Issue1. Vol.1 (April, 2013) - IIT Mandi

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ESSENT Society for Collaborative Research and Innovation, IIT MandiPiezoelectric Propertiesof Diphasic FerroelectricPZT–PVDF and PZT–PMMA CompositesDr. Venkata Krishnan, Assistant Professor,School of Basic Sciences, IIT Mandi.Dr. Venkata Krishnan is an assistant professorof chemistry at the school of basic sciences atIIT Mandi. He obtained his Ph.D. in physicalchemistry in 2006 from the University ofStuttgart in Germany. Subsequently, he workedas a post-doctoral researcher from 2006 to2010 at the University of Pennsylvania in U.S.A.and then as a research associate from 2010 to2012 at the National Institute for MaterialsScience, Tsukuba, Japan. During his academiccareer, he has received several fellowships andawards. Recently, he has received the DSTINSPIRE faculty award in chemical sciences in2011. His broad research interests are in thefields of materials chemistry and x-ray science.He has published many research articles inreputed international journals.AbstractFerroelectric ceramic-polymer composites are ofspecial interest in transducer/sensor applicationsbecause of their several advantages over pureferroelectric ceramics. The composites haveimproved mechanical properties, low densityand better durability. In this work, thepiezoelectric properties of PZT-Polymercomposites of 0-3 connectivity, prepared by hotpresstechnique are presented, wherein aferroelectric polymer PVDF and a nonferroelectricpolymer PMMA were used asmatrices. The density, piezoelectric straincoefficient d 33 , piezoelectric voltage coefficientg 33 , dielectric constant k and microhardness ofthe two types of composites measured as afunction of volume fraction of PZT in thepolymers indicate that the PZT–PVDFcomposites exhibit better piezoelectricsensitivity than PZT–PMMA composites, whichcould be attributed to the ferroelectric nature ofthe polymer PVDF.1. IntroductionThe best known material for piezoelectricapplications is the ferroelectric ceramic leadzirconate titanate (PZT). PZT has highpiezoelectric parameters, making it an extremelysensitive sensor/actuator material. But it has thedisadvantage of being highly dense and brittle.To get a less dense and more compliantferroelectric material, composites of PZT andpolymers have been proposed and widelystudied [1-3]. The properties of the compositescan be tailored by changing the connectivity ofthe phases and the volume fraction of theceramic in the composite. Of the ten differentconnectivity patterns [1], 0-3 connectivity is thesimplest and easily achievable.The parameters of interest in the application ofthese materials as transducers are thepiezoelectric strain coefficient (d), piezoelectricvoltage coefficient (g), piezoelectric constants (eand h), electromechanical coupling factor,density and mechanical parameters such ascompliance constant and mechanical strength.The d and g coefficients measure the26 ESSENT|Issue1|Vol1
ESSENT Society for Collaborative Research and Innovation, IIT Mandiperformance of piezoelectric sensors in thereceiver mode whereas the e and h coefficientsare used to express the ability of thepiezoelectric actuators in the transmitting mode.The piezoelectric constants d, g, e and h aretensors of rank 3. They are defined by as below[3],dgehijijijij⎛ dD ⎞i= ⎜ ⎟dT⎝ j ⎠⎛ dE ⎞i= ⎜ ⎟dT⎝ j ⎠⎛ dD ⎞i= ⎜ ⎟dS⎝ j ⎠EDE⎛ dE ⎞i= −⎜⎟dS⎝ j ⎠⎛ dS=⎜⎝ dEji⎞⎟⎠⎛ dSj ⎞=⎜dD⎟⎝ i ⎠TT⎛ dTj ⎞= −⎜dE⎟⎝ i ⎠DS⎛ dTj ⎞= −⎜dD⎟⎝ i ⎠Scomposites were prepared by hot-presstechnique described in literature [4]. The solventused was dimethyl formamide (DMF) for PZT–PVDF composite and acetone for PZT–PMMAcomposites. Samples of specific dimensionswere obtained by applying a pressure of 115 x10 6 Nm -2 . The samples were electroded on boththe faces using conductive silver epoxy(Chemtronics USA). The electroded sampleswere poled at 3.5 x 10 6 Vm -1 for one hour at120 o C for PZT–PVDF composites and at 90 o Cfor PZT- PMMA composites, depending on themelting point of the respective polymer. Forpoling, the sample was kept immersed insilicone oil bath to ensure uniform heating andto avoid arcing. It is to be mentioned that thesamples suffered electrical breakdownfrequently and several experiments need to beperformed.Here i = 1,2,3 and j = 1, 2, 3, 4, 5,6. T j is thestress (tensor of rank 2 expressed in matrixnotation) , S j is the strain (tensor of rank 2expressed in matrix notation), E i is the electricfield (vector) and D i is the electric displacement(vector). In this work, the piezoelectricparameters d 33 , g 33 , dielectric constant k, andmicrohardness are studied as a function ofvolume fraction of PZT in the polymers PVDFand PMMA. Here 3 refers to the polingdirection. The parameters d 33 and g 33 aredenoted by d and g in the rest of the text.In this work, a ferroelectric polymer,polyvinylidene fluoride (PVDF) and a nonferroelectricpolymer, polymethyl methaacrylate(PMMA) were used along with PZT to preparecomposites of 0-3 connectivity and theirpiezoelectric properties were studied.2. Experimental MethodsThe PZT powder was purchased from AmericanPiezoceramics. The polymers PVDF andPMMA were from Aldrich chemicals. TheTable 1. Comparison of the theoretical andexperimental density values of PZT–PVDF and PZT–PMMA compositesThe density of the composite samples wasdetermined by knowing the mass and volume.The mass of the samples was measured using adigital balance of 0.1 mg resolution and thevolume was determined from the dimensions.The dielectric constant of the samples, at a fixedfrequency of 1 KHz, was measured using aPiezometer (Take Control Piezometer SystemPM35) in mode C. The piezoelectric straincoefficient (d) of the composite samples wasmeasured using the Piezometer System in modeD. The frequency of the dynamic force wasfixed at 103 Hz. The microhardness of thecomposite samples were measured using27 ESSENT|Issue1|Vol1
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Issue1. Vol.1 (April, 2013) - IIT Mandi

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