Introduction
High-temperaturesuperconductorsusuallyrefertomaterialsthataresuperconductingabovethetemperatureofliquidnitrogen(77K).Whensuperconductorswerediscovered(1911),theywereattractedbytheirpeculiarproperties(namely,zeroresistance,diamagnetism,andquantumtunnelingeffect).Butintheseventy-fiveyearssincethen,allthesuperconductorsthathavebeendiscoveredonlyshowsuperconductivityatextremelylowtemperatures(23K),sotheirapplicationshavebeengreatlyrestricted.
Discovery
In1986,BernozandMullerdiscoveredthe35Ksuperconductinglanthanumbariumcopperoxygensystem.Thisbreakthroughdiscoveryledtothediscoveryofaseriesofrareearthbariumcopperoxidesuperconductorsathighertemperatures.Throughelementreplacement,atthebeginningof1987,WuMaokun(ZhuJingwu)oftheUnitedStatesandZhaoZhongxianoftheChineseInstituteofPhysicsannouncedthediscoveryofa90Kyttrium-barium-copper-oxygensuperconductor,achievingthefirstbreakthroughinthetemperaturebarrierofliquidnitrogentemperature(77K).BernozandMulleralsowonthe1987NobelPrizeinPhysicsfortheirpioneeringwork.
Thistypeofsuperconductorisusuallycalledahigh-temperaturesuperconductorbecauseitscriticaltemperatureisabovethetemperatureofliquidnitrogen(77K).Thediscoveryofyttrium-barium-copper-oxygensuperconductorsabovethetemperatureofliquidnitrogenhasprovidedordinaryphysicslaboratorieswiththeconditionsforconductingsuperconductingexperiments.Therefore,therehasbeenanupsurgeinexploringnewhigh-temperaturesuperconductorsaroundtheworld.Attheendof1987,ChinesescholarShengZhengzhiandothersfirstdiscoveredthefirstrareearth-freethallium-barium-copper-oxygenhigh-temperaturesuperconductor.Inearly1988,Japandevelopedabismuth-strontium-calcium-copper-oxygensuperconductorwithacriticaltemperatureof110K.InFebruary1988,ShengZhengzhiandothersfurtherdiscoveredthe125Kthalliumbariumcalciumcopperoxygensuperconductor.Afewyearslater(1993)Frenchscientistsdiscovereda135Kmercury-barium-calcium-copper-oxygensuperconductor.
Classification
High-temperaturesuperconductorsincludefourcategories:90Krareearthseries,110Kbismuthseries,125Kthalliumseries,and135Kmercuryseries.Theyallcontaincopperandoxygen,sotheyarecollectivelyreferredtoascopper-basedsuperconductors.Theyhaveasimilarlayeredcrystallinestructure,andthecopperoxidelayerisasuperconductinglayer.High-temperaturesuperconductorshavealreadyachievedpracticalapplicationsandhavebeguntobenefitmankind.Forexample,yttrium-barium-copper-oxygensuperconductorsandbismuthsuperconductorshavebeenmadeintohigh-qualitysuperconductingcables.Thedevicemadeofthallium,barium,calcium,copperandoxygensuperconductingfilmwasinstalledinthetransmissiontowerofmobilephonesasearlyastheendofthelastcenturytoincreasecapacityandreducedisconnectionandinterference.
Examples
High-temperaturesuperconductingcopperoxidesuperconductorsincludea1.85Ba0.15CuO4,andYBCO(yttrium-barium-copper-oxygencompound),bothofwhicharefamousmaterialsforbreakingthroughliquidnitrogen"TemperatureBarrier"(77K).
203 | H2S(150GPahighpressure) | Hydrogen-basedsuperconductor |
195 | Thesublimationpointofdryice | |
138 | Hg12Tl3Ba30Ca30Cu45O127 | CopperOxideSuperconductor |
110 | Bi2Sr2Ca2Cu3O10(BSCCO) | |
92 | YBa2Cu3O7(YBCO) | |
77 | Boilingpointofliquidnitrogen | |
43 | SmFeAs(O,F) | Iron-basedsuperconductor |
41 | CeFeAs(O,F) | |
26 | LaFeAs(O,F) | |
20 | Boilingpointofliquidhydrogen | |
18 | Nb3Sn | Metallow-temperaturesuperconductor |
10 | NbTi | |
4.2 | Hg(mercury) |
Outlook
TheexplorationofnewandhighertemperaturesuperconductorshasbeenintenseIsgoingon.Becausethetheoryofhigh-temperaturesuperconductivityhasnotbeenwellestablished,theprogressofexploratoryworkisslow.Althoughnewsuperconductorsandhighertemperaturesuperconductivityhavebeenreportedfromtimetotime,realnewbreakthroughshavenotyetbeenmade.
Whydomanysuperconductingmaterialsneedtobesuperconductingataverylowtemperature?Itisbecauseatroomtemperature,therearegapsbetweenconductoratoms.Whenelectronsmovebetweenatoms,theymustpassthroughthesegapsandcollidewiththeatoms,causingtheatomstovibrateandheattoformresistance.Atextremelylowtemperatures,therearealmostnogapsbetweenconductoratoms,andelectronscanpassfreelywithoutcollidingwithatoms.Inthefuture,theresearchofroomtemperaturesuperconductingmaterialsshouldselectappropriatemixturesofdifferentelements,sothatatomsofdifferentsizesandshapesarecombinedtogether,sothattherearenogapsbetweenatoms,sothatelectronscanpassthroughfreelyanddonotcollidewithatoms.Thedifficultyinthedevelopmentofroomtemperaturesuperconductingmaterialsisthattheatomsofmanymaterialswillvibrateatroomtemperature,andthegapsbetweentheatomsarerelativelylarge.Aslongasthemixingelementsareproperlyselected,superconductingmaterialsatroomtemperaturecansoonbemass-produced.
WebelievethatthedescendantsofYanhuang,whohavemadeoutstandingachievementsinthefieldofcopper-basedhigh-temperaturesuperconductors,willcertainlymakemorebrilliantcontributionstothejourneyofrealizingthedreamofhumanroomtemperaturesuperconductors.
criticaltransitiontemperatureTc(Kelvin,K) | Material/substanceboilingpoint | Type |
138K | Hg12Tl3Ba30Ca30Cu45O127 | Copperoxidesuperconductor |
110K | Bi2Sr2Ca2Cu3O10(BSCCO) | |
92K | YBa2Cu3O7(YBCO) | |
77K | N2 | —— |
43K | SmFeAs(O,F) | Iron-basedsuperconductor |
41K | CeFeAs(O,F) | |
26K | LaFeAs(O,F) | |
20K | H2boilingpoint | —— |
18K | Nb3Sn | Metallow-temperaturesuperconductor |
10K | NbTi | |
4.25K | He’sboilingpoint | —— |
4.2K | Hg(mercury) | Metallow-temperaturesuperconductor |