Study on the Electrical Properties and the Ac Conductance Response of ZnO-Based Varistor

2014 ◽  
Vol 1070-1072 ◽  
pp. 625-629
Author(s):  
Xue Tong Zhao ◽  
Rui Jin Liao ◽  
Jian Ying Li
Keyword(s):  
Activation Energy ◽  
Grain Size ◽  
Electrical Properties ◽  
Electric Field ◽  
Grain Growth ◽  
Relaxation Peak ◽  
Breakdown Electric Field ◽  
Zno Varistor ◽  
Ac Conductance

ZnO-based varistor ceramics with different recipes were prepared in this research. It was found that the grain growth was restrained with the addition of Ba2+. SEM results indicated that the grain size of ZnO varistor ceramics with Ba2+ was reduced to 4.7 μm. Correspondingly, the breakdown electric field of the ZnO varistor samples were extremely enhanced to 8730 V/cm. The results of ac conductance response showed that two relaxation peak 1 and 2 with activation energy at about 0.24 eV and 0.36 eV were observed in 100-250 K, which were not affected by additives. However, a new conductance relaxation peak 3 in 300-450 K for sample B and C can be found, whose activation energy were varied from 0.55 eV to 0.65 eV with the addition of Ba2+. It was put forward that the electrical properties of ZnO varistor ceramics may be associated with the conductance relaxation peak 3.

Effect of WO3 Doping on Microstructural and Electrical Properties of ZnO-Pr6O11 Based Varistor Materials

2013 ◽  
Vol 591 ◽  
pp. 54-60
Author(s):  
Xiu Li Fu ◽  
Yan Xu Zang ◽  
Zhi Jian Peng
Keyword(s):  
Grain Size ◽  
Electrical Properties ◽  
Grain Growth ◽  
Doping Level ◽  
Nonlinear Coefficient ◽  
Current Voltage ◽  
Average Grain Size ◽  
Current Voltage Characteristics ◽  
Voltage Performance

The effect of WO3doping on microstructural and electrical properties of ZnO-Pr6O11based varistor materials was investigated. The doped WO3plays a role of inhibitor in ZnO grain growth, resulting in decreased average grain size from 2.68 to 1.68 μm with increasing doping level of WO3from 0 to 0.5 mol%. When the doping level of WO3was lower than 0.05 mol%, the nonlinear current-voltage characteristics of the obtained varistors could be improved significantly with increasing amount of WO3doped. But when the doping level of WO3became higher, their nonlinear current-voltage performance would be dramatically deteriorated when more WO3was doped. The optimum nonlinear coefficient, varistor voltage, and leakage current of the samples were about 13.71, 710 V/mm and 13 μA/cm2, respectively, when the doping level of WO3was in the range from 0.03 to 0.05 mol%.

Effect of Nb2O5 Addition to the Electrical Properties of Fe2TiO5 Ceramics-Based NTC Thermistor

2015 ◽  
Vol 827 ◽  
pp. 262-265 ◽  
Author(s):  
Wiendartun ◽  
Risdiana ◽  
Fitrilawati ◽  
Rustam E. Siregar
Keyword(s):  
Activation Energy ◽  
Grain Size ◽  
Electrical Properties ◽  
Electrical Resistance ◽  
Single Phase ◽  
Mixed Powder ◽  
Ntc Thermistor ◽  
Constant Activation Energy

The aims of this research is to identify the effect of Nb2O5addition on the electrical properties of Fe2TiO5ceramics-based NTC thermistor.The concentration of Fe2O3and TiO2was proportional to Fe2TiO5, whereas the concentration value of Nb2O5were 0, 0.5 and 1.0 mole %, respectively. Within two hours, the mixed powder was pressed at 4 ton/cm2to form pellets and sintered at 1300 °C in air. It can perceived from the XRD data that the sintered ceramics had single phase of Fe2TiO5, pseudobrookite. From SEM data, it is found that addition of Nb2O5decreases the grain size. The addition of Nb2O5increases thermistor constant, activation energy and electrical resistance of Fe2TiO5ceramics. The values of thermistor constant of Nb2O5added-Fe2TiO5ceramics were relatively large, indicated that the ceramics were aplicable as the NTC thermistor.

Grain Boundary Relaxation in a Fe-Cr-Al Alloy

2011 ◽  
Vol 415-417 ◽  
pp. 2134-2137
Author(s):  
Zheng Cun Zhou ◽  
Q. Z. Wang ◽  
J. Du ◽  
H. Yang ◽  
Y.J. Yan
Keyword(s):  
Activation Energy ◽  
Grain Size ◽  
Internal Friction ◽  
Grain Boundary ◽  
Relaxation Peak ◽  
Al Alloy ◽  
Relaxation Strength ◽  
Exponential Factor ◽  
Friction Temperature ◽  
Boundary Relaxation

The features of grain boundary relaxation of a (wt.%)Fe-25Cr-5Al alloy have been investigated using a multifunction internal friction apparatus. The grain boundary relaxation peak appears at about 630oC on the internal friction-temperature curves for the alloy. The peak temperature shifts toward high temperature with increasing frequency. In terms of Arrihenius relation, the activation energy is calculated to be 4.07(±0.15)eV and the pre-exponential factor is 6.2×10-24±1s. Grain boundary relaxation strength remarkably decreases with increasing grain size. When grain size reaches 520μm, the grain boundary relaxation peak almost disappears.

Impedance spectroscopy of grain boundaries in nanophase ZnO

1995 ◽  
Vol 10 (9) ◽  
pp. 2295-2300 ◽  
Author(s):  
J. Lee ◽  
J.-H. Hwang ◽  
J.J. Mashek ◽  
T.O. Mason ◽  
A.E. Miller ◽  
...  
Keyword(s):  
Activation Energy ◽  
Grain Size ◽  
Electrical Properties ◽  
Oxygen Partial Pressure ◽  
Partial Pressure ◽  
Grain Boundaries ◽  
Defect Characterization ◽  
Impedance Spectra ◽  
Gas Condensation ◽  
Average Grain Size

Sintered compacts of nanophase ZnO (∼60 nm average grain size, presintered at 600 °C) were made from powders (∼13 nm) prepared by the gas-condensation technique. Impedance spectra were taken as a function of temperature over the range 450–600 °C and as a function of oxygen partial pressure over the range 10−3−1 atm (550 and 600 °C only). The activation energy was determined to be 55 kJ/mole (0.57 eV) and was independent of oxygen partial pressure. The oxygen partial pressure exponent was −1/6. Impedance spectra exhibited nonlinear I-V behavior, with a threshold of approximately 6 V. These results indicate that grain boundaries are governing the electrical properties of the compact. Ramifications for oxygen sensing and for grain boundary defect characterization are discussed.

Microstructure Stability of a Fine-Grained AZ31 Magnesium Alloy Processed by Constrained Groove Pressing During Isothermal Annealing

2017 ◽  
Vol 139 (8) ◽  
Author(s):  
Kai Soon Fong ◽  
Ming Jen Tan ◽  
Fern Lan Ng ◽  
Atsushi Danno ◽  
Beng Wah Chua
Keyword(s):  
Activation Energy ◽  
Grain Size ◽  
Magnesium Alloy ◽  
Grain Growth ◽  
Isothermal Annealing ◽  
Az31 Magnesium Alloy ◽  
Growth Equation ◽  
Alloy Plate ◽  
Microstructure Stability ◽  
Average Grain Size

In this study, an AZ31 magnesium alloy plate was processed by constrained groove pressing (CGP) under three deformation cycles at temperatures from 503 to 448 K. The process resulted in a homogeneous fine grain microstructure with an average grain size of 1.8 μm. The as-processed microstructure contained a high fraction of low-angle grain boundaries (LAGB) of subgrains and dislocation boundaries that remained in the structure due to incomplete dynamic recovery and recrystallization. The material's yield strength was found to have increased from 175 to 242 MPa and with a significant weakening of its initial basal texture. The microstructure stability of the CGP-processed material was further investigated by isothermal annealing at temperature from 473 to 623 K and for different time. Abnormal grain growth was observed at 623 K, and this was associated with an increased in nonbasal grains at the expense of basal grains. The effect of annealing temperature and time on the grain growth kinetics was interpreted by using the grain growth equation,  Dn+D0n=kt, and Arrhenius equation, k=k0 exp (−(Q/RT)). The activation energy (Q) was estimated to be 27.8 kJ/mol which was significantly lower than the activation energy for lattice self-diffusion (QL = 135 kJ/mol) and grain boundary diffusion (Qgb = 92 kJ/mol) in pure magnesium. The result shows that grain growth is rapid but average grain size still remained smaller than the as-received material, especially at the shorter annealing time.

High-κ Dielectrics for 4H-Silicon Carbide: Present Status and Future Perspective

2021 ◽  
Author(s):  
Amna Siddiqui ◽  
Rabia Yasmin Khosa ◽  
Muhammad Usman
Keyword(s):  
Silicon Carbide ◽  
High Temperature ◽  
Electrical Properties ◽  
Electric Field ◽  
High Power ◽  
Present Status ◽  
Wide Bandgap ◽  
Future Perspective ◽  
Breakdown Electric Field ◽  
High Breakdown Electric Field

Owing to its superior material and electrical properties such as wide bandgap and high breakdown electric field, 4H-silicon carbide (4H-SiC) has shown promise in high power, high temperature, and radiation...

Cold sintering ZnO based varistor ceramics with controlled grain growth to realize superior breakdown electric field

2021 ◽  
Vol 41 (1) ◽  
pp. 430-435
Author(s):  
Xuetong Zhao ◽  
Jie Liang ◽  
Jianjie Sun ◽  
Jing Guo ◽  
Sinan Dursun ◽  
...  
Keyword(s):  
Electric Field ◽  
Grain Growth ◽  
Breakdown Electric Field

Effect of Ho2O3 Doping on Performance of ZnO Varistor

2008 ◽  
Vol 368-372 ◽  
pp. 507-509
Author(s):  
Zhen Ya Lu ◽  
Yu Xiang Liu ◽  
Zhi Wu Chen ◽  
Jian Qing Wu
Keyword(s):  
Electrical Properties ◽  
Grain Growth ◽  
Nonlinear Coefficient ◽  
High Current ◽  
Zno Varistor ◽  
Current Area ◽  
Electric Filed ◽  
Nonlinear Performance ◽  
Effective Dopant ◽  
Surge Current

The effect of Ho2O3 doping on the electrical properties and microstructure of ZnO base varistor was investigated. It was found that Ho2O3 is an effective dopant for increasing the breakdown electric filed. The Ho2O3 doping can also improve the nonlinear performance both in low and high current area. But excessive doping of Ho2O3 will decrease the withstanding surge current. With 0.8mol% Ho2O3 doping, the varistor samples exhibit a breakdown voltage of about 400V/mm, a nonlinear coefficient of 80 and the withstanding surge current of 8/20μs, waveshape is higher than 5kA. Ho2O3 dopant can hinder ZnO grain growth and make the crystal grains more uniform.

Effect of Sintering Temperature on Electrical Properties of ZnO Varistor Ceramics

2012 ◽  
Vol 442 ◽  
pp. 31-34
Author(s):  
Chang Qi Xia ◽  
Qi Bin Liu ◽  
Mo He
Keyword(s):  
Grain Size ◽  
Electrical Properties ◽  
Leakage Current ◽  
High Voltage ◽  
Sintering Temperature ◽  
Voltage Gradient ◽  
Varistor Ceramic ◽  
Zno Varistor ◽  
Zno Varistors ◽  
Ceramic Sintering

To obtain ZnO varistors with high voltage gradient, ZnO varistors were fabricated by traditional ceramic sintering technique, the effect of different sintering temperature (1135～1155 °C) on electrical properties of ZnO varistors were investigated. The experimental results show that with increasement of sintering temperature, the grain size of ZnO varistor ceramic becomes bigger, the voltage gradient of varistor decreases and the density is improved. When the sintering temperature is at 1135 °C, the voltage gradient of varistor is up to 329V/mm, the leakage current is 8μA and the density is 96.4%. When the sintering temperature is at 1140 °C, the voltage gradient of varistor is 301V/mm, the leakage current is 4μA and the density is 96.6%. Compared the results at 1135 °C with 1140 °C , it is found that the comprehensive electrical properties of ZnO varistors reach maximum at 1140 °C.

Study of 4.5%mol Y2O3-Doped ZrO2 with Submicrometer Grain Size

2014 ◽  
Vol 805 ◽  
pp. 570-575
Author(s):  
Eleomar Lena ◽  
Adriana Scoton Antonio Chinelatto ◽  
Adilson Luiz Chinelatto
Keyword(s):  
Electron Microscopy ◽  
Activation Energy ◽  
Scanning Electron Microscopy ◽  
Grain Size ◽  
Electrical Properties ◽  
Pechini Method ◽  
Oxygen Flow ◽  
X Ray Diffraction ◽  
X Ray ◽  
Scanning Electron

The aim of this study was to obtain 4.5%mol Y2O3-doped ZrO2dense with submicrometer grain size and studying the effects of using oxygen flow during calcination in the electrical properties of bodies sintered. The powders were synthesized by the Pechini method. After synthesis, the resins were dried and the calcinations were performed in air and in oxygen flow at 600°C for 2 h. The powders were pressed with 1600 MPa and sintered by Two Step Sintering (TSS) at 1500°C / 5 min and 1200°C, 1300oC, 1400°C, remaining at these temperatures for 2 and 10 hours. The sinterized samples were characterized by X-ray diffraction, apparent density, scanning electron microscopy and impedance spectroscopy. The apparent densities were greater than 94% for all conditions of calcination and sintering. The value of the activation energy was 0.7eV for the grain and 0.9 eV for the grain boundaries.

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