High-resistance Phase Research Articles

High permeability Fe@SiO2@ Mn0.5Zn0.5Fe2O4 soft magnetic composite (SMC) materials which formed via high temperature in-situ reaction

The permeability of the Fe Soft Magnetic Composite (SMC) materials need further improve to broaden their application prospect. This research work presents a novel high permeability SMC material which has a low core loss (Pcv). The Fe particles formed an elongated strip shape structure through the ball milling process, and the high permeability Mn0.5Zn0.5Fe2O4 ferrite phase was formed around the elongated strip shape Fe particles via a high temperature in-situ reaction process (ZnO + MnO + Fe2O3–Mn0.5Zn0.5Fe2O4). While the added high resistive SiO2 phase aggregated at the long strip shape Fe particle outer surface and effectively increased the resistivity of the SMCs. As the percentage of the Mn0.5Zn0.5Fe2O4 ferrite coating increase, the permeability of the double layer coated SMCs gradually increased from 38 for the 1 wt% Mn0.5Zn0.5Fe2O4 coated SMCs to 170 for the 18 wt% Mn0.5Zn0.5Fe2O4 coated SMCs. The 3 wt% Mn0.5Zn0.5Fe2O4 coated SMCs has the lowest core loss (Pcv) of 86.9 W/kg at 10 mT, 500 kHz.

In-Situ Construction of Electronically Insulating and Air-Stable Ionic Conductor Layer on Electrolyte Surface and Grain Boundary to Enable High-Performance Garnet-Type Solid-State Batteries.

Lithophobic Li2CO3/LiOH contaminants and high-resistance lithium-deficient phases produced from the exposure of garnet electrolyte to air leads to a decrease in electrolyte ion transfer ability. Additionally, garnet electrolyte grain boundaries (GBs) with narrow bandgap and high electron conductivity are potential channels for current leakage, which accelerate Li dendrites generation, ultimately leading to short-circuiting of all-solid-state batteries (ASSBs). Herein, a stably lithiophilic Li2ZO3 is in situ constructed at garnet electrolyte surface and GBs by interfacial modification with ZrO2 and Li2CO3 (Z+C) co-sintering to eliminate the detrimental contaminants and lithium-deficient phases. The Li2ZO3 formed on the modified electrolyte (LLZTO-(Z+C)) surface effectively improves the interfacial compatibility and air stability of the electrolyte. Li2ZO3 formed at GBs broadens the energy bandgaps of LLZTO-(Z+C) and significantly inhibits lithium dendrite generation. More Li+ transport paths found in LLZTO-Z+C by first-principles calculations increase Li+ conductivity from 1.04×10-4 to 7.45×10-4Scm-1. Eventually, the Li|LLZTO-(Z+C)|Li symmetric cell maintains stable cycling for over 2000h at 0.8mAcm-2. The capacity retention of LiFePO4|LLZTO-(Z+C)|Li battery retains 70.5% after 5800 ultralong cycles at 4C. This work provides a potential solution to simultaneously enhance the air stability and modulate chemical characteristics of the garnet electrolyte surface and GBs for ASSBs.

A novel linear temperature thermistor in the xAl2O3-(1-x)CdSnO3 system

Negative Temperature Coefficient (NTC) thermistors, known for their high sensitivity and fast response, find wide applications in national economy, military, aerospace and various other fields. The study of NTC thermistors with linear temperature-resistance is of great significance in streamlining circuit designs and developing high-performance electronic ceramics. This study focuses on the synthesis of a linear thermistor material in xAl2O3-(1-x)CdSnO3 system by a solid-phase reaction method. Through the introduction of th high-resistance Al2O3 phase, a three-dimensional conductive network is established with Al2O3 and CdSnO3, resulting in the acquisition of linear electrical properties. These properties have exhibited excellent linear NTC variation within the temperature range of 308 K–458 K. Notably, at x = 0.2, the thermistor shows the highest linearity (R2 = 0.9984). Additionally, the complex impedance spectral analysis has helped build resistive and capacitive conductivity models revealing the linearization mechanisms.

Activation of implanted Si, Ge, and Sn donors in high-resistivity halide vapor phase epitaxial β-Ga2O3:N with high mobility

Activation of implanted donors into a highly-resistive, nitrogen-doped homoepitaxial β-Ga2O3 has been investigated. Nitrogen acceptors with the concentration of ∼1017 cm−3 were incorporated during epitaxial growth yielding low-doped (net donor concentration <1014 cm−3) films subsequently implanted with Si, Ge, and Sn. Upon Ohmic contact formation to the implanted regions, sheet resistance values of 314, 926, and 1676 Ω/sq were measured at room temperature for the Si-, Ge-, and Sn-implanted samples, respectively. Room temperature Hall measurements resulted in sheet carrier concentrations and Hall mobilities of 2.13 × 1014 /93, 8.58 × 1013/78, and 5.87 × 1013/63 cm2/(V s), respectively, for these three donor species. Secondary ion mass spectroscopy showed a volumetric dopant concentration of approximately 2 × 1019 cm−3 for the three species, resulting in carrier activation efficiencies of 64.7%, 40.3%, and 28.2% for Si, Ge, and Sn, respectively. Temperature-dependent Hall effect measurements ranging from 15 to 300 K showed a nearly constant carrier concentration in the Si-implanted sample, suggesting the formation of an impurity band indicative of degenerate doping. With a bulk carrier concentration of 1.3 × 1019 cm−3 for the Si implanted sample, a room temperature mobility of 93 cm2/(V s) is among the highest reported in Ga2O3 with a similar carrier concentration. The unimplanted Ga2O3:N regions remained highly resistive after the surrounding areas received implant and activation anneal. These results open the pathway for fabricating Ga2O3 devices through the selective n-type doping in highly resistive epitaxial Ga2O3.

Discharge characteristics and spatial-temporal evolution of Cu-Ni alloy wire explosion

Electrical explosion of wires (EEW) driven by pulse current can produce plasmas with high energy density, and is accompanied by electromagnetic pulses, strong shock waves, etc., therefore it is widely adopted in Z-pinch, electrothermal chemical weapons, oil and gas exploitation and other fields. Compared to pure metal, alloy has characteristics of the high resistivity, adjustable composition, and complex phase transitions. It has great potential in regulating parameters of EEW. This paper presents an experimental study on exploding Cu, Ni, and Cu-Ni alloy (constantan) wires in atmospheric air under a microsecond time-scale pulsed current. Through the diagnoses of electrical parameters and self-emission images, the discharge characteristics and spatial-temporal evolution of explosion products were obtained. Features of the alloy wire explosion in phase transition and plasma were acquired as well. Experiments revealed that in the early stage of EEW, the high resistivity of the alloy could improve the energy deposition efficiency, namely 52% for Cu, 74% for Ni, and 78% for Cu-Ni, while after the explosion, performance of the alloy wire was closer to that of the Ni wire. The initial expansion rate of the plasma channel reached 5 mm/μs level but then decayed. The expansion process of alloy wire endured longer, and the average resistivity went up slowly after the breakdown. Also, a correlation was found between plasma radiation and metal aerosol in spatial scale. Especially, the alloy aerosol has crossed striation features (10−1 mm), but it is more uniform than Cu aerosol generally.

Low resistance-drift characteristics in Cr2Ge2Te6-based phase change memory devices with a high-resistance crystalline phase

Resistance drift affects the reliability of data reading in phase change material (PCM)-based memory devices. In general, resistance drift occurs in high-resistance amorphous state in the PCM-based memory devices. The conduction mechanism such as Poole-Frenkel conduction (PF) in amorphous PCMs causes severe resistance drift in the device. Cr2Ge2Te6 (CrGT) exhibiting a phase transition between low-resistance amorphous and high-resistance crystalline phases demonstrates band conduction in the amorphous phase and mixed conduction with band conduction and nearest-neighbor hopping conduction in the crystalline phase. Since the conduction mechanisms of both phases in the CrGT are not governed by PF, the resistance-drift characteristics are expected to be different from that in conventional PCMs. In this study, the resistance-drift characteristics of the CrGT-based devices were investigated. The fabricated CrGT-based devices exhibited a cyclic endurance of ~7 × 105 times with a clear difference in resistance between the high- and low-resistance states. The drift coefficient, v, at 40 °C was evaluated for the CrGT- and Ge-Sb-Te (GST)-based devices; the value of v for the CrGT-based device was smaller than that for the GST-based device in both high- and low-resistance states. The current–voltage analysis revealed that mixed-conduction mechanism plays an important role to suppress the resistance drift in the high-resistance state of the CrGT-based devices. These findings provide new insights to realize a low resistance-drift PCM-based memory device.

Water seepage detection using resistivity method around a pumped storage power station in China

To detect water seepage and ensure the safety of Pumped Storage Power Station (PSPS) facilities, we apply the electrical resistivity method to evaluate the leakage when the water level is on the rise. We check whether there is a leakage channel near the cavern group of the underground powerhouse. We conduct the field survey and integrate the results with regional geological data to determine the distribution of faults and large cracks. Granite intrusions generate a variation of high and low resistance phases, representing granite porphyry and tuff, respectively. The interface between the two lithologies is the location of the fault zone. In general, the apparent resistivity of two does not change much, indicating that the rock masses are relatively stable. The internal fractures of the rock masses are not developed, and there is no visible water content. However, from the location of the lithological contact interface, the rock mass is broken. Therefore, we recommend that before constructing the lower reservoir, anti-seepage treatment should be carried out.

Effect of Rare Earth Elements on Stability and Sintering Resistance of Tetragonal Zirconia for Advanced Thermal Barrier Coatings

The effect of dopant species on the sintering resistance of zirconia-based ceramics remains a huge challenge in terms of both experiment and theory. As one of the most popular materials for high-temperature protective coatings, it is still urgent to obtain rare earth-doped ZrO2 with high sintering resistance and good phase stability. Here, the sintering resistance and phase stability of rare earth oxides (La2O3, Nd2O3, Gd2O3, and Y2O3)-stabilized zirconia (ZrO2) were thoroughly studied by theoretical and experimental methods. According to experimental data, ZrO2 doped with rare earth ions with larger radii (La3+, Nd3+, and Gd3+) exhibited improved sintering resistance at reduced tetragonal phase stability. Molecular dynamics simulation results revealed that rare earth ions with larger ionic radii are prone to segregation at grain boundaries, which can more effectively reduce the grain boundary energy in the materials under consideration. Therefore, the proposed approach involving doping of NdO1.5 (~1 mol%) and YO1.5 (YbO1.5, 6 mol%) in ZrO2 is considered to be a promising route for the effective preparation of sinter-resistant ZrO2-based ceramics for refractory and thermal barrier materials.

Investigation of switching uniformity in resistive memory via finite element simulation of conductive-filament formation

Herein, we present simulations of conductive filament formation in resistive random-access memory using a finite element solver. We consider the switching material, which is typically an oxide, as a two-phase material comprising low- and high-resistance phases. The low-resistance phase corresponds to a defective and conducting region with a high anion vacancy concentration, whereas the high-resistance phase corresponds to a non-defective and insulating region with a low anion-vacancy concentration. We adopt a phase variable corresponding to 0 and 1 in the insulating and conducting phases, respectively, and we change the phase variable suitably when new defects are introduced during voltage ramp-up for forming. Initially, some defects are embedded in the switching material. When the applied voltage is ramped up, the phase variable changes from 0 to 1 at locations wherein the electric field exceeds a critical value, which corresponds to the introduction of new defects via vacancy generation. The applied voltage at which the defects percolate to form a filament is considered as the forming voltage. Here, we study the forming-voltage uniformity using simulations, and we find that for typical planar-electrode devices, the forming voltage varies significantly owing to the stochastic location of the initial defects at which the electric field is “crowded.” On the other hand, a protruding electrode can improve the switching uniformity drastically via facilitating the deterministic location of electric-field crowding, which also supported by the reported experimental results.

Non-metallic electrical transport properties of a metastable λ -Ti3O5 thin film epitaxially stabilized on a pseudobrookite seed layer

A metastable phase of Ti3O5, λ-Ti3O5, has been studied as a promising optoelectronic material applicable to optical memories and switching devices because it undergoes structural phase transitions, accompanied by changes in optical and electrical properties, under a variety of external stimuli such as heat, visible light, pressure, and electrical current. Theoretical calculations and optical and magnetic measurements have suggested that λ-Ti3O5 is a metal. However, its electrical transport properties have not been directly measured to date because λ-Ti3O5 has so far been synthesized only as nanocrystals or aggregates thereof. In this study, we synthesized (100)-oriented λ-Ti3O5 epitaxial thin films on perovskite LaAlO3 (110) substrates by pulsed laser deposition. Precise control of oxygen supply during the growth and introduction of a MgTi2O5 seed layer with a pseudobrookite structure enabled epitaxial growth of λ-Ti3O5. These λ-Ti3O5 epitaxial thin films showed a lower electrical resistivity ρ (∼7.9 × 10−2 Ω cm) than bulk single crystals of β-Ti3O5 (high resistance phase) at 300 K. On the other hand, the ρ value of the λ-Ti3O5 thin films exhibited a semiconducting temperature dependence with negative dρ/dT.

Degradation of CdTe SC during operation: modeling and experiment

The mechanisms of CdTe SС degradation during operation are experimentally studied. Two mechanisms of degradation of such solar cells are identified. The first is the generation of defects in the transition region, which is caused by excess charge carriers and defects. The second is the increase in the back barrier. The study of the current-voltage and voltage-capacitance characteristics of solar cells allowed proposing a model of degradation of solar cells based on CdTe. It is found that the presence of copper in the back contact is associated with better initial efficiency, but also the fastest degradation during operation. In accordance with the proposed model, the occurrence of additional elementary defects as a result of dissociation of three types of point defect complexes (Cu i + –2Cu Cd – ) – , (V Cd2 – –Cu i+ ) – , (2Cu Cd – –V Te+ ) – is explained. Shunting of the n - p heterojunction and phase transformations from the p + -Cu 2 -x Te side due to electrodiffusion of Cu Cd – with p -CdTe at the n -CdS/ p -CdTe and p -CdTe/ p + -Cu 2-x Te boundaries is considered. On the other hand, the diffusion of Cu i + (interstitial copper) into the absorber volume is possible. Electrodiffusion of defects from heterojunctions to the absorber volume is possible, which leads to the compensation of effective acceptor centers and a decrease in the lifetime of minority charge carriers and, accordingly, a decrease in J ph . In addition, there is a growth of shunting metal chains along the longitudinal grain boundaries of p -CdTe between n - p and р - р + heterojunctions and the possibility of appearance of high-resistance phases of the Cu-Te system. The proposed model explains the possibility of occurrence of the р + – Cu 2– δ S phase on the CdS/CdTe boundary, which constrains the passage of the photoactive part of the solar spectrum in p -CdTe

Ovonic threshold switching selectors for three-dimensional stackable phase-change memory

Abstract

Secondary phase induced electrical conductivity and improvement in thermoelectric power factor of zinc antimonide films

The urgent global need to develop sustainable energy conversion methods and to minimize green-house gas emissions has intensified interest in finding more efficient and non-polluting means for power generation. Thermoelectric materials directly convert heat into electricity which can be used for power generation and waste heat recovery. The waste heat is mostly in the intermediate temperature range and current materials are economically unviable for the recovery of heat loss. Zinc antimonide, β-Zn4Sb3, has one of the highest figures of merit (ZT) owing to its phonon-glass-electron-crystal (PGEC) structure with potential application in the intermediate temperatures (500 K–900 K). It shows poor thermal stability and often includes secondary phases zinc antimony (ZnSb) and zinc (Zn) which deteriorate its thermoelectric properties. Zn4Sb3 films were prepared by ion beam sputtering and their electrical and thermoelectric properties were studied following annealing at temperatures up to 400 °C. Rutherford backscattering spectroscopy (RBS) and electron diffraction spectroscopy results showed formation of Zn-rich Zn4Sb3 films. X-ray diffraction (XRD) and Raman results corroborated the formation of the β-Zn4Sb3 phase along with the presence of a ZnSb secondary phase. Annealing the zinc antimonide films increased electrical conductivity (σ) by three orders of magnitude with σ ∼ 3.7 × 104 Sm−1 for films annealed at 400 °C. Increased conductivity is associated with increased charge carrier density and mobility due to decomposition of the ZnSb secondary phase and improved crystalline quality of the films. The highest Seebeck coefficient of α ∼171 μVK−1 was found for films annealed at 100 °C. The power factor (α2σ) increased with annealing temperature, and the maximum value of α2σ ∼7.5 μWm−1K−2 was obtained for films annealed at 400 °C due to the correspondingly high electrical conductivity. Our findings indicate that the thermoelectric properties of Zn4Sb3 films can be tuned via annealing-induced suppression of the high-resistance ZnSb secondary phase, leading to multifold changes in the electrical conductivity and Seebeck coefficient.

Analysis of Cable Screen Currents for Diagnostics Purposes

This paper presents current flow in cable screens and a cable screen earthing system. Moreover, the paper presents the methodology for the detection of problems in cable screens, such as open phase in a cable screen and high contact resistance of a cable screen in a cable joint. The is based on cable screen current measurements and allows for localization of the erroneous connection–high contact resistance or open phase. The phenomenon is simulated in PowerFactory Software. Moreover, exemplary cable screen current measurements are presented.

Electrical transport mechanism of the amorphous phase in Cr2Ge2Te6 phase change material

A Cr2Ge2Te6 (CrGT) phase change material (PCM) was studied. Different from conventional PCMs, it shows an inverse resistance change between a low-resistance amorphous phase and a high-resistance crystalline phase. Moreover, the anomalous low resistivity in the amorphous CrGT is considered to be due to a large carrier density, but the mechanism of electrical transport is still not clear. In this study, the electrical transport mechanism of the amorphous CrGT was discussed based on the temperature dependence of the resistivity, carrier density, mobility, and current–voltage characteristics. Above 300 K, the conduction mechanism of the amorphous CrGT was thermally activated band conduction, which is different from the conventional Ge–Sb–Te PCMs that show Poole–Frenkel conduction in the amorphous phase. Below 300 K, the amorphous CrGT shows hopping conduction, changing from variable range hopping (Mott VRH) to Efros–Shklovskii variable range hopping (ES-VRH) with decreasing temperature. The crossover from Mott VRH to ES-VRH was observed at around 200 K. Furthermore, the Fermi level was not pinned at the center of bandgap; instead, it was located near the valence band.

Simulation of Electric Arc Characteristics Based on MATLAB/Simulink

In high-voltage circuit breakers and high-speed railway Pantograph-OCS system, the plasma arc directly causes economic loss to the ablation of the equipment. It is important to study the electrical characteristics of the arc. Therefore, based on MATLAB/Simulink, several existing arc models are simulated to obtain the voltage and current waveforms of the arc and the volt-ampere characteristics. Through comparative analysis, the applicable conditions, advantages and disadvantages of several models are clarified, which provides a reference for the improvement of future arc models. The results show that the high-current arcing phase and the high-resistance and low-current phase of the arc are considered separately, and the simulation results are more accurate. The arc model time constant and the dissipated power are regarded as the functions of the arc conductance, and the simulation results can better reflect the dynamic changes of the arc conductance.

Re-amorphization of GeSbTe alloys not through a melt-quenching process

Ge–Sb–Te (GST) alloys are one of the most successful chalcogenides used in rewritable optical discs and electric non-volatile memories. In these materials the structural phase transition between amorphous and crystalline states is used for recording. Here, we report that a melt-quenching method is not necessarily the only way to form a high-resistance phase. We found that amorphous-like grains with high resistance are formed in the GST crystal film by holding it at above the crystallization temperature under an external magnetic field, followed by cooling accompanied with pulse current injection. The treatment may open new route for ultra-low current switching phase change memory.

Anisotropy of mechanical and thermal properties of perovskite LaYbO3: first-principles calculations

ABSTRACTLaYbO3 ceramic material with a perovskite structure has the advantages of a high melting point, sintering resistance and high-temperature phase stability. It is a promising candidate for a structurally and functionally integrated material. However, the anisotropy of physical properties of LaYbO3 has rarely been studied. Herein, the anisotropy of the mechanical and thermal properties of LaYbO3 was studied by first-principles calculations. The elastic coefficients, Young’s modulus, Poisson’s ratio and minimum thermal conductivity of LaYbO3 were found to exhibit anisotropic characteristics. In particular, the sound velocity of the longitudinal wave was nearly twice that of the transverse wave. Especially, the minimum thermal conductivity of LaYbO3 at high temperature was found to be as low as 0.88 W/m K, indicating that the compound has potential for use in thermal insulation applications.

Highly oriented pyrolytic and natural graphite under high pressure

The pressure dependences of highly oriented pyrolytic graphite and natural graphite were studied at long exposure under pressure. The results obtained give evidence for formation of a high-resistance phase of carbon.

Addition impact of nano-carbon black on the performance of MgO.CaO compounds

In the present work, the influence of adding nano-carbon black (0, 0.5, 1, 1.5, 2, 2.5 and 3wt%) on the performance of MgO-CaO composites is discussed. Physical (bulk density, apparent porosity, and hydration resistance), mechanical (cold crushing strength), and thermo-chemical (corrosion resistance) properties of the specimens were evaluated. After formulation and shaping, all compositions were tempered at 250°C for 12h. Results indicated that by replacing nano-carbon black (up to 2wt%) in the MgO-CaO compositions, cold crushing strength values increased and then decreased (from 2.5 to 3wt%). Also, the use of nano-carbon black increased the hydration and corrosion resistance of the specimen due to (і) covering surfaces of the MgO and CaO grains (іі) creating a dense matrix and reducing porosities, and (ііі) formation of high hydration and corrosion resistance phase such as in-situ carbide phase (Al4C3) at operating temperature (1650°C). Generally, results showed that the use of carbon black nanoparticles (even in a small quantity) has a significant effect on the improvement of properties in MgO-CaO composites.