Effect of poling procedure on the properties of lead zirconate titanate/vinylidene fluoride-trifluoroethylene composites

TLDR: In this paper, the PZT powder was incorporated into a P(VDF-TrFE) copolymer matrix for pyroelectric sensor and piezoelectric transducer applications.

Abstract: Lead zirconate titanate/vinylidene fluoride-trifluoroethylene [PZT/P(VDF-TrFE)] 0–3 composites for pyroelectric sensor and piezoelectric transducer applications have been fabricated by incorporating PZT powder into a P(VDF-TrFE) copolymer matrix. The properties of these composites can be tailored to suit designated applications by varying the ceramic volume fraction and by using different poling procedures. As both phases in the composite are ferroelectric, and the piezoelectric coefficients of the ceramic and copolymer phases have opposite signs while the pyroelectric coefficients have like signs, special ways can be used to produce three groups of samples with (1) only the ceramic phase poled, (2) two phases poled in the same direction to achieve reinforced pyroelectric activity and reduced piezoelectric activity, and (3) two phases poled in opposite directions to obtain reinforced piezoelectric activity and reduced pyroelectric activity. In this work, original experimental results on the properties of ...

Figures

FIG. 4. Pyroelectric coefficient p of the composites as afunction of volume fraction of ceramicf. When the ceramic and copolymer phases are pole the same direction ~m!, reinforcement occurs. When the two phases are poled in opposite directions ~3!, partial cancellation is obtained. ~d! represents p of composites with only the ceramic phase poled.

FIG. 3. Piezoelectric d33 coefficient of the composites as a function of volume fraction of ceramicf. When the ceramic and copolymer phases a poled in the same direction ~m!, partial cancellation occurs. When the two phases are poled in opposite directions ~3!, reinforcement is obtained. ~j! represents d33 of composites with only the ceramic phase poled.

FIG. 2. Piezoelectric effect in a P~VDF-TrFE! copolymer, ~a! before tension, ~b! under tension. The spontaneous polarization decreases as the volume increases.

FIG. 1. Piezoelectric effect in a ceramic with tetragonal ABO3 structure ~e.g., PZT!, ~a! before tension, ~b! under tension. The polarization increases as the separation of the positive and the negative charge centers increases.

Full text

Effectofpolingprocedureonthepropertiesofleadzirconatetitanate/
vinylidenefluoride-trifluoroethylenecomposites
H.L.W.Chan,
a)
P.K.L.Ng,andC.L.Choy
DepartmentofAppliedPhysicsandMaterialsResearchCenter,TheHongKongPolytechnicUniversity,
Hunghom,Kowloon,HongKong
~Received20January1999;acceptedforpublication16March1999!
Leadzirconatetitanate/vinylidenefluoride-trifluoroethylene@PZT/P~VDF-TrFE!#0–3composites
forpyroelectricsensorandpiezoelectrictransducerapplicationshavebeenfabricatedby
incorporatingPZTpowderintoaP~VDF-TrFE!copolymermatrix.Thepropertiesofthese
compositescanbetailoredtosuitdesignatedapplicationsbyvaryingtheceramicvolumefraction
andbyusingdifferentpolingprocedures.Asbothphasesinthecompositeareferroelectric,andthe
piezoelectriccoefficientsoftheceramicandcopolymerphaseshaveoppositesignswhilethe
pyroelectriccoefficientshavelikesigns,specialwayscanbeusedtoproducethreegroupsof
sampleswith~1!onlytheceramicphasepoled,~2!twophasespoledinthesamedirectiontoachieve
reinforcedpyroelectricactivityandreducedpiezoelectricactivity,and~3!twophasespoledin
oppositedirectionstoobtainreinforcedpiezoelectricactivityandreducedpyroelectricactivity.In
thiswork,originalexperimentalresultsonthepropertiesofPZT/P~VDF-TrFE!compositespoled
underdifferentconditionsarepresentedandpossiblereasonsbehindthereinforcementand
cancellationofpiezoelectricandpyroelectricpropertiesarediscussed.©1999AmericanInstitute
ofPhysics.@S0003-6951~99!01120-1#
TheP~VDF-TrFE!70/30mol%copolymer~suppliedby
Piezotech!usedinthepresentstudyhasaCurietemperature
T
ch
at103°CuponheatingandT
cc
at70°Cuponcoolingas
measuredbydifferentialscanningcalorimetry.Theleadzi-
conatetitanate~PZT!powderPKI502issuppliedbyUltra-
sonicPowdersLtd..Thecopolymerpelletsaredissolvedin
methyl-ethyl-ketoneandsuitableamountsofPZTpowder
areblendedintotheP~VDF-TrFE!solutiontoformcompos-
iteswithdifferentvolumefractionsofceramic
f
. After
evaporationofthesolvent,thecompositeswerecompression
moldedintodisksamples15mmindiameterandabout0.4
mmthick.Thepolingprocedureforthethreegroupsof
samplesisasfollows:
Group1:Samplesareheatedto120°C~aboveT
ch
!and
anelectricfieldE
0
of;35kV/mmisappliedtothecompos-
itefor1h.ThefieldE
0
isthenswitchedoffbeforecoolingto
roomtemperature.AsE
0
isswitchedoffaboveT
ch
whilethe
copolymerisstillinaparaelectricstate,onlytheceramic
phaseispoled.Toverifythis,thesameprocedureisapplied
toacopolymersample.Thecopolymersamplehasnodetect-
ablepiezoelectricandpyroelectricactivities,thusshowing
thatitisnotpolarized.
Group2:Thepolingprocedureissimilartothatapplied
togroup1samplesexceptthatE
0
ismaintainedwhilecool-
ingtoroomtemperature.AsthesamplecoolsthroughT
ch
andT
cc
withE
0
stillapplied,thecopolymerphaseispoledin
thesamedirectionastheceramicphase.
Group3:Thepolingprocedureissimilartothatapplied
togroup2samplestoproducecompositeswithbothphases
poledinthesamedirection.Inordertopolarizetheceramic
phaseinanoppositedirectionrelativetothecopolymer,
thesesamplesarereheatedto50°Candthenapolingfieldof
10kV/mmisappliedinthereversedirectionfor0.5h.The
samplesarethencooledtoroomtemperaturewiththere-
versepolingfieldkepton.Astheappliedfieldismuchlower
thanthecoercivefieldofP~VDF-TrFE!,thepolarizationin
thecopolymerphaseisnotaffectedbutthepolarizationin
thePZTphaseisreversed.
Thepiezoelectricd
33
coefficientofthesampleswas
measuredusingaPennebakermodel8000piezod
33
meter
fromAmericanPiezo-CeramicsInc..Thepyroelectriccoef-
ficientpofthesampleswasmeasuredusingthedigitalinte-
grationtechnique.
1
BelowtheCurietemperature~;350°C!,PZThasate-
tragonalABO
3
unitcellstructure
2
whichgivesitaspontane-
ouspolarizationP
s
asitscenterofpositivechargedoesnot
coincidewithitsnegativechargecenter~Fig.1!.Poling
causesP
s
toaligninthethicknessdirection.Whensubjected
a!
Electronicmail:apahlcha@polyu.edu.hk
FIG.1.PiezoelectriceffectinaceramicwithtetragonalABO
3
structure
~e.g.,PZT!,~a!beforetension,~b!undertension.Thepolarizationincreases
astheseparationofthepositiveandthenegativechargecentersincreases.
APPLIEDPHYSICSLETTERS VOLUME74,NUMBER20 17MAY1999
30290003-6951/99/74(20)/3029/3/$15.00 ©1999AmericanInstituteofPhysics
Copyright ©2001. All Rights Reserved.

toatensilestress,theseparationbetweenthetwocharge
centersincreasestherebyresultinginalongerdipolemoment
armandhenceahigherP
s
.AsP
s
increases,positive
chargeswillbegeneratedontheanode~theelectrodesub-
jectedtopositivevoltageduringpoling!andhencePZThas
apositivepiezoelectricd
33
coefficient.P~VDF-TrFE!hasa
semicrystallinestructure;thedipolesexistintherigidcrystal
lamellas
3
andcanbealignedalongthethicknessdirectionby
theapplicationofanexternalpolingfield.Afterbeingpoled
andthensubjectedtoatensilestress,thethicknessincrease
ariseslargelyfromthedeformationoftheamorphous
region,
4
sotherigidcrystallamellasaredispersedinalarger
volume~Fig.2!,therebycausingadecreaseinP
s
(P
s
ispro-
portionaltothedipolemomentperunitvolume!andhencea
decreaseofthepositivechargesontheanode.Hence,
P~VDF-TrFE!copolymerhasanegativepiezoelectricd
33
co-
efficientduetothisdimensionaleffect.
4
Asthepiezoelectric
coefficientsintheceramicandthecopolymerhaveopposite
signs,hencewhentheceramicandcopolymerphasesinthe
PZT/P~VDF-TrFE!compositesarepoledinthesamedirec-
tion~group2!,theirpiezoelectricactivitiespartiallycancel
andwhentheyarepoledinoppositedirections~group3!,
theirpiezoelectricactivitiesarereinforced~Fig.3!.Samples
withonlytheceramicphasepoled~group1!havepiezoelec-
triccoefficientsinbetweenthoseofgroup2andgroup3
samples~Fig.3!.
Formostpyroelectricceramics,theirpyroelectriccoeffi-
cientsarenegativebecausethespontaneouspolarizationde-
creasesasthetemperatureincreases.Thisisbecauseasthe
temperatureincreases,theincreaseinthermalenergycauses
thedisorderingofdipoleswhichresultsinadecreaseofposi-
tivechargesontheanode.Forpyroelectricpolymers,their
pyroelectriccoefficientsarealsonegativebecausethedisor-
deringofcrystallinedipolesincreaseswithincreasingtem-
perature which causes a decrease in spontaneous
polarization.
5
Hence,whentheceramicandthecopolymer
phasesinthePZT/P~VDF-TrFE!compositesarepoledinthe
samedirection~group2!,theirpyroelectricactivitiesarere-
inforcedandwhentheyarepoledinoppositedirections
~group3!,thepyroelectricactivitiespartiallycancel~Fig.4!.
Group1sampleshavepyroelectriccoefficientsinbetween
thatofgroup2andgroup3samples~Fig.4!.
Insummary,wehavepreparedPZT/P~VDF-TrFE!0–3
compositeswiththeceramicandcopolymerphasespoledin
specialways.Thepiezoelectricandpyroelectricpropertiesof
thesecompositesvarygreatlywiththepolingprocedures.
Compositeswiththeceramicandcopolymerphasespoledin
thesamedirectioncanbeusedassensingelementsinpyro-
electricsensors
6
astheyhaveenhancedpyroelectricactivity
butreducedpiezoelectricactivity,therebyminimizingthe
vibrationinducedelectricalnoise.Compositeswiththece-
ramicandcopolymerphasespoledinoppositedirectionscan
beusedtofabricateultrasonictransducers
7
astheyhavere-
inforcedpiezoelectricpropertybutreducedsensitivityto
temperaturefluctuation.
FIG.2.PiezoelectriceffectinaP~VDF-TrFE!copolymer,~a!beforeten-
sion,~b!undertension.Thespontaneouspolarizationdecreasesasthevol-
umeincreases.
FIG.3.Piezoelectricd
33
coefficientofthecompositesasafunctionof
volumefractionofceramic
f
. When the ceramic and copolymer phases are
poledinthesamedirection~m!,partialcancellationoccurs.Whenthetwo
phasesarepoledinoppositedirections~3!,reinforcementisobtained.~j!
representsd
33
ofcompositeswithonlytheceramicphasepoled.
FIG.4.Pyroelectriccoefficientpofthecompositesasafunctionofvolume
fractionofceramic
f
. When the ceramic and copolymer phases are poled in
thesamedirection~m!,reinforcementoccurs.Whenthetwophasesare
poledinoppositedirections~3!,partialcancellationisobtained.~d!repre-
sentspofcompositeswithonlytheceramicphasepoled.
3030 Appl.Phys.Lett.,Vol.74,No.20,17May1999 Chan,Ng,andChoy
Copyright ©2001. All Rights Reserved.

Theworkdescribedinthispaperwassubstantiallysup-
portedbyagrantfromtheResearchGrantsCouncilofthe
HongKongSpecialAdministrativeRegion~ProjectNo.
PolyU5159/98P!.
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L.E.Cross,inFerroelectricCeramics:TailoringPropertiesforSpecific
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VerlagBasel,1992!,pp.1–86.
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M.G.BroadhurstandG.T.Davis,Ferroelectrics60,3~1984!.
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M.G.Broadhurst,G.T.Davis,J.E.McKinney,andR.E.Collins,J.
Appl.Phys.49,4992~1978!.
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T.Furukawa,J.X.Wen,K.Suzuki,Y.Tashina,andM.Date,J.Appl.
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3031Appl.Phys.Lett.,Vol.74,No.20,17May1999 Chan,Ng,andChoy
Copyright ©2001. All Rights Reserved.

Frequently asked questions

Q1. What contributions have the authors mentioned in the paper "Effect of poling procedure on the properties of lead zirconate titanate/ vinylidene fluoride-trifluoroethylene composites" ?

In this work, original experimental results on the properties of PZT/P~VDF-TrFE ! Composites poled under different conditions are presented and possible reasons behind the reinforcement and cancellation of piezoelectric and pyroelectric properties are discussed. 

Q2. What is the effect of the ceramic and copolymer phases on the piezoelectric?

Composites with the ceramic and copolymer phases poled in the same direction can be used as sensing elements in pyroelectric sensors6 as they have enhanced pyroelectric activity but reduced piezoelectric activity, thereby minimizing the vibration induced electrical noise. 

Q3. What is the pyroelectric coefficient of the composites?

For pyroelectric polymers, their pyroelectric coefficients are also negative because the disordering of crystalline dipoles increases with increasing temperature which causes a decrease in spontaneous polarization. 

Q4. What is the effect of the poling field on the ceramic phase?

As the applied field is much lower than the coercive field of P~VDF-TrFE!, the polarization in the copolymer phase is not affected but the polarization in the PZT phase is reversed. 

Q5. How is the poling procedure used to produce composites?

In order to polarize the ceramic phase in an opposite direction relative to the copolymer, these samples are reheated to 50 °C and then a poling field ofa! 

Q6. What is the pyroelectric activity of composites with the ceramic and copolymer?

Composites with the ceramic and copolymer phases poled in opposite directions can be used to fabricate ultrasonic transducers7 as they have reinforced piezoelectric property but reduced sensitivity to temperature fluctuation.ll Rights Reserved. 

Q7. What is the pyroelectric coefficient of composites?

composites are poled in the same direction ~group 2!, their piezoelectric activities partially cancel and when they are poled in opposite directions ~group 3!, their piezoelectric activities are reinforced ~Fig. 3!. Samples with only the ceramic phase poled ~group 1! have piezoelectric coefficients in between those of group 2 and group 3 samples ~Fig. 3!.For most pyroelectric ceramics, their pyroelectric coefficients are negative because the spontaneous polarization decreases as the temperature increases. 

Q8. What is the d33 coefficient of PZT?

After being poled and then subjected to a tensile stress, the thickness increase arises largely from the deformation of the amorphous region,4 so the rigid crystal lamellas are dispersed in a larger volume ~Fig. 2!, thereby causing a decrease in Ps (Ps is proportional to the dipole moment per unit volume! 

Q9. What is the composition of the PZT/PVDF-TrFE?

70/30 mol % copolymer ~supplied by Piezotech! used in the present study has a Curie temperature Tch at 103 °C upon heating and Tcc at 70 °C upon cooling as measured by differential scanning calorimetry. 

Q10. What is the pyroelectric activity of composites?

composites are poled in the same direction ~group 2!, their pyroelectric activities are reinforced and when they are poled in opposite directions ~group 3!, the pyroelectric activities partially cancel ~Fig. 4!. Group 1 samples have pyroelectric coefficients in between that of group 2 and group 3 samples ~Fig. 4!.In summary, the authors have prepared PZT/P~VDF-TrFE! 

Q11. What is the poling procedure for the ceramic phase?

As the sample cools through Tch and Tcc with E0 still applied, the copolymer phase is poled in the same direction as the ceramic phase. 

Q12. What is the name of the composite?

Lead zirconate titanate/vinylidene fluoride-trifluoroethylene @PZT/P~VDF-TrFE!# 0–3 composites for pyroelectric sensor and piezoelectric transducer applications have been fabricated by incorporating PZT powder into a P~VDF-TrFE! copolymer matrix. 

Q13. What are the properties of the composites?

only the ceramic phase poled, ~2! two phases poled in the same direction to achieve reinforced pyroelectric activity and reduced piezoelectric activity, and ~3!