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Preparation of PZN-Based Ceramics Using a SequentialMixing Columbite MethodChen-Liang Li a & Chen-Chia Chou aa Department of Mechanical Engineering, National Taiwan University of Science andTechnology, Taipei 106, TaiwanPublished online: 18 Jun 2010.

To cite this article: Chen-Liang Li & Chen-Chia Chou (2003) Preparation of PZN-Based Ceramics Using a Sequential MixingColumbite Method, Integrated Ferroelectrics: An International Journal, 55:1, 955-963, DOI: 10.1080/10584580390259425

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Integrated Ferroelectrics, 55: 955–963, 2003Copyright C© Taylor & Francis Inc.ISSN: 1058-4587 print/ 1607-8489 onlineDOI: 10.1080/10584580390259425

Preparation of PZN-Based Ceramics Usinga Sequential Mixing Columbite Method

CHEN-LIANG LI and CHEN-CHIA CHOU∗

Department of Mechanical Engineering, National Taiwan University of Scienceand Technology, Taipei 106, Taiwan

(Received April 19, 2003)

In this experiment Pb(Zn1/3Nb2/3)O3(PZN)-BaTiO3 (BT)-Pb(Zr0.52Ti0.48)O3 (PZT)ceramics were prepared using solid state reactions via columbite method by mixingthe relevant oxides and were processed employing conventional sintering techniques.Dielectric, ferroelectric and piezoelectric properties were evaluated and the corre-sponding microstructures were examined using transmission electron microscopy(TEM) and energy dispersive spectroscopy (EDS). The experimental results implythat it is difficult to prepare PZN-PZT-BT ceramics with a full perovskite structureusing a conventional columbite method, i.e., PZN was prepared using the columbitemethod and then mixed, calcined and sintered with PT, PZ and BT. A modifiedapproach (MC) of mixing and calcining all B-site elements first, then mixing andsintering with all A site elements was adopted. Electrical properties were enhancedbut a small amount of pyrochlore phase still exists. Finally, a mixing and calcining se-quence (sequential mixing columbite, SMC) of well calcined B-site elements, firstlywith BaO then with PbO was utilized. A full perovskite structure of the specimenwith excellent electrical properties can be obtained. Microstructural investigationsshowed Ba segregation at triple junctions for IC and MC processes, implying that sta-bilization of the perovskite structure of the specimens was not completely achieveddue to element segregation.

INTRODUCTION

Lead zinc niobate, Pb(Zn1/3Nb2/3)O3 (PZN), is a relaxor type of ferroelec-tric material with a partially disorder perovskite structure. It undergoes adiffuse phase transition near 140◦C and the crystal symmetry is rhom-bohedral at room temperature as it transits to a cubic symmetry [1]. Thesolid solution between PZN with rhombohedral symmetry and PbTiO3 (PT)

∗E-mail: ccchou@mail.ntust.edu.tw

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with tetragonal symmetry has a morphotropic phase boundary (MPB) near10 mol% PT [2]. Single crystals with composition near MPB shows ex-tremely large dielectric constant (k � 22,000) and piezoelectric coefficientsKp ∼ 92%, d33 ∼ 1500pC/N [3]. However, it is very difficult to synthesizeperovskite PZN or PZN-PT ceramics near MPB using conventional ceramicprocessing due to the formation of a pyrochlore phase. The reason behindthe observed difficulties in the preparation of pure perovskite PZN or PZN-PT ceramics was examined using the single crystal prepared by the PbOflux method or hot isostatic processing (HIP) [4–6]. It is reported that per-ovskite PZN or 0.9PZN-0.1PT crystals are thermodynamically unstable overa wide range of temperatures (600–1400◦C) rapidly yielding a pyrochlorephase and PbO as it decomposes [7]. To date, the most useful method tostabilize the perovskite structure is to include additives such as BaTiO3

(BT) and SrTiO3 and so on [8–10]. It is believed that a large tolerance fac-tor and ionic nature perovskite material can stabilize the PZN perovskitestructure [11]. However, the formation of the pyrochlore phase has beenobserved in lead-based Pb(B1,B2)O3 type ferroelectric compounds whichare supposed to possess perovskite structure. Yet the columbite method waseffective in decreasing the pyrochlore phase in Pb(B1,B2)O3 ceramics sys-tem. The columbite method can be employed to prepare pyrochlore free forthe Pb(Mn1/3Nb2/3)O3 ceramic system, but it was difficult to use in a PZNceramic system, indicating that atomic arrangement and phase formation inPZN ceramics may be correlated with preparation procedures or sequences,even if a columbite method was adopted.

In this study, we attempted to find the best processing sequences to synthe-size a perovskite PZN ceramic system. It is believed that there are differentreaction routes when using different processing procedures. Therefore wemodify the mixing sequences during material processing, based upon thestructural and microstructural analysis, in order to obtain PZN ceramicswith appropriate electric properties.

EXPERIMENTS

The specimens studied in this investigation were fabricated accord-ing to the formulas x(0.94 Pb(Zn1/3Nb2/3)O3 + 0.06 BaTiO3) + (1 −x)PbZr0.52Ti0.48O3. The compounds were prepared using three preparationsequences: the first one employed the conventional columbite method to pre-pare each component and then mixed them together (individual columbite,IC). Where appropriate amounts of ZnO and Nb2O5 were ball-milled in

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ZrO2 media with isopropyl alcohol for 8 h and, after drying, the mixture wascalcined at 1000◦C for 6 h. The zinc columbite was attrition-milled withan equal amount of PbO and BaTiO3 and Pb(Zr0.52Ti0.48)O3. The mixturewas then calcined at 950◦C for 2 h. The second approach was carried out bymodifying the mixing sequence of powders is modified (columbite method,MC). Here appropriate amounts of ZnO, Nb2O5, ZrO2, TiO2 was mixedand pre-calcined at 1000◦C for 6 h. This precursor was then mixed withPbO, BaCO3 and ball-milled for 24 h. The mixed powder was then calcinedat 950◦C for 2 h. The last preparation takes into account the mixing se-quence of A-site elements method the sequential mixing columbite method(SMC). Appropriate amounts of ZnO, Nb2O5, ZrO2, TiO2 was mixed andpre-calcined at 1000◦C for 6 h. Then the precursor was mixed with BaCO3

and ball-milled for 24 h and pre-calcined again at 1000◦C for 6 h. The lastprecursor was mixed with PbO and ball-milled for 24 h. This mixed powderwas then calcined at 950◦C for 2 h.

To reduce compositional heterogeneity all the calcined powder were ball-milled for 24 h and then calcined at 950◦C for 2 h again. A binder of 5% PVAwas added to powders and pellets of 1.2 mm thickness and 10 mm diameterwere formed. Samples were sintered at 1150◦C for 2 h in a conventionalfurnace.

The structure of samples was investigated using powder X-ray diffrac-tion (XRD). Percentage of the perovskite phase was calculated from theX-ray peak intensities using the following equation: % perovskite =Iperovskite(110)/(Iperovskite(110) + Ipyrochlore(222)). The microchemical homogene-ity of the specimens were examined using an EDAX Energy DispersiveX-Ray Spectrometer (EDS) on a Field Emission Gun Transmission Micro-scope (FEG-TEM).

The pellets were polished and sputtered with gold and then a silver pastewere painted as electrodes and on both sides of the sample the fired at600◦C for 30 mins. Polarization was measured using a modified ‘Sawyer-Tower’ circuit. Dielectric measurements were conducted using an HP4194Aautomated system with a temperature controlled chamber to measure thedielectric constant of the specimens as a function of temperature between1 KHz and 1 MHz. The samples were heated at a rate of 3◦C/min.

RESULTS AND DISCUSSION

The ferroelectric structure in all compounds was estimated using a bondvalence method [12]. This method can be used to estimate the stability ofthe perovskite structure for all values of x . The perovskite structure of the

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specimens with the compositions we choose should be stable after fabrica-tion. However, the pyrochlore phase can not be removed during the calci-nation and sintering process. The XRD patterns for the sintered samples at1150◦C for 2 h with various values of x using the IC process are shownin Fig. 1. However, the free pyrochlore phase can only be eliminated whenx = 0.5 and under-going the sintering process at 1150◦C for 2 h. The datashowed that the amount of the pyrochlore phase increased as x increased.These results show that most of compositions fabricated using the IC processcan not get rid the pyrochlore phase. We need a new process to improve thequality of the specimens, and therefore we tried to modify the columbite

FIGURE 1 X-ray diffraction patterns of variant x for IC method (a) calcined powder(b) sintering samples.

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FIGURE 2 Percentage of pyrochlore phase for variant x compound was calcinedand sintering by IC and MC method.

method. The pyrochlore phase did not appear for all compositions after thedouble-calcinaion process at 950◦C for 2 h using the MC approach. But thesamples exhibited pyrochlore phase after sintering at 1150◦C for 2 h when xwas greater than 0.7. The amount of pyrochlore phase for the various valuesof x using both the IC and MC methods are shown in Fig. 2. It is clear thatthe MC method is more effective in reducing the pyrochlore phase than theIC method. The range of x values that can be used to synthesize a singleperovskite phase increased to 0.7. In samples where pyrochlore phase ap-peared, amount of the pyrochlore phase was still lower than that found in theIC samples. The problem is that the MC method still could not remove thepyrochlore phase for all compositions. When x is greater than 0.7, the py-rochlore phase increased as x increased. Why was the MC method unable tosynthesize perovskite structure for high PZN composition? We investigatedthe atom distribution using the EDAX Energy Dispersive X-Ray Spectrome-ter (EDS) on Field Emission Gun Transmission Electron Microscope (FEG-TEM). The theoretical value of percentage of the Ba ion is 1.5 at%, butthose in the matrix and triple junction are 0.34 at% and 3.62 at% respec-tively from EDS chemical composition analysis, implying that most of theBa ions had segregated at the grain boundaries. So the pyrochlore phase cannot be removed by simply using Ba ions to stabilize the perovskite phase, ifthe Ba ions were not dissolved in the matrix. To solve this problem we useda new process taking into account the dissolution of A site atoms named.

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FIGURE 3 X-ray diffraction patterns of variant x for SMC method (a) calcinedpowder (b) sintering samples.

“sequential mixing columbite method” (SMC). XRD patterns for specimenswith various values of x using the SMC process for calcined powder andsintered samples are shown in Fig. 3. All specimens were will synthesizedwith the perovskite phase under a double calcined process at 950◦C for 2 hand sintering process at 1150◦C for 2 h when using the SMC process.

Dielectric constant and piezoelectric properties of K p variations for aPZN-BT-PZT specimen with x = 0.5 as a function of temperature are shownin Fig. 4. The electrical properties were affected by the adopted fabricationprocess. The dielectric property is the worst for the samples that under-went

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FIGURE 4 Dielectric constant vs temperature for x = 0.5 at variant process.

the IC process. The maximum for the dielectric constant shifted to a lowertemperature as Ba ions were dissolved in the grains. We can synthesizespecimens with a whole perovskite structure for the specimens of x = 0.5using all the processes. But the lattice constant of the perovskite phase ex-hibit a difference between the IC and SMC methods. The XRD patterns ofsamples from the IC process show two different perovskite structures co-existing in the same samples. But SMC samples clearly showed a tetragonalstructure in the XRD patterns. It had been studied that the micro-regionheterogeneity would affect the phase structures and dielectric properties inPZN-PT-BT ceramic system [13, 14]. A perovskite structure may be synthe-sized using the conventional columbite route (IC process), but the structureof the specimen could vary when under-going an anneal process. The authorfound that a heterogeneous composition will affect the phase structure. Thepowder exhibited no perovskite structure after the calcination process, butthe specimens with x = 0.5 did show a perovskite phase after sintering forexperiments using the IC process. The result indicates that inhomogeneityoccur in specimens. But the calcined powder still had a single perovskitephase for the MC and SMC process. In the IC approach, perovskite BaTiO3

and PZT were used to synthesize a new perovskite PZN-BT-PZT phase.The tolerance factor and electronegativity difference for BaTiO3 and PZTwere large, and therefore BT and PZT were stable phases. It is difficult tostabilize the perovskite PZN phase through solid state diffusion. Therefore,the IC method was process to form a compositional inhomogeneity in the

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specimen, and it neither improved the electric properties nor created a stableperovskite structure by the addition of BaTiO3. On the other hand, usingBaO and TiO2 to synthesize BaTiO3required a temperature of 1200◦C andPZT was difficult to synthesize using an oxide-mixing method. Whereas thepowders having a single perovskite phase for both the MC and SMC pro-cesses can be achieved after being calcined at 950◦C for 2 h, implying thatformation of the powders had a different chemical route when a differentprocess was used. Furthermore, the melting point of BaO is higher than PbO.Therefore using PbO was easier to form a perovskite structure with B-siteprecursor. When all the A-sites were occupied by Pb ions, the Ba ions willsegregate at the grain boundary. If the Ba ions could not dissolve into thegrains, addition of Ba was not able to stabilize the perovskite structure forPZN under the sintering temperature. Therefore the sintered samples withsome compositions have a pyrochlore phase for the MC process. In orderfor all elements to occupy the sites accurately they must be sequenced ap-propriately during a synthesis process. Therefore, A-site components withhigher activily to be dissolved in the system need to be added later. TheSMC method uses this concept so it was easier to synthesize perovskite theceramics for all compositions.

CONCLUSIONS

There are different chemical reaction routes for the different synthesis pro-cesses for the PZN-BT-PZT ceramic system. Perovskite structure of BT andPZT are too stable to diffuse into the matrix to suppress the pyrochlore phasein PZN ceramics. The MC method was effective in synthesizing perovskitePZN-BT-PZT ceramics. However, A-site components with different activitydetermine the chemical reaction driving force such that the reaction of ele-ments with high temperature requirement needs to be processed with priorityin the calcined process. Therefore the SMC method is the best process tosynthesize a perovskite PZN-BT-PZT ceramic.

REFERENCES

[1] Jun Kuwata, Kenji Uchino, and Shoichiro Nomura, Ferroelectrics 22, 863–867 (1979).[2] Jun Kuwata, Kenji Uchino, and Shoichiro Nomura, Ferroelectric 37, 579–582 (1981).[3] Seung-Eek Park and T. R. Shrout, Journal of Applied Physics 82(4), 1804–1811 (August

15, 1997).[4] L. Zhang, M. Dong, and Z.-G. Ye, Materials Science & Engineering. B, Solid-Stat 78(2/3),

96 (Dec 15, 2000).

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[5] Maureen L. Mulvihill, Seung Eek Park, George Risch, Zhuang Li, and Kenji Uchino,Jpn. J. Appl. Phys. Part 1, 35(7), 3984–3990 (July 1996).

[6] Takamitsu Fujiu, Akira Tanaka, and Tadashi Takenaka, Japanese Journal of AppliedPhysics Part 2, 30(2) B L298 (Feb 15, 1991).

[7] San-Yuan Chen, Chien-Min Wang, and Syh-Yuh Cheng, Materials Chemistry and Physics52(3), 207 (Mar 01, 1998).

[8] Arvind Halliyal, Umesh Kumar, Robert E, Newwnham, and Leslie E. Cross, Am. Ceram.Soc. Bull. 66(4) 671–676 (1987).

[9] Thomas R. Shrout and Arvind Halliyal, Am. Ceram. Soc. Bull. 66(4) 704–711 (1987).[10] Tadashi Takenaka, Amar S. Bhalla L. Eric Cross, and Koichiro Sakata, J. Am. Ceram.

Soc. 72(6) 1016–1023 (1989).[11] C. A. Randall, A. S. Bhalla, T. R. Shrout, and L. E. Cross, J. Mater. Res. 5(4), 829–834

(Apr 1990).[12] Naoki Wakiya, Kazuo Shinozaki, and Nobuyasu Mizutani, J. Am. Ceram. Soc. 80(12),

3217–3220 (1997).[13] Min-Chul Chae, Nam-Kyoung Kim, Jeong-Joo Kim, and Sang-Hee Cho, J. Mater. Sci.

33, 1343–1348 (1998).[14] Xiaoli Wang, J. Mater. Sci. 34, 6027–6033 (1999).

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