Applied physics A

DOI:10.1007/s00339-006-3613-1Appl.Phys.A84,335–339(2006)

MaterialsScience&ProcessingAppliedPhysicsA

f.qin1

y.q.cai1

x.yao1,2,u

x.h.zeng1

q.l.rao1

g.li1

y.jiang1

y.r.li3

b.w.tao3LPEgrowthofPZNTfilmusing

superheatingYBCOthinfilmasseedlayer

1DepartmentofPhysics,ShanghaiJiaoTongUniversity,800DongchuanRoad,Shanghai200240,P.R.China2StateKeyLaboratoryforMetalMatrixComposites,ShanghaiJiaoTongUniversity,1954HuashanRoad,Shanghai200030,P.R.China3InstituteofMicroelectronicsandSolidStateElectronics,UniversityofElectronicScienceandTechnologyofChina,Chengdu610054,P.R.China

Received:30September2005/Acceptedversion:22April2006Publishedonline:24May2006•©Springer-Verlag2006

ABSTRACTAsuperheatingYBa2Cu3O7−δ(YBCOorY123)thinfilmwasappliedasaseedlayertogrowPb[(Zn1/3Nb2/3)0.91Ti0.09]O3(PZNT)filmsbyaliquidphaseepitaxy(LPE)process.Inthepresentwork,theYBCOthinfilmunderwentagrowthtemperatureof1050◦C,whichwasabout40◦Chigherthanitsperitectictemperature.Itisveryinter-estingthatthesuperheatedYBCOseedfilmcouldbeusedtogrownotonlyNd1+xBa2−xCu3O7−δ(NBCO)filmswithsimi-larcompositionsbutalsoPZNTfilmswithcompletelydifferentcompositions.TheXRDanalysisconfirmedthatthePZNTfilmgrownontheYBCOseededMgOsubstratehadagoodepi-taxialrelationshipof[100](001)PZNT//[100](001)YBCO//[100](001)MgO.ComparedwiththePZNTfilmsdirectlygrownonMgOsubstrates,theLPEPZNTfilmonYBCO/MgOpresentedabettersurfacemorphology.ItwasfoundthatthesuperheatingYBCOseedfilmplaysacrucialrolefortheLPEgrowthofPZNTintheprocess.Furthermore,thesuperheatingmechanismwasdiscussedintermsofthermodynamictheoriesaswell.

PACS77.84.-s;61.10.Nz;68.37.Hk;81.15.Lm;82.45.Mp

1Introduction

Sincethesuperheatingphenomenonwasfirstre-

portedbyDaegesin1986,manyscientistshavegainednew

interestinthisfieldofsuchaninterestingphenomenon[1–4].

Mostofthesuperheatingphenomenahavebeenobservedin

theembeddedandlow-dimensionalsystems,suchasnanopar-

ticles,nanowiresandthinfilms.Itwasfoundthatwhenthe

nanoparticlesareproperlyembeddedinahigh-Tmmetal,the

meltingpointcanbeelevatedtosomedegreeabovetheequi-

libriumTmforbulksolids.Forexample,Agparticlescanbe

superheatedupto25KaboveT0for1minwithoutmelting

whentheyarecoatedbyCu[4].OtheranaloguessuchasIn,

Pd,CdandTiembeddedinAlandPdinZn,Cuwereobserved

tosuperheatinthesameway[5–9].However,mostofthem

arerestrictedtothemetalsortheiralloys.

Inourpreviouswork,wereportedanovelsuperheat-

ingphenomenonintheYBa2Cu3O7−δ(YBCOorY123)

superconductingthinfilm,whichisanoxidematerialandin-

volvesaperitecticmelting.Firstly,fromthesuccessfulYBCO

uFax:+86-21-54741040,E-mail:xyao@sjtu.edu.cnseededNd1+xBa2−xCu3O7−δ(NdBCO)thickfilmgrowth

(YSNG),wefoundthatYBCOfilmcanendureaheatingpro-

cessuptothetemperature1055◦C,whichis45◦Cabove

itsmeltingpoint(Tp)[10].Later,byusingahightempera-

tureopticalmicroscope(HTOM)forinsituobservation,we

studiedandclarifiedthesuperheatingmechanism[11–13].

Further,weutilizedthesuperheatingpropertyofYBCOthin

filmforotherseed-requiredRE1+xBa2−xCu3Oδ(REBCO,

RE=rareearthelement)processes,e.g.,themelt-textured

growthofYBCObulks[14].Inthatprocess,YBCOshowed

theintrinsicsuperheatingpropertybywithstandingahigh

temperatureoveritsTpaswell.Suchaseed-filmwithalow-

peritectic-temperatureforthegrowthmaterialsatahigh

processingtemperatureisverypromisingforitsextensive

applicationofYBCOseededREBCOgrowth.

FortheYBCOfilmseededREBCOgrowth,YBCOand

REBCOnotonlyhavethesamecrystalstructure,butalso

sharesimilarelementsorbondings.Thequestionaddressed

inthepresentworkiswhetherthesuperheatingeffectstill

workswhenmostelementsofYBCOfilmaredifferentfrom

thoseinLPEfilmmaterials.Inordertoprovethispoint,

Pb[(Zn1/3Nb2/3)0.91Ti0.09]O3(PZNT),whichiscompletely

differentfromYBCOinchemicalcomposition,isfirstlytaken

intoconsiderationduetoitssimilarcrystalstructure,small

misfittotheYBCOanditsproperprocessingtemperature

(about1050◦C),whichisintherangeofYBCOsuperheating

temperature.

PZNTisarelaxorferroelectricmaterialwithhighdi-

electricconstants,lowdielectricloss,extremelylargepiezo-

electricstrain(>1%)andelectromechanicalcouplingfactor

(k33>90%).Suchsinglecrystalsareexpectedtofindappli-

cationsinpiezoelectricdevices,suchasmedicalultrasonic

transducers,actuators,andsonars[15–20].Conventionally,

PZNTcrystalsaregrownbyafluxmethodormodifiedBridg-

mantechnique[21,22].Recently,weobtainedPZNTthick

filmsonSTOsubstratesbytheliquidphaseepitaxy(LPE)

growthmethod.ThePZNTfilmsgrownbyLPEmaybeanal-

ternativetothesinglecrystalsfortheapplicationaswafers.

Inthiswork,weexpecttorealizeheteroepitaxialgrowthof

aPZNTthickfilmbyutilizingYBCOthinfilmasaseedlayer.

2Experimentalprocedure

YBCOthinfilmsweredepositedonMgOsin-

glecrystallinesubstratesbypulsedlaserdeposition(PLD)