Technicalprinciple
Zeroresistance
Whenthesuperconductingmaterialisinthesuperconductingstate,theresistanceiszero,whichcantransmitelectricenergywithoutloss.Ifamagneticfieldisusedtoinduceaninducedcurrentinthesuperconductingloop,thiscurrentcanbemaintainedwithoutattenuation.This"continuouscurrent"hasbeenobservedmanytimesinexperiments.
Diamagnetism
Whenthesuperconductingmaterialisinthesuperconductingstate,aslongastheappliedmagneticfielddoesnotexceedacertainvalue,thelinesofmagneticforcecannotpenetrate,andthemagneticfieldinthesuperconductingmaterialisalwayszero.
Criticaltemperature
Thetemperatureatwhichthesuperconductingmaterialchangesfromthenormalstatetothesuperconductingstate(orviceversa)whentheexternalmagneticfieldiszero,expressedasTc.TheTcvaluevarieswithdifferentmaterials.ThelowestTcmeasuredforsuperconductingmaterialsistungsten,whichis0.012K.By1987,themaximumvalueofthecriticaltemperaturehadincreasedtoabout100K.
Criticalmagneticfield
Thestrengthofthemagneticfieldrequiredtodestroythesuperconductingstateofthesuperconductingmaterialandtransformittothenormalstate,expressedinHc.TherelationshipbetweenHcandtemperatureTisHc=H0[1-(T/Tc)2],whereH0isthecriticalmagneticfieldat0K.
Criticalcurrentandcriticalcurrentdensity
ThecriticaltemperatureTcofasuperconductorisrelatedtoitsisotopemassM.ThelargertheM,thelowertheTc,whichiscalledtheisotopeeffect.Forexample,amercuryisotopewithanatomicweightof199.55hasaTcof4.18Kelvin,whileamercuryisotopewithanatomicweightof203.4hasaTcof4.146Kelvin.
Whenthecurrentthroughthesuperconductingmaterialreachesacertainvalue,thesuperconductingstatewillbedestroyedandtransformedintothenormalstate,whichisexpressedbyIc.Icgenerallydecreaseswiththeincreaseoftemperatureandexternalmagneticfield.TheIccarriedbytheunitcross-sectionalareaiscalledthecriticalcurrentdensity,whichisrepresentedbyJc.
Theseparametersofsuperconductingmaterialslimittheconditionsfortheapplicationofmaterials,sofindingnewsuperconductingmaterialswithhighparametershasbecomeanimportantresearchtopic.TakeTcasanexample.Fromthediscoveryofsuperconductivity(Hg,Tc=4.2K)bytheDutchphysicistH.Kaimerlin-Onnesin1911,itwasnotuntil1986thatthehighestTcfoundreached23.2K.(Nb3Ge,1973).In1986,SwissphysicistK.A.MillerandFederalGermanphysicistJ.G.Bednorzdiscoveredthesuperconductivityofoxideceramicmaterials,therebyincreasingtheTcto35K.Afteronlyoneyear,theTcofthenewmaterialhasincreasedtoabout100K.Thisbreakthroughopenedupbroadprospectsfortheapplicationofsuperconductingmaterials,andMillerandBednorzalsowonthe1987NobelPrizeinPhysics.
Mainproducts
Thereare28elementswithsuperconductivityundernormalpressure.Amongthem,niobium(Nb)hasthehighestTc,whichis9.26K.Themainpracticalapplicationsinelectricalengineeringareniobiumandlead(Pb,Tc=7.201K),whichhavebeenusedinthemanufactureofsuperconductingACpowercables,high-Qresonators,etc.②
Alloymaterials
Theadditionofsuperconductingelementstosomeotherelementsasalloycomponentscanimprovetheoverallperformanceofsuperconductingmaterials.Forexample,thefirstappliedniobium-zirconiumalloy(Nb-75Zr)hasaTcof10.8KandaHcof8.7tex.Niobium-titaniumalloysweresubsequentlydeveloped.AlthoughTcisslightlylower,Hcismuchhigherandcancarrymorecurrentinagivenmagneticfield.ItsperformanceisNb-33Ti,Tc=9.3K,Hc=11.0tex;Nb-60Ti,Tc=9.3K,Hc=12tex(4.2K).Theperformanceofternaryalloyisfurtherimproved.TheperformanceofNb-60Ti-4TaisTc=9.9K,Hc=12.4tex(4.2K);theperformanceofNb-70Ti-5TaisTc=9.8K,Hc=12.8tex.
Compound
Superconductingelementscombinedwithotherelementsoftenhavegoodsuperconductingproperties.Forexample,Nb3Sn,whichhasbeenwidelyused,hasTc=18.1KandHc=24.5tex.OtherimportantsuperconductingcompoundsincludeV3Ga,Tc=16.8K,Hc=24tex;Nb3Al,Tc=18.8K,Hc=30tex.
Forexample:superconductingceramics
Intheearly1980s,MillerandBednorzbegantonoticethatcertainoxideceramicmaterialsmayhaveSuperconductivity.TheirteamtestedsomematerialsandfoundaTc=35Ksuperconductivityinlanthanum-barium-copper-oxidein1986.In1987,scientistsfromChina,theUnitedStates,Japanandothercountriesdiscoveredthatinbarium-yttrium-copperoxide,Tchassuperconductivityintheliquidnitrogentemperaturezone,makingsuperconductingceramicsasuperconductingmaterialwithgreatdevelopmentprospects.
Scientificresearch
1.Magneticfluxdynamicsandsuperconductingmechanismofunconventionalsuperconductors
MainlystudythemagneticfieldinthemixedstateregionThemechanismofthewiremovement,thenatureoftheirreversiblewire,thecauseanditsrelationshipwiththemagneticfieldandtemperature,thedependenceofthecriticalcurrentdensityonthemagneticfieldandtemperature,andtheanisotropy.Theresearchofsuperconductivitymechanismfocusesonthestudyofmagnetoresistance,Halleffect,fluctuationeffect,FermisurfacepropertiesandThigh-temperaturesuperconductivityunderastrongmagneticfieldinthenormalstate,suchasorganicsuperconductors,andhasbroadapplicationprospectsinstrongelectricity.Low-temperaturesuperconductors,etc.,willalsocarryoutresearchontheirpropertiesunderstrongmagneticfields.
2.Researchonthepropertiesoflow-dimensionalcondensedmatterunderastrongmagneticfield
Thelow-dimensionalitymakesthelow-dimensionalsystemexhibitcharacteristicsthatthethree-dimensionalsystemdoesnothave.Low-dimensionalinstabilityresultsinavarietyoforderedphases.Astrongmagneticfieldisaneffectivemeanstorevealthecharacteristicsoflow-dimensionalcondensedmatter.Themainresearchcontentsinclude:thestructureandsourceoforganicferromagnetism;themechanismandmagnetismoforganic(includingfullerene)superconductors;thespecificpropertiesofthenonlinearelementexcitationinthetwo-dimensionalelectrongasunderastrongmagneticfield;thephasetransitionoflow-dimensionalmagneticmaterialsMagneticinteraction;transportandcarriercharacteristicsoforganicconductorsinamagneticfield;bandstructureandFermisurfacecharacteristicsinamagneticfield,etc.
3.Opticalandelectricalpropertiesofsemiconductormaterialsunderstrongmagneticfields
Strongmagneticfieldtechnologyisbecomingmoreandmoreimportanttothedevelopmentofsemiconductorscience,becauseAmongvariousphysicalfactors,theexternalmagneticfieldistheonlyphysicalfactorthatchangesthespatialsymmetryofmomentumwhilekeepingthecrystalstructureunchanged.Therefore,themagneticfieldisparticularlyimportantinthestudyofsemiconductorenergybandstructureandthestudyofelementalexcitationandinteraction.effect.Byconductingexperimentalresearchontheopticalandelectricalpropertiesofsemiconductormaterialsunderstrongmagneticfields,itispossibletofurtherunderstandandgrasptheopticalandelectricalphysicalpropertiesofsemiconductors,soastomakebasicexplorationsforthemanufactureofsemiconductordeviceswithvariousfunctionsandthedevelopmentofhightechnology.
4.Physicalproblemsintheultra-finescaleunderstrongmagneticfields
Manynewphenomenaandstrangepropertiesthatconventionalmaterialsdonothaveappearintheultra-fine-scalesystemThisiscloselyrelatedtothemicrostructureofthistypeofmaterial,especiallytheelectronicstructure.Thestrongmagneticfieldprovidesapowerfulmeansforstudyingtheelectronicstateandtransportcharacteristicsofultra-fine-scalesystems.Itcannotonlyfurtherrevealthestrangephenomenathatthesematerialsaredifficulttoappearundernormalconditions,butalsoprovidearicherunderstandingoftheirphysicalpropertiesatadeeperlevel.Scientificinformation.Mainlyresearchtheelectrontransport,electroniclocalizationandcorrelationcharacteristicsofultra-fine-scalemetalsandsemiconductorsunderstrongmagneticfields;quantumsizeeffects,quantumconfinementeffects,small-sizeeffects,surfaceandinterfaceeffects;andultra-fine-scaleoxidesandcarbonizationTheopticalpropertiesandenergygapfinestructureofcompoundsandnitrides.
5.Strongmagneticfieldchemistry
Theeffectofstrongmagneticfieldontheelectronspinandnuclearspinofchemicalreactionscanleadtotherelaxationofthecorrespondingchemicalbonds,resultinginnewThefavorableconditionsforbondformationinducephysicalandchemicalchangesthatcannotbeachievedundernormalconditions,andobtainnewmaterialsandnewcompoundsthatcouldnotbepreparedbefore.Strongmagneticfieldchemistryisanewfieldwithstrongapplicationfoundation,withaseriesoftheoreticaltopicsandbroadapplicationprospects.contribute.Aconceptuallyimportantdevelopmentinthe1980swasthediscoveryofthequantumHalleffectandthefractionalquantumHalleffect.Thiswasdiscoveredwhenstudyingthetransportphenomenonoftwo-dimensionalelectrongasunderastrongmagneticfield(wontheNobelPrizein1985).ThediscoveryofthequantumHalleffectandthefractionalquantumHalleffectarousedtheenthusiasmofphysiciststoexploreitsorigins,andinestablishinganaturalbenchmarkforresistance,thebasicphysicalconstantse,handfinestructureconstants(=e2/h(0cSuchapplicationshaveshowngreatsignificance.Theultimaterevealofthemechanismofhigh-temperaturesuperconductivitywillalsodependtoalargeextentonpeople’sexplorationofthepropertiesofhigh-temperaturesuperconductorsunderastrongmagneticfield.
FamiliarwiththehistoryofphysicsEveryoneknowsthattheimportantsignoftheevolutionfromsolidphysicstocondensedmatterphysicsliesintheexpansionofitsresearchobjects,fromperiodicstructurestonon-periodicstructures,fromthree-dimensionalcrystalstolow-andhigh-dimensionalsystems,andevenfractalsystems.Thesenewobjectsexhibitalargenumberofnewcharacteristicsandphysicalphenomena,andthephysicalmechanismisverydifferentfromthetraditionalones.Theproductionofthesenewobjectsandtheinterpretationofneweffectsandphenomenahaveenabledthecontinuousenrichmentanddevelopmentofcondensedmatterphysics.Inthisprocess,extremeconditionshavealwaysplayedavitalrole,becauseextremeconditionsoftenmakecertainfactorsstandoutwhileinhibitingotherfactors,sothattheoriginallycomplexprocessbecomessimpler,whichisconducivetodirectlyunderstandingthenatureofphysics..
Comparedwithotherextremeconditions,astrongmagneticfieldhasitsowncharacteristics.Theroleofastrongmagneticfieldistochangethephysicalstateofasystem,thatis,tochangetheangularmomentum(spin)andtheorbitalmotionofchargedparticles,so,Italsochangesthestateofthephysicalsystem.Itisinthispointthatthestrongmagneticfieldisdifferentfromsomeotherexpensivemethodsinphysics,suchasneutronsourcesandsynchrotrons,andtheydonotchangethephysicalstateofthesystemunderstudy.Itcangeneratenewphysicalenvironmentandleadtonewcharacteristics,andthisnewphysicalenvironmentandnewphysicalcharacteristicsdonotexistwithoutamagneticfield.Lowtemperaturecanalsoleadtonewphysicalstates,suchassuperconductivityandphasechange,Butthestrongmagneticfieldisverydifferentfromthelowtemperature.Itismoreeffectivethanthelowtemperature.Thisisbecausethemagneticfieldquantizesthetelemotionandenergyofthechargedandmagneticparticles,andbreaksthetimereversalsymmetry,givingthemmoreuniqueproperties.
Thestrongmagneticfieldcanchangethesymmetryofthemomentumspacewhilekeepingthecrystalstructureunchanged.Thisisveryimportantforthestudyoftheenergybandstructureofsolidsandtheexcitationandinteractionofsolids.ComplexcostsofsolidsThericesurfacestructureisconfirmedbytheprinciplethatthestrongmagneticfieldallowsthefreemovementofelectronsandholesinaspecificdirection,whichleadstotheoscillationofmagnetizationandmagnetoresistance.TheresearchonthestructureandcharacteristicsoftheFermisurfaceinsolidshasalwaysbeencondensedmatterphysics.Frontiertopicsinthefield.Manymajorhotspotsinthebasicresearchofcondensedmatterphysicstodayareinseparablefromtheextremeconditionsofstrongmagneticfields,andmanyareevenbasedonresearchunderstrongmagneticfields.Forexample,Bosecondensationonlyoccursinmomentumspace.Observedinrealspace,thisphenomenoncanonlybepossibleinanon-uniformstrongmagneticfield.Anotherexampleisthemechanismofhigh-temperaturesuperconductivity,quantumHalleffectresearch,physicalproblemsinnanomaterialsandmesoscopicobjects,andgiantmagnetoresistanceeffects.Thephysicaloriginoftheorganicferromagnetism,thestructureandsourceoforganicferromagnetism,themechanismandmagnetismoforganic(includingfullerene)superconductors,thephasetransitionandmagneticinteractionoflow-dimensionalmagneticmaterials,solidTheenergybandstructureandFermisurfacecharacteristicsinthephysicsandthestudyofelementaryexcitationandtheirinteractions,etc.,researchworkunderastrongmagneticfieldwillhelptocorrectlyunderstandandrevealtheseproblems,therebypromotingthefurtherdevelopmentandimprovementofcondensedmatterphysics..
Themovementofchargedparticleslikeelectrons,ions,etc.andcertainpolarmoleculeswillproducefundamentalchangesinamagneticfield,especiallyinastrongmagneticfield.Therefore,studyingtheinfluenceofstrongmagneticfieldonchemicalreactionprocess,surfacecatalysisprocess,material,especiallymagneticmaterialformationprocess,biologicaleffectandliquidcrystalformationprocess,etc.,maymakenewdiscoveriesandgeneratenewinterdisciplinarytopics.Theapplicationofstrongmagneticfieldtomaterialscienceopensupanewpathforthedevelopmentofnewfunctionalmaterials.WorkinthisareaishighlyvaluedabroadandisalsobeginningtobedemandedinChina.Itispreciselybecauseoftheimmeasurableapplicationprospectsofhigh-temperaturesuperconductorsinthefuturestrongcurrentfieldthatithasattractedtheattentionofthescientificandtechnologicalcirclesandevengovernmentsofvariouscountries.Therefore,theresearchofphysicsandchemistryunderstrongmagneticfieldhasveryimportantscientificandtechnicalsignificancefromtheperspectiveofbasicresearchandtheperspectiveofapplication.Throughthisresearch,itwillnotonlyhelptotransformthecontemporaryfundamentals.Theresearchisgoingtoadeeperlevel,anditwillalsoplayanimportantroleinpromotingthedevelopmentofthenationaleconomy.
Historyofdevelopment
In1911,DutchphysicistOnnis(1853-1926)discoveredthattheresistivityofmercurydidnotgraduallydecreasewithtemperatureasexpected,butWhenthetemperaturedropstonear4.15K,theresistanceofmercurysuddenlydropstozero.Certainmetals,alloysandcompounds,whenthetemperaturedropstoacertaintemperaturenearabsolutezero,theirresistivitysuddenlydecreasestoanunmeasurablephenomenoniscalledsuperconductivity,andsubstancesthatcancausesuperconductivityarecalledsuperconductors..Thetemperatureatwhichasuperconductorchangesfromanormalstatetoasuperconductingstateiscalledthetransitiontemperature(orcriticaltemperature)TCofthissubstance.Ithasbeenfoundthatmostmetalelementsandthousandsofalloysandcompoundsexhibitsuperconductivityunderdifferentconditions.Forexample,thetransitiontemperatureoftungstenis0.012K,zincis0.75K,aluminumis1.196K,andleadis7.193K.
Theuniquecharacteristicsofsuperconductorsmakeitpossibletobewidelyusedinvariousfields.However,becausetheearlysuperconductorsexistedintheextremelylowtemperatureconditionsofliquidhelium,theapplicationofsuperconductingmaterialswasgreatlyrestricted.Peoplehavebeenexploringhigh-temperaturesuperconductors.From1911to1986,itincreasedfrom4.2Kofmercuryto23.22Kofniobiumandgermaniumin75years,andonlythendiditincreaseby19K.
In1986,amajorbreakthroughwasmadeintheresearchofhigh-temperaturesuperconductors.The“superconductivity”whichisaimedatresearchingmetaloxideceramicmaterialsandlookingforhigh-criticaltemperaturesuperconductorshasbeenlaunched.Morethan260experimentalgroupsallovertheworldparticipatedinthiscompetition.
InJanuary1986,scientistsBenozandMüllerattheInternationalBusinessMachinesLaboratoryinZurich,Switzerland,firstdiscoveredthatbarium,lanthanum,copperoxideisahigh-temperaturesuperconductor,raisingthesuperconductingtemperatureto30K;Then,theFacultyofEngineeringoftheUniversityofTokyoinJapanraisedthesuperconductingtemperatureto37K;theUniversityofHoustonannouncedthattheChinese-AmericanscientistZhuJingwuhadraisedthesuperconductingtemperatureto40.2K.
InearlyJanuary1987,theKawasakiNationalInstituteofMolecularResearchinJapanraisedthesuperconductingtemperatureto43K;soontheJapanInstituteofElectronicsResearchraisedthesuperconductingtemperatureto46Kand53K.TheresearchgroupledbyZhaoZhongxianandChenLiquanoftheInstituteofPhysicsoftheChineseAcademyofSciencesobtained48.6Kstrontiumlanthanumcopper-oxygensuperconductorsandsawsignsoftransformationofsuchsubstancesat70K.OnFebruary15th,theUnitedStatesreportedthatZhuJingwuandWuMaokunhadobtained98Ksuperconductors.OnFebruary20th,Chinaalsoannouncedthediscoveryofsuperconductorsabove100K.OnMarch3,Japanannouncedthediscoveryofa123Ksuperconductor.OnMarch12th,PekingUniversityinChinasuccessfullyconductedsuperconductingmagneticlevitationexperimentswithliquidnitrogen.OnMarch27th,ChineseAmericanscientistsdiscoveredthatthereweresignsofsuperconductivitywithatransitiontemperatureof240Kinoxidesuperconductingmaterials.Soon,theFacultyofEngineeringatKagoshimaUniversityinJapandiscoveredthatceramicmaterialscomposedoflanthanum,strontium,copper,andoxygenhadsignsofsuperconductivityatatemperatureof14°C.Ahugebreakthroughinhigh-temperaturesuperconductors,theuseofliquidnitrogeninsteadofliquidheliumasasuperconductingrefrigeranttoobtainsuperconductorshasenabledthedevelopmentandapplicationofsuperconductingtechnologyonalargescale.Nitrogenisthemaincomponentofair,andtheefficiencyofliquidnitrogenrefrigeratorsisatleast10timeshigherthanthatofliquidhelium,sothepriceofliquidnitrogenisactuallyonly1/100ofthatofliquidhelium.Liquidnitrogenrefrigerationequipmentissimple.Therefore,althoughtheexistinghigh-temperaturesuperconductorsmustbecooledwithliquidnitrogen,theyareconsideredtobeoneofthegreatestscientificdiscoveriesinthe20thcentury.
Applicationfield
Theexcellentpropertiesofsuperconductingmaterialshavemadeitpossibletoshowattractiveapplicationprospectstomankindfromthedayitwasdiscovered.However,theactualapplicationofsuperconductingmaterialsisrestrictedbyaseriesoffactors.Thisisfirstlyitscriticalparameters,andsecondly,therearealsoissuessuchastheprocessofmaterialproduction(forexample,howtomakebrittlesuperconductingceramicsintoflexiblewireshasaseriesofprocessproblems.).Bythe1980s,themainapplicationsofsuperconductingmaterialswere:①Usingthesuperconductivityofthematerialtomakemagnets,usedinmotors,high-energyparticleaccelerators,magneticlevitationtransportation,controlledthermonuclearreactions,energystorage,etc.;canbeusedtomakepowercablesforLarge-capacitypowertransmission(powerupto10000MVA);communicationcablesandantennascanbemade,anditsperformanceisbetterthanconventionalmaterials.②Thefrictionlessgyroscopeandbearingcanbemadebyusingthecompletediamagnetismofthematerial.③UsingtheJosephsoneffect,aseriesofprecisionmeasuringinstruments,radiationdetectors,microwavegenerators,logicelements,etc.canbemade.UsingtheJosephsonjunctionasthelogicandstorageelementsofacomputer,itsoperationspeedis10-20timesfasterthanthatofahigh-performanceintegratedcircuit,anditspowerconsumptionisonlyaquarter.
Researchanddevelopmentproducts
OnMarch28,2014,theresearchteamoftheJapanInstituteofMaterialandMaterialsresearchedandsynthesizednewsuperconductingcompoundscontaininggoldandsilicon.
Theresearchteamchemicallyreactedgoldwithsiliconandstrontiumdisilicideunderthehightemperatureandhighpressureconditionsof1500degreesand60,000atmospherestoproduceanewtypeofsuperconductorcalled"SrAuSi3".ThesuperconductingstateisreachedatKabsolutetemperature.Accordingtotheoreticalcalculationandanalysis,theelectronicstructureofthenewsuperconductorhasanincreasednumberofelectrons,strongerelectronicmagnetism,andstrongerspin-orbitcouplingcomparedwiththegoldelementwithalargeratomicnumber.ItbelongstothecompoundofBaNiSn3structure.Theresearchresultshavebeenpublishedin"MaterialsChemistry"editedbytheAmericanChemicalSociety.