CERAMICSINTERNATIONAL

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Ceramics International 41 (2015) 9328–9336

Study of sintering behavior of PAN–PZT using dilatometry and co-relationwith piezoelectric properties

Jun Sae Hana, Kwang Hyun Chungb, Ravi Bollinac, Kyungseop Kimd, Cheeyoung Johd,Hee Seon Seod, Seong Jin Parka,n

aDepartment of Mechanical Engineering, Pohang University of Science and Engineering (POSTECH), Pohang 790-784, Republic of KoreabKyungwon Industry. Co. Ltd., 1260-4 Shihung-si, Kyonggi-do, Republic of Korea

cMahindra Ecole Centrale, Survey No: 62/1A, Bahadurpally Jeedimetla, Hyderabad 500043, IndiadAgency for Defense Development, P.O.Box 18, Jinhae-shi, Republic of Korea

Received 9 February 2015; received in revised form 26 March 2015; accepted 27 March 2015Available online 10 April 2015

Abstract

The sintering behavior of Pb(Al0.5Nb0.5)O3–Pb(Zr0.52Ti0.48)O3 (PAN–PZT) ceramics was investigated. The sintering process of PAN–PZT wasdivided into four stages based on the amount of in-situ linear shrinkage: (Stage 1) initial stage at sintering temperature RTrTsr to 770 1C,(Stage 2) perovskite formation stage at 770rTsr990 1C, (Stage 3) densification stage at 990rTsr1265 1C and (Stage 4) Pb-loss stage atTs41265 1C. During stage 1, heating of PAN–PZT compact did not cause structural changes except the thermal expansion. During stage 2, thePZT-perovskite structure was formed by rearrangement of crystals. During stage 3, the specimen was rapidly densified with two peaks of strainrate. During stage 4, Pb was volatilized and this loss resulted in sudden increase of shrinkage. On analyzing the sintering stages, the optimizedsintering conditions were considered as 1250 1C just before of Pb-loss stage. The effects of Ts on the crystal structure, microstructure and thepiezoelectric performance were analyzed and documented.& 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Keywords: A. Sintering; D. Perovskites; PAN–PZT; Dilatometry; Ceramics

1. Introduction

Pb(Zr0.52Ti0.48)O3 (lead zirconate titanate, PZT) is one of themost widely used piezoelectric ceramic due to its superiorpiezoelectric performance. The ferroelectric and piezoelectricnature of PZT ceramics has led to numerous applications inelectronic devices, such as actuators, sensors, capacitors,resonators and high-power transducers [1–5]. Furthermore,PZT ceramics could be modified or doped with differentadditives, which make them specific applications. Kovalet al. [6] have modified the PZT structures by addition ofvarious amount of PMN. The xPMN-(1–x)PZT ceramicssystem shows d33 in the range of 121–430 pC/N. Gao et al. [7]

have reported about 0.2PZN–0.8PZT ceramics with the addition ofWO3 while showing a d33 as 314 pC/N. Chao et al. [8] investigateabout the effects of CuO addition to the Pb(Zr0.25Ti0.48)O3–Pb(Mg1/3Nb2/3)O3–Pb(Zn1/3Nb2/3)O3 ceramics with the 280 pC/N ofd33. Zhang et al. [9,10] have reported about the high energy ballmilling technique using Pb0.99Nb0.02[(Zr0.60Sn0.40)0.94Ti0.06]0.98O3

and (1!x) BiScO3–xPbTiO3 which are in a morphotropic phaseboundary (MPB)Among various PZT systems, the mixture of Pb(Al0.5Nb0.5)O3

(lead aluminum niobate, PAN) and PZT (PAN–PZT) is promisingfor special applications due to its temperature stability with highcurie temperature. Kim et al. [11] have suggested about a solidsolution system of 0.05PAN–0.95PZT doped with Nb2O5 andMnO2. The doping of Nb2O increased from 0 to 1 wt%, thepiezoelectric properties, the !T3=!0, d33, kp, values increased and Qm

value slightly decreased. In contrary, MnO2 increased the Qm value

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http://dx.doi.org/10.1016/j.ceramint.2015.03.2810272-8842/& 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

nCorresponding author. Tel.: "82 54 279 2182.E-mail address: sjpark87@postech.ac.kr (S.J. Park).

dramatically and decreased !T3=!0, d33, kp values. The optimizedpiezoelectric properties were obtained as 340 pC/N of d33 with392 1C of curie temperature when PAN–PZT"0.7 wt% Nb2O5

with 0.5 wt% MnO2 ceramics sintered at 1200 1C for 1 h. Leeet al. [12] have investigated about effect of CuO addition onsintering temperature and piezoelectric properties of 0.05Pb(Al0.5Nb0.5)O3!0.95Pb (Zr0.52Ti0.48)O3"0.7 wt% Nb2O5"0.5wt% MnO2. Doping of CuO in PAN–PZT ceramics can lowerthe sintering temperature due to the liquid phase sintering whileshowing the 361 pC/N of d33 sintered at 900 1C with the 1 wt% ofCuO. We choose to investigate about further research about PAN–PZT ceramics for high temperature applications due to its superiord33 with temperature stability in comparison to other piezoelectricceramics.

The properties of PAN–PZT ceramics such as density,piezoelectric charge constant, dielectric constant are stronglydependent on the manufacturing process. In the powderprocessing technology, sintering conditions especially thesintering temperature Ts mainly determines the final propertiesand hence the performance of piezo ceramics. The crystalstructures, grain sizes, and density vary with respect to Tshence have direct effect on the final properties and finally thevaporization of Pb should be avoided since it dramaticallychanges the piezoelectric properties. Yue et al. [13] observeabout correlation between sintering temperature and themicrostructure results in different piezoelectric performancein PMN–PZT ceramics by manufactured via electrophoreticdeposition (EPD) method. From their experimental data, it isobserved that excessive Pb loss occurs at 1300 1C and grainsize was increased from 3 to 9 mm sintering at 1200 to1300 1C. Wang et al. [14] report about the effects of sinteringtemperature and time with a densification, microstructure andproperty using of PZT/ZnO nanowhisker manufactured viagel-casting technique. Liu et al. [15] investigate about sinteringtemperature from 1150 to 1250 1C while indicating an increasein bulk density and grain size correlation to increase inpiezoelectric properties. It is reported that the excessive hightemperature results the evaporation of Pb with lower piezo-electric performances. Lead volatilization increases with tem-perature and also the sintering holding time [16–18]. Theexcessive holding time also brings the Pb loss, which is notsuitable for processing and final properties.

In order to develop the sintering process for piezoelectricPAN–PZT ceramics, careful consideration should be given tothe Pb volatilization phase. This is a time-consuming processand requires multiple sets of experiments to determine theexact nature of the sintering process. We suggested that theunderstanding of the sintering process can be advanced byinvestigating the shrinkage behavior of the material duringsintering. Shrinkage behavior of compact correlated directly tothe densification process occurring during sintering. Somedilatometry studies have been reported for W–Cu powders[19], nano-CeO2 particles [20] and synthetic hydroxyapatites[21]. The sintering stages of each material were reported andbased on that results, optimized sintering condition could bedeveloped without conducting the time consuming sinteringexperiments. Dilatometry with piezoelectric material has been

performed as a part of investigation process without much indepth analysis [22,23]. The purpose of this work is to under-stand the sintering behavior and predict the optimum sinteringtemperature by analyzing the dilatometry behavior of thePAN–PZT ceramics. This allows for every analysis fordifferent compositions without performing the time-consuming individual sintering experiment. Finally, we inves-tigate the powder metallurgy the through press sinter methodto fabricate PAN–PZT ceramics. Once the process conditionsare understood and optimized, we would like to move tominiature shaped ceramics via ceramic injection molding forhigh temperature applications.In the present study, sintering behavior of PAN–PZT

ceramics was investigated by identifying distinct stages ofthe sintering. Four distinguishable stages were defined basedon in-situ dilatometer measurements: (Stage 1) initial stage atsintering temperature RTrTsr to 770 1C, (Stage 2) perovs-kite formation stage at 770rTsr990 1C, (Stage 3) densifica-tion stage at 990rTsr1265 1C and (Stage 4) Pb-loss stage atTs41265 1C. Especially at Pb-loss stage at 1265 1C, evapora-tion of Pb was measured. It should be noted that the optimizedTs was determined as 1250 1C just before the Pb-loss stage.Based on the defined stages, the effects of Ts on the crystalstructure, microstructure and the piezoelectric performancewere analyzed. At stage 2, crystal structure was rearrangedas forming the PZT-perovskite structure and at stage 4, apyrochlore phase was observed due to Pb loss. The sinteredgrain size increases with increase of sintering Ts but in stage 4Pb volatilization brings about abnormal grain growth, which isdetrimental to the final properties. Consequently, the materialproperty including density d33 and dielectric constant showmaximum values at 1250 1C which was slightly lower than thetemperature at which Pb loss begins as estimated fromdilatometry analysis.

2. Experimental procedures

2.1. Powder characteristics

The synthesized Pb(Al0.5Nb0.5)O3–Pb(Zr0.52Ti0.48)O3 (PAN–PZT) powder was provided by Kyungwon Industry Co.Limited. The starting materials were PbO, Al2O3, Nb2O5,ZrO2 and TiO2. The mixtures of the starting powders were ballmilled in distilled water for 24 h using zirconia ball. Themixture was dried for 24 h and calcined at 850 1C for 1 h inair atmosphere. The calcined powder was mixed with additives(Nb2O5). Fig. 1 shows the shape morphology of providedpowder observed by the scanning electron microscope (SEMPhilips XL30S FEG). It can be found that the fine powders werein irregular shapes and agglomerated. Fig. 2 shows the measuredparticle size distributions of PAN–PZT powder by the particlesize distribution analyzer (Horiba LA-950V2). Measured meanparticle size was up to 2. 13 mm which is a bit higher than theempirical observations made in the SEM. This is attributed tothat fact that the agglomeration of the powder skewed the laserparticle size to slightly higher value. Table 1 summarizes someimportant characteristics of powder. The tap density and the

J.S. Han et al. / Ceramics International 41 (2015) 9328–9336 9329

apparent density were measured using a tap density volumeter(Bettersize BT-300); the pycnometer density, which was used asa reference value for the theoretical density, was measured using

an automatic helium pycnometer (Micromeritics AccuPyc1330). The piezoelectric charge constant, used as a referencevalue for its piezoelectric performance was provided by thepowder manufacturer.

2.2. Compaction

Green bodies for the sintering experiment were prepared bydie compaction using a universal testing machine (ShimadzuUDH-50). An aqueous solution of 8 wt% polyvinyl alcohol(PVA) and 92 wt% water was used as a binder for green bodyformation. The melting temperature range was from 180 to190 1C and decomposition temperature was 200 1C. PAN–PZTpowder was mixed with 5 wt% of PVA solution and com-pacted into a cylindrical die (diameter 7.00 mm; height11.15 mm). The compressive test was conducted in the rangeof pressure 50rPr400 MPa to analyze the compactionbehavior and the tap density of mixture was used as a0 MPa pressure. The green bodies for sintering experimentswere prepared at P#100 MPa, which gave them green relativedensity as 59%.

2.3. Sintering and dilatometry

Prepared green bodies were sintered in a closed crucible toprevent evaporation of Pb. Kingon et al. [16,17] discuss aboutthe importance of Pb loss and its effect on sintering kinetics ofPZT. In this study, we use a closed crucible with extra PAN–PZT powder to create PbO rich atmosphere to avoid Pb lossdue to evaporation. Effect of crucible types on the variations ofmass was analyzed using a thermal gravity analyzer (TGA,Mettler TGA/DSC 1). The in-situ linear shrinkage wasmeasured using a dilatometer (Netzsch DIL 402 C) to identifythe sintering stages of PAN–PZT ceramics. The heating profileconsisted of initial heating from RT to 600 1C at 3.33 1C/min,a PVA burn-out process at 600 1C for 60 min, and subsequentheating from 600 to 1300 1C at 1.67 1C/min is shown in Fig. 3.The heated sample was held at 1300 1C for 90 min, and thencooled with 10 1C/min cooling rate. The dilatometer experi-ments were conducted in argon atmosphere and three sets ofexperiments were conducted to check for repeatability. Duringheating, the linear shrinkage of specimen was measured andthe change of strain rate was calculated based on the shrinkagedata. Based on the results of dilatometer experiment, samplesfor characterization were prepared at nine temperatures. Thesamples were sintered as following specified heat profiles at700rTsr1300 1C as shown in Table 2. A-01 to A-04 wasprepared for the crystal structure analysis and B-01 to B-05was prepared for the material property analysis. Except the

Fig. 1. Shape morphology of PAN–PZT powder as observed by SEM showingirregular shaped particles.

Fig. 2. Particle size distributions of PAN–PZT powder; D10#0.97 μm,D50#2.13 μm, D90#4.53 μm.

Table 1Characteristics of PAN–PZT powder.

Particle size (D10) Particle size (D50) Particle size (D90) Apparent density Tap density Pycnometer density Piezoelectric charge constant (d33)

0.97 (μm) 2.13 (μm) 4.53 (μm) 1.03 (103 kg/m3) 2.03 (103 kg/m3) 7.98 (103 kg/m3) 420 (10!12 C/N)

Fig. 3. Heating profile for dilatometer experiment.

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holding temperature, same sintering conditions were main-tained in all the experiments. 5 samples were sintered at eachcondition and average results are used for the study.

2.4. Characterization

The sintered samples were characterized for sintered density,crystal structure, microstructure and piezoelectric properties. TheXRD pattern was analyzed using an X-ray diffractometer (XRDRIGAKU D/MAX-2500/PC) to investigate the change in crystalstructure. The microstructures of sintered samples were observedusing a scanning electron microscope (SEM, Philips XL30SFEG) and their elemental compositions were detected usingEDAX/EDS. The bulk densities were measured using theArchimedes method and the sample mass was measured to checkfor any mass variations. To assess the piezoelectric performance,silver was deposited as electrodes on both top and bottom side.The poling process was conducted in an oil bath at 150 1C, at avoltage of 1.5 kV/mm and a holding time of 50 min. Thepiezoelectric charge constant, dielectric constant, resonancefrequency for effective electromechanical coupling coefficient,mechanical quality factor were measured using d33 meter(Piezotest PM100) and impedance analyzer (Agilent 4294 A).

3. Results and discussion

3.1. Compressibility

Fig. 4 shows the compressibility curve for PAN–PZTceramics indicating the relationship between compactionpressure and relative density of die pressed green parts. Inthis curve, the tap density of PAN–PZT powder and PVAmixture were measured and used as 0 MPa densities. Thegreen density increased rapidly with compaction pressure fromP#50 to 200 MPa, then increased slowly at P4200 MPa. Wehave observed during experimentation that if the green densityis too low, defects occur after sintering or poling and if thegreen density is too high, cracks form after compaction. Basedon these preliminary results, we chose P#100 MPa to achieverelative green density as 59%. All samples for sintering

experiment were prepared with the same compaction condi-tions showing the same green densities.

3.2. Sintering behavior

The type of crucible has significant effect on sinteringbehavior of PAN–PZT, as seen from Fig. 5, thermal gravi-metric analysis of PAN–PZT powder varied according tocrucible type used. In the conventional open crucible, thereduction of mass due to Pb loss was observed at 750 1C, butin a closed crucible, variation of mass was not observed up to900 1C, i.e., this crucible with extra PZT powder prevented Pbloss even up to 900 1C. For sintering experiment, samples weresintered in this closed crucible with extra PAN–PZT powder toprevent Pb loss by enriching the content of PZT in theatmosphere.In-situ linear shrinkage was measured to analyze sintering

behavior of PAN–PZT with the given heating schedule asmentioned in Fig. 3. Fig. 6 shows the linear shrinkage ofcompacted specimen and Fig. 7 shows the calculated strain rates.Strain rate was calculated by dividing the measured shrinkage bymeasuring time. Changes of shrinkage and strain rates show fourdistinct stages at RTrTsr770 1C, 770rTsr990 1C, 990rTsr1265 1C and 1265rTsr1300 1C.

Table 2Heating schedules with nine temperatures; A-01–A-04 for crystal structureanalysis and B-01–B-05 for material property analysis.

Label Heating rate Holding temperature(1C)

Holdingtime

Atmosphere

A-01 1.67 1C/min 700 90 min Air with closedcrucibleA-02 800

A-03 900A-04 1000B-01 1200B-02 1225B-03 1250B-04 1275B-05 1300

Fig. 4. Compressibility curve for the PAN–PZT powder with respect topressure.

Fig. 5. Relations between temperature and mass with respect to crucible type.

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During stage 1 named as initial stage, the PAN–PZT showedlittle amount of shrinkage and no Pb loss was observed.During stage 2 namely the perovskite formation stage, thesample starts to shrink, and strain began to change even thoughthe temperature was not sufficient for pre-sintering to occur.These changes were caused by rearrangement of the crystalsand formation of perovskite structure similar to that happeningin the process of calcination. The calcination process is one ofthe steps in the manufacturing process of PZT powder. At thisstep, the PZT powder forms the perovskite crystal structureand it is widely conducted at around at the two-thirds ofsintering temperature. The crystal structure change at this stagewas analyzed using XRD pattern and detail results arediscussed in the next section.

During stage 3 namely the densification stage, a drasticchange of shrinkage and two peaks of strain rate wereobserved; these changes were due to major densificationoccurring in this temperature range. Prior studies on ceramicpowders, reported only one peak in the strain rate [24].However, in this study two peaks were observed (at 1115and 1165 1C), which are due to the liquid phase formation andrapid sintering due to the liquid phase. There was no additivematerial for low sintering temperature but in the high Ts, liquidphase occurred causing rapid densification and subsequentgrain growth. In first peak, particle rearrangement and theformation of the first liquid occurred and in the second peak,

specimen is densified [25]. During stage 4 namely as Pb-lossstage at Ts41265 1C, the specimen suddenly shrank withchange of strain rate; this change occurred due to loss of Pb.Although a closed crucible was used, Pb loss was acceleratedat high Ts, and the resultant mass reduction caused theshrinkage and change in strain rate. Pb usually volatilized attemperatures to PbO at these temperatures close to 1265 1C.This is seen from EDAX/EDS and the property measurementsconducted.

3.3. Crystal structure

The XRD pattern analysis was conducted to observe thechanges of crystal structure during sintering at700rTsr1000 1C as shown in Fig. 8. For specimens sinteredat Tso900 1C, phase change was not observed and the X-raypattern was similar to the pattern of calcined powder. Speci-mens sintered at 1000 1C showed the change of crystalstructure as forming the perovskite structure, which indicatesthat the phase change during sintering caused variations ofshrinkage and strain rate, as observed during the second stageof sintering. The XRD patterns of samples sintered at 1200–1300 1C were measured as shown in Fig. 9. Samples sinteredat Tso1275 1C showed morphotropic phase boundary, and thecrystal structure did not change; this result corresponds to theobservation that sintering in this temperature range does notchange the crystal structure. At TsZ1300 1C, phase changeoccurred and the secondary phase appeared; this temperaturebelongs to stage 4 of sintering process, during which Pb lossaffect the phase change, the shrinkage, and the strain rate asmaking the secondary phase. The measured secondary phasewas a pyrochlore peak as observed in previous research [26]on the effects of sintering holding time on the sintering processof PMN–PZT.

Fig. 6. Linear shrinkage during sintering process with four stages.

Fig. 7. Calculated strain rate during sintering process with four stages.

Fig. 8. Crystal structure of the PAN–PZT at temperature of stage 2 (perovskiteformation).

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3.4. Microstructure and EDAX/EDS analysis

Fig. 10 shows microstructures of sintered surface of speci-mens with respect to the different temperatures. As Tsincreased, grain size increased. Grain sizes of specimenssintered at 1200–1300 1C were measured by line intersectsmethod and the empirical values were 1.6, 2.0, 2.7, 3.5 and4.1 mm. At 1200rTsr1250 1C grain size enlargement washomogeneous, but at 1275 1C and 1300 1C, abnormally largegrains were observed and the distribution of grain size becameinhomogeneous. Especially at 1300 1C, the grains becameangular due to the evaporation of Pb from inside the sinteredbody. During stage 3 of sintering, increase of Ts enlarged thegrain size homogeneously, but at stage 4, Pb loss resulted inabnormal grain size enlargement with inhomogeneous size

distributions and shapes. Conventionally larger grains corre-spond to higher piezoelectric and dielectric properties [27].Although the increase of grain size with respect to high Ts canenhance the piezoelectric performance, but exceeding thecritical sintering temperature will cause loss of Pb andadversely affect the piezoelectric properties, due to determinein density and deteriorate of the microstructure.Fig. 11 shows the results of EDAX/EDS analysis performed

on specimens that had been sintered at 1250 1C and 1300 1C.The Pb content was also significantly lower in the specimensintered at 1300 1C than in the specimen sintered at 1250 1C.A qualitative element analysis was conducted at two positionson each specimen. Contents were the same at the two positionsin the specimen sintered at 1250 1C, but differed at the twopositions in the specimen sintered at 1300 1C. These resultsindicate that at 1300 1C, a significant amount of Pb hadevaporated, and that this resulted in inhomogeneous elementcontent.

3.5. Property measurement

Fig. 12 shows relations between sintering temperatures andmaterial properties including the bulk density and the dielectricconstant. Increase of Ts densified the PZT ceramics andresulted in an increase of bulk density, but at 1275 and1300 1C, density decreased due to the evaporation of Pb whichwas expected as seen with dilatometer experimental results.The sintered density achieved was maximum (98.6% ofrelative density) at Ts#1250 1C. For the dielectric property,it shows similar trends to the density while showing amaximum value at Ts#1250 1C.Fig. 13 shows relations between sintering temperatures and

the piezoelectric properties including the piezoelectric chargeFig. 9. Crystal structure of the PAN–PZT in temperature of stages 3 and 4(densification and Pb loss).

Fig. 10. Microstructures of sintered PAN–PZT ceramics with respect to different sintering temperatures.

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constant (d33), effective electro-mechanical coupling coeffi-cient (Keff). The effective electro-mechanical coupling coeffi-cient (Keff) for length mode was calculated using the squareroot of the ratio of the stored mechanical energy over input

electrical energy using obtained resonance frequency (fr) andanti-resonance frequency (fa) as Eq. (1) [28]. For the standardspecimen, electromechanical coupling coefficient (kp) is widelyevaluated, but for structural applications, in this work ascylindrical type, Keff can be used for the evaluation ofelectromechanical coupling property [29,30]. Each piezoelec-tric property showed similar trends to the density whileshowing peak at Ts=1250 1C. Therefore, the increase ofdensity and the grain size enlargement enhance the piezo-electric properties. However, at Ts41250 1C each propertydecreased dramatically due to Pb loss and decrease in bulkdensity. The decrease of the relative density at Ts=1300 1Cwas $2% due to Pb loss, but the decrease of the d33 was up to85%. This large change in piezoelectric charge with smalldecrease in Pb content indicates that the Pb evaporation wasthe key factor that determines the performance of the piezo-electric ceramics. In this study the optimal Ts was 1250 1C,which is slightly lower than the temperature at which Pb lossbegins.

Keff #

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1!f rf a

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Table 3 summarizes measured piezoelectric properties withthe optimized sintering condition, Ts at 1250 1C. The maximumpiezoelectric charge constant (d33) was 415' 10!12C/N, whichwas 99% of the reference value from powder manufacturer. TheKeff for length and radial mode were 57 and 29%, respectively.The mechanical quality factors (Qm) which indicates thesharpness of resonance were 37 and 85 for length and radialmode, respectively.

4. Conclusions

As investigating the sintering behavior of PAN–PZT cera-mics, dilatometry was efficiently used as technique to identify

Fig. 11. Element compositions of PAN–PZT ceramics with respect to different temperatures and measuring positions.

Fig. 12. Relations of sintering temperatures to the relative density and thedielectric constant.

Fig. 13. Relations of sintering temperatures to the piezoelectric chargeconstant and the effective electromechanical coupling coefficient.

J.S. Han et al. / Ceramics International 41 (2015) 9328–93369334

sintering stages in PAN–PZT and correlate the sinteringbehavior to microstructure and final piezoelectric properties.The sintering process of PAN–PZT ceramics was divided into(Stage 1) initial stage, (Stage 2) perovskite formation stage,(Stage 3) densification stage and (Stage 4) Pb-loss stage. Assintering temperature Ts increased, perovskite structureformed; during the second stage, the crystal structure ofcalcined powder was rearranged with little shrinkage. Duringthe third stage, the PAN–PZT powder densified and showedtwo peaks of strain rate, possibly due to liquid phaseformation. During the Pb-loss stage, Pb evaporated due tothe high temperature. Pb loss caused change of the crystalstructure causing secondary phases and angular large abnormalgrains in the microstructure. The resultant compositions hadnon-uniform distributions, and this non-uniformity and the Pbloss reduced the piezoelectric performance drastically. Theoptimal sintering temperature was determined as 1250 1Cwhich is slightly lower than the temperature at which Pb-lossstage begins as estimated from dilatometry analysis.

Acknowledgments

This research was financially supported by a grant to MEMSResearch Center for National Defense funded by DAPA/ ADD(No. UD120014FD).

References

[1] G.H. Haertling, Ferroelectric ceramics: history and technology, J. Am.Ceram. Soc. 82 (1999) 797–818.

[2] Z. Yang, Y. Hou, H. Pan, Y. Chang, Structure, microstructure andelectrical properties of (1-x-y)Bi0.5Na0.5TiO3!xBi0.5K0.5-TiO3!yBi0.5Li0.5TiO3 lead-free piezoelectric ceramics, J. Alloy.Compd. 480 (2009) 246–253.

[3] S.Y. Cheung, S.L. Fu, C.C. Wei, Low-temperature sintering of PZTceramics, Ceram. Int. 13 (1987) 223–231.

[4] M.A. Mohiddon, K.L. Yadav, Dielectric dispersion study of Mn-dopedPLZT (8/65/35), Phys. Status Solidi A 206 (2009) 1606–1615.

[5] J.A. Gallego-Juarez, Piezoelectric ceramics and ultrasonic transducers,J. Phys. E: Sci. Instrum. 22 (1989) 804–816.

[6] V. Koval, C. Alemany, J. Briancin, H. Brunckova, K. Saksl, Effect ofPMN modification on structure and electrical response of xPMN-(1-x)PZT ceramic systems, J. Eur. Ceram. Soc. 23 (2003) 1157–1166.

[7] F. Gao, C.J. Wang, X.C. Liu, C.S. Tian, Effect of tungsten on thestructure and piezoelectric properties of PZN–PZT ceramics, Ceram. Int.33 (2007) 1019–1023.

[8] X. Chao, D. Ma, R. Gu, Z. Yang, Effects of CuO addition on theelectrical responses of the low-temperature sintered Pb(Zr0.52Ti0.48)O3!Pb(Mg1/3Nb2/3)O3!Pb(Zn1/3Nb2/3)O3 ceramics, J. Alloy. Compd.491 (2010) 698–702.

[9] L. Zhang, Z. Xu, Y. Feng, Y. Hu, X. Yao, Synthesis, sintering andcharacterization of PNZST ceramics from high-energy ball millingprocess, Ceram. Int. 34 (2008) 709–713.

[10] L. Zhang, Z. Xu, Z. Li, S. Xia, X. Yao, Preparation and characterizationof high Tc (1!x) BiScO3!xPbTiO3 ceramics from high energy ballmilling process, J. Electroceram. 21 (2008) 605–608.

[11] S.J. Kim, J.Y. Han, J.W. Choi, C.Y. Kang, H.J. Kim, D.Y. Jeong, M.Y. Sung, S.J. Yoon, Piezoelectric and dielectric properties of 0.05Pb(Al0.5Nb.0.5)O3–0.95Pb(Zr0.52Ti0.48)O3 ceramics doped with Nb2O5 andMnO2, Jpn. J. Appl. Phys. 46 (2007) 691–694.

[12] J.Y. Lee, J.W. Choi, M.G. Kang, S.J. Kim, T.K. Ko, S.J. Yoon, Effect ofCuO addition on sintering temperature and piezoelectric properties of0.05Pb(Al0.5Nb0.5)O3!0.95Pb(Zr0.52Ti0.48)O3"0.7 wt% Nb2O5"0.5 wt% MnO2 ceramics, J. Electroceram. 23 (2009) 572–575.

[13] J. Yue, M. Leung, E. Haemmerle, M. Hodgson, G. Li, W. Gao, Theinfluence of sintering conditions on the dielectric and piezoelectricproperties of PbZrTiO–PbMgNbO ceramic tubes, J. Alloy. Compd. 470(2009) 465–469.

[14] D.W. Wang, M.S. Cao, J. Yuan, R. Lu, H.B. Li, H.B. Lin, Q.L Zhao, D.Q. Zhang, Effect of sintering temperature and time on densification,microstructure and properties of the PZT/ZnO nanowhisker piezoelectriccomposites, J. Alloy. Compd. 509 (2011) 6980–6986.

[15] W. Liu, J. Xu, R. Lv, Y. Wang, H. Xu, J. Yang, Effects of sinteringbehavior on piezoelectric properties of porous PZT ceramics, Ceram. Int.40 (2014) 2005–2010.

[16] A.I. Kingon, J.B. Clark, Sintering of PZT ceramics: I, atmospherecontrol, J. Am. Ceram. Soc. 66 (1983) 253–256.

[17] A.I. Kingon, J.B. Clark, Sintering of PZT Ceramics: II, Effect of PbOcontent on densification kinetics, J. Am. Ceram. Soc. 66 (1983) 256–260.

[18] C.H. Wang, S.J. Chang, P.C. Chang, Effect of sintering conditions oncharacteristics of PbTiO3!PbZrO3!Pb(Mg1/3Nb2/3)O3!Pb(Zn1/3Nb2/3)O3, Mater. Sci. Eng. B-Adv. Funct. Solid-State Mater. 111 (2004)124–130.

[19] S.S. Ryu, Y.D. Kim, I.H. Moon, Dilatometric analysis on the sinteringbehavior of nanocrystalline W–Cu prepared by mechanical alloying,J. Alloy. Compd. 335 (2002) 233–240.

[20] Y. Kinemuchi, K. Watari, Dilatometer analysis of sintering behavior ofnano-CeO2 particles, J. Eur. Ceram. Soc. 28 (2008) 2019–2024.

[21] E. Landi, A. Tampieri, G. Celotti, S. Sprio, Densification behaviour andmechanisms of synthetic hydroxyapatites, J. Eur. Ceram. Soc. 20 (2000)2377–2387.

[22] A. Frattini, A. Di Loreto, O. De Sanctis, Parameter optimization in thesynthesis of BZT ceramics to achieve good dielectric properties, J. Mater.2013 (2013) 1–6.

[23] X.X. Wang, K. Murakami, O. Sugiyama, S. Kaneko, Piezoelectricproperties, densification behavior and microstructural evolution of lowtemperature sintered PZT ceramics with sintering aids, J. Eur. Ceram.Soc. 21 (2001) 1367–1370.

[24] C. Genuist, F.J. Haussonne, Sintering of BaTiO3: dilatometric analysis ofdiffusion models and microstructure control, Ceram. Int. 14 (1988)169–179.

[25] J. Marchi, J.C. Bressiani, A.A. Bressiani, Dilatometric studies of(SiO2!RE2O3!Al2O3) silicon carbide ceramics, Mat. Res 8 (2005)201–205.

[26] C.H. Wang, S.J. Chang, P.C. Chang, Effect of sintering conditions oncharacteristics of PbTiO3!PbZrO3!Pb(Mg1/3Nb2/3)O3!Pb(Zn1/3Nb2/3)O3, Mater. Sci. Eng. B-Adv. Funct. Solid-State Mater. 111 (2004)124–130.

Table 3Piezoelectric properties of sintered specimen Ts at 1250 1C.

Basic property Length mode Radial mode

!T3 =!0(–) d33 (pC/N) tan " (%) fr (kHz) Zr (Ω) fa (kHz) Za (Ω) Keff (%) Qm (–) fr (kHz) Zr (Ω) fa (kHz) Za (Ω) Keff (%) Qm (–)

1680 415 1.56 336 133 408 24 57 37 57 1357 59 74 29 85

J.S. Han et al. / Ceramics International 41 (2015) 9328–9336 9335

[27] T.M. Kamel, G. de With, Grain size effect on the poling of soft Pb(Zr, Ti)O3 ferroelectric ceramics, J. Eur. Ceram. Soc. 28 (2008) 851–861.

[28] H.W. Kim, A. Batra, S. Priya, K. Uchino, D. Markley, R.E. Newnham,H.F. Hofmann, Energy harvesting using a piezoelectric cymbal transducerin dynamic environment, Jpn. J. Appl. Phys. 43 (2004) 6178–6183.

[29] M.W. Hooker, Properties of PZT-based piezoelectric ceramics between –

150 and 250 1C, Technical Report NASA/CR (1998) 208708.[30] A.H. Meitzler, D. Berlincourt, F.S. Welsh, H.F. Tiersten, G.A. Coquin,

A.W. Warner, IEEE Standard on Piezoelectricity, ANSI/IEE Standard(1987) 176.

J.S. Han et al. / Ceramics International 41 (2015) 9328–93369336