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<p>Preface xiii</p> <p>Acknowledgments xv</p> <p><b>1 Introduction of Varistor Ceramics 1</b></p> <p>1.1 ZnO Varistors 1</p> <p>1.2 Fabrication of ZnO Varistors 3</p> <p>1.2.1 Preparation of Raw Materials 4</p> <p>1.2.2 Sintering of ZnO Varistors 5</p> <p>1.3 Microstructure 6</p> <p>1.4 Typical Parameters of ZnO Varistors 7</p> <p>1.5 History of ZnO Varistors 9</p> <p>1.6 Applications of ZnO Varistors 12</p> <p>1.7 Alternative Varistor Ceramics 17</p> <p>1.8 Ceramic–Polymer Composite Varistors 18</p> <p>References 22</p> <p><b>2 Conduction Mechanisms of ZnO Varistors 31</b></p> <p>2.1 Introduction 31</p> <p>2.2 Basic Concepts in Solid-State Physics 33</p> <p>2.2.1 Atomic Energy Level and Energy Band of Crystal 33</p> <p>2.2.2 Metal, Semiconductor, and Insulator 35</p> <p>2.2.3 Characteristics of Fermi–Dirac Function 37</p> <p>2.2.4 Impurity and Defect Energy Level 38</p> <p>2.3 Energy Band Structure of a ZnO Varistor 39</p> <p>2.3.1 Energy Band Structure of a ZnO Grain 39</p> <p>2.3.2 DSB of a ZnO Varistor 40</p> <p>2.3.3 Microscopic Origin of DSB 41</p> <p>2.3.4 Asymmetric <i>I–V</i> Characteristics of the DSB 43</p> <p>2.4 Conduction Mechanism of a ZnO Varistor 45</p> <p>2.4.1 Conduction Model Based on Thermionic Emission Process 46</p> <p>2.4.2 Minority Carrier Generation Process 49</p> <p>2.4.3 The Bypass Effect Model 51</p> <p>2.5 Dielectric Characteristics of a ZnO Varistor 51</p> <p>2.5.1 Explanation to Dielectric Properties of a ZnO Varistor 52</p> <p>2.5.2 Effect of Interfacial Charge Relaxation on Conducting Behavior of ZnO Varistors Under Time-Varying Electric Fields 54</p> <p>2.5.3 Determination of Barrier Height and Related Parameters 58</p> <p>2.5.4 Determination of Deep Donor Level in the ZnO Varistor 59</p> <p>2.5.5 Determination of Grain and Grain Boundary Conductivity 60</p> <p>References 62</p> <p><b>3 Tuning Electrical Characteristics of ZnO Varistors 67</b></p> <p>3.1 Introduction 67</p> <p>3.2 Liquid-Phase Fabrication 68</p> <p>3.2.1 Microstructure of ZnO Varistor 68</p> <p>3.2.2 Polymorph of Bismuth Oxide 71</p> <p>3.2.3 Influence of Bi₂O₃ Concentration 72</p> <p>3.2.4 Volatilization of Bismuth Oxide 72</p> <p>3.3 Preparing and Sintering Techniques 74</p> <p>3.3.1 Fabrication 74</p> <p>3.3.2 Fabrication Stages 75</p> <p>3.3.3 Effect of Pores 76</p> <p>3.4 Role of Oxygen at theGrain Boundary 78</p> <p>3.5 Dopant Effects 79</p> <p>3.5.1 Effects of Additives 79</p> <p>3.5.2 Donor Dopants 82</p> <p>3.5.3 Acceptor Dopants 86</p> <p>3.5.4 Amphoteric Dopants 87</p> <p>3.5.4.1 Monovalent Dopants 88</p> <p>3.5.4.2 Trivalent Dopants 89</p> <p>3.5.5 Effects of Rare Earth Oxides 92</p> <p>3.5.6 Dopants for Improving the Stability 93</p> <p>3.5.7 Evidence for Hydrogen as a Shallow Donor 95</p> <p>3.6 Role of Inversion Boundaries 95</p> <p>3.7 High Voltage Gradient ZnO Varistor 98</p> <p>3.8 Low Residual Voltage ZnO Varistor 101</p> <p>3.8.1 Residual Voltage Ratio 101</p> <p>3.8.2 Low Residual Voltage ZnO Varistors by Doping Al 103</p> <p>3.8.3 Low Residual Voltage ZnO Varistors by Doping Ga 106</p> <p>3.8.4 Low Residual Voltage ZnO Varistors with High Voltage Gradient 108</p> <p>References 110</p> <p><b>4 Microstructural Electrical Characteristics of ZnO Varistors 125</b></p> <p>4.1 Introduction 125</p> <p>4.2 Methods to Determine Grain Boundary Parameters 126</p> <p>4.2.1 The Indirect Method 126</p> <p>4.2.2 The Direct Microcontact Methods 126</p> <p>4.3 Statistical Characteristics of Grain Boundary Parameters 129</p> <p>4.3.1 Nonuniformity of Barrier Voltages 129</p> <p>4.3.2 Distribution of Barrier Voltage 131</p> <p>4.3.3 Distribution of Nonlinear Coefficient 132</p> <p>4.3.4 Distribution of Leakage Current Through Grain Boundary 133</p> <p>4.3.5 Discussion on Microcontact Measurement 133</p> <p>4.4 Classification of Grain Boundaries 134</p> <p>4.5 Other Techniques to Detect Microstructurally Electrical Properties of ZnO Varistors 137</p> <p>4.5.1 Scanning Probe Microscopy-Based Techniques 137</p> <p>4.5.2 Galvanic Determination of Conductive Areas on a Varistor Surface 139</p> <p>4.5.3 Line Scan Determination of Differences in Breakdown Voltage Within a Varistor 141</p> <p>4.5.4 Current Images in SEM 141</p> <p>4.6 Test on Fabricated Individual Grain Boundary 142</p> <p>4.6.1 Thin Film Approach 143</p> <p>4.6.2 Surface In-Diffusion Approach 143</p> <p>4.6.3 Bicrystal Approach 143</p> <p>References 145</p> <p><b>5 Simulation on Varistor Ceramics 149</b></p> <p>5.1 Introduction 149</p> <p>5.2 Grain Boundary Model 151</p> <p>5.2.1 <i>I–V</i> Characteristic Model of Grain Boundary 151</p> <p>5.2.2 GB Model Considering Conduction Mechanism 154</p> <p>5.3 Simulation Model of <i>I–V</i> Characteristics 159</p> <p>5.3.1 Simple 2D Simulation Model 159</p> <p>5.3.2 2D Simulation Models Based on the Voronoi Network 161</p> <p>5.3.3 Consideration on Pores and Spinels 164</p> <p>5.3.4 Algorithm to Solve Equivalent Circuit 165</p> <p>5.3.5 Model Verification 169</p> <p>5.4 Simulation Model for Thermal Characteristics 170</p> <p>5.4.1 Thermal Conduction Analysis 171</p> <p>5.4.2 Pulse-Induced Fracture Analysis 173</p> <p>5.5 Simulations on Different Phenomena 174</p> <p>5.5.1 Simulation on Microstructural Nonuniformity 174</p> <p>5.5.2 Simulation on Current Localization Phenomenon 175</p> <p>5.5.3 Influence of Microstructural Parameters on Bulk Characteristics 179</p> <p>5.5.3.1 Influence of ZnO Grain Parameters 180</p> <p>5.5.3.2 Influence of Grain Boundary Parameters 183</p> <p>5.5.4 Influential Factors on Residual Voltage Ratio 186</p> <p>References 188</p> <p><b>6 Breakdown Mechanism and Energy Absorption Capability of ZnO Varistor 193</b></p> <p>6.1 Introduction 193</p> <p>6.2 Impulse Failure Modes of ZnO Varistors 194</p> <p>6.3 Mechanisms of Puncture and Fracture Failures 197</p> <p>6.3.1 Mechanisms of Puncture Failure 197</p> <p>6.3.2 Mechanism of Fracture Failure 201</p> <p>6.4 Simulation of Puncture and Fracture Failures 204</p> <p>6.4.1 Puncture Destruction Simulation 204</p> <p>6.4.1.1 Puncture Simulation in Microstructure 206</p> <p>6.4.2 Cracking Failure Simulation in Microstructure 208</p> <p>6.5 Thermal Runaway 209</p> <p>6.5.1 Power Loss of ZnO Varistor 210</p> <p>6.5.2 Thermal Runaway Mechanism 210</p> <p>6.5.3 Tests to Ensure the Thermal Stability Characteristics 213</p> <p>6.6 Influences of Different Factors on Failures of ZnO Varistors 213</p> <p>6.6.1 Influence of Microstructural Nonuniformity 213</p> <p>6.6.2 Influence of Electrical Nonuniformity in Microstructure 216</p> <p>6.6.3 Simulation Analysis on Breakdown Modes 217</p> <p>6.7 Influential Factors on Energy Absorption Capability 218</p> <p>6.7.1 Influence of the Applied Current 218</p> <p>6.7.2 Influence of Varistor Cross-sectional Area 221</p> <p>6.7.3 Simulation Analysis on Surge Energy Absorption Capability 221</p> <p>6.8 Discussions on Energy Absorption Capability 225</p> <p>6.8.1 Energy Absorption Capability Determined by Fracture Failure 225</p> <p>6.8.2 Energy Absorption Capability Determined by Puncture Failure 226</p> <p>6.8.3 Discussion on Nonuniformity of Energy Absorption Capability 228</p> <p>6.8.4 Additives Effect on Energy Absorption Capability 229</p> <p>6.8.5 Other Measures to Improve Energy Absorption Capability 230</p> <p>References 230</p> <p><b>7 Electrical Degradation of ZnO Varistors 235</b></p> <p>7.1 Introduction 235</p> <p>7.2 Degradation Phenomena of ZnO Varistors 237</p> <p>7.2.1 Degradation Phenomena of the Varistor Bulk 237</p> <p>7.2.2 Degradation of Grain Boundary 242</p> <p>7.2.3 Pulse Degradation Characteristics 245</p> <p>7.2.4 Topographic Information for Degradation Analysis 247</p> <p>7.3 Migration Ions for the Degradation of ZnO Varistors 249</p> <p>7.3.1 Grain Boundary Defect Model 249</p> <p>7.3.2 Experimental Proof of Ion Migration 251</p> <p>7.3.3 Identification of Dominant Mobile Ions 252</p> <p>7.3.4 Three-Dimensional Extension 256</p> <p>7.4 Degradation Mechanism of ZnO Varistors 257</p> <p>7.4.1 DC Degradation Mechanism 258</p> <p>7.4.2 AC Degradation Mechanism 258</p> <p>7.4.3 Nonuniform Degradation Mechanism 260</p> <p>7.4.4 Pulse Degradation of ZnO Varistors 262</p> <p>7.4.4.1 Degradation Mechanism Under Impulse Current 263</p> <p>7.4.4.2 Superimposing Degradation 264</p> <p>7.5 Role of Interior Microcracks on Degradation 266</p> <p>7.6 Antidegradation Measures 267</p> <p>7.6.1 Specific Preparation Procedures 268</p> <p>7.6.2 Optimization of Formula 269</p> <p>7.6.2.1 Dopant Effects on Improving AC Degradation Characteristics 270</p> <p>7.6.2.2 Dopant Effects on Improving Impulse Degradation Property 271</p> <p>References 272</p> <p><b>8 Praseodymium/Vanadium/Barium-Based ZnO Varistor Systems 281</b></p> <p>8.1 Praseodymium System 281</p> <p>8.1.1 Doping Effects 281</p> <p>8.1.2 Effect of Sintering Processes 285</p> <p>8.1.3 High-Voltage Applications 288</p> <p>8.1.4 Low-Voltage Applications 288</p> <p>8.2 Vanadium System 289</p> <p>8.2.1 Doping Effects 290</p> <p>8.2.2 Electrical Characteristics 291</p> <p>8.2.3 Microstructural Characteristics 292</p> <p>8.2.4 Effects of Vanadium Oxide on Grain Growth 294</p> <p>8.3 Barium System 295</p> <p>8.3.1 Preparation and Electrical Characteristics 295</p> <p>8.3.2 Microstructural Characteristics 296</p> <p>8.3.3 Improving Stability Against Moisture 298</p> <p>8.4 ZnO–Glass Varistor 298</p> <p>References 300</p> <p><b>9 Fabrications of Low-Voltage ZnO Varistors 307</b></p> <p>9.1 Introduction 307</p> <p>9.2 Exaggerating Grain Growth by Seed Grains 308</p> <p>9.3 Synthesis of Nanocrystalline ZnO Varistor Powders 309</p> <p>9.3.1 Gas-Phase Processing Methods 309</p> <p>9.3.2 Combustion Synthesis 311</p> <p>9.3.3 Sol–Gel Methods 311</p> <p>9.3.4 Solution-Coating Method 315</p> <p>9.4 Nanofillers in ZnO Varistor Ceramics 320</p> <p>9.5 Sintering Techniques to Control Grain Growth 321</p> <p>9.5.1 Step-sintering Approach 321</p> <p>9.5.2 Microwave Sintering Method 322</p> <p>9.5.3 Spark Plasma Sintering Technique 324</p> <p>References 327</p> <p><b>10 Titanium-Based Dual-function Varistor Ceramics 335</b></p> <p>10.1 SrTiO3 Varistors 335</p> <p>10.1.1 Introduction 335</p> <p>10.1.2 Microstructure of SrTiO₃ Varistors 336</p> <p>10.1.3 Preparation of SrTiO₃ Varistors 336</p> <p>10.1.4 Performance of SrTiO₃ 338</p> <p>10.1.5 Conduction Mechanism of SrTiO₃ 339</p> <p>10.2 TiO₂-Based Varistors 341</p> <p>10.2.1 Introduction 341</p> <p>10.2.2 Preparation of TiO₂-Based Varistors 342</p> <p>10.2.3 Mechanism of TiO₂ Capacitor–Varistor Ceramics 342</p> <p>10.2.4 Doping of TiO₂-Based Varistors 343</p> <p>10.2.4.1 Acceptor-Doped TiO₂-Based Varistors 343</p> <p>10.2.4.2 Donor-Doped TiO₂-Based Varistors 344</p> <p>10.2.4.3 Codoping Effects of Acceptor and Donor Dopants 345</p> <p>10.2.4.4 Sintering Additives in TiO₂-Based Varistors 347</p> <p>10.2.5 Development of TiO₂-Based Varistors 348</p> <p>10.3 CaCu₃ Ti₄O₁₂ Ceramics 348</p> <p>10.3.1 Introduction 348</p> <p>10.3.2 Structure of CCTO 349</p> <p>10.3.2.1 Crystal Structure 349</p> <p>10.3.2.2 Phase and Microstructure 350</p> <p>10.3.3 Performances of CCTO Ceramics 352</p> <p>10.3.3.1 Nonohmic Current–Voltage Characteristic 352</p> <p>10.3.3.2 Colossal Permittivity 354</p> <p>10.3.3.3 Dielectric Loss 357</p> <p>10.3.4 Mechanism 358</p> <p>10.3.4.1 IBLC Model 358</p> <p>10.3.4.2 Conducting Mechanism 362</p> <p>10.3.4.3 Polarization Mechanism of Grains 364</p> <p>10.3.4.4 A Polaronic Stacking Fault Defect Model 365</p> <p>10.3.5 Role of Dopants 366</p> <p>10.3.5.1 Role of Doping CuO 366</p> <p>10.3.5.2 Doping Mechanisms to Tune CCTO Performances 368</p> <p>10.4 BaTiO3 Varistors of PTCR Effect 375</p> <p>10.4.1 Introduction 375</p> <p>10.4.2 Doping Effects 377</p> <p>10.4.3 Preparation of BaTiO₃ Ceramics 379</p> <p>10.4.4 PTCR Effect of BaTiO₃ Ceramics 381</p> <p>10.4.5 Varistor Characteristics of BaTiO₃ Ceramics 384</p> <p>References 386</p> <p><b>11 Tin Oxide Varistor Ceramics of High Thermal Conductivity 407</b></p> <p>11.1 Preparation of SnO₂-Based Varistors 407</p> <p>11.2 Electrical Performances of SnO₂-Based Varistors 410</p> <p>11.3 Mechanism of SnO₂-Based Varistors 414</p> <p>11.3.1 Formation of Grain Boundary Potential Barrier 414</p> <p>11.3.2 Atomic Defect Model 415</p> <p>11.3.3 Admittance Spectroscopy Analysis 417</p> <p>11.3.4 Capacitance–Voltage Analysis 420</p> <p>11.3.5 Effect of Thermal Treatment 421</p> <p>11.4 Role of Dopants in Tuning SnO₂-Based Varistors 423</p> <p>11.4.1 Dopants for Densifying SnO₂-Based Varistors 423</p> <p>11.4.2 Acceptor Doping 424</p> <p>11.4.3 Donor Doping 427</p> <p>11.5 Thermal Performances 429</p> <p>11.6 Degradation Behaviors 431</p> <p>11.7 Development of SnO₂-Based Varistors 432</p> <p>References 434</p> <p><b>12 WO₃-Based Varistor Ceramics of Low Breakdown Voltage 441</b></p> <p>12.1 Introduction 441</p> <p>12.2 Tungsten Oxide 442</p> <p>12.3 Preparation of WO₃-Based Varistors 444</p> <p>12.4 Electrical Performances 446</p> <p>12.5 Improving the Electrical Stability 448</p> <p>12.6 Mechanism Model of WO₃-Based Varistors 449</p> <p>12.7 Doping Effects 452</p> <p>12.7.1 The Addition of Rare Earth Oxides 452</p> <p>12.7.2 The Addition of CuO 453</p> <p>12.7.3 The Addition of Al₂O₃ 454</p> <p>12.7.4 The Addition of TiO₂ 455</p> <p>12.7.5 The Addition of Other Additives 455</p> <p>References 456</p> <p>Index 461</p>

<p><b><i>Jinliang He</i></b><i> is the Chang Jiang Scholars Distinguished Professor of China's Ministry of Education with the Department of Electrical Engineering of the Tsinghua University, Beijing, China. Currently Jinliang He is the Chair of the High Voltage and Insulation Technology Research Institute at the Tsinghua University. His research interests cover dielectric materials and electroceramics, transient electromagnetics and electromagnetic compatibility in power systems and electronic systems as well as advanced power transmission technology. During 2014 to 2018, he had been assigned by China Science and Technology Ministry as the Chief Scientist in charge of a 5-year China National Fundamental Research Project. He has co-authored more than 310 papers in peer-reviewed international journals and transactions and more than 200 papers in refereed Chinese-language journals. He has published 5 academic monographs, and 2 textbooks. He was elected a Fellow of IEEE in 2007 and a Fellow of IET in 2011 for his contribution to lightning protection and grounding technology in power transmission system , and a Fellow of HPEM in 2018 for contributions to the understanding and protection of lightning discharges and electromagnetic effects. Jinliang He received the "Technical Achievement Award" and "Certificate of Acknowledgement" of the IEEE-EMC Society, respectively in 2010 and 2011, the Hoshino Prize (6th session) by the Institute of Electrical Installation Engineers of Japan in 2013, the Distinguished Contribution Award from Asia-Pacific International Conference on Lightning in 2015, the Rudolf Heinrich Golde Award from International Conference on Lightning Protection in 2016, and 2018 IEEE Herman Halperin Electric Transmission and Distribution Award for contributions to lightning protection of power transmission systems, including advancing analytic methods and innovation in line surge arresters. He is the recipients of two Chinese national awards for scientific and technological progress, a Chinese national invention award, and 20 provincial and ministerial science and technology awards.</i>

<p>Completely up-to-date, this is the first comprehensive monograph on metal oxide varistors with a focus on microstructure, conduction mechanisms, device failures, ageing, additives impacts and future varistor systems. <p>As such, it covers the fundamentals and applications of metal oxide varistors, including their macro-characteristics, microstructural properties and the device-internal physical and electrical mechanisms. The author reflects on the achievements made in varistor research and proposes new approaches to analyze and predict the macro-characteristics, employing such methods as micro-contact measurements and numerical simulations. In addition, he looks at future directions for varistor research, such as ZnO varistors with a high voltage gradient and low residual voltage and further varistor types based on TiO₂, SnO₂ and WO_3.

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