Low DC Conductivity Research Articles

XLPE high voltage insulation; A link between DC conductivity and microstructure

Crosslinked low-density polyethylene (XLPE) with its simple chemical composition is currently used as the most promising material for the insulation layer in extruded power cables. The processability of low-density polyethylene during extrusion followed by its crosslinking results in an infusible network that withstands high operating temperatures. One of the most important electrical properties that determine the insulation performance is the high voltage DC conductivity (direct-current conductivity under a high electric field). A lower DC conductivity at elevated temperatures decreases the losses in the insulation and hence lowers the risk of thermal runaway. The DC conductivity in pure polyethylene (PE) is predominantly due to electronic transport, and in the case of XLPE the DC conductivity is also affected by the combined effects of the concentration of crosslinking byproducts and the semicrystalline microstructure. The semicrystalline microstructure is complex, and it includes the lamellar morphology, the micrometer-sized superstructure, and the degree of crystallinity. These parameters inter-play to affect the final DC conductivity. This article first describes an overview of XLPE insulation of extruded HVDC cable and then addresses the less-known link among polymer processing, microstructure, and macroscale property (DC conductivity) of XLPE. The revealing of this link leads to a deep understanding of XLPE microstructure and possible ways to improve XLPE insulating properties during polymer processing.

The Li2Ti6O13 and Li2Zr6O13 composite as a high-performance anode for alkali-ion batteries: a molecular dynamics study.

The current development of technology has highlighted the necessity of compounds that enhance the durability and performance of alkali-ion batteries. The anodes of these batteries need to overcome the challenges of low dc-conductivity at ambient temperatures and interfacial resistance between the solid-state electrolyte. By conducting large-scale molecular dynamics simulations, we investigated the transport properties of Li2Ti6O13 and Li2Zr6O13 mono- and bi-crystals, as well as Li2Ti6O13@Li2Zr6O13 composites. While the monocrystalline and bi-crystalline Li2Zr6O13 show similar transport properties, the composite materials, combining both compounds, exhibit the highest diffusion coefficients and dc-conductivity. The transport properties of the composite materials are found to be significantly higher than those mono- and bi-crystalline samples due to the Li interstitial mechanism and the presence of grain boundaries. Our study offers valuable insights for the development of high-performance energy storage materials.

ELECTROCHEMICAL EVALUATION OF HUMIDITY BASED PROTON CONDUCTIVITY OF ALUMINIUM(III) TARTRATE

Aluminium(III) tartrate was synthesized by simple solution crystallization and its humidity dependent proton conductivity was evaluated using electrochemical impedance spectroscopy. The compound exhibited very low DC conductivity and AC conductivity in the as synthesized form and dried conditions. However, upon exposing to 100% relative humidity(RH) the AC conductivity of the compound increased significantly with time and is several orders greater than DC conductivity. The structural stability of the compound was analysed by FTIR and PXRD experiments. The compound has good structural stability on hydration, dehydration and rehydration. The proton conductivity of the sample decreased several orders on dehydration and it bounces back to original value on rehydration. The complex exhibited reversible proton conductivity with respect to moisture. The variation of proton conductivity with temperature implies that the compound exhibits Grotthuss type proton conductivity.

Solution processed low operating voltage SnO2 thin film transistor by using Li2SnO3/TiO2 stacked gate dielectric

A thin layer of sol–gel derived lithium stannate (Li2SnO3) was deposited by a spin coating method that shows high areal capacitance with low DC conductivity which originated due to the mobile lithium ion (Li+) and low carrier concentration. The DC conductivity of this Li2SnO3 thin film has been reduced further by adding a sol–gel derived titanium-oxide (TiO2) layer. Moreover, bilayer thin film effective areal capacitance also increases due to the higher relative permittivity of TiO2 layer. The measured areal capacitance of such Li2SnO3 /TiO2 bilayer thin films is 518 nF/cm2 with a low current density of 3.8 X 10-5 A/cm2 under 5 V external bias, can fulfil the requirement as gate dielectric of a low operating voltage (≤3V) thin film transistor (TFT). For identifying its applicability as gate insulator, a solution-processed tin oxide (SnO2) thin film transistor (TFT) was fabricated with Li2SnO3/TiO2 stacked gate dielectric. In this TFT structure, thin film of TiO2, SnO2 and Li2SnO3 are all polycrystalline in nature. The electrical characterization of TFT has been done under DC mode operation in ambient atmosphere measurement which remain almost unaltered under 11 cyclic measurements. The optimized TFT required only 3.0 V external bias that shows an electron mobility of 3.47 cm2 V−1 s−1 with on/off ratio of 50.

DC ELECTRICAL CONDUCTIVITY OF TETRA-DIIMINOBENZENE-PAMINOBENZENEPHTHALOCYANINATO METAL (II) & (III)

In this work a complex of Schiff base of tetra-diiminobenzene-P-amino benzenephthalocyaninato with tetra diimino-benzene as peripheral groups. The compounds were synthesized with different central metal ions(Al, Fe, Cu and Zn) were synthesized, identified by elemental analysis and spectroscopically, their dc electrical conductivity of their thin films were measured with and without iodine doping. The dc electrical conductivity of iodine doped thin films of the compounds were compared with iodine un-doped thin films of the compounds. The study shows that the measured dc electrical conductivity of the doped Schiff base has higher dc conductivity than un-doped. It shows that the conductivity of the bridged phthalocyanines of aluminum Schiff base has higher dc conductivity than the others, while planar phthalocyanines of zinc Schiff bases has lower dc conductivity. The study, also, shows that the peripheral groups on the phthalocyanine rings as the Schiff base have clear influence on the dc conductivity of all compounds. The stacking and the bridging of the phthalocyanine rings has also effect on the dc electrical conductivity. The bridged compounds have higher conductivity than unbridged compounds

Dielectric relaxation and high recoverable energy density in (1-x)(0.3BiFeO3-0.7SrTiO3)-xK0.5Na0.5NbO3 ceramics

(1-x)(0.3BiFeO3-0.7SrTiO3)-xK0.5Na0.5NbO3 (BFO-STO-xKNN, x=0–0.05) ceramics were synthesized by solid state sintering for energy storage application. The grain size of BFO-STO-xKNN increased with KNN content until x=0.01 and then decreased as x increased further. In contrast, the lattice parameter of BFO-STO-xKNN decreased initially with KNN addition and then increased as x increased further. The initial decrease in lattice parameter was explained by the reduced chemical expansion associated with oxygen vacancies, while the latter increase was due to larger ionic sizes of the dopants. The dielectric response in samples without KNN addition resulted from the Maxwell-Wagner effect with the occurrence of a low frequency (500 Hz) peak at room temperature, while the dielectric relaxation in KNN added samples appeared to have the Debye type with the relaxation peak occurring at a high frequency beyond 106 Hz. The BFO-STO samples free of KNN showed a finite DC conductivity due to electronic hopping between Fe2+/Fe3+, which was absent in KNN added samples, and hence they showed extremely low DC conductivity. KNN-added BFO-STO exhibited slim hysteresis loops ideal for energy storage application. A high recoverable energy density (Wrec) of 3.20 J/cm3 with 88.0% efficiency (η) was achieved with the x=0.01 samples at the applied field of 273 kV/cm. The x=0.01 samples also showed good thermal stability of Wrec and η, which varied only 4.0% and 0.8%, respectively, over the temperature range between 25 and 100 °C.

Dielectric Properties of Polypropylene by Deashing Method for DC Polymer Film Capacitors

In this paper, a novel deashing method was proposed to prepare polypropylene (PP) materials with different ash contents (80 ~ 560 ppm). Effects of the ash on dielectric and energy storage characteristics of PP in polymer film capacitors were studied. The experimental results reveal that a low content of ash will help to improve the dielectric properties. Compared to the sample with 560 ppm of ash content, the PP film with 60 ppm ash possesses a lower DC conductivity (1.85×10-14S/m). After the purification, the decline of the ash content in PP prevents the local electric field distortion and enhances the breakdown strength, which is beneficial for the improvement of the discharge energy density. Meanwhile, the reduction in the number of carriers ionized by the ash weakens the transport behavior and reduces the conductivity. It is concluded that the PP with high purity shows a great potential in polymer film capacitors.

Dielectric and Energy Storage Properties of Polypropylene by Deashing Method for DC Polymer Film Capacitors

In this paper, a novel deashing method is proposed to prepare polypropylene (PP) materials with different ash contents (60–500 ppm). Effects of the ash on dielectric and energy storage characteristics of PP in polymer film capacitors are studied. The experimental results reveal that a low content of ash will help to improve the dielectric properties. Compared to the sample with 500 ppm of ash content, the PP film with 60 ppm ash possesses a higher breakdown strength (587.1 kV/mm), a lower DC conductivity (1.12 ×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−14</sup> S/m) and dielectric loss factor (3 ×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−4</sup> ). In addition, the energy storage property also shows a remarkabe improvement, the discharge energy density can be up to 3.22 J/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> and the discharge efficiency remains at a high level. After the purification, the decline of the ash content in PP prevents the local electric field distortion and enhances the breakdown strength, which is beneficial for the improvement of the discharge energy density. Meanwhile, the reduction in the number of carriers ionized by the ash weakens the transport behavior and reduces the conductivity. It is concluded that the PP with high purity shows a great potential in polymer film capacitors.

Effect of Mechanical Alloying on Structural and Electrical Properties of (P&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;5&lt;/sub&gt;)&lt;sub&gt;(x)&lt;/sub&gt;-(Y&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;)&lt;sub&gt;(0.03)&lt;/sub&gt;-(ZrO&lt;sub&gt;2&lt;/sub&gt;)&lt;sub&gt;(0.97)&lt;/sub&gt; Electrolyte

Pentavalent phosphorous oxide doped yttria-stabilized zirconia (P2O5)X-(Y2O3)0.03-(ZrO2)0.97 with x=0.06 mol.% was achieved via an economical technique using mechanical alloying (MA) technique. Three types of nanocomposite powders of electrolyte were produced by high-energy ball milling with different milling times. The phases of synthesized electrolyte powders and sintered electrolytes were illustrated by X-ray diffraction (XRD). The average particle sizes of powders indicated around (360, 245, and 48) nm at milling duration (1, 10, and 45) hrs, respectively. The XRD analysis results of 1 h MA electrolyte powder obtained tetragonal ZrO2, while the 45 h MA electrolyte manifested a minority phase of monoclinic ZrO2. Then, the XRD of the sintered electrolyte with the optimum electrical properties appeared two phases. The major phase of the tetragonal zirconium yttrium oxide and a minor phase was a monoclinic zirconium oxide. The average grain sizes of the three types of the sintered manufacturing electrolytes were (7.638, 2.642, and 1.245 µm) after the mechanical alloying duration of (1, 10, and 45) hrs, respectively and sintered at 1873 °K. The DC conductivity (σ) studied corresponded to the influence of milling times on the microstructure for each sintered electrolyte. From the results, the synthesized sintered electrolyte with a long MA duration gave a maximum DC (σ) 1.03E-1S.m. And, the DC conductivity (σ) was 1.11E-02 of electrolyte produced with 10 hr mechanical alloying. Otherwise, the lower DC conductivity got with the electrolyte prepared in the lowest milling duration was 8.9 E-2 S.m.

Study of strontium doped Nd2FeO4+δ cathode material for intermediate temperature solid oxide fuel cells application

The series of Nd2–x Sr x FeO4+δ (x = 0.1 - 0.4) single phase compound is prepared with crystallite size in submicron range using combustion synthesis technique. The agglomeration of the submicron sized crystallites resulted into formation of porous electrode layer is realized from scanning electron microscopy. The dcconductivity results showed maximum σ for x = 0.2, which also exhibited minimum activation energy. The comparative low dc conductivity with literature reports is due to high porosity as obtained from agglomerated submicron crystallites. Variation in conductivity in Nd2–x Sr x FeO4+δ is Sr-dependent and understood f rom defect chemistry. The complex impedance plots of the symmetric cell showed decrease in the real axis intercept with increased temperature in turn reduced area specific resistance (ASR). Nd1.8Sr0.2FeO4+δ cathode exhibits lowest ASR (= 1.92±0.015 Ohm cm2) at 973 K. The oxygen partial pressure dependent ASR indicated that the charge transfer at electrode-electrolyte interface is the rate limiting factor while oxygen reduction reaction (ORR).

Performance of dopamine modified 0.5(Ba0.7Ca0.3)TiO3-0.5Ba(Zr0.2Ti0.8)O3 filler in PVDF nanocomposite as flexible energy storage and harvester

We demonstrate the potential of dopamine modified 0.5(Ba0.7Ca0.3)TiO3-0.5Ba(Zr0.2Ti0.8)O3 filler incorporated poly-vinylidene fluoride (PVDF) composite prepared by solution cast method as flexible energy storage and harvesting devices. Filler surface functionalization with dopamine acts as a bridging factor between the filler and the polymer matrix, resulting in better filler dispersion. The improved dielectric loss tangent (<0.02) and dielectric permittivity ranges from 9 to 34 are found beneficial for both energy harvesting and storage. Additionally, a significantly low DC conductivity (<10−9 ohm−1cm−1) for all composites was achieved leading to an improved breakdown strength and charge accumulation capability. Maximum breakdown strength of 134 kV/mm and corresponding energy storage density 0.72 J/cm3 were obtained from the filler content 10 wt%. The improved energy harvesting performance was characterized by obtaining a output voltage (Vout) = 1.84 V along with maximum power density of 11.4 µW/cm3 for the filler content of 10 wt% of the poled sample. Thus, the results show 0.5(Ba0.7Ca0.3)TiO3-0.5Ba(Zr0.2Ti0.8)O3/PVDF composite has the potential for energy storage and harvesting applications that can significantly suppress the excess energy loss arises while utilizing different material.

Ion association as a main shortcoming in polymer blend electrolytes based on CS:PS incorporated with various amounts of ammonium tetrafluoroborate

This work presents a successfulness of the methodology of solution cast technique for fabrication of polymer blend electrolytes based on chitosan (CS): potato starch (PS) doped with various amounts of ammonium tetrafluoroborate (NH4BF4). In this work we demonstrated that association of ions is the main drawback for the NH4BF4 salt. Low DC conductivity of the films displays the non availability of the present system for applications. To look at the electrical properties, structural, and morphological properties, electrochemical impedance spectroscopy (EIS), X-ray diffraction (XRD), and Field emission scanning electron microscopy (FESEM), respectively were used. From the EIS measurement the highest conductivity of the system was found to be 3.07 × 10−8 S/cm which is too low for device applications including batteries and supercapacitors. The increase of bulk resistance is an indication for the recombination of cation and anion of the salt at high concentration. Sharp peaks were observed in the XRD spectra at high salt concentration. The morphological outcomes display protruded salts with large size at high salt concentration. The large value of dielectric constant at low frequency region is associated to electrode polarization (EP) while their decline with increasing frequency is ascribed to the lag of polarization of ion with respect to the quick orientation of dipole species because of the applied AC field. The M″ peak asymmetry displays the distribution of relaxation time.

Electrical insulation performance of cross‐linked polyethylene/MgO nanocomposite material for ±320 kV high‐voltage direct‐current cables

AbstractPolymeric nanocomposite insulations are receiving the widespread attention of the electrical cable industry. This paper presents the electrical insulation performance of as‐received commercial 320 kV high‐voltage direct‐current (HVDC) cross‐linked polyethylene (XLPE)/MgO nanocomposite material with reference to the pure XLPE. The results of this commercial‐grade electrical insulation material are not reported hitherto. The scanning electron microscopy confirms the well‐dispersed nanofiller inside the polymer matrix. The DC electrical insulation performance is investigated by DC breakdown strength, space charge, DC electrical conductivity, and surface potential decay measurements. The test samples are subjected to the thermal aging at 135°C for 30 days. The un‐aged nanocomposite exhibits 20% higher DC breakdown strength, negligible hetero space charge accumulation, and the lower DC conductivity by one order than the un‐aged pure XLPE. Moreover, thermally aged nanocomposite shows more restraint to the deterioration of its properties. After the thermal aging, the DC breakdown strength decreased by 38% and 20% in the pure XLPE and its nanocomposite, respectively. Thermally aged nanocomposite shows negligible hetero charges and an increase in the DC conductivity by one order. However, the pure XLPE shows higher hetero charge accumulation and the increased DC conductivity by one order. In un‐aged XLPE nanocomposite higher crystallinity, higher deep trap density, and the lower carbonyl index are found to be the primary attributes of its improved performance. It is postulated that these significantly unchanged attributes can be the reason for the better anti‐thermal aging properties of the XLPE nanocomposite.

Investigation on dielectrical and space charge characteristics of peek insulation used in aerospace high‐voltage system

Because of the insulation issue in the high‐voltage system of spacecrafts, the dielectric and space charge characteristics of polyether‐ether‐ketone (PEEK) insulating material are studied in this paper. The electric conduction, trap parameters and space charge characteristic of PEEK, especially the space charge distribution after 50 keV high‐energy electron radiation, are measured and analyzed, respectively. From the test results, a low DC conductivity (∼10−16 S/cm) and an activation energy of 0.1–0.2 eV are estimated. It indicates that the conductivity is insensitive to the temperature. In addition, a deep chemical trap (2 eV) is evaluated in the PEEK sample. The slight space charge accumulation and the high threshold field for charge injection of the PEEK sample are dominated by the pulsed electro‐acoustic (PEA) results. Compared to the polyimide sample (PI), the space charge accumulations are lower in PEEK, and the charge dispersions in the PEEK after irradiation are faster than those in PI. Based on the experimental results, it can be inferred that the space charge properties are ascribed to the deep traps. From the microstructure analysis, it can be seen that the benzene ring and carbonyl group in the PEEK chemical structure would introduce deep traps, resulting in a higher injection barrier and less space charge accumulation. The results show that PEEK sample is a superior insulating material, and the excellent dielectric and space charge characteristics are beneficial for application in spacecraft. © 2019 Institute of Electrical Engineers of Japan. Published by John Wiley &amp; Sons, Inc.

Effect of graphene nanoplatelets on space charge and breakdown strength of PP/ULDPE blends for HVDC cable insulation

In this paper, polypropylene (PP) is blended with ultra low density polyethylene (ULDPE) content to 5, 15, 25 wt% by melt blending to modify its stiffness and brittleness. The mechanical tests show that both the flexibility and tensile strength of PP are enhanced by the addition of ULDPE with a content of 15 wt%, but the other contents show a weaken elongation at break and tensile strength. Graphene nanoplatelets of 0, 0.005, 0.01 and 0.05 wt% are introduced into the PP/ULDPE (15 wt%) blend to improve its dielectric properties. The DC conductivity, space charge behavior, distribution of trap levels, and breakdown strength of PP/ULDPE/graphene nanocomposites were investigated. The results show that PP/ULDPE/graphene nanocomposites with the nanofiller content of 0.01 wt%, have lower DC conductivity, reduced space charge, and higher breakdown strength. The improved dielectric properties are largely attributable to the deep traps in the interfacial zones between the graphene nanoplatelets and PP/ULDPE blends which restricts the carrier injection and transportation in polymer. It is shown that the PP/ULDPE/graphene nanocomposites with 15 wt% ULDPE and 0.01 wt% graphene nanoplatelets show good dielectric properties for application in HVDC cable insulation.

Effect of graphene oxide particles on space charge accumulation in LDPE/GO nanocomposites

This paper focuses on the space charge characteristics of low-density polyethylene (LDPE)/ graphene oxide (GO) nanocomposites, as well as the corresponding trap level distributions. The relative permittivity, DC conductivity, DC breakdown strength and space charge behaviors of nanocomposites with GO filler content of 0, 0.001, 0.005, 0.01, 0.05, and 0.1 wt% were studied. The trap level distributions were investigated using the isothermal discharge current (IDC) method. The experimental results show that the 0.01 wt% LDPE/GO nanocomposites have a significantly lower relative permittivity, a lower DC conductivity, a higher breakdown strength and a smaller amount of space charge accumulation than that of the neat LDPE. With increased GO content, the space charge accumulation of the nanocomposites shows an increasing trend. It is indicated that the certain content of GO nanoparticles could introduce large quantities of deep carrier traps, which suppress the transport of charge carriers and further restrain the space charge injection and accumulation. The experimental results reveal that the GO nanoparticles show great promise for use in HVDC cable applications, which could reduce particle agglomeration due to its insignificant addition.

Trap Modulated Charge Carrier Transport in Polyethylene/Graphene Nanocomposites

The role of trap characteristics in modulating charge transport properties is attracting much attentions in electrical and electronic engineering, which has an important effect on the electrical properties of dielectrics. This paper focuses on the electrical properties of Low-density Polyethylene (LDPE)/graphene nanocomposites (NCs), as well as the corresponding trap level characteristics. The dc conductivity, breakdown strength and space charge behaviors of NCs with the filler content of 0 wt%, 0.005 wt%, 0.01 wt%, 0.1 wt% and 0.5 wt% are studied, and their trap level distributions are characterized by isothermal discharge current (IDC) tests. The experimental results show that the 0.005 wt% LDPE/graphene NCs have a lower dc conductivity, a higher breakdown strength and a much smaller amount of space charge accumulation than the neat LDPE. It is indicated that the graphene addition with a filler content of 0.005 wt% introduces large quantities of deep carrier traps that reduce charge carrier mobility and result in the homocharge accumulation near the electrodes. The deep trap modulated charge carrier transport attributes to reduce the dc conductivity, suppress the injection of space charges into polymer bulks and enhance the breakdown strength, which is of great significance in improving electrical properties of polymer dielectrics.

Eddy current imaging with an atomic radio-frequency magnetometer

We use a radio-frequency 85Rb alkali-vapor cell magnetometer based on a paraffin-coated cell with long spin-coherence time and a small, low-inductance driving coil to create highly resolved conductivity maps of different objects. We resolve sub-mm features in conductive objects, we characterize the frequency response of our technique, and by operating at frequencies up to 250 kHz we are able to discriminate between differently conductive materials based on the induced response. The method is suited to cover a wide range of driving frequencies and can potentially be used for detecting non-metallic objects with low DC conductivity.

Optical and electrical properties of stainless steel oxynitride thin films deposited in an in-line sputtering system

The optical and electrical properties of stainless steel oxynitride thin films have been studied for different flow rates of the reactive gases during the deposition process. Films were deposited in an in-line magnetron sputtering system under similar conditions as those found in large area industrial systems. The study of the optical properties was performed by IR-VIS spectrophotometry, DC conductivity measurements were performed by the four point method and the microstructural study and chemical analysis were performed by XRD, FESEM and XPS. The results show the transition of sample films from metal to semiconductor, as well as the feasibility of obtaining visible absorbing coatings with low DC conductivity from low-cost materials. The deposited films show the typical growth structure for samples produced in in-line deposition systems commonly used in the large area coatings industry.

Effects of Interfacial Charge on the DC Dielectric Properties of Nanocomposites

The interfacial charge phenomenon of MgO/low-density polyethylene (LDPE) and SiO2/LDPE nanocomposites was measured by synchrotron radiation small-angle X-ray scattering. Based on the Porod theory, the Porod curve of SiO2/LDPE nanocomposite shows negative divergence but the LDPE and MgO/LDPE do not, which reveals that interfacial charge may exist in the SiO2/LDPE nanocomposite. The DC dielectric properties of the nanocomposites are closely related to the interfacial charge. Experimental results show that the SiO2/LDPE nanocomposite has lower DC conductivity, less space charge, and higher DC breakdown strength than the MgO/LDPE nanocomposite. It is thought that the interfacial charge has a positive effect on the DC dielectric performance of nanocomposites, and the mechanism could be attributed to the scattering effects of the interfacial charge on the carrier migration. There is no obvious interfacial charge in the MgO/LDPE nanocomposite, but it still has excellent DC dielectric properties compared with LDPE, which indicates that the interfacial charge is not the only factor affecting the dielectric properties; the dipole interface layer and the reduction of free volume can also inhibit the migration of carriers and decrease electrons free path, improving the dielectric performance.