passivation of n- and p-Type Silicon Surfaces With Spray-Coated Sol-Gel Silicon Oxide Thin Film

Thermally grown SiO2 is widely used for silicon surface passivation in solar cells and other applications due to excellent interfacial properties. SiO2 films with thickness in the range of 17 nm deposited by industrially viable spray-coating technique on both n- and p-type silicon are reported. Low values of interface state density of ${1.4}\times {10}^{{10}}$ cm $^{\boldsymbol -{2}}$ eV $^{\boldsymbol -{1}}$ on n-type and ${2.0}\times {10}^{{10}}$ cm $^{\boldsymbol -{2}}$ eV $^{\boldsymbol -{1}}$ on p-type were achieved. Fixed oxide charges in the range of 7.1– ${9.4}\times {10} ^{{11}}$ cm $^{\boldsymbol -{2}}$ and 3.9– ${6.5}\times {10} ^{{11}}$ cm $^{\boldsymbol -{2}}$ on n- and p-type, respectively, are obtained. Excellent passivation results in the effective surface recombination velocity of 0.97 cms $^{\boldsymbol -{1}}$ and 8.07 cms $^{\boldsymbol -{1}}$ at minority carrier concentration of $10^{{15}}$ cm $^{\boldsymbol -{3}}$ on n- and p-type Czochralski silicon, respectively, without the use of capping layer. SiO2 film exhibits dielectric breakdown field strength of 4.3 MVcm $^{\boldsymbol -{1}}$ and 5.6 MVcm $^{\boldsymbol -{1}}$ and leakage current density of ${2.2}\times 10 ^{\boldsymbol -{8}}$ Acm $^{\boldsymbol -{2}}$ and ${1.1}\times {10} ^{\boldsymbol -{8}}$ Acm $^{\boldsymbol -{2}}$ at 1 MVcm $^{\boldsymbol -{1}}$ on n- and p-type silicon, respectively. These values are superior to sol-gel-based SiO2 films reported previously and are comparable to or better than those reported for other methods for the growth or deposition of SiO2 on silicon. Amorphous nature of the film is validated by high-resolution transmission electron microscopy (TEM). The X-ray photoelectron spectroscopy (XPS) analysis shows nearly stoichiometric SiO x film.

Time-stable giant energy density and high efficiency in lead free (Ce,Mn)-modified (Na0.8K0.2)0.5Bi0.5TiO3 ceramic film capacitor

The current urgent desire of the renewable energy has imposed much challenge and inspiration for the design and development of the lead-free dielectric capacitors. High recoverable energy storage density (Wrec) and efficiency (η) associated with long-time stability are highly demanded for the pulsed power systems. Here, we present a significantly enhanced energy storage performance in (Ce,Mn) hybrid doped (Na0.8K0.2)0.5Bi0.5TiO3–BiFeO3 [(Ce,Mn):NKBT-BFO] ceramic film capacitor deposited on indium tin oxide (ITO)/glass substrate. Meanwhile, the pure NKBT-BFO, Ce doped NKBT-BFO and Mn doped NKBT-BFO are studied for comparison. A large Wrec of 58.3 J/cm3 together with a high η of 58.1% is realized in (Ce,Mn):NKBT-BFO at 2200 kV/cm, which is proposed by the formation of a slim loop with a large difference between the remanent polarization (Pr) and maximum polarization (Pmax) at a high dielectric breakdown field strength. Moreover, the energy storage property is weakly dependent on time with small variations of Wrec (<23.4%) and η (<11.3%) over a long time range of 2 days–6 months. These results indicate that the (Ce,Mn)-codoped NKBT-BFO ceramic thin film has great potential for the applications in lead-free energy storage film capacitors.

Electron attachment induced ion transport – Part II: The evolution of blocking of charge transport

Electron attachment to the front side of an ion conducting glass which is in contact with a metal electrode at the back side induces transport of cations towards the front side of the sample. Contrary to conventional expectation charge transport is not blocked instantaneously but rather decays over an extended time of up to several days. Quantitative analysis of cation deficient zones at the interface between the glass and the back side electrode and their time evolution demonstrates that the electric field operative in this zone transiently exceeds the dielectric breakdown field strength, such that electrons escape into the metal electrode. This favors electro-neutrality of the cation deficient zone and consequently delays the evolution of blocking character. Charge transport will eventually stop once the electric potential applied (dc) drops across this zone. The physical reason for blocking of charge transport in this case is not that charge carriers cannot pass this zone but the absence of an electric field in the bulk sample. This conclusion is further supported by the observation that Cu+ ions escape from a sputtered copper electrode and enter into the cation deficient zone. As a consequence, usage of copper should be avoided when ion-blocking is an important goal.

Dielectric breakdown strength measurements with silicone-based single-layer dielectric elastomer transducers

Dielectric elastomer transducers (DETs) consist of an elastic dielectric film sandwiched between compliant electrodes. Applying an electric voltage leads to an electrostatic pressure between the electrodes which causes a deformation of the DET due to the elastic dielectric. The dielectric breakdown field strength of the elastomer restricts the applied voltage. For highly efficient DETs, their dielectric breakdown strength during operation has to be known. In this work, eight different breakdown test scenarios with self-fabricated single-layer DET samples made of the silicone film Elastosil® Film 2030 (Wacker Chemie AG) are conducted. They differ in type of the applied electrical voltage (DC/AC), mechanical load of the silicone film and setup of the DET samples. The DETs show a nominal dielectric breakdown strength between 96 and 200 V μm−1 during operation depending on the applied voltage, prestretch and the setup of the DET. Applying protective silicone film layers on top and bottom of the electrodes leads to a reduced damage of the DET after the breakdown of the weakest point and prevents the complete failure of the transducer.

Flexible ceramic film capacitors for high-temperature power electronics

Flexible ceramic film capacitors with high dielectric constant and high breakdown strength hold special promise for applications in power electronics. We deposited lanthanum-doped lead zirconate titanate (PLZT) films on aluminum-metallized polyimide films at room temperature by an aerosol deposition (AD) process and examined the electrical and dielectric properties of the PLZT films over a wide temperature range between −55 and 175 °C. The PLZT film capacitors fabricated by high deposition rate AD process not only satisfy X8R temperature rating but also exhibit superior volumetric and gravimetric specific capacitance. At room temperature, we measured a dielectric constant of ≈85, dielectric loss of ≈0.012, energy density of ≈13.2 J/cm3 with an applied voltage of ≈1000 V. A mean dielectric breakdown field strength (EB) of ≈1.25 MV/cm was determined by Weibull analysis for the ≈8-μm-thick PLZT film capacitors fabricated on flexible aluminum-metallized polyimide substrates. These results revealed that the PLZT-based ceramic film capacitors meet the requirements for advanced high-temperature power inverters. Our results demonstrated that AD process offers the greatest potential for producing low-cost, robust, compact and light-weight ceramic film capacitors with enhanced reliability for power inverters of electrical drive vehicles and various power electronic devices that are critical for high-efficiency energy conversion and renewable energy systems.