4 Microstructural Electrical Characteristics of ZnO Varistors 125
4.1 Introduction 125
4.2 MethodstoDetermineGrainBoundaryParameters 126
4.2.1 TheIndirectMethod 126
4.2.2 TheDirectMicrocontactMethods 126
4.3 StatisticalCharacteristicsofGrainBoundaryParameters 129
4.3.1 NonuniformityofBarrierVoltages 129
4.3.2 DistributionofBarrierVoltage 131
4.3.3 DistributionofNonlinearCoe?cient 132
Contents
4.3.4 DistributionofLeakageCurrentThroughGrainBoundary 133
4.3.5 DiscussiononMicrocontactMeasurement 133
4.4 Classi?cationofGrainBoundaries 134
4.5 OtherTechniquestoDetectMicrostructurallyElectricalPropertiesofZnOVaristors 137
4.5.1 ScanningProbeMicroscopy-BasedTechniques 137
4.5.2 GalvanicDeterminationofConductiveAreasonaVaristor Surface 139
4.5.3 LineScanDeterminationofDi?erencesinBreakdownVoltageWithinaVaristor 141
4.5.4 CurrentImagesinSEM 141
4.6 TestonFabricatedIndividualGrainBoundary 142
4.6.1 ThinFilmApproach 143
4.6.2 SurfaceIn-Di?usionApproach 143
4.6.3 BicrystalApproach 143 References 145
5 Simulation on Varistor Ceramics 149
5.1 Introduction 149
5.2 GrainBoundaryModel 151
5.2.1 I–V CharacteristicModelofGrainBoundary 151
5.2.2 GBModelConsideringConductionMechanism 154
5.3 SimulationModelof I–V Characteristics 159
5.3.1 Simple2DSimulationModel 159
5.3.2 2DSimulationModelsBasedontheVoronoiNetwork 161
5.3.3 ConsiderationonPoresandSpinels 164
5.3.4 AlgorithmtoSolveEquivalentCircuit 165
5.3.5 ModelVeri?cation 169
5.4 SimulationModelforThermalCharacteristics 170
5.4.1 ThermalConductionAnalysis 171
5.4.2 Pulse-InducedFractureAnalysis 173
5.5 SimulationsonDi?erentPhenomena 174
5.5.1 SimulationonMicrostructuralNonuniformity 174
5.5.2 SimulationonCurrentLocalizationPhenomenon 175
5.5.3 In?uenceofMicrostructuralParametersonBulkCharacteristics 179
5.5.3.1 In?uenceofZnOGrainParameters 180
5.5.3.2 In?uenceofGrainBoundaryParameters 183
5.5.4 In?uentialFactorsonResidualVoltageRatio 186 References 188
6 Breakdown Mechanism and Energy Absorption Capability of ZnO Varistor 193
6.1 Introduction 193
6.2 ImpulseFailureModesofZnOVaristors 194
6.3 MechanismsofPunctureandFractureFailures 197
6.3.1 MechanismsofPunctureFailure 197
6.3.2 MechanismofFractureFailure 201
6.4 SimulationofPunctureandFractureFailures 204
6.4.1 PunctureDestructionSimulation 204
6.4.1.1 PunctureSimulationinMicrostructure 206
6.4.2 CrackingFailureSimulationinMicrostructure 208
6.5 Thermal Runaway 209
6.5.1 PowerLossofZnOVaristor 210
6.5.2 ThermalRunawayMechanism 210
6.5.3 TeststoEnsuretheThermalStabilityCharacteristics 213
6.6 In?uencesofDi?erentFactorsonFailuresofZnOVaristors 213
6.6.1 In?uenceofMicrostructuralNonuniformity 213
6.6.2 In?uenceofElectricalNonuniformityinMicrostructure 216
6.6.3 SimulationAnalysisonBreakdownModes 217
6.7 In?uentialFactorsonEnergyAbsorptionCapability 218
6.7.1 In?uenceoftheAppliedCurrent 218
6.7.2 In?uenceofVaristorCross-sectionalArea 221
6.7.3 SimulationAnalysisonSurgeEnergyAbsorptionCapability 221
6.8 DiscussionsonEnergyAbsorptionCapability 225
6.8.1 EnergyAbsorptionCapabilityDeterminedbyFractureFailure 225
6.8.2 EnergyAbsorptionCapabilityDeterminedbyPunctureFailure 226
6.8.3 DiscussiononNonuniformityofEnergyAbsorptionCapability 228
6.8.4 AdditivesE?ectonEnergyAbsorptionCapability 229
6.8.5 OtherMeasurestoImproveEnergyAbsorptionCapability 230 References 230
7 Electrical Degradation of ZnO Varistors 235
7.1 Introduction 235
7.2 DegradationPhenomenaofZnOVaristors 237
7.2.1 DegradationPhenomenaoftheVaristorBulk 237
7.2.2 DegradationofGrainBoundary 242
7.2.3 PulseDegradationCharacteristics 245
7.2.4 TopographicInformationforDegradationAnalysis 247
7.3 MigrationIonsfortheDegradationofZnOVaristors 249
7.3.1 GrainBoundaryDefectModel 249
7.3.2 ExperimentalProofofIonMigration 251
7.3.3 Identi?cationofDominantMobileIons 252
7.3.4 Three-DimensionalExtension 256
7.4 DegradationMechanismofZnOVaristors 257
7.4.1 DCDegradationMechanism 258
7.4.2 ACDegradationMechanism 258
7.4.3 NonuniformDegradationMechanism 260
7.4.4 PulseDegradationofZnOVaristors 262
7.4.4.1 DegradationMechanismUnderImpulseCurrent 263
7.4.4.2 SuperimposingDegradation 264
7.5 RoleofInteriorMicrocracksonDegradation 266
7.6 AntidegradationMeasures 267
7.6.1 Speci?cPreparationProcedures 268
7.6.2 OptimizationofFormula 269
Contents
7.6.2.1 DopantE?ectsonImprovingACDegradationCharacteristics 270
7.6.2.2 DopantE?ectsonImprovingImpulseDegradationProperty 271 References 272

 2/4   首页 上一页 1 2 3 4 下一页 尾页

教材 研究生/本科/专科教材 工学

在线阅读