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2、RESEARCHARTICLEMATERIALSSCIENCECopyright©2018TheAuthors,someNegative-pressurepolymorphsmadebyrightsreserved;exclusivelicenseeheterostructuralalloyingAmericanAssociationfortheAdvancement1†1,2344ofScience.NoclaimtoSebastianSiol,*AaronHolder,JamesSteffes,LauraT.Schelhas,Kev
3、inH.Stone,originalU.S.Government11143LaurenGarten,JohnD.Perkins,PhilipA.Parilla,MichaelF.Toney,BryanD.Huey,Works.Distributed111WilliamTumas,StephanLany,AndriyZakutayev*underaCreativeCommonsAttributionTheabilityofamaterialtoadoptmultiplestructures,knownaspolymorphism,isafascinatingnatura
4、lphenomenon.NonCommercialVariouspolymorphswithunusualpropertiesareroutinelysynthesizedbycompressionunderpositivepressure.How-License4.0(CCBY-NC).ever,changingamaterial’sstructurebyapplyingtensionundernegativepressureismuchmoredifficult.Weshowhownegative-pressurepolymorphscanbesynthesize
5、dbymixingmaterialswithdifferentcrystalstructures—ageneralapproachthatshouldbeapplicabletomanymaterials.Theoreticalcalculationssuggestthatitcostslessenergytomixlow-densitystructuresthanhigh-densitystructures,duetolesscompetitionforspacebetweentheatoms.Proof-of-conceptexperimentsconfirmth
6、atmixingtwodifferenthigh-densityformsofMnSeandMnTestabilizesaMn(Se,Te)alloywithalow-densitywurtzitestructure.ThisMn(Se,Te)negative-pressurepolymorphhas2×to4×lowerDownloadedfromelectroneffectivemasscomparedtoMnSeandMnTeparentcompoundsandhasapiezoelectricresponsethatnoneoftheparentcompoun
7、dshave.Thisexampleshowshowheterostructuralalloyingcanleadtonegative-pressurepolymorphswithusefulproperties—materialsthatareotherwisenearlyimpossibletomake.INTRODUCTIONlargerions[alsoknownas“chemicalpressure”inFe-basedsupercon-Polymorphismistheabilityofamaterialtoadoptmultiplecrystalstru
8、c-ductors(14)]andannealingthelow-densityprecursorsathightem-http://advances.sciencemag.org/tures,oftenwithdifferentproperties.Thisnaturalphenomenonissoperature[forexample,inoxideperovskites(15)]cantunethematerial’sinterestingthatithasbeenfeaturedinpopularfiction,forexampleprope