Structural, dielectric and piezoelectric properties of 0–3 PZT/PVDF composites

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Structural, dielectric and piezoelectric propertiesof 0–3 PZT/PVDF composites

Vineet Tiwari, Geetika Srivastavan

Department of Physics and Materials Science and Engineering, Jaypee Institute of Information Technology, Noida 201307, INDIA

Received 13 January 2015; received in revised form 23 February 2015; accepted 27 February 2015

Abstract

Piezoelectric composite films of ([PZT]x/[PVDF]1�x) with 0–3 connectivity were prepared using a solution cast technique. The films withdifferent volume fractions of PZT ceramics in the morphotropic phase boundary were prepared in the form of thin films for the optimized thermalprocessing conditions. It is seen that the increase in the content of PZT ceramic in the PVDF matrix not only increases the dielectric constant ofthe composites but also enhances the β phase in the PVDF polymer, thereby resulting in the overall improved dielectric and piezoelectric behaviorof the system. The as-synthesized films exhibited superior dielectric and piezoelectric properties than reported in the literature.& 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Keywords: A. Films; B. Composites; C. Dielectric properties; C. Piezoelectric properties

1. Introduction

Lead based perovksites such as lead zirconate titanate PZTand its solid solutions are the most exploited ferroelectricmaterials known for their applications in sensors and actuators.These materials exhibit excellent dielectric and piezoelectricproperties at the morphotropic phase boundary (MPB) [1–5].However, these piezoceramics are brittle in nature and aredifficult to conform to the desired shapes and structures. Thesedisadvantages limit their use in applications where flexibility isdesired. Polymers such as PVDF are known for their flex-ibility, mechanical strength, piezoelectric properties and caneasily conform to different shapes and structures [6–9]. Thesearch for the new materials which can combine the comple-mentary features of a polymer and a ceramic has led to thesignificant research in the field of composite materials [10–13].Composites made up of ferroelectric ceramic and polymer hasbeen extensively studied for their excellent properties. Thesecomposite films combine the interesting features of both the

10.1016/j.ceramint.2015.02.14815 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

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s article as: V. Tiwari, G. Srivastava, Structural, dielectric and piex.doi.org/10.1016/j.ceramint.2015.02.148

phases which includes high dielectric and piezoelectric proper-ties of the ceramic and the flexibility and mechanical toleranceof the polymer. Their properties can be engineered for specificrequirements depending on the volume fraction, connectivityand properties of the constituent phases [14–19].There have been extensive studies on PZT based polymer

composites with 0–3 connectivity [15–27]. Most of the studiesdealt with the material properties of the films synthesizedunder the conditions which resulted in α rich PVDF phase. Thebasic intention of the present study is to synthesize PZT/PVDFcomposites in the 0–3 connectivity phase with β rich phase inPVDF under optimized processing conditions and to investi-gate the structural and material properties of these films as afunction of volume fractions of PZT in PVDF matrix. Thisinformation is necessary for the designing of the compositeswith optimum properties for specific applications.PZT ceramic particles were prepared in the MPB region

with Zr/Ti=50/50 so as to obtain better dielectric and piezo-electric properties in the system. PZT ceramic powders weresynthesized by adopting low temperature calcination routewhich yields a pure perovskite phase via stabilization ofA3B4O13 pyrochlore phase as reported in our earlier study[28–32]. Further, it was found in our previous study that the

zoelectric properties of 0–3 PZT/PVDF composites, Ceramics International

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Fig. 1. The x-ray diffraction profile of PZT ceramic material with Zr/Ti¼50/50.

Fig. 2. The x-ray diffraction profile patterns of [PZT]x/[PVDF]1�x system(a) x¼0 (b) x¼0.1 (c) x¼0.2 (d) x¼0.3.

V. Tiwari, G. Srivastava / Ceramics International ] (]]]]) ]]]–]]]2

thermal processing conditions play an important role indeciding the crystalline phase and hence in turn the materialproperties of PVDF films [10]. Therefore, the optimizedprocessing conditions obtained in our previous studies wereemployed to synthesize PZT based PVDF films aimed toincorporate the advantages of PZT ceramic and PVDF polymer[10,29–32].

2. Materials and methods

PbZr0.5Ti0.5O3 ceramic powders were synthesized by adopt-ing low temperature calcination route. The raw materials ofanalytical grade such as PbO, ZrO2 and TiO2 were mixed inethanol in stoichiometric ratio and were calcined at 700 1C foran hour. These powders were kept at 1280 1C in a lead richatmosphere for 2 h [28–32]. 15 wt% of PVDF granules weredissolved in 20 ml of dimethylsulfoxide (DMSO) and 80 ml ofacetone by stirring in a magnetic stirrer at 40 1C for 30 min.The volume fraction of synthesized PZT ceramic powders wascalculated by the following relation [33]:

vf ¼wf

wfþwmðρfþρmÞwhere

vf is the volume fraction of the PZT particles,wf and ρf are the weight fraction and the density of PZT

ceramic particles while wm and ρm are the weight fraction anddensity of the PVDF polymer matrix respectively.

The different volume fractions of PZT particles were addedto the PVDF solution and the solution was further stirred for30 min. The solutions with different volume fractions of PZTviz 0%, 10%, 20% and 30% PZT particles were cast over petridish by the solution cast technique and kept at 60 1C for 4days. The obtained films were treated at 80 1C for 5 h and laterrapidly quenched at 20 1C [10].

The FTIR spectra of these composite films were recorded bya Perkin-Elmer Spectrometer for structural investigation. Thestructural characterization of these films was also carried byx-ray diffraction using CuKα radiation on an XRD-6000 fromShimadzu Analytical, Japan. The dielectric measurements werecarried using LCR meter, Hioki, Japan for 1 kHz. These filmswere poled in silicone oil bath at 80 1C with an electric field of10 kV/mm. The samples were aged for 24 h. The piezoelectriccoefficients, d33, were obtained using a Berlincourt Piezod33 meter.

3. Results and discussions

3.1. Structural analysis

3.1.1. XRD studiesFig. 1 shows the XRD profile of PZT ceramic particles

synthesized with Zr/Ti¼50/50 [30]. The XRD pattern of purePZT ceramic powder revealed the formation of pure perovskitephase. No extra impurity peak or pyrochlore phase was seenwithin the detection limit of XRD. The triplet splitting of (200)pseudocubic peak confirmed that the PZT system is in the

Please cite this article as: V. Tiwari, G. Srivastava, Structural, dielectric and pie(2015), http://dx.doi.org/10.1016/j.ceramint.2015.02.148

morphotropic phase boundary region [30]. Fig. 2 shows theXRD patterns of the pure PVDF and PVDF–PZT films withdifferent compositions synthesized under optimized processingconditions [10,30]. The peaks corresponding to PZT peaks andα, β and γ phases of PVDF have been denoted by varioussymbols. The characteristic peaks around 21.91, 311, 381,





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44.51, 491 and 551 are signatures of perovksite phase while thepeaks corresponding to 2θ values around 19.91, 20.31 and20.91 are ascribed to α, γ and β phases respectively of PVDF[10]. Further, the XRD pattern of the pure synthesized PVDFfilm revealed a mixture of α, β and γ phases. All the XRDpeaks of the composite films with different volume fractions ofPZT ceramics in the PVDF matrix have been indexed as thoseof PZT perovskite structure and of α, β and γ phases of PVDFpolymer and have been labeled in the figure.

It can be seen from the figure that the perovskite phaseincreased with the volume content of PZT ceramic in thePVDF as expected. The deconvolution of the XRD peakscorresponding to the various crystalline phases of PVDF andthe perovskite phase of PZT was done for the composite filmswith different volume contents of PZT in the PVDF matrix.Fig. 3 shows the typical deconvoluted XRD peak profiles ofPVDF and [PVDF]1�x/[PZT]x. It can be seen from the figurethat as-synthesized pure PVDF and PZT/PVDF compositefilms under optimized thermal processing condition revealed βenrich phase and the total crystalline content in the film is alsofairly large as is depicted by sharp characteristic peaks. Hence,

Fig. 3. A typical deconvoluted XRD pattern for the quantification of α, β and γphases present in the (a) PVDF film (b) [PZT]x/[PVDF]1�x composites withx¼0.1.


in order to quantify the crystalline content in these films, theintegrated peak intensities of the various phases wereconsidered.The total crystalline content of the composite film, χCT, is

calculated by the relation:

χCT ¼AðαþβþγþcÞ

A αþβþγþcð ÞþAðamorphous phaseÞThe total crystalline content in the PVDF matrix, χT, can be

evaluated using the expression:

χT ¼AðαþβþγÞ

A αþβþγþcð ÞþAðamorphous phaseÞwhere A αþβþγð Þ is the area under curve corresponding to allthe crystalline peaks associated with PVDF, A αþβþγþcð Þ isthe total area corresponding to the crystalline phase of PVDFand PZT phases and A(amorphous phase) represents the arearelated to the amorphous PVDF content.Further, the quantification of the crystalline phases of α, β

and γ phases, χα, β, γ, in PVDF polymer is done by consideringthe integrated intensity of the deconvoluted peaks of the sameand is described by

χα;β;γ ¼Aðα; β; γÞ

AðαþβþγÞwhere A(α,β,γ) is the area of deconvoluted curve associatedwith peaks of α,β or γ phases and A(αþβþγ) is the total areaassociated with the crystalline phase of PVDF only. Thevariation in the total crystalline content of the composite filmsand the amount of α, β and γ phases in the PVDF matrix withthe volume content of PZT ceramic have been shown in Fig. 4.It can be seen from the figure that the crystalline content isenhanced with the increase in the volume content of PZTceramic in the composite. Further, it can also be seen that the βphase content enhances with the volume content of PZT in thePVDF matrix while α and γ phases are suppressed. However,the total crystalline content in the PVDF matrix for all thestudied composites is found to be within 50–55%. Hence, theincrease in β phase is a result of the transformation from α andγ phases as is evident from the figure. Since, β phase is

Fig. 4. The variation in the crystalline content of α, β,γ phases of PVDF alongwith the total crystallinity with the volume % of PZT ceramic in thePZT/PVDF composite.





Fig. 5. The variation in the Fβ % of PVDF with the volume % of PZT ceramicin the composite.

Fig. 6. The FTIR spectra of the [PZT]x/[PVDF]1�x system (a) x¼0 (b) x¼0.1(c)x¼0.2 (d) x¼0.3.

Fig. 7. A typical deconvoluted FTIR spectra for the quantification of α, β andγ phases present in the PVDF film.


responsible for the piezoelectric behavior in the PVDF, hence,the relative phase fraction is calculated as follows [10]:

Fβ ¼χβ

χαþχβ

The variation in the relative phase fraction of β phase in thecomposite films with the volume content of PZT is plotted inFig. 5. It can be seen from the figure that the β phase content in thecomposite increases with the increase in volume content of PZT.

3.1.2. FTIR studiesFig. 6 shows the FTIR spectra of PVDF and PZT/PVDF

composites. The different vibration modes at 604, 657 and774 cm�1 have been attributed to the perovskite phase of PZT.The α phase is characterized by the vibration bands at 764,795, 855 cm�1 while 778, 795 and 834 cm�1 are consideredto be signatures of γ phase and 840 cm�1 corresponds to the βphase of PVDF films. All the characteristic vibration bandsassociated with α, β and γ phases of PVDF are seen in case ofpure films but only the intense peaks of PVDF phaseassociated with vibration bands at 855 ,840 and 834 cm�1

could be observed for the composite films due to relativeintense peaks of PZT perovksite phase. The mixed α, β and γphases of PVDF along with the characteristic vibration bandsof perovskite phase of PZT is found in all the composite films.Fig. 7 shows a typical deconvoluted FTIR spectra for thequantification of α, β and γ phases present in the PVDF film.The phase content of the crystalline phases of the PVDF in thecomposite films was evaluated by the method given elsewhere[10]. The results obtained from the FTIR spectra were found tobe in close agreement with the XRD data. The relative phasecontent of β phase is found to be enhanced with the PZTinclusion in the composite as also revealed by XRD patterns.

3.2. Dielectric properties

Fig. 8 shows the variation in the dielectric constant withtemperature for PVDF and PVDF/PZT composite filmssynthesized under optimized processing conditions. A disper-sive anomaly in the dielectric behavior is seen around 80 1C


for pure PVDF film which is attributed to the wide angleoscillations of dipoles of the polymer followed by theirrotation with the main chain co-operation in the crystallinephase. The addition of the ceramic content to the polymer isseen to shift this anomaly in the dielectric constant to a highertemperature region. The addition of ceramics in the PVDFmatrix results in the hindrance of the movement of parts of thepolymer chain and hence, the thermal event is shifted towards





Fig. 8. The variation in the dielectric permittivity with temperature fordifferent volume contents of PZT ceramic in the [PZT]x/[PVDF]1�x system.

Table 1Summarized piezoelectric property of PZT/PVDF composites.

System [PZT]x/[PVDF]1�x Piezoelectric coupling coefficient, d33, pC/N

x¼0 �32x¼0.1 60x¼0.2 71x¼0.3 84

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higher temperature [33,34]. The transition temperature Tc inthe composites associated with the transformation from alltrans to a disordered mixture of TGTGʹ and TTTGTTTGʹ inPVDF is found to shift to a higher temperature with theaddition of ceramic content. It can be seen from the figure thatthis transition temperature of phase transformation from ferro-electric to paraelectric phase is 102 1C for pure PVDF films,while it is found to be 138 1C for 30% volume content of PZTin the composite. The dielectric permittivity is found toincrease from 60 to 72 with the increase in volume contentfrom 0 to 30 volume % of PZT in the composite. This increasein the dielectric permittivity is observed with the increase inthe ceramic content of the polymer as expected due to theincreasing contribution of the PZT ceramic and due to the βenriched PVDF in the composite. It is also found that thedielectric permittivity obtained in the present study is alsohigher than reported in the literature which may be due to theoptimized processing conditions adopted for the synthesis ofthese composites [35].

3.3. Piezoelectric properties

Table 1 shows the variation of piezoelectric couplingcoefficient d33 with different volume percentages of ceramicin the composites. The neat PVDF synthesized film showed thed33 value as �32pC/N whereas with the increase in thevolume content of PZT ceramic from 0.1 to 0.3 in the polymermatrix, it is observed to increase from 60pC/N to 84pC/N. Thisincrease in the piezoelectric response with the increase in the


volume content of ceramic may be attributed to the increasingcontribution of PZT and β enrich phase of PVDF in thecomposite films [36].

4. Conclusions

The thin composite films of PZT/PVDF with differentcompositions were synthesized under optimized processingconditions. These films were highly flexible and containedPZT ceramic particles uniformly distributed over the film. Thestructural characterization revealed the ceramic is in the MPBregion for pure PZT powders. The pure films of PVDF andPZT/PVDF are found to be mixture of α,β,γ and perovksitephases along with the amorphous phase. The crystallinecontent is found to increase with the addition of PZT ceramicin the composite films. The increase in volume content ofceramic particles in the films contributed to the increase indielectric and piezoelectric properties. It is also observed thatthe addition of PZT ceramic in the PVDF matrix led to anincrease in β phase which further enhanced the dielectric andpiezoelectric properties of the composite films.

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Structural, dielectric and piezoelectric properties of 0–3 PZT/PVDF composites

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