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Varistors, due to their unique properties, are materials commonly used in surge protection devices. Their reliability, however, requires periodic inspection, which should specifically include assessment of their moisture content. So far, no method has been developed that would directly and non-invasively allow for the assessment of the moisture content of a varistor. In this work, an attempt was made to use dielectric spectroscopy for this purpose, i.e., measurements of dielectric parameters in the frequency domain. The tests were carried out on samples of materials based on silicon carbide. The result of the tests was the determination of the dependence of the dielectric response of the tested materials on moisture content, which after further tests may be the starting point for the development of a method for determining the moisture content of varistor surge arresters. [ABSTRACT FROM AUTHOR]

Conventional varistors rely on the formation of a Double Schottky Barrier within the intergranular region of ZnO via acceptor doping and a Bi2O3 phase. This work has been able to yield varistor-like behavior via cold sintered ZnO composites by placing 2D hBN flakes on the grain boundaries within the ZnO matrix. Above the percolation threshold, a network of resistive hBN barriers is formed which prevents current from flowing through the more conductive ZnO. However, at a given voltage, electrons can tunnel through the hBN if the layers are kept thin enough. Within this narrow band of hBN content, samples have been fabricated with α values as high as 9.5. The composite system demonstrated Schottky conduction at low fields before switching to Fowler-Nordheim tunneling at high fields. This microstructural design was able to show greater nonlinearity compared to previous attempts at creating varistor materials through the unique cold sintering process (CSP).

The ceramic varistors SnO2 –Co3O4 –Nb2O5–Cr2O3 with the addition of CaCO3, SrCO3 or BaCO3 were sintered at temperatures 1250 and 1350°C, then their structures and electrical properties were studied. In all samples, the SnO2 cassiterite phase with a rutile-type structure and the Co2 SnO4 phase with a spinel-type structure were observed. All materials exhibited a highly nonlinear dependence of the current density on the electric field with the nonlinearity coefficient 24–50. When alkaline earth metal carbonates were added, the grain size of all samples decreased and the electric field E1 increased. The addition of CaCO3 lead to the decrease of the low-field electrical conductivity of varistors. The lowest low-field conductivities 4·10–13 and 6·10–13 Ω–1 cm–1 were found in the samples with CaCO3 addition baked at 1250 and 1350°C, respectively. The observed effect is due to the increase of the potential barrier height at the SnO2 grain boundaries by 7 and 13%, respectively, and the decrease of the grain size by 26 and 28% compared to SnO2-based varistor ceramics without CaCO3 addition. [ABSTRACT FROM AUTHOR]

This study presents the characterization and optimization of BaTiO3-doped ZnO-based varistors for electrical and electronic applications. The varistors were prepared using a conventional ceramic procedure and were sintered at a temperature of 1,000 °C with different concentrations of BaTiO3 (0 and 3 mol%) added to the Bi2O3/ZnO-based varistor composition (99.5 mol% ZnO and 0.5 mol% Bi2O3). The results showed that the addition of BaTiO3 led to the formation of various oxides and solid solutions, such as Bi12TiO20, BaTiO3, and (Bi2O3)0.80 (BaO)0.20. The dielectric constant and grain size decreased with increasing BaTiO3 content, while the non-linearity coefficient, electric fields (Eb) increased, and dielectric loss (Tand) decreased. The optimized varistor contains 2 mol% BaTiO3 and an electric field of 148.08 V/mm, which are superior to those of the BaTiO3/Bi2O3/ZnO-based varistor. During this study, we were able to observe that a slight addition of BaTiO3 will increase the breakdown voltage and the coefficient of nonlinearity and this will allow us to develop lowdimensional varistors and install them in the high-voltage domain. [ABSTRACT FROM AUTHOR]

Pores form inside the ZnO varistor during the sintering process, especially in the edge area. The pore defects frequently lead to breakdown of the varistor. In this study, a simulation model was developed to calculate the electric field and energy density within the varistor. The presence of edge pores resulted in the distortion of the electric field and uneven energy distribution, causing a decrease in the energy capacity of the varistor. Combining the simulations with the results of impact energy tolerance tests on varistors, the mechanism of varistor failure induced by edge pores was revealed. To enhance the energy capacity of varistors, a repair medium with high permeability was developed herein. By employing a secondary sintering method, new grains were grown within the open pores at the edge of the varistor, improving the energy capacity of the varistor from 600 to 1000 A for a 2 ms square wave. Moreover, the mismatch between coefficients of thermal expansion was addressed. This work helped clarify the effects of edge defects in varistors, and a strategy for enhancing their energy capacity was demonstrated. [ABSTRACT FROM AUTHOR]

We analyzed the distribution of Co and Mn in the microstructure of ZnO varistor and discussed the effects of Co and Mn addition on electrical properties from the viewpoint that the influences of Co and Mn on the grain boundary layer, not on ZnO grains, are important. ZnO varistor showed excellent non-ohmic properties even when Mn was not incorporated into the ZnO grains. It was also found that the grain boundary layers consisted of thin intergranular layers between ZnO grains and grain boundary multiple points. The spinel particles remain at the grain boundary multiple points, and then react with the liquid phase, which is mainly composed of Bi2O3, to form ZnO with conductive properties during the cooling process. In ZnO varistor, the grain boundary multiple points are connected in a mesh-like structure, and if leakage currents occur at these points, the non-ohmic characteristics are degraded. Co and Mn are soluble in the spinel phase and act to increase chemical stability, and they suppress the reaction with the liquid phase, thereby maintaining the insulating properties of the grain boundary multiple points and contributing to the improvement of non-ohmic properties. [ABSTRACT FROM AUTHOR]

This work aims to study the effect of Mn 2 O 3 additions on the electrical properties and microstructure characteristics of a SnO 2 -based ceramic varistor system doped additionally with Sb 2 O 5 , Cr 2 O 3 , and CoO. The specimens were prepared using conventional ceramic processing and homogenized by a high-energy ball milling system using the following composition: (98.99-X) % SnO 2 – 0.05% Cr 2 O 3 – 0.05% Sb 2 O 5 – 1.00% CoO – X% Mn 2 O 3 where X = 0.00, 0.05, 0.10, 0.20, 0.50 and 1% mol. Characterization by TG-DSC/DTA, XRD, XPS, and SEM/EDS, and the proposed chemical and defect-formation reactions allowed the conclusion that Mn 2 O 3 additions produce alterations of the microstructure consisting of the in situ formation of the spinel Co 2 MnO 4 secondary phase and modification of the potential barriers in the intergranular regions, where, in addition, oxygen vacancies are formed. With the 0.05 mol % Mn 2 O 3 , the grain size (average in the range of 2–3 μm) drops by 20 %, thus augmenting the grain boundaries. Altogether, this leads to a decrease in the nonlinearity coefficient (α) and an advantageous displacement of the breakdown electric field (E B). The 0.05 mol % Mn 2 O 3 specimen compares favorably with the reference material by surpassing the E B value by a factor of 8. Elucidation of Mn2+ and Co2+ in 1 mol % Mn 2 O 3 specimens by XPS suggests the role of MnO and CoO as intermediate phases, essential for Co 2 MnO 4 formation. The pathway for in situ formation of Co 2 MnO 4 is set forth based on the above characterization techniques in conjunction with proposed chemical and defect-formation reactions. [ABSTRACT FROM AUTHOR]

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The effect of Al addition in ZnO varistors revealed to be the suppression of grain growth, not the lowering of the electric resistance of ZnO. This Al effect can explain the change in the E-J characteristics by the following three points. (i) The grain boundary becomes thinner and the proportion of boundary layers with a thickness of 10 nm or less increases, which enlarges the effective cross-sectional area of the tunnel current generation. (ii) The delay in densification during the sintering makes it easier for pores to remain at the grain boundary, which increases discontinuities of boundary layers between ZnO grains and increases leakage current, resulting in reduced non-ohmic properties in the low current range. (iii) Abnormal grain growth of ZnO is suppressed and the particle size becomes more uniform, which improves non-ohmic characteristics. This paper proposes a new barrier model for the conduction mechanism of ZnO varistors, based on the tunneling effect and taking into account the influences caused by microstructural inhomogeneities specific to polycrystalline ceramics, such as discontinuities in grain boundary layers and variations in ZnO grain size. [ABSTRACT FROM AUTHOR]

Copyright of Piezoelectrics & Acoustooptics is the property of Piezoelectric & Acoustooptic and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

With the great leaps forward in the development of the railway, the importance of safe operation and maintenance has become increasingly prominent. Varistor is the key component insurge protective devices for railway communication and signaling equipment, it is necessary to study a description model of the varistor degradation process and predict its lifetime through condition monitoring. Among the monitoring parameters, nonlinear coefficient is an important index to measure the health of varistors. Considering that the degradation process of varistors is the cumulative effect of surge history, and its nonlinear coefficient has a time–series relationship, a life prediction model for varistors based on BiLSTM is proposed. The model innovatively uses nonlinear coefficient as the characterization of the deterioration degree of varistors and uses a small-scale network to predict the development trend of nonlinear coefficient automatically and accurately. Verified by surge impact experiments, the model can accurately predict the state of nonlinear coefficient according to historical data and has the potential for engineering applications in predicting the life of varistors. [ABSTRACT FROM AUTHOR]

Purpose. Evaluation influence structural state polymer phase on the response voltage and coefficient nonlinearity of a multilayer varistor based on zinc oxide. Methodology. Zinc oxide consisted of 97% zinc oxide and 3% total oxides of Bi2O3, Co3O4, MnO2, B2O3, SbO3, ZrO2, Al2O3. At a temperature of 1573°K, the synthesis of semiconductor ceramics based on Zinc oxide was carried out. For composite of thermoplastic polymers and Zinc oxide, non-polar and polar polymers, high pressure polyethylene and polyvinylidene fluoride were used. The composites were obtained by hot pressing at the melting temperature of the polymer phase and a pressure of 15 MPa. After that, using silver paste, measuring electrodes 10 mm in diameter were applied to the surface of the synthesized samples, and then current–voltage characteristics were measured. Modification of composites under action of gas-discharge plasma was carried out in a special cell that creates a dielectric-gas-composite system. The structure of the composites was studied by X-ray diffraction analysis and IR spectroscopy. Findings. The obtained experimental results show that the size of the particles of the inorganic phase significantly affects the current-voltage characteristics of the composite varistor: at a given thickness of the composite varistor, the operation voltage decreases markedly, and the nonlinearity coefficient increases. Numerous experimental results obtained by us show that the impact of electric discharge plasma on the polymer Zinc oxide-composite leads to a significant change in the permittivity and the concentration of local levels at the interface of the composite. The results research showed that effect electrical plasma on the opening voltage depends on the polarity of polymer matrices. Moreover, plasma processing itself significantly changes the structure of the polymer phase at composite. Originality. The magnitude of the potential barrier at phase boundary is mainly determined by the volume fraction and size of the main structural element of ZnO ceramics. Changing the structural state of the polymer matrix allows the adjust response voltage and coefficient nonlinearity of volt-ampere characteristic of the multilayer varistor. Practical value. The discovered development of electron-ion processes at polymer phase of the varistor indicates the need to take into account change in its service characteristics from the duration and intensity of use. The result obtained has a certain practical significance, since it indicates not only the reason for the change in properties, but also the need to develop measures to increase the service life of the varistor.

The effects of La2O3 on the behaviours of ZnO nanoparticle–Bi2O3–Mn2O3 varistors were determined. The discs with various La2O3 compositions (0.0–3.0 mol%) were prepared via traditional ceramic techniques and their characteristics were investigated. The results demonstrate that La2O3 remarkably affects the varistor samples, in which the size of grain diminished from 29.3 to 8.5 µm according to increasing La2O3 content from 0.0 to 3.0 mol%. The significant response within the varistor sample fabricated from ZnO nanoparticles through sintering process at 1200oC perhaps caused by the surface properties of the powdered ZnO nanoparticles. X-ray diffraction results show that the addition of La2O3 to the varistor resulted in additional peaks, which can be attributed to the construction of La-based phases through the sintering process at high temperature. The spinal phases of the (Bi48ZnO73) and (Mn3O4) diminish with the 3.0 mol% content of La2O3. The varistor samples with 2.0 mol% La2O3 show a superior spinal phase construction of (Bi48ZnO73) and (Mn3O4) and La-based phases, resulting in homogeneous grain size. La2O3 doping substantially enhanced the electrical behaviours of the disc sample with a notable increase in breakdown voltage from 2614.8 to 5730.7 V/mm caused by the increase in La2O3 doping concentration from 0.0% to 3.0 mol%. The improvement was associated with the potential lanthanide ion segregation caused by its greater ionic radius to the boundaries between ZnO grains, thus enhancing its electrical properties. Moderate La2O3 doping concentration at 1.0 mol% improved the non-linear characteristics of the sample (α = 66) and 4400 V/mm breakdown voltage was introduced, while a significant amount of La2O3 doping concentration (more than 1.0 mol%) caused its deterioration (α = 35). The increase in donor concentration Nd to 2.1 × 1020 cm−3 for the varistor doped with 1.0 mol% La2O3 is accompanied by a decrease of interfacial states density NIS to 2.2 × 1012 cm−2 eV−1, in addition to decrease in depletion layer ω to 3.9 nm. The leakage currents of the sample decreased from 0.473 to 0.310 mA/cm2 with the increase of La2O3 doping contents from 0.0% to 2.0 mol% and then increased to 0.596 mA/cm2 at 3.0 mol% La2O3 doping concentration. Therefore, La2O3 may be added to dominate the microstructural characteristics and electrical behaviours of ZnO–Bi2O3–Mn2O3 varistor manufactured using powdered ZnO nanoparticles.

This paper introduces a novel approach to fault localization in transmission lines with series compensation using nonlinear optimization. The objective function minimization provides information on the fault distance and the current at which the protective varistor starts conducting. Terminal source data, the maximum current capacity of the capacitor, and the operating curve of the metal oxide varistor protection element are not required. The proposed method successfully met the predefined objectives, with a maximum error of 1.13% in simulated scenarios. In validating the method using real cases from a Brazilian energy concessionaire, the errors were below 0.5%. [ABSTRACT FROM AUTHOR]

In the work, a theoretical analysis of high-voltage surge (HVS) passing from a power supply network through the path "voltage limiter - low-pass filter" is carried out, with the aim to evaluate the effectiveness of the filter on reducing the amplitude of the residual HVS at the input of electrical and/or radio-electronic equipment. As a low-pass filter (LPF), an L-shaped filter was chosen. Typical means of limiting the amplitude of the HVS (gas-filled arresters, varistors, and suppressors) are analyzed, and their shortcomings are shown. The justification of the equivalent scheme for theoretical analysis is given. The analysis revealed a direct relationship between the cut-off frequency of the LPF, which is determined by the nominal values of its elements, and the amplitude of the residual HVS at the mains input of the equipment, and also showed the effectiveness of inserting the LPF between the output of a typical HVS voltage limiter and the mains input of the mentioned equipment from the point of view of additional reduction of the residual HVS amplitude. References 18, figures 6. [ABSTRACT FROM AUTHOR]

The dual strategies of A-site deficiency and addition of ZnO sintering aid have been employed to optimise stability and densify the high-temperature proton conductor Ba 0.95 Ce 0.8 Y 0.2 O 3-δ at 1200 °C (B95CYZn-1200). Structural analysis performed by Rietveld refinement based on X-ray diffraction data indicated perovskite phase with monoclinic symmetry (space group, I2/m). Raman spectroscopy revealed the presence of ZnO for material sintered at 1200 °C, which most likely partially resides in grain-boundary regions, leading to enhanced electrical transport observed by impedance spectroscopy at low temperature. Anomalous and reproducible frequency-dependent impedance behaviour below 500 °C, observed in various atmospheres, is suggested to be attributable to the varistor-type properties of ZnO. The electrical conductivity of B95CYZn-1200 in the range 500–900 °C is typical of perovskite proton conductors but with greater conductivity than both Ba-stoichiometric BaCe 0.8 Y 0.2 O 3-δ and ZnO-free Ba 0.95 Ce 0.8 Y 0.2 O 3-δ in wet O 2 and N 2 , reaching ∼ 1.1 S m−1 at 550 °C in wet O 2. Resistance to carbonate formation and mechanical breakdown was demonstrated via prolonged impedance measurements in CO 2 - and H 2 -containing atmospheres in the range 600–700 °C. • ZnO sintering aid optimises densification of Ba 0.95 Ce 0.8 Y 0.2 O 3-δ at 1200 °C. • High stability of ZnO-added Ba 0.95 Ce 0.8 Y 0.2 O 3-δ in CO 2 and H 2 atmospheres. • Higher conductivity of Ba 0.95 Ce 0.8 Y 0.2 O 3-δ attributable to ZnO. • Grain-boundary ZnO induces varistor action at low temperature. [ABSTRACT FROM AUTHOR]

With the great leaps forward in the development of the railway, the importance of safe operation and maintenance has become increasingly prominent. Varistor is the key component insurge protective devices for railway communication and signaling equipment, it is necessary to study a description model of the varistor degradation process and predict its lifetime through condition monitoring. Among the monitoring parameters, nonlinear coefficient is an important index to measure the health of varistors. Considering that the degradation process of varistors is the cumulative effect of surge history, and its nonlinear coefficient has a time–series relationship, a life prediction model for varistors based on BiLSTM is proposed. The model innovatively uses nonlinear coefficient as the characterization of the deterioration degree of varistors and uses a small-scale network to predict the development trend of nonlinear coefficient automatically and accurately. Verified by surge impact experiments, the model can accurately predict the state of nonlinear coefficient according to historical data and has the potential for engineering applications in predicting the life of varistors.

The global increase in electrical device consumption has escalated the demand for excellent surge protectors. As a state-of-the-art technology, varistor has received considerable attention due to its outstanding versatility and wide range of applications. Hence, it is crucial to understand the development trend of varistor to expand the collaboration networks and propel its advancement. In this bibliometric article, several procedures were presented and analyzed to determine the global research trend of varistor based on the publication output each year, leading countries, most prolific authors, and co-occurrences of author keywords. After several stages of collecting and refining the textual information from the Scopus database, a total number of 2122 research articles and conference papers were retrieved between 1951 and 2021. Results show that since 1975, the annual number of publications has increased significantly, with 2020 recording the highest value of 1363 articles. China, the United States, South Korea, and Japan contributed around 60% of the total articles published. Moreover, three of the most prolific institutions associated with the research topic were ranked among the top 200 universities globally. The analysis of varistor research progress will provide a common overview of collaborative networks and potential collaborators for a better broadening of knowledge.

We present a method for increasing the dielectric constant of CaTiO3/CaCu3Ti4O12 (CTO/CCTO) composites and retaining a low-loss tangent (tanδ) by doping with Ge dopant. The Ge-doped CTO/CCTO composites were fabricated using a one-step processing method. The phase composition and microstructure analyses confirmed the existence of CTO and CCTO phases, in which Ge doping ions can be substituted into both phases. The mean grain sizes of the two phases were slightly reduced by decreasing the porosity. Doping the CTO/CCTO with Ge doping ions resulted in a high dielectric constant by ~ two times, while a very low tanδ value of ~0.01 did not change. Furthermore, the dielectric constant changed by less than ±15% in the temperature range of −60 – 150°C. The nonlinear current density–electric field properties of CTO/CCTO can also be enhanced. Impedance spectroscopy showed a heterogeneous microstructure with enhanced grain boundary properties after doping with Ge dopants, giving rise to enhanced nonlinear electrical properties. The decreased grain resistivity due to Ge substitution is confirmed to originate from the increase in the Ti3+/Ti4+ ratio, which was analyzed using X–ray photoelectron spectroscopy .

In order to decrease the humidity sensitivity of SnO2 –Co3 O4 –Nb2 O5 –Cr2 O3 varistor ceramics, lead oxide was added and the electric characteristics of synthesized materials with the PbO concentration of 0, 0.1, 0.5, 0.7, 1 and 2 mol.% in the air with relative humidity of 10–86% were investigated. All tested samples have non-linear current–voltage characteristics with large values of the nonlinearity coefficient of 38–51. The optimal concentration of PbO addition in ceramics is 0.5–0.7 mol.%. The addition of such quantity of lead oxide to the ceramics leads to the decrease of the breakdown electric field up to 4390 V/cm and the humidity sensitivity coefficient up to 172. The increase of the PbO concentration provides the increase of the electrical conductivity of samples at low fields. The barrier mechanism of electrical conductivity of the studied ceramics is proved by the obtained values of potential barrier heights of 0.85–0.90 еV on the SnO2 crystallite boundaries. [ABSTRACT FROM AUTHOR]

This study aims to determine the basic physical properties of varistor, which is a protective element in a surge protection device (SPD) used to prevent damage to electric and electronic equipment due to lightning. To do this, we conducted tests of insulation resistance, leakage current, heating characteristics, accelerated aging, impulse current, and operating duty according to temperature. To measure insulation resistance and leakage current, an S1-1568 insulation resistance tester was used. To measure the temperature rise according to a change in the external environment, a convection oven was employed. For the impulse current test, a surge current generator of a direct lightning strike, which was designed and manufactured according to the IEEE and UL standards, was used. We verified that the leakage current increased and the insulation resistance decreased as the voltage and outside temperature were applied to the varistor. This meant that heating and deterioration accelerated due to the leakage current, depending on the place where the SPD was applied. Heat accumulation due to constant heating could cause a change in the physical properties of a varistor and degradation of performance, leading to failure. The impulse current test results of the varistor through the operating duty test showed that changes in insulation resistance and leakage current did not occur significantly with an increase in the number of impulse applications when the less than the maximum surge currents. On the other hand, the maximum surge current was exceeded, the insulation resistance rapidly decreased, which also rapidly increased the leakage current.

Varistors are widely used in dc circuit breaker (DCCB) application as fault energy absorption elements, which is not an application the varistors are originally designed for. The fault energy stress adversely impacts the varistor lifetime, thus affecting DCCB reliability and performance. This article presents two methods for choosing the appropriate varistor type and arrangement in a DCCB by linking 1) varistor lifetime and 2) DCCB component- and system-level parameters. The first method uses a set-based design approach with random Latin hypercube sampling to narrow down viable solutions. In comparison, the second method relies on a point-based design approach and proposes an integer programming problem to optimize varistor lifetime. Both procedures are applied to the selection of varistors in 1) a 12 kV DCCB rated for 2-kA nominal current and a peak fault current of 15 kA and 2) a reduced-scale 1.2-kV DCCB hardware prototype, using publicly available varistor data. The article shows the possibility of design for varistor lifetime in DCCB applications, and concludes that both selection procedures provide consistent, reasonable, and verifiable results. However, the results also pinpoint the significant gaps and call for future work on impulse stress versus lifetime relationships for DCCB varistors. [ABSTRACT FROM AUTHOR]

Metal oxide varistors (MOVs) with steady decrease and continuous increase in power loss are generally distinguished as stable and instable, respectively. In this article, the power loss of modern stable MOVs were found to anomalously increase, when the aging voltage was even lowered. In other words, those MOVs were superficially stable in harsh conditions but instable in mild conditions, which was against common sense. In addition, a crossover phenomenon and an overall deterioration in the current–voltage characteristics were observed in the forward and reverse directions, respectively. The unique aging results were in well consistency with the numerical simulation, where redistribution of ions in depletion layers was involved. For modern stable MOVs with adamant interface states, the formation of “U”-shaped ion distribution in depletion layers resulted in increased barrier height at high voltages but decreased height at low voltages. For an arbitrary MOV, the evolution of power loss during aging was a result of competition between consumption of interface states and re-distribution of ions in depletion layers. Therefore, the power loss might not be sufficient to represent the degradation of MOVs. Quantitative studies deep into the dynamics of point defects of Schottky barriers of MOVs are urgent. [ABSTRACT FROM AUTHOR]

The effects of the sintering conditions on the phase compositions, microstructure, electrical properties, and dielectric responses of TiO2-excessive Na1/2Y1/2Cu3Ti4.1O12 ceramics prepared by a solid-state reaction method were investigated. A pure phase of the Na1/2Y1/2Cu3Ti4.1O12 ceramic was achieved in all sintered ceramics. The mean grain size slightly increased with increasing sintering time (from 1 to 15 h after sintering at 1070 °C) and sintering temperature from 1070 to 1090 °C for 5 h. The primary elements were dispersed in the microstructure. Low dielectric loss tangents (tan δ~0.018–0.022) were obtained. Moreover, the dielectric constant increased from ε′~5396 to 25,565 upon changing the sintering conditions. The lowest tan δ of 0.009 at 1 kHz was obtained. The electrical responses of the semiconducting grain and insulating grain boundary were studied using impedance and admittance spectroscopies. The breakdown voltage and nonlinear coefficient decreased significantly as the sintering temperature and time increased. The presence of Cu+, Cu3+, and Ti3+ was examined using X-ray photoelectron spectroscopy, confirming the formation of semiconducting grains. The dielectric and electrical properties were described using Maxwell–Wagner relaxation, based on the internal barrier layer capacitor model. [ABSTRACT FROM AUTHOR]

A high-resistance Si-based AlInGaN/GaN heterojunction epitaxy specifying AlN/AlGaN laminated buffer layers and AlInGaN barrier layer with 45% Al composition was successfully produced to show a high electron density of $1.93\times10$ 13 cm−2 and mobility of 2829.24 cm2/Vs and based on which a novel varistor is proposed in this work. The varistor is composed with a narrow groove etched into the GaN channel and Ti/Al/Ni/Au (20/130/50/50 nm) metal electrodes attached to the epitaxy surface. The processes to fabricate the varistor were investigated in-depth, including a narrow groove etching based on dry-wet hybrid cyclic etching technology employing oxygen plasma and hydrochloric acid and an optimized metal electrodes ohmic contact process based on HCl:H2O = 1:10 liquid surface treatment and annealing at 875 °C to achieve a low contact resistance of $0.45 \Omega \cdot $ mm. The device with a groove width of $3 ~\mu \text{m}$ and length of $600 ~\mu \text{m}$ exhibits typical varistor characteristics with opening voltage ($V_{{\mathrm {ON}}}$) of 33.8 V and a high nonlinear coefficient of 82.97 in the current range from 1 to 10 mA. The $V_{{\mathrm {ON}}}$ value of the varistors is directly proportional to the narrow groove width with a scaling coefficient of 10.18 V/ $\mu \text{m}$ , which means $V_{{\mathrm {ON}}}$ can be adjusted by altering the width of the groove. The varistor with a simple structure could be used in GaN on-chip integrated switches, electro-static discharge (ESD) protection, and other applications. [ABSTRACT FROM AUTHOR]

ZnO-Bi2O3-metal oxide systems are successfully utilized as varistors due to their non-linear I-V behavior. The electrical properties of ZnO-based varistors strongly depends on grain boundary phase composition and microstructural features. In this study, ZnO-based varistors containing different amount of CuO (0–2 mol%) were sintered by conventional and spark plasma sintering (SPS) methods, which resulted different I-V characteristics. While the samples sintered by SPS method were observed to have smaller grain size, more homogenous microstructure and higher density, grain boundary thickness reduced due to removal of bismuth, which was the result of high vacuum environment during sintering step. Since the barrier thickness of SPSed samples decreased, a lower breakdown electrical field (Eb) value was recorded in comparison to conventionally sintered samples. It was also detected that Eb values of both conventional and SPS samples increased with increasing CuO content. [ABSTRACT FROM AUTHOR]

We present a method for increasing the dielectric constant of CaTiO3/CaCu3Ti4O12 (CTO/CCTO) composites and retaining a low-loss tangent (tanδ) by doping with Ge dopant. The Ge-doped CTO/CCTO composites were fabricated using a one-step processing method. The phase composition and microstructure analyses confirmed the existence of CTO and CCTO phases, in which Ge doping ions can be substituted into both phases. The mean grain sizes of the two phases were slightly reduced by decreasing the porosity. Doping the CTO/CCTO with Ge doping ions resulted in a high dielectric constant by ~ two times, while a very low tanδ value of ~0.01 did not change. Furthermore, the dielectric constant changed by less than ±15% in the temperature range of −60 – 150°C. The nonlinear current density–electric field properties of CTO/CCTO can also be enhanced. Impedance spectroscopy showed a heterogeneous microstructure with enhanced grain boundary properties after doping with Ge dopants, giving rise to enhanced nonlinear electrical properties. The decreased grain resistivity due to Ge substitution is confirmed to originate from the increase in the Ti3+/Ti4+ ratio, which was analyzed using X–ray photoelectron spectroscopy. [ABSTRACT FROM AUTHOR]

The global increase in electrical device consumption has escalated the demand for excellent surge protectors. As a state-of-the-art technology, varistor has received considerable attention due to its outstanding versatility and wide range of applications. Hence, it is crucial to understand the development trend of varistor to expand the collaboration networks and propel its advancement. In this bibliometric article, several procedures were presented and analyzed to determine the global research trend of varistor based on the publication output each year, leading countries, most prolific authors, and co-occurrences of author keywords. After several stages of collecting and refining the textual information from the Scopus database, a total number of 2122 research articles and conference papers were retrieved between 1951 and 2021. Results show that since 1975, the annual number of publications has increased significantly, with 2020 recording the highest value of 1363 articles. China, the United States, South Korea, and Japan contributed around 60% of the total articles published. Moreover, three of the most prolific institutions associated with the research topic were ranked among the top 200 universities globally. The analysis of varistor research progress will provide a common overview of collaborative networks and potential collaborators for a better broadening of knowledge. [ABSTRACT FROM AUTHOR]

The influence of sintering time on the microstructure and electrical properties of ZnO-CoO-SLS (soda lime silica) glass varistor based ceramics has been investigated. With increased sintering time, the density of the sintered pellets increased from 5.060 to 5.644 g/cm3 resulting in an increase of the nonlinear coefficient and barrier height of the ZnO-CoO-SLS glass varistor ceramics from 6.742 to 8.252 and 0.846 to 0.955 eV, respectively. The breakdown voltage is inversely proportional to the leakage current. The breakdown voltage increases from 183.7 to 278.6 V/cm and the leakage current decreases from 5.832 to 4.324 μA/cm2 as the sintering time is increased from 60 to 150 minutes but as the increase sintering time of 150 minutes their value decreases to 222.8 V/cm and increases to 5.078 μA/cm2. The high nonlinearity of 7.366 with lowest leakage current of 4.324 μA/cm2 has been achieved from the varistor sintered at 150 minutes, breakdown voltage of 278.6 V/cm and barrier height of 0.954 eV.

The increasing demand for the development and utilization of renewable energy resources has lead to a growing interest in the development of LVDC systems. The dc grid provides more flexibility in integrating different forms of renewable energy sources effectively. However, the lack of a reliable protection mechanism remains the main drawback in the growth of dc distribution systems. Unlike ac systems, the absence of a natural zero crossing in dc systems for arc extinction makes the use of a conventional mechanical circuit breaker (MCB) a less reliable solution. The use of a solid-state circuit breaker (SSCB) results in fast fault interruption but reduces the overall efficiency of the system due to the on-state voltage drop of the semiconductor devices. A hybrid circuit breaker (HCB) combining MCB and SSCB yields better static and dynamic performances but the main challenges remains in the demagnetization of the transmission line inductance after a fault interruption and an arc formation between the MCB contacts. This paper proposes a hybrid circuit breaker (HCB) which is suitable for fast fault interruption in low voltage dc (LVDC) systems while alleviating the above issues. Proposed topology employs a semiconductor switch as well as an actively switched capacitor branch in parallel with the main mechanical breaker to facilitate fast current commutation during a fault. The mechanical breaker forming the main branch is turned off at zero voltage. This eliminates the arc formation across the moving contacts of the breaker. Moreover, the fault interruption process does not require a varistor for network demagnetization following the fault current commutation. This paper also presents a discharging mechanism for the capacitor in a practical implementation. Operation of the proposed dc circuit breaker is evaluated through a prototype tested in the laboratory.

Composites based on nonlinear tungsten oxide ceramics and a polyethylene matrix with a volume fraction of ceramic filler from 10 vol % to 43 vol % were studied. It was shown that composites are an isotropic mixture of WO 3 grains in a polymer matrix. The current-voltage characteristics of the composites were nonlinear. Composites have a high positive temperature coefficient of resistance up to 15.8 K-1 in the temperature range of 40–75 °C. It is shown that the temperature coefficient of resistance is positive and increases with increasing electric field strength. The decrease in the electrical conductivity of composites with increasing temperature is explained by the expansion of the polymer matrix and the rupture of the current-conducting channels between the conducting grains of the varistor ceramics. The dependence of the electrical conductivity of the composite on the volume fraction of varistor ceramics is well described within the framework of a three-dimensional percolation model for a two-phase system. [ABSTRACT FROM AUTHOR]

There is a lack of reports where dry milling methods have been used in the preparation of varistor based ceramics. Dry milling methods have been demonstrated to be able to produce fine and homogeneous sample powders. Soda lime silica (SLS) glass powder have also been used as dopants in ZnO varistor ceramics. This work focuses on the effect of dry milling on the microstructural and electrical properties of ZnO0.98-x-SLSx-CoO0.02. The sample mixtures were prepared via a solid state method with x = 0.5, 1.0, 1.5, and 2.0 mol%. XRD managed to detect Zn2SiO4 as secondary phase in the sintered samples. The results show that the average grain size decreased from 26.1 to 21.6 µm and densities of the varistor samples increased as x increased. The varistor sample that was sintered at 1100°C and doped with 2 mol% SLS glass powder shows good electrical properties with nonlinear coefficient, (α) 6.97, breakdown voltage 261.1 V/cm and leakage current (JL) 4.87 µA/cm2.

Transport through grain boundaries in polycrystals is described from first principles using quantum scattering theory, explicitly including Feshbach resonances to account for intermittently trapped electronic surface states. An effective T -matrix is derived then used to calculate the electrical conductivity which exhibits breakdown, a sharp increase at a critical intergrain bias. Under typical conditions where the electron thermal energy,kBT, is much less than the intergrain barrier height,φb, the electrical conductivity has the formσ∼T-1/2e-φb/kBT. Temperature dependence of the conductivity is also considered for thermal energies much larger than the applied bias, as may be realized in tightly-compressed grains., (© 2024 IOP Publishing Ltd. All rights, including for text and data mining, AI training, and similar technologies, are reserved.)

The effects of La2O3 on the behaviours of ZnO nanoparticle–Bi2O3–Mn2O3 varistors were determined. The discs with various La2O3 compositions (0.0–3.0 mol%) were prepared via traditional ceramic techniques and their characteristics were investigated. The results demonstrate that La2O3 remarkably affects the varistor samples, in which the size of grain diminished from 29.3 to 8.5 µm according to increasing La2O3 content from 0.0 to 3.0 mol%. The significant response within the varistor sample fabricated from ZnO nanoparticles through sintering process at 1200oC perhaps caused by the surface properties of the powdered ZnO nanoparticles. X-ray diffraction results show that the addition of La2O3 to the varistor resulted in additional peaks, which can be attributed to the construction of La-based phases through the sintering process at high temperature. The spinal phases of the (Bi48ZnO73) and (Mn3O4) diminish with the 3.0 mol% content of La2O3. The varistor samples with 2.0 mol% La2O3 show a superior spinal phase construction of (Bi48ZnO73) and (Mn3O4) and La-based phases, resulting in homogeneous grain size. La2O3 doping substantially enhanced the electrical behaviours of the disc sample with a notable increase in breakdown voltage from 2614.8 to 5730.7 V/mm caused by the increase in La2O3 doping concentration from 0.0% to 3.0 mol%. The improvement was associated with the potential lanthanide ion segregation caused by its greater ionic radius to the boundaries between ZnO grains, thus enhancing its electrical properties. Moderate La2O3 doping concentration at 1.0 mol% improved the non-linear characteristics of the sample (α = 66) and 4400 V/mm breakdown voltage was introduced, while a significant amount of La2O3 doping concentration (more than 1.0 mol%) caused its deterioration (α = 35). The increase in donor concentration Nd to 2.1 × 1020 cm−3 for the varistor doped with 1.0 mol% La2O3 is accompanied by a decrease of interfacial states density NIS to 2.2 × 1012 cm−2 eV−1, in addition to decrease in depletion layer ω to 3.9 nm. The leakage currents of the sample decreased from 0.473 to 0.310 mA/cm2 with the increase of La2O3 doping contents from 0.0% to 2.0 mol% and then increased to 0.596 mA/cm2 at 3.0 mol% La2O3 doping concentration. Therefore, La2O3 may be added to dominate the microstructural characteristics and electrical behaviours of ZnO–Bi2O3–Mn2O3 varistor manufactured using powdered ZnO nanoparticles. [ABSTRACT FROM AUTHOR]

Se realizó el estudio y análisis de la supresión de impulsos tipo atmosférico al pararrayo de un Sistema de Distribución Eléctrica, basado en la comparación de resultados teóricos desarrollados con el software Matlab – Simulink y los experimentales realizados en el laboratorio de Alta Tensión de la Universidad Politécnica Salesiana del Ecuador, con el objeto de entender el comportamiento eléctrico y matemático de la protección al sistema de distribución. Se utilizó el circuito equivalente del modelo dependiente de la frecuencia de la IEEE "Modeling of metal oxide surge arresters”. El análisis matemático consistió en construir las ecuaciones del circuito equivalente y utilizar la herramienta de Matlab que extrapole con la mejor aproximación el comportamiento de las resistencias no lineales del pararrayo, además se modeló el circuito generador de impulso atmosférico definido en las normas ANSI/IEEE Standard 4-1995 requerido para la supresión.

One-dimensional ZnO composites doped with different Co contents (0 mol.%, 1 mol.%, and 1.5 mol.%) were successfully prepared by the reflux method. Microstructural studies of the as-obtained powders were studied by x-ray powder diffraction, Fourier transform infrared spectra, and scanning electron microscopy (SEM) with energy-dispersive x-ray spectroscopy. SEM observation showed that the morphology of ZnO particles is influenced by the concentration of Co doping, which formed rod-like and quasi-spherically shaped particles. All samples indicated a hexagonal wurtzite structure. When the Co content increased from 0 mol.% to 1.5 mol.%, the calculated crystallite size decreases from 56.62 nm to 54.38 nm. The change in bond length, lattice parameters, and micro-strain for Co-doped ZnO powders indicate that Co ions have entered the ZnO lattice. The study of the optical properties of ZnO powders proves that the doping of Co increases the absorptance and reduces the band gap of ZnO. The 1.0 mol.% Co-doped ZnO varistor sintered at 1200°C for 2 h has a breakdown voltage of 345.3 V/mm and nonlinear coefficient of 11.7. [ABSTRACT FROM AUTHOR]

In this research, ZnO–Bi2O3–Mn2O3 varistors manufactured from 20 nm ZnO powder and doped with different amounts of Er2O3 were fabricated via the conventional ceramic processing method. The effect of various Er2O3 concentrations (0.5–2.0 mol%) on the sintered density, structural improvement, and nonlinear behavior of the 20 nm ZnO–Bi2O3–Mn2O3 varistors was discussed. Different Er2O3 concentrations exerted considerable influence on the varistors. The addition of large amounts of Er2O3 led to the inhibition of grain growth by increasing the amount of the Er2O3‐rich spinel phase. X‐ray diffraction analysis showed that the addition of Er2O3 to the varistor systems led to the development of Er2O3‐rich phases during sintering. During sintering, the considerable surface area of the nanoparticle powder resulted in numerous interactions in the surfaces of the ceramics manufactured from 20 nm ZnO powder. The electrical behaviors of the varistors were substantially influenced by Er2O3. E1 mA evidently increased from 2,144.7 to 5,482.2 V/mm with the increment in doping amount. The nonlinear coefficient also dramatically increased with the increase in Er2O3 content. The ZnO nanoparticle–Bi2O3–Mn2O3 varistors doped with 1.0–2.0 mol% Er2O3 possessed high voltage and nonlinearity and were stable against DC‐accelerated aging stress. [ABSTRACT FROM AUTHOR]

The electric discharge across a varistor granule filled air gap under a fast‐rising voltage pulse was investigated for surge protection applications. The effects of temperature and pressure on the arc and the electrical conduction were analyzed by the characteristic changes in voltage waveforms triggered by a fast‐rising high voltage pulse. In addition to the gap size, experimental results show that competing mechanisms among arc conduction, conduction through the varistor granule network, thermionic emission from Joule heating at granule‐to‐granule contact points, and the magnitude of the switching voltage dictate the maximum surge protection voltage for the filled air gap. Experimental evidence indicated that accumulated degradation was created at small contact points between varistor granules by repetitive assaults from longer duration, high voltage pulses. The uniqueness of using varistor over other dielectric granules in an air gap for surge protection is identified and discussed. [ABSTRACT FROM AUTHOR]

Rutile-TiO2 ceramics are very promising electronic ceramic materials which can be applied in varistors because of their good electrical properties. In this work, Dy2O3 was used to improve the electrical properties of a TiO2 varistor doped with 0.60 mol.% Nb2O5 and 0.30 mol.% SiO2. Results showed that the TiO2 varistor doped with 0.30 mol.% Dy2O3 possessed optimal electrical properties with good nonlinear coefficient ( α = 5.7 ), very low breakdown voltage ( E B = 1.34 V mm - 1 ) and colossal dielectric constant ( ε r = 8.01 × 10 5 ). The microstructural analysis showed that after the incorporation of Dy2O3 into the TiO2 varistor, the grains tended to be more semiconducting due to the defect carriers derived from the substitution of Dy3+ for Ti4+. Meanwhile, the moderate dopant of Dy2O3 also increased the grain size and narrow grain boundary. Consequently, the breakdown voltage decreased, while the nonlinear coefficient and dielectric constant improved. [ABSTRACT FROM AUTHOR]

A conventional ceramic processing method was applied to manufacture high‐density 20‐nm ZnO‐Bi2O3‐Mn2O3 varistor ceramics. Different cooling rates in the range of 135–540°C/h led to a relatively slight influence on the microstructure, varistor voltage, and leakage current. In contrast, these rates strongly affected the nonlinear exponent. The specific surface area of the 20‐nm ZnO nanoparticle may have led to an intense solid‐state reaction even at a low cooling rate. Superior nonlinearity, with 59.7 μA nonlinear current leakage and 273.5 μA leakage current, was achieved at the 135°C/h cooling rate. The differences in the cooling rates led to a remarkable change in the material's stability under direct current (DC)‐accelerated aging stress in the following order: 135°C/hr ˃ 270°C/hr˃405°C/hr ˃ 540°C/hr. [ABSTRACT FROM AUTHOR]

To control power flow and manage fault level in meshed MV networks, back-to-back voltage source converters (B2B-VSCs) are being used. However, their high cost and relatively low efficiency are of concerns. Partially rated series compensators, such as SSSCs or UPFCs, are desired but come with the challenge of protecting the device during grid faults. Their potential of use has been limited in comparison with the fully rated back-to-back converters. This paper proposes a new system topology including thyristor crowbars and a varistor to protect the SSSC in an MV network and improve the reliability and flexibility of the network operation. Using the proposed method, the time required for isolating the series compensator from the grid is reduced from at least 20 ms, corresponding to the interruption time of conventional circuit breakers, down to 3 μs in the worst case in addition to the grid fault detection delay. The performance is evaluated by simulation. A small-scale single-phase prototype operating at 230 V/16 A is tested in order to demonstrate the concept. [ABSTRACT FROM AUTHOR]

This study investigated electrical properties and microstructure of zinc oxide varistors containing MnO2, Cr2O3, V2O5 and TiO2. To this end, nanosize ZnO particles were synthesised by the polyacrylamide-gel method and doped with minor amounts of MnO2 (0.5 mol-%), Cr2O3 (0.5 mol-%), V2O5 (2 mol-%) and TiO2 in the range of 2–15 mol-%. The prepared samples sintered at 1050°C in air for 2 h. It was observed that TiO2 promoted grain growth of ZnO particles. X-ray examination showed hexagonal ZnO structure as a main phase and Zn2TiO4 and ZnV2O4 as minor secondary phases. The nonlinear coefficient and threshold voltage of the prepared samples were in the range of 3.3–7.9 and 1120–4700 V cm−1 respectively, in which both of them increased with increase in TiO2 content. Among the prepared samples, the varistor with 15 mol-% TiO2 exhibited the best performance in terms of nonlinearity. The nonlinear electrical behaviour was explained by theory of formation of the potential barriers at grain boundaries. [ABSTRACT FROM AUTHOR]