Ferroelectrics Synthesis and Electrical Properties of ...

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Synthesis and Electrical Properties of 0.65PMN-0.35PZ Ceramics Prepared via Combustion Technique a

Chittakron Kornphom & Theerachai Bongkarn

b

a

Department of Physics, Faculty of Science , Naresuan University , Phitsanulok , 65000 , Thailand b

Research Center for Academic Excellence in Applied Physics , Naresuan University , Phitsanulok , 65000 , Thailand Published online: 09 Dec 2013.

To cite this article: Chittakron Kornphom & Theerachai Bongkarn (2013) Synthesis and Electrical Properties of 0.65PMN-0.35PZ Ceramics Prepared via Combustion Technique, Ferroelectrics, 456:1, 81-88, DOI: 10.1080/00150193.2013.846610 To link to this article: http://dx.doi.org/10.1080/00150193.2013.846610

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Ferroelectrics, 456:81–88, 2013 Copyright © Taylor & Francis Group, LLC ISSN: 0015-0193 print / 1563-5112 online DOI: 10.1080/00150193.2013.846610

Synthesis and Electrical Properties of 0.65PMN-0.35PZ Ceramics Prepared via Combustion Technique

Downloaded by [Theerachai Bongkarn] at 21:07 09 December 2013

CHITTAKRON KORNPHOM1 AND THEERACHAI BONGKARN2,∗ 1

Department of Physics, Faculty of Science, Naresuan University, Phitsanulok 65000, Thailand 2 Research Center for Academic Excellence in Applied Physics, Naresuan University, Phitsanulok 65000, Thailand In this study, the effects of calcination temperature and sintering temperature on the phase formation, microstructure and electrical properties of the 0.65PMN-0.35PZ (PMN-PZ) ceramics were investigated. These ceramics were prepared by combustion technique. The pure pseudo-cubic perovskite phase of PMN-PZ powders was obtained for the sample calcined at 850◦ C for 2 h. The PMN-PZ ceramics exhibited the pure pseudo-cubic perovskite phase for the samples sintered at the temperatures lower than 1200◦ C. When the sintering temperature increased, the average grain size increased from 0.46 to 2.36 μm. The density, linear shrinkage and maximum dielectric constant of PMN-PZ ceramics increased with increasing sintering temperatures up to 1200◦ C and then decreased. The highest density, highest linear shrinkage and highest dielectric constant at Tc of 7.76 g/cm3, 11.86% and 20052 respectively, were obtained on the sample sintered at 1200◦ C. The Pr , Ec , (using electric field of 30 kV/cm) and d33 of 24.27 μC/cm2, 3.49 kV/cm and 150 pC/N, respectively, were measured on this sample. Keywords PMN-PZ; phase formation; microstructure; dielectric properties; combustion technique

Introduction 0.65Pb(Mg1/3 Nb2/3 )O3 -0.35PbZrO3 (PMN-PZ) perovskite ferroelectric ceramic has attracted increasing attention in the recent years. This ceramic is an important material due to its good dielectric (∼10000), high piezoelectric (∼100 pC/N) and excellent ferroelectric properties (∼20μ C/cm2) [1–3]. Consequently, it has been employed as a micro-actuator for the precisely positioned magnetic head in the high-density hard disk drives and used in the precision machine tools [4, 5]. PMN-based ceramic can be fabricated using conventional solid-state reaction methods, but it always exhibits second phases of pyrochlore [1–3]. That leads to poor electrical properties and physical properties. For obtaining pure PMN-based ceramics, high firing temperature and long time are required. Recently, S. M. Gupta et al. [3] successfully fabricated the single perovskite phase PMN-PZ ceramic via the conventional dry route. It consists of two steps calcination, forming columbite MgNb2 O6 Received December 11, 2012; in final form March 16, 2013. ∗ Corresponding author. E-mail: [email protected]

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(MN) (>1000◦ C for 2–6 h) and reacting MN with PbO and ZrO2 at 900◦ C for 2 h. The pure PMN-PZ ceramic with 95% of the theoretical density was obtained on the sample sintered at 1200◦ C for 2 h. In our previous work, the pure ferroelectric ceramics such as; 0.33Pb(Mg1/3 Nb2/3 ) O3- 0.67PbTiO3 [6] PbZrO3 [7], (Pb1−x Bax )ZrO3 [7], BaTiO3, Ba(Ti1−x Zrx )O3 [8] and (Ba1−x Srx )(Zrx Tix−1 )O3 [9] have been successfully synthesized at low temperature using the combustion technique. The combustion technique is a simple process. It is of low cost and it produces high quality ultra-fine powders. This technique involves a self-sustained reaction between the reactant materials and the fuel (e.g., glycine) which supplies a liquid medium at the start of the reaction. The reaction occurs more easily in the liquid system because the reactant diffusion coefficients are higher than in the solid [10]. It usually results in products with high density and good electrical properties [6–9]. The purpose of this research is to try preparation of PMN-PZ ceramics by the combustion method. The effect of firing temperatures on phase formation, microstructure, dielectric, ferroelectric and piezoelectric properties of PMN-PZ ceramics were studied.

Experimental The raw materials of 0.65Pb(Mg1/3 Nb2/3 )O3 -0.35PbZrO3 powder was synthesized by the combustion method using reagents PbO (99%), MgNO3 .6H2 O (99%), Nb2 O5 and ZrO2 (99%). The raw materials with excess 3 wt% of PbO and ethanol were ball milled with stabilized zirconia balls for 24 h. The suspensions were dried and the powders were ground and sieved. The powders were mixed with glycine (C2 H5 NO2 ) in the ratio of 1:1.66. The powders were calcined at various calcination temperatures from 700◦ C to 1000◦ C for 2 h. Thereafter, the calcined powders mixed with 3 wt% of PVA aqueous solution then milled for 12 h. The mixed solution dried and the powders were uniaxially pressed into pellets of 15 mm in diameter under 80 MPa pressure. Subsequently, the pellets were sintered between 1000◦ C and 1300◦ C with a dwell time of 2 h. The crystal structure and microstructure were studied by the X-ray diffraction (XRD) and scanning electron microscope (SEM). The average particle size and average grain size of the samples were determined by the linear interception method. The density of the sintered ceramics was measured by Archimedes method. Dielectric measurement was performed using an LCR meter (Agilent 4263B), at the measuring frequency of 1 kHz. The ferroelectric hysteresis (P-E) loop was measured by a computer controlled modified Sawyer-Tower circuit. The piezoelectric constant d33 was measured by a Berlincourt Piezo Meter system.

Results and Discussion The XRD patterns of PMN-PZ powders calcined between 700 and 1000◦ C for 2 h are shown in Fig. 1. The crystal structure of all samples is a pseudo-cubic perovskite structure. At calcined temperatures below 850◦ C, the XRD patterns of PMN-PZ powders exhibited the pyrochlore phase of Pb2 Nb2 O7 and impurity phase of MgO. The percentage of perovskite phase in the powders obtained at different calcined temperatures was determined by the following equation; % Perovskite phase =

Iperov × 100 Iperov + Ipyrochlore + IMgO


0.65PMN-0.35PZ Ceramics Prepared via Combustion

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Figure 1. XRD patterns of PMN-PZ powders calcined at various temperatures for 2 h: (•) pyrochlore phase and () MgO.

Where Iperov is the intensity of highest perovskite peak (110) and Ipyrochlore , IMgO are the highest intensity peaks of pyrochlore and impurity phases. The percent of the perovskite phase increased as the calcining temperature increased (Table 1). The 100% of the perovskite phase was obtained for the samples calcined at the temperatures higher than 850◦ C. The pure PMN-PZ powders calcined at 850◦ C were pressed into pellets and sintered from 1000◦ C to 1300◦ C for 2 h. The X-ray diffraction patterns of PMN-PZ sintered samples are exhibited in Fig. 2. The patterns revealed single pseudo-cubic perovskite phase in the samples sintered below 1200◦ C. The second phase of pyrochlore was present in the ceramics sintered at temperatures higher than 1200◦ C. The% of perovskite phase of PMN-PZ ceramic calculated by equation (1) decreased when sintering temperature increased from 1200◦ C to 1300◦ C (Table 2). The evaporation of PbO may cause this problem [1, 6, 11]. Figure 3(a)–(d) illustrate the SEM photographs of the PMN-PZ powders calcined between 700◦ C and 1000◦ C for 2 h. All samples have an agglomerated form. At low calcination temperatures, the powders exhibit a rather rounded morphology (Fig. 3(a, b)). Table 1 Percent of perovskite phase and average particle size of PMN-PZ powders Calcined temperature (◦ C) 700 750 800 850 900 950 1000

% Perovskite phase

Average particle size (μm)

52.7 80.2 98.4 100.0 100.0 100.0 100.0

0.16 0.27 0.50 0.67 0.97 1.52 1.62


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Figure 2. XRD patterns of PMN-PZ ceramics sintered at various temperatures for 2 h: (•) pyrochlore phase.

The powders calcined at higher temperatures exhibit an irregular shape mixing. (Fig. 3(c, d)). The average particle size of the powders increases from 0.16 to 1.62 μm with the increase of the calcined temperatures from 700◦ C to 1000◦ C as listed in Table 1.

Figure 3. The SEM micrographs of PMN-PZ powders calcined at; (a) 700◦ C, (b) 800◦ C (c) 900◦ C and (d) 1000◦ C for 2 h.



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Figure 4. SEM photographs of PMN-PZ pellets sintered at; (a) 1000◦ C, (b) 1100◦ C, (c) 1200◦ C and (d) 1250◦ C for 2 h.

Figure 4(a)–(d) show the SEM micrographs of PMN-PZ pellets sintered at different temperatures. The grain morphology exhibited an almost spherical shape. At a low sintering temperature (1000◦ C), the ceramics consisted of small and loosely bonded grains as shown in Fig. 4(a). The sample sintered at 1100◦ C exhibited non-uniform grain growth (Fig. 4(b)). The grain growth continuously increased while the porosity decreased when sintering temperature increased up to 1200◦ C (Fig. 4(c)). At higher than 1250◦ C (Fig. 4(d)) the grains melted homogeneously and the grain boundaries started to disappear while the porosity increased much. The average grain size of the ceramic increased from 0.46 μm to 2.36 μm when sintering temperature increased (Table 2). The grain size of the samples sintered at higher than 1250◦ C can not be measured due to the homogeneous grain boundary melt. Figure 5 shows the density and linear shrinkage of PMN-PZ ceramics as a function of sintering temperature. The linear shrinkage of ceramics increased successively with increasing sintering temperature. The density of ceramics increased when sintering temperature increased up to 1200◦ C and thereafter it decreased. The density results are consistent with the microstructure changes. The highest density (%TD – theoretical density) via the combustion technique was 96.2% (Table 2). That was higher than the density of the samples prepared by the conventional dry route (∼95%) [1–3]. The dielectric properties as a function of temperature at frequencies of 1 kHz for PMN–PZ ceramics sintered at temperatures between 1000◦ C and 1300◦ C are shown in Figure 6. The dielectric constant (εr ) at room temperature increased while the dielectric loss (tanδ) decreased when sintering temperatures increased up to 1200◦ C and thereafter

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Table 2 Percent of perovskite phase, average grain size, %T.D., Tc , and dielectric properties of PMN-PZ ceramics


% PerSintering temperature ovskite phase (◦ C) 1000 1050 1100 1150 1200 1250 1300

100 100 100 100 100 31.1 28.3

Average grain size (μm) %T.D. 0.46 0.97 1.11 2.14 2.36 — —

79.1 79.7 91.4 94.1 96.2 90.1 75.0

εr at Troom 802 1241 1274 2220 2772 2355 1684

tan δ at Troom TC (◦ C) εr at Tc 1.178 1.116 0.920 0.867 0.055 0.264 0.333

135.3 132.8 131.3 96.7 89.8 87.5 86.2

3169 4191 4559 8612 20052 13933 7672

tan δ at Tc 0.027 0.032 0.037 0.044 0.058 0.051 0.040

the change was in the opposite direction as listed in Table 2. At sintering temperature of 1200◦ C, the specimen has the highest εr and lowest tan δ of 2772 and 0.055, respectively. The εr of the specimen fabricated by the combustion technique was higher than that made by the conventional dry route (∼1700) [3]. The εr curve has a peak between 85◦ C and 135◦ C. This peak corresponds to the Curie temperature (Tc ) which is the transition temperature from the ferroelectric (FE) to the paraelectric (PE) phase [1–3]. The exact transition temperature was derived from tan δ curve. The Tc tends to decrease when the sintering temperature increases as listed in Table 2. The εr at Tc of PMN-PZ ceramics increased from 3169 to 20052 when sintering temperature increased from 1000◦ C to 1200◦ C and then decreased (Table 2). The value of dielectric loss at Tc was in the range of 0.027–0.058 as listed in Table 2. The dielectric properties are in good correlation with the density, microstructure and XRD results. The εr value at Tc of the PMN-PZ ceramics prepared via combustion technique was higher than that obtained by the conventional dry route (εr ∼ 10000) [3].

Figure 5. The density and linear shrinkage of PMN-PZ ceramics sintered at various temperatures.



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Figure 6. Temperature dependence of (a) dielectric constant and (b) dielectric loss of PMN-PZ ceramics sintered at various temperatures.

The room temperature P–E hysteresis loop of PMN–PZ ceramic sintered at 1200◦ C, and having the highest density, measured at the coercive electric field of 30 kV/cm is represented in Figure 7. The P–E loop of this specimen is slim and well-saturated. That means the PMN-PZ ceramic has excellent ferroelectric properties. The remnant polarization (Pr ) and the coercive field (Ec ) of samples were 24.27 μC/cm2 and 3.49 kV/cm. Moreover, the highest density PMN-PZ ceramic exhibited the piezoelectric property (d33 ) of 150 pC/N. G. Singh et al. and S. M. Gupta et al. reported the d33 , Pr and Ec (measured at electric field of 30 kV/cm) of PMN-PZ ceramic of 100 pC/N, 23.1 μC/cm2 and 5.0 kV/cm, respectively. That implies that the ferroelectric and piezoelectric properties of the PMN-PZ ceramics obtained by combustion method are better than the PMN-PZ ceramics produced by the conventional dry route [1, 3]. The combustion technique possesses the capability to obtain a very pure powder for dense PMN-PZ ceramics with good dielectric, piezoelectric and ferroelectric properties. Therefore, the combustion technique could be considered as an alternative way for fabrication of PMN-based ceramics.

Figure 7. Polarization vs. electric field of PMN-PZ ceramic sintered at 1200◦ C for 2 h.

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Conclusion Dense 0.65PMN-0.35PZ ferroelectric ceramics free of the pyrochlore phase were synthesized successfully by combustion technique using one step calcination. The effect of firing conditions on the crystal structure, microstructure and dielectric properties of PMN-PZ samples have been studied A single pseudo-cubic perovskite phase of PMN-PZ powder calcined at 850◦ C for 2 h in air was achieved. The pure pseudo cubic perovskite phase of PMN-PZ was obtained in the specimens sintered at temperatures from 1000◦ C to 1200◦ C. The optimal morphology, highest density, and highest dielectric constant were found for the sample sintered at 1200◦ C for 2 h. In particular, the highest density ceramic exhibited high d33 of 150 pC/N, large remnant polarization Pr of 24.27 μC/cm2 and small coercive field Ec of 3.49 kV/cm. The results on the crystal structure, physical properties, dielectric behavior and ferroelectric properties were consistent with each other. Consequently, this research demonstrates suitability and capability of the combustion technique for producing high quality PMN-PZ ferroelectric ceramics.

Acknowledgments This work was financially supported by Industry/University Cooperative Research Center (I/UCRC) in HDD Component, the Faculty of Engineering, Khon Kaen University and National Electronics and Computer Technology Center, National Science and Technology Development Agency. Thanks also to Department of Physics, Faculty of Science, Naresuan University for supporting facilities. Acknowledgments to Prof. Dr. Galina Popovici for helpful comments and corrections of the manuscript.

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