relaxor polymer

Direct spectroscopic evidence of field-induced solid-state chain conformation
transformation in a ferroelectric relaxor polymer
Shihai Zhang, Baojin Chu, Bret Neese, Kailiang Ren, Xin Zhou, and Q. M. Zhang

Citation: Journal of Applied Physics 99, 044107 (2006); doi: 10.1063/1.2169659
View online: http://dx.doi.org/10.1063/1.2169659
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Directspectroscopicevidenceoffield-inducedsolid-statechain
conformationtransformationinaferroelectricrelaxorpolymer

ShihaiZhang,BaojinChu,BretNeese,KailiangRen,XinZhou,andQ.M.Zhang
a͒
MaterialsResearchInstitute,ThePennsylvaniaStateUniversity,UniversityPark,Pennsylvania16802
andDepartmentofElectricalEngineering,ThePennsylvaniaStateUniversity,UniversityPark,
Pennsylvania16802

͑Received6September2005;accepted12December2005;publishedonline27February2006͒

FerroelectricrelaxorP͑VDF-TrFE-CFE͒terpolymercangenerateahysteresis-freepolarizationof
47mC/m2atanelectricfieldof100MV/mandisattractiveformanypotentialactuatingand
sensingapplications.Fouriertransforminfraredspectraunderelectricfieldrevealthatthislarge
polarizationoriginatesfromthefield-inducedcrystallinephasetransformation.Thenonpolar
TGTGЈchainconformationinP͑VDF-TrFE-CFE͒canbeconvertedintopolartrans͑TmϾ4andT3G͒
conformationunderhighelectricfieldandthelattercanbeeffectivelyalignedtotheappliedfield
direction.Furthermore,thisconformationtransformationiscompletelyreversibleandnohysteresis
canbeobservedduringtheswitchingofappliedelectricfield.Incontrast,normalferroelectric
polymerP͑VDF-TrFE͒exhibitssquarepolarizationloopwithverysmallreversiblepolarization.
©2006AmericanInstituteofPhysics.͓DOI:10.1063/1.2169659͔

I.INTRODUCTION
Ferroelectricmaterialshavebeenwidelyusedforthe
electrictomechanicalenergyconversionandforgenerating
mechanicalactuationinresponsetoexternalelectrical
stimulation.1–3Conventionalferroelectricpolymerpoly͑vi-
nylidenefluoride͒͑PVDF͒anditscopolymerswithtrifluoro-
ethylene͑TrFE͓͒P͑VDF-TrFE͔͒exhibitstrongferroelectric-
itywhentheyareinthe␤crystallinephasewithordered
polarlongtrans͑T
mϾ4
͒chainconformation.Thelargemac-

roscopicpolarizationinP͑VDF-TrFE͒originatesfromthe
spontaneouspolarizationfromC–Fdipolesandthestrain
responsemainlyfromtheC–Fbondstretchingandreorien-
tationunderhighelectricfield,exhibitingtypicalelectro-
strictivebehaviorwithstrainquadraticallydependingonthe
chargedensity.
1,4
Duetothefactthattheferroelectricpoly-

merisalreadyinapolarizedstate,thechangeofpolarization
underfieldissmall,resultinginsmallusablestrainandlow
electromechanicalresponse.
Recently,byemployingdefectmodifications5suchas
high-energyelectronirradiation6orbyintroducingabulky
thirdmonomersuchas1,1-chlorofluoroethylene͑CFE͒,7it
hasbeenshownthatthenormalferroelectricP͑VDF-TrFE͒
canbeconvertedintoaferroelectricrelaxorandtheelectro-
mechanicalresponsecanbesignificantlyenhanced.Figure1
comparesthepolarizationhysteresisloopsofnormalferro-
electricP͑VDF-TrFE͒copolymerwitharelaxorferroelectric
P͑VDF-TrFE-CFE͒terpolymer,anditisclearthatamuch
largerreversiblepolarizationchangecanbeinducedinthe
latter.Forexample,thepolarizationcanbeincreasedby
47mC/m
2
fortheterpolymerwhentheelectricfieldchanges

from0to100MV/m͑frompointAtoB͒,whereasthere-
versiblechangeinpolarizationisonly11mC/m2fornormal
ferroelectricP͑VDF-TrFE͒copolymer͑frompointAЈtoBЈ͒.
Asaresult,ahysteresis-freeelectrostrictivestrainofmore

than7%canbeinducedintheP͑VDF-TrFE͒-basedferro-
electricrelaxorpolymers,whileinP͑VDF-TrFE͒copolymer,
themaximumstrainisatabout1%whilethehysteresis-free
strainisontheorderof0.1%.
8
Ithasbeenshownthatinthe

relaxorferroelectricterpolymertheall-transpolarchaincon-
formation͑T
mϾ4
͒inthenormalferroelectricP͑VDF-TrFE͒is

destabilizedandreplacedbythedisorderedtrans-gauche
conformation͑TGTG
ЈandT3GT3GЈ
͒andthepolar␤crys-

talliteisconvertedintoadifferentcrystallinephasewithcell
latticeclosetothatoftheparaelectriccrystalline
␣
phase.

6,7,9

Toprovidebetterunderstandingonthemolecularlevel
mechanismsresponsibleforthelargeandreversiblepolariza-
tionchangeintherelaxorferroelectricpolymer,wehave
carriedoutadetailedFouriertransforminfrared͑FTIR͒spec-
troscopestudytoexaminetheevolutionofvariousmolecular
conformationswithelectricfieldsincetheIRabsorbance
bandpositionisverysensitivetothelocalchainenviron-
ment.Previousstudiesfoundthatthedifferentchainconfor-
mationsinPVDF-basedpolymers,T
mϾ4,T3GT3
GЈ,and

a͒
Electronicmail:qxz1@psu.eduFIG.1.͑Coloronline͒Bipolarpolarizationloopofcopolymerandterpoly-mermeasuredat10Hzalternatingfield.

JOURNALOFAPPLIEDPHYSICS99,044107͑2006͒
0021-8979/2006/99͑4͒/044107/4/$23.00©2006AmericanInstituteofPhysics99,044107-1
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