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1、PiezoelectricityIn1880,JacquesandPierreCuriediscoveredanunusualcharacteristicofcertaincrystallineminerals:whensubjectedtoamechanicalforce,thecrystalsbecameelectricallypolarized.Tensionandcompressiongeneratedvoltagesofoppositepolarity,andinproportiontotheappliedforce.Subsequently,theconverseofthi
2、srelationshipwasconfirmed:ifoneofthesevoltage-generatingcrystalswasexposedtoanelectricfielditlengthenedorshortenedaccordingtothepolarityofthefield,andinproportiontothestrengthofthefield.Thesebehaviorswerelabeledthepiezoelectriceffectandtheinversepiezoelectriceffect,respectively,fromtheGreekwordp
3、iezein,meaningtopressorsqueeze.Althoughthemagnitudesofpiezoelectricvoltages,movements,orforcesaresmall,andoftenrequireamplification(atypicaldiscofpiezoelectricceramicwillincreaseordecreaseinthicknessbyonlyasmallfractionofamillimeter,forexample)piezoelectricmaterialshavebeenadaptedtoanimpressiver
4、angeofapplications.Thepiezoelectriceffectisusedinsensingapplications,suchasinforceordisplacementsensors.Theinversepiezoelectriceffectisusedinactuationapplications,suchasinmotorsanddevicesthatpreciselycontrolpositioning,andingeneratingsonicandultrasonicsignals.Inthe20thcenturymetaloxide-basedpiez
5、oelectricceramicsandotherman-madematerialsenableddesignerstoemploythepiezoelectriceffectandtheinversepiezoelectriceffectinmanynewapplications.Thesematerialsgenerallyarephysicallystrongandchemicallyinert,andtheyarerelativelyinexpensivetomanufacture.Thecomposition,shape,anddimensionsofapiezoelectr
6、icceramicelementcanbetailoredtomeettherequirementsofaspecificpurpose.Ceramicsmanufacturedfromformulationsofleadzirconate/leadtitanateexhibitgreatersensitivityandhigheroperatingtemperatures,relativetoceramicsofothercompositions,and"PZT"materialscurrentlyarethemostwidelyusedpiezoelectricceramics.H
7、owarepiezoelectricceramicsmade?Atraditionalpiezoelectricceramicisamassofperovskitecrystals,eachconsistingofasmall,tetravalentmetalion,usuallytitaniumorzirconium,inalatticeoflarger,divalentmetalions,usuallyleadorbarium,andO2-
