Electrical Properties Of ZnO Varistors Research Articles

Effects of radius and electronegativity of donors on the microstructure and mechanical, thermal, and electrical properties of ZnO varistors

Effects of radius and electronegativity of donors on the microstructure and mechanical, thermal, and electrical properties of ZnO varistors

Effect of Co-Doping of Al3+, In3+, and Y3+ on the Electrical Properties of Zinc Oxide Varistors under Pre-Synthesizing BiSbO4.

Under the premise of using the solid-phase method to pre-sinter Bi2O3 and Sb2O3 into BiSbO4 as a substitute for equal amounts of Bi2O3 and Sb2O3 in the formula, the effects of co-doping with In(NO3)3, Al(NO3)3, and Y(NO3)3 on the microstructure and electrical properties of ZnO varistors were studied. The experimental results show that with an increase in In3+-doped molar concentration, the leakage current of the ZnO varistor shows a rapid decrease and then a slow increase trend. However, the nonlinear coefficient is the opposite of it. With the combined effect of the rare earth element Y3+, the average grain size is significantly reduced, which leads to an increase in the voltage gradient. At the same time, a certain amount of doped In3+ and Al3+ is dissolved into the grains, resulting in a decrease in grain resistance and thus a low level of residual voltage. The varistor with 0.6 mol% In3+, 0.1 mol% Al3+, and 0.9 mol% Y3+ doping ratios exhibits excellent overall performance. The nonlinear coefficient is 62.2, with the leakage current being 1.46 µA/cm2 and the voltage gradient being 558 V/mm, and the residual voltage ratio is 1.73. The prepared co-doped ZnO varistors will provide better protection for metal oxide surge arresters.

Bi–Er–O pre-synthesized phase (Bi1-xErx)2O3 doped ZnO varistors with high nonlinear coefficient and low leakage current

The content of free oxygen Oad at the ZnO grain boundaries has an important impact on the double Schottky barrier and electrical properties of ZnO varistors. In this work, Bi–Er–O pre-synthesized (BE) phase (Bi1-xErx)2O3 (0.25 < x < 0.455) with high conductivity of Oad was prepared using Bi2O3 and Er2O3 as raw materials, and the effects of the BE phase doping on the phase, grain boundary properties, and electrical properties of ZnO–Bi2O3–Sb2O3–Co2O3–MnO2–Cr2O3–SiO2 varistors were studied. XRD analysis shows that the lattice constant of the BE phase (Bi1-xErx)2O3 is between (Bi0.75Er0.25)2O3 and BiErO3. With increasing doping content of the BE phase from 0 to 0.75 wt%, part of Er3+ still exists in the form of the BE phase (Bi1-xErx)2O3 at the ZnO grain boundaries, and its content increases with increasing doping content of the BE phase. The conductivity of Oad in (Bi1-xErx)2O3 is much higher than that in Bi2O3, resulting in the generation of a large number of negative O′ and O″ at the ZnO grain boundaries, and decreasing concentration of the intrinsic point defect zinc interstice Zni. So the donor concentration Nd decreases, the height of the grain boundary barrier increases, the depletion layer widens, and the electrical properties are improved. By analyzing the low-temperature permittivity spectra, it was calculated that with increasing doping content of the BE phase from 0 to 0.75 wt%, the concentration of oxygen vacancy VO• decreases inappreciably, but the concentration of zinc interstice Zni•• decreases by about 23%. When the doping amount of the BE phase is 0.75 wt%, the nonlinear coefficient α of the obtained ZnO varistors is 73.9 ± 0.6, and the leakage current density JL is only 0.3 ± 0.1 μA/cm2. This study provides an important reference for improving the electrical properties of ZnO varistors by manipulating the Bi-rich phase structure to improve the double Schottky barrier characteristics.

Effects of refining methods and time on suspension, microstructure, and electrical properties of ZnO varistors

Effects of refining methods and time on suspension, microstructure, and electrical properties of ZnO varistors

Effect of Sc2O3 doping on microstructure and electrical properties of ZnO–Bi2O3-based varistors

ZnO varistors are widely used in electrical systems. In this study, the effects of different contents of Sc2O3 doping on the microstructure and electrical properties of ZnO varistors were systematically analyzed. The results show that the doping of Sc2O3 is conducive to the uniform growth of the ZnO grains and improves the breakdown field strength of varistors. At the same time, Sc2O3 doping improves the barrier height of the varistors, resulting in a significant increase in nonlinear coefficient and a decrease in leakage current density. The sample doped with 0.15 mol% Sc2O3 exhibited excellent electrical properties with breakdown field strength of 696.13 V/mm, a leakage current density of 1.26 μA cm−2, and a nonlinear coefficient of 55.00. The Sc2O3 doped samples have good performance, which is of guiding significance for the study of other trivalent and tetravalent ion doping with a radius similar to that of Zn2+.

The effect of grinding media on suspensions, microstructures, and comprehensive electrical properties of ZnO varistors

The effect of grinding media on suspensions, microstructures, and comprehensive electrical properties of ZnO varistors

Electrical properties of ZnO/&lt;inline-formula&gt;&lt;tex-math id="Z-20220101164636"&gt;\begin{document}${\boldsymbol{\beta}} $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="2-20210635_Z-20220101164636.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="2-20210635_Z-20220101164636.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;-Bi&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; interfaces featuring aggregation defect under external electric fields

The safe operation of power equipment largely depends on the overvoltage protection level of the arrester. The ZnO varistors are widely used as the core components of the arresters in power systems because of the excellent nonlinear volt-ampere characteristics. In order to study the electrical properties of ZnO varistors under different external electric fields from the microstructure, the method of first-principles based on density functional theory (DFT) is used, and structure of ZnO/&lt;i&gt;β&lt;/i&gt;-Bi&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; interface containing zinc interstitial (Zn&lt;sub&gt;i&lt;/sub&gt;) and oxygen vacancy (V&lt;sub&gt;o&lt;/sub&gt;) defects is built. The results show that the V&lt;sub&gt;o&lt;/sub&gt; defect migrates after full relaxation. The Zn&lt;sub&gt;i&lt;/sub&gt; shifts to the interface under an external electric field. The interface energy increases rapidly after the electric field intensity has exceeded 0.1 V/Å, which means that the interaction force between the interfaces becomes larger, the distance between ZnO and &lt;i&gt;β&lt;/i&gt;-Bi&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; layers decreases, and the conductivity increases rapidly. The differential charge density, work function and Bader charge analysis method are used to calculate the barrier height at the interface, which proves that the built-in electric field is an important cause ingredient responsible for the non-linear volt-ampere characteristics of ZnO varistors. The effects of atomic orbital energy level, trap energy level and energy gap on the macroscopic conductivity of ZnO varistors are analyzed by using the method of density of states analysis. In this work are analyzed the different electrical parameters of the ZnO/&lt;i&gt;β&lt;/i&gt;-Bi&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; interface with aggregation defects by adjusting the intensity of the external electric field, and a new idea is provided for learning the electrical characteristics of ZnO varistors.

Effect of Sintering Temperature on the Microstructure and Electrical Properties of Zno Varistors

Effect of Sintering Temperature on the Microstructure and Electrical Properties of Zno Varistors

Effect of Sintering Temperature on the Microstructure and Electrical Properties of Zno Varistors

Effect of Sintering Temperature on the Microstructure and Electrical Properties of Zno Varistors

The role of oxide optimization in improving the electrical properties of ZnO varistors

The role of oxide optimization in improving the electrical properties of ZnO varistors

Effects of raw particle size and annealing on microstructure, electrical and mechanical behaviors of ZnO-based varistors

In this paper, the effect of the raw particle size and the annealing process on the compositions, microstructure, mechanical, thermal, and electrical properties of ZnO varistors was investigated using X-ray diffraction, infrared, X-ray photoelectron spectroscopy, scanning electron microscopy, electric field–current density, capacitance–voltage, mechanical, and thermal expansion measurements. Furthermore, the ZnO grain growth mechanism during the annealing process was discussed in detail. Results show that when the raw particle size equaled 90 nm and sintering was performed at 1100 °C for 2 h, the obtained ZnO-based varistors possessed excellent mechanical, thermal, and electrical properties; the E1mA, α, JL, and K values were 1015.3 V mm–1, 37.98, 2.45 μA cm–2, and 1.37, respectively, due to the highest bulk density and the finest uniform particle size distribution. When annealing occurred at 300 °C for three times, values of σf, KIC, E1mA, α, JL, and K reached 175.35 MPa, 1.96 MPa m1/2, 1180.2 V mm–1, 43.58, 2.15 μA cm–2, and 1.2, indicating improvements of approximately 14.7%, 4%, 16.2%, 14.7%, − 12.2%, and 11.11% compared with those of the non-annealed ZnO-based varistors, respectively, being due to the improved uniformity of grain size distribution and the re-distribution of donor Al3+ and Y3+ in the ZnO crystal and grain boundary. The annealing process lead to the transformation of Sb3+ to Sb5+ in the ZnO crystal, which could generate two additional coordination sites. The newly generated sites could combine with O2- in other crystals to increase the grain growth, resulting in clear grain growth on the surface, improved grain size distribution, and regular grain shape in the interior of ZnO-based varistors.

B2O3- and Y2O3-doped ZnO varistor ceramics: Enhanced voltage gradient and nonlinear properties for UHV

In this paper, the effects of boron and yttrium co-doping on the electrical properties of ZnO varistors were determined. The presence of both B3+ and Y3+ co-dopant improved the electrical performance of varistor ceramics. The nonlinearity coefficient α and potential barrier ϕb were increased noticeably. The nonlinearity coefficient α was 73 and ϕb was 2.75 eV, at the same time, a voltage gradient of 425 V/mm and leakage current of 0.9 μA/cm2 were obtained. This work provided a way to enhance the protective effects of ZnO varistor arresters for ultra-high voltage power transmission systems.

Effects of dispersant content and pH on dispersion of suspension, microstructures and electrical properties of ZnO varistors

This article systematically studies the relationship between the dispersity of the mixed suspension, the microstructures and the electrical properties of the ZnO varistors by adjusting the dispersant content and the pH value. The suspension dispersity was measured by viscosity, zeta potential, particle size distribution and TEM observation. The structure of the as-prepared ZnO varistors was characterized by XRD and SEM. The electrical properties were investigated by testing E-J characteristics, breakdown voltage, leakage current, nonlinear coefficient, 8/20 μs waveform current impulse and accelerated aging performance. When the suspension reached the best dispersion condition of 0.3 wt% dispersant and the original pH value, the ZnO varistors had optimum electrical properties: breakdown voltage gradient of 299.95 V mm−1, leakage current IL of 0.33 μA, voltage ratio U5kA/U1mA of 1.686, nonlinear coefficient of 46.71, and a downward trend of power consumption in the accelerated aging test.

Study on ZnO Varistors Doped with Y2O3 by Microwave Two-step Sintering

The zinc oxide varistor prepared in this paper is mainly composed of submicron zinc oxide powder and dopants, and is prepared by two-step sintering method, which is in contrast with traditional sintering method and ordinary microwave sintering method. The effects of microwave sintering temperature and holding time on the microstructure and electrical properties of ZnO varistors were investigated. The results show that the potential gradient of microwave sintering is higher than that of traditional sintering, but the leakage current also increases. Compared with ordinary microwave sintering, the two-step sintering can further effectively reduce the grain size, enhance densification, not only improve the potential gradient, but also reduce leakage current. In two-step sintering, increasing sintering temperature can effectively reduce leakage current and non-linear coefficient, but the potential gradient is also greatly reduced. When the holding time is more than 1 hour, there is little difference in electrical performance. When the holding time is too small, its electrical performance is weak overall.

Effects of sizes of additive particles on suspensions, microstructures, and electrical properties of ZnO varistors

AbstractThe effects of the sizes of the additives on the dispersion of the mixed suspensions, the microstructures, and the comprehensive electrical properties of the ZnO varistors were investigated. The particle size distribution, the viscosity, and the zeta potential of the suspension were characterized to evaluate the effect of the sizes of the additives on the dispersion of the metal oxide particles. The potential gradient, the leakage current, the nonlinear coefficient, the voltage ratio, and the aging coefficient were considered to estimate the effect of the sizes of the additives on the performance of the ZnO varistors. The electrical testing results showed that a proper amount of milling of the additive particles could improve the comprehensive electrical properties, while an excessive milling produced the opposite effect. When the milling time of the additive particles reached 30 minutes, the dispersion of ZnO‐additive mixed suspension was the best. The as‐prepared varistors showed the optimal electrical performance with potential gradient of 310 V/mm, leakage current of 1 μA, nonlinear coefficient of 32.7, voltage ratio of 1.69, and aging coefficient of 0.59.

Influence of CaO doping on phase, microstructure, electrical and dielectric properties of ZnO varistors

In present study, impact of CaO doping on microstructure and phase electrical properties of a ZnO varistor is being reported. The doped ZnO nanopowders were prepared by solution combustion followed by conventional sintering. The ZnO particle size of powders decreased from 22 to 17 nm with CaO doping was noted. Decrease in grain size of the sintered samples from 4.54 to 1.19 μm with CaO doping was observed. This is attributed to Ca4Bi6O13 and Ca0.89Bi3.11O5.58 secondary phase formations apart from pyrochlore and spinel phases. A breakdown field as high as 21 kVcm−1 in X = 1.00 sample was obtained. The Coefficient of nonlinearity (α) decreased from 95 to 42 is due to decrease in carrier concentrations. Increase in resistivity with CaO doping and decrease in resistivity beyond X = 2.5 were noted. The electric modulus plots yielded two relaxations at a temperature in the range 100–300 °C and frequency in the range 0.1 Hz-1MHz. Activation energy (Ea) decreased from 0.65 to 0.50 eV for a region I and from 0.89 to 0.75 eV for region II with CaO doping was observed.

Effect of Pr6O11 doping on the microstructure and electrical properties of ZnO varistors

ZnO-Pr6O11 based varistors have anticipated application prospect in electrical system, but the study of the detailed microstructure is still poor. In this paper, the effect of Pr6O11 doping on the microstructure (such as element distributions and grain boundary characteristics) and electrical properties of the ZnO-Pr6O11–Co2O3–Cr2O3–Y2O3 varistors manufactured by the conventional solid-state sintering procedure was studied detailedly. Without Pr6O11 doping, the elements have the similar distributions in the interior and grain boundaries of ZnO phase, and the double Schottky barrier cannot be formed. With Pr6O11 doping, Pr6O11 liquid phase dissolving a large number of Zn, Cr, and Y forms during sintering and Pr6O11 solid phase forms in the ZnO grain boundaries during cooling, so the double Schottky barriers form. The voltage gradients E1 mA and nonlinearity coefficients α of the samples with Pr6O11 contents of 0.25–1 mol% are much larger than those of the sample without Pr6O11 doping, and the values of α and E1 mA increase with Pr6O11 content increasing from 0 to 1 mol%. The values of α and E1 mA simultaneously depend on the double Schottky barrier height ϕb and the CPE exponent αCPE. Finally, the ZnO varistor with a voltage gradient of 333.6 V/mm and a nonlinearity coefficient of 24.4 was obtained by Pr6O11 doping of 1 mol%. The detailed study of the microstructure and related mechanism is of great importance for preparing ZnO-Pr6O11 based varistors with excellent electrical properties.

Structural and electrical properties of zno varistor with different particle size for initial oxides materials

&#x0D; &#x0D; &#x0D; We report here structural, electrical and dielectric properties of ZnO varistors prepared with two different particle sizes for initial starting oxides materials (5 µm and 200 nm). It is found that the particle size of ZnO does not influence the hexagonal wurtzite structure of ZnO, while the lattice parameters, crystalline diameter, grain size and Zn-O bond length are affected. The nonlinear coefficient, breakdown field and barrier height are decreased from 18.6, 1580 V/cm and 1.153 eV for ZnO micro to 410 V/cm, 7.26 and 0.692 eV for ZnO nano. While, residual voltage and electrical conductivity of upturn region are increased from 2.08 and 2.38x10-5 (Ω.cm)-1 to 4.55 and 3.03x10-5 (Ω.cm)-1. The electrical conductivity increases by increasing temperature for both varistors, and it is higher for ZnO nano than that of ZnO micro. The character of electrical conductivity against temperature is divided into three different regions over the temperature intervals as follows; (300 K ≤ T ≤ 420 K), (420 K ≤ T ≤ 580 K) and (580 K ≤ T ≤ 620 K), respectively. The activation energy is increased in the first region from 0.141 eV for ZnO micro to 0.183 eV for ZnO nano and it is kept nearly constant in the other two regions. On the other hand, the average conductivity deduced through dielectric measurements is increased from 2.54x10-7 (Ω.cm)-1 for ZnO micro to 49x10-7 (Ω.cm)-1. Similar behavior is obtained for the conductivities of grains and grain boundaries. The dielectric constant decreases as the frequency increases for both varistors, and it is higher for ZnO nano than that of ZnO micro. These results are discussed in terms of free excited energy and strength of link between grains of these varistors.&#x0D; &#x0D; &#x0D;

Electrical properties of ZnO varistor ceramics modified by rare earth-yttrium and gallium dopants

Scanning electron microscopy, electric field-current density measurements, capacitance-voltage testing, X-ray diffraction analysis, and energy dispersive X-ray spectroscopy were performed to study the effects of rare earth-yttrium and gallium doping on the microstructure and electrical properties of ZnO varistors. Our results indicated that the introduction of gallium and yttrium strengthened the barrier height of grain boundaries and led to a decrease in the grain resistance. Both the voltage gradient and nonlinear coefficient of the samples increased and then decreased as the gallium doping level was increased at a given rare earth-yttrium. The residual voltage ratio and the leakage current varied with the opposite relationship. The findings of this study could help to improve the protective effects of surge protection devices assembled from ZnO ceramic varistors and enhance the stability of power systems.

Al-doped ZnO varistors prepared by a two-step doping process

ABSTRACTIt is difficult to dope Al into main grains of ZnO varistor ceramics, especially for small doping amount. Generally, all raw materials including Al dopant are directly mixed together and sintered into ceramics. However, in this direct doping process, Al is apt to stay in grain boundaries, and almost does not enter grains. This does harm to the electrical properties of ZnO varistors. In this paper, we proposed a two-step doping process. Al2O3 powder was first mixed only with a part of the ZnO powder and pre-sintered. The pre-sintered powder was mixed with other additives such as Bi2O3 and the rest ZnO. Then ZnO varistor ceramics were prepared via solid state sintering processes. Results showed that two-step doped ZnO varistors exhibited improved electrical properties with a significant increased nonlinear coefficient and a great decreased leakage current compared to directly doped ones because more Al was incorporated into ZnO grains.