高压电性能ZnO掺杂PNN-PFN-PZT压电陶瓷材料

Available online at www.sciencedirect.com Ceramics International 39 (20 bi Pb ic , K l St 016 sed ine 2 Abstract 1. Introduction structure, a relaxor type Pb(B1B2)O3-PZT ceramic was devel- oped. Up to now, numerous solid solution systems comprising normal and relaxor ferroelectrics with outstanding piezoelectric and dielectric properties have been developed, such as 0.5Pb additives on the electrical properties of PNN–PZT ceramics, and both good ferroelectric and pyroelectric properties (2Pr¼21 μC/cm2, 2Ec¼7.7 kV/cm, FD¼452 μC/cm2 K) were 3+ obtained for the 1.0 mol% Y doped sample. Gao et al. [16] found that the PMN–PNN–PZT ceramics modified with Zn2+ and Li+ ions exhibited excellent electrical properties (d33¼397 0272-8842/$ - see front matter & 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved. http://dx.doi.org/10.1016/j.ceramint.2013.05.055 nCorresponding authors. Tel./fax: +86 25 84891123. E-mail addresses: qiu@nuaa.edu.cn (J. Qiu), kjzh@nuaa.edu.cn (K. Zhu). Lead zirconate titanate (PZT) ceramics have attracted tremendous attention since the 1970s due to their excellent piezoelectric and electromechanical properties near the mor- photropic phase boundary (MPB) [1–4]. Besides, the PZT- based ceramics are widely employed in many applications, ranging from electrostrictive actuators and transducers, to sensors and ultrasonic devices [5–9]. Typically, the PZT- based relaxor ferroelectrics have a general formula of Pb (B1B2)O3 (where B1 stands for Mg 2+, Ni2+, Zn2+, Fe3+, Mn4+, or Sn4+; and B2 stands for Nb 5+, Sb5+, or W6+). In an effort to enhance piezoelectric activities and stabilize the perovskite (Zn1/3Nb2/3)O3–0.5Pb(Zr0.47Ti0.53)O3 [10], 0.3Pb(Ni1/3Nb2/3) O3–xPbTiO3–(0.7−x)PbZrO3 (x¼0.33–0.43) [11], Pb(Mn1/3 Sb2/3)O3–Pb(Zn1/3Nb2/3)O3–Pb(Zr0.52Ti0.48)O3 [12], Pb(Sn1/3 Sb2/3)O3–Pb(Zn1/3Nb2/3)O3–PbZrO3–PbTiO3 [13], and so on. Relaxor-type PZT-based ceramics doped with numerous oxides (ZnO, CuO, La2O3, Fe2O3, CeO2, MnO2, etc.) have been intensively investigated to further improve the physical and electrical properties for actual industrial applications. For example, Zhang et al. [14] found that Ce-doped PNW–PMN– PZT ceramics with good temperature stability achieve favor- able piezoelectric and dielectric properties (d33¼388 pC/N, kp¼0.6). Kang et al. [15] investigated the effect of Y2O3 1/3 2/3 3 1/2 1/2 3 0.3 0.7 3 ratio) were prepared by the conventional mixed-oxide method. The effects of ZnO content on the microstructure and piezoelectric properties were systematically investigated. Increasing ZnO additive promotes the phase structure transformation from rhombohedral to tetragonal, indicating the presence of the morphotropic phase boundary in the ZnO-modified PNN–PFN–PZT system. The results show that ZnO doping significantly improves the coercive field (Ec), Curie temperature (Tc), and temperature stability (Δfr/fr 30 1C, Δd31/d31 30 1C) of the PNN–PFN–PZT–xZ ceramics, although the piezoelectric constant (d33, d31) decreases slightly with increasing ZnO content. Taking into consideration the piezoelectric property and temperature stability, the obtained ceramic sample with x¼0.04 exhibited favorable properties, which are listed as follows: d33¼810 pC/N, kp¼0.647, εr¼6243, tan δ¼2.74%, Ec¼4.7 kV/cm, and Tc¼136 1C. & 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved. Keywords: A. Sintering; C. Dielectric properties; C. Piezoelectric ceramics; D. ZnO Quaternary piezoelectric ceramics Pb(Ni Nb )O –Pb(Fe Nb )O –Pb(Zr Ti )O –xZnO (PNN–PFN–PZT–xZ, x¼0.0–0.08 in molar Microstructure, temperature sta ZnO-modified Pb(Ni1/3Nb2/3)O3– piezoelectr Jianzhou Du, Jinhao Qiun State Key Laboratory of Mechanics and Control of Mechanica Nanjing 210 Received 2 March 2013; received in revi Available onl CERAMICS INTERNATIONAL 13) 9385–9390 lity and electrical properties of (Fe1/2Nb1/2)O3–Pb(Zr0.3Ti0.7)O3 ceramics ongjun Zhun, Hongli Ji ructures, Nanjing University of Aeronautics and Astronautics, , PR China form 1 May 2013; accepted 1 May 2013 3 May 2013 www.elsevier.com/locate/ceramint Chinese Academy of Sciences, China). The electromechanical coupling factor (kp, k31), piezoelectric constant (d31), and mechanical quality factor (Qm) were determined through the resonance and anti-resonance method with an LCR analyzer (HP4294A, Agilent, America) based on IEEE standards. The Curie temperature (Tc) and temperature stability of the ceramic samples were analyzed using an HP4294A precision impedance analyzer in a controlled furnace at a heating rate from room temperature to 300 1C. The polarization hysteresis loops (P–E) were measured using a ferroelectric analyzer system (TF2000, aixACCT Systems GmbH, Germany) at 5 Hz based on a modified Sawyer-Tower circuit. 3. Results and discussion 3.1. Microstructure analysis national 39 (2013) 9385–9390 pC/N, εr¼2628) and high Curie temperature (Tc¼251 1C) at a low sintering temperature of 960 1C. Yan et al. [17] studied the effect of MnO2 on the phase structure and ferroelectric behavior of PMN–PZT ceramics and found that the Mn ion substitution on Zr and Ti sites induced a hardening effect. In our previous report [18], PNN–PZT ternary ceramics doped with appropriate amount of Fe2O3 exhibited high piezoelectric constant (d334870 pC/N), large planar electro- mechanical coupling factor (kp40.7), high dielectric constant (εr45690), and low dielectric loss (tan δo3%), yet Tc is only 120 1C near the MPB area, seriously restricting its potential application at high temperature. Hence, the temperature stabilities of PZT-based piezoelectric properties have also been studied [19,20]. It was reported that ZnO doping can effec- tively improve thermal stability of PZT–PMnN [21,22], Mn4 +/Nb5+-modified PZT [23], PZT–PMnS [24], and PMW– PNN–PZT [25] ceramics with good piezoelectric and dielectric properties. Similar results have also been found in the ZnO- doped lead-free KNN-based ceramics [26–28]. In this work, ZnO was used as an additive in PNN–PFN– PZT multicomponent system to improve the dielectric proper- ties and Curie temperature. Herein, an effort has been made to provide feasible candidates with both excellent piezoelectric and temperature stabilities for practical applications. The effects of ZnO content on the microstructure, electrical proper- ties, and temperature stabilities of the ceramics were studied. 2. Experimental procedure The ceramics with compositions of 0.5Pb(Ni1/3Nb2/3)O3– 0.05Pb(Fe1/2Nb1/2)O3–0.45Pb(Zr0.3Ti0.7)O3+xZnO (abbreviated as PNN–PFN–PZT+xZ, where x=0.0, 0.02, 0.04, 0.06, and 0.08) were prepared by a conventional mixed-oxide method. Reagent-grade PbO, NiO, Nb2O5, ZrO2, TiO2, Fe2O3, and ZnO oxide powders were used as the starting materials. Excess 1 wt % PbO was added mainly to compensate for the lead loss at a high temperature and suppress the pyrochlore phase during the sintering process. The mixed powders were ball milled in alcohol for 12 h with agate balls and jar. The slurry was dried, calcined in an alumina crucible at 1050 1C for 4 h, and re-milled for 10 h. The powders were dried and uniaxially pressed into disks at 200 MPa using polyvinyl alcohol (PVA) as a binder. All samples were sintered at 800 1C for 5 h to burn off the PVA, and then sintered at 1200 1C for 2 h in a sealed aluminum crucible. The bulk densities (ρ) of the sintered samples were measured through the Archimedes method. The crystal struc- tures of the samples were determined at room temperature by X-ray diffraction (XRD, D/Max-2500, Rigaku, Japan). The surface morphologies were observed by a scanning electron microscope (SEM, JMS-5610LV, Tokyo, Japan). Silver elec- trodes were coated on both sides of polished ceramic disks, which were then fired at 550 1C for 10 min. The samples were poled in silicone oil at 60 1C by applying a DC electric field of 2 kV/mm for 20 min. J. Du et al. / Ceramics Inter9386 The piezoelectric constant (d33) was measured through a quasistatic piezoelectric d33 meter (ZJ-3A, Institute of Acoustics, Fig. 1 shows the XRD patterns of the PNN–PFN–PZT+xZ ceramics with different ZnO contents sintered at 1200 1C. All samples exhibit a pure ABO3 perovskite structure without obvious pyrochlore or secondary phase (e.g., Pb2Nb2O7, Pb3Nb4O13, and Pb5Nb4O15). It is indicated that ZnO can diffuse into the PNN–PFN–PZT lattice and form a new solid solution. The previous studies [13,29–31] have demonstrated that the lower symmetrical crystal structures can be indexed by splitting the diffraction peaks (hkl), such as a single (200) peak indexed as rhombohedral symmetry, or (110) and (200) peaks splitting indexed as a tetragonal symmetry. For further analysis of the effect ZnO doping on the phase structure of the PNN–PFN–PZT +xZ ceramics, (002) and (200) peaks were zoomed in the 2θ range of 44–461 as shown in Fig. 1(b). The pure PNN–PFN–PZT ceramics, presenting the single peak of (200)R, are primarily indexed as the rhombohedral phase. It can be observed that the (200)R peak gradually splits into (002)T and (200)T peaks with the increasing of ZnO content, indicating a phase shift from rhombohedral to tetragonal near the MPB. The rhombohedral and tetragonal phases coexist as x increases from 0.04 to 0.06, Fig. 1. XRD patterns of PNN–PFN–PZT+xZ (x¼0.0–0.08) ceramics with different ZnO contents in the 2θ range of 20–701 (a) and (b) enlarged (002) and (200) peaks within 44–461 sintered at 1200 1C. O c rnat Fig. 2. SEM micrographs of PNN–PFN–PZT+xZ ceramics with different Zn (d) x¼0.08. J. Du et al. / Ceramics Inte which is similar to MPB behavior concerning the PZT–PMS– PZN, PSN–PZN–PZT, and PZT–PZN–PNN ceramics [12,13,19]. This phase transition can be ascribed to the Zn2+ ions diffusion into the B-site ions of the BO6 octahedron. Fig. 2 shows the SEM micrographs of the PNN–PFN–PZT +xZ ceramics with different ZnO contents sintered at 1200 1C for 2 h. The PNN–PFN–PZT ceramic without ZnO doping shows clear grain boundary and dense microstructure with a reduced amount of porosity (Fig. 2(a)). The bulk density decreases slightly with the increasing ZnO content, while the grain size remains almost unchanged. The density in the range of 94–96% of the theoretical value can also be achieved in all samples (Table 1). However, with further increase of x to 0.08, the excessive ZnO segregates at the grain boundary and forms a liquid phase with the lower melting oxides such as PbO, NiO, and Nb2O5. This result corresponds well with the SEM photo- graphs shown in Fig. 2(c, d). This phenomenon is also consistent with those in widely reported ZnO-doped PZT–PMnN [22], PMS–PZT [24], and PMW–PNN–PZT [25] ceramic systems. 3.2. Piezoelectric, dielectric, and ferroelectric properties Fig. 3 shows the piezoelectric and dielectric properties of the PNN–PFN–PZT+xZ ceramics sintered at 1200 1C as a function of Table 1 The physical properties of PNN–PFN–PZT–xZ ceramics sintered at 1200 1C for 2 Sample ρ (kg/m3) εr tan δ (%) d33 (pC/N) x¼0.0 7965 5697 2.82 885 x¼0.02 7908 6101 2.88 831 x¼0.04 7881 6243 2.74 810 x¼0.06 7831 5670 2.49 750 x¼0.08 7814 5159 2.25 657 ontents sintered at 1200 1C for 2 h: (a) x¼0.0, (b) x¼0.02, (c) x¼0.04 and ional 39 (2013) 9385–9390 9387 ZnO content x. With the ZnO content x increasing from 0.0 to 0.08, both d33 and kp decrease gradually from 885 pC/N and 0.707 to 657 pC/N and 0.608, respectively, as shown in Fig. 3(a). The relative dielectric constant εr reached a maximum value of 6243 at x¼0.04, and then decreases with the increasing ZnO content. The varying trend of the tan δ versus x is similar to that of the εr, and the peak value of tan δ is 2.88% at x¼0.02. The enhancement of the dielectric property is caused mainly by the phase transition behavior near the MPB. The variations of densities, piezoelec- tric constants, and dielectric constants are listed in Table 1 to comprehensively evaluate the performance of the obtained cera- mics. It is shown that the PNN–PFN–PZT+xZ ceramics with x¼0.04 exhibit excellent dielectric and piezoelectric properties (εr¼6243, tan δ¼2.74%, d33¼810 pC/N, d31¼−342 pC/N, kp¼0.647, k31¼0.357, and Qm¼46.7) at room temperature. Fig. 4 shows the P–E hysteresis loops of the PNN–PFN– PZT+xZ ceramics measured at room temperature. It is shown that both pure and Zn-doped ceramic samples exhibit square- like well-saturated hysteresis loops. The remnant polarization (Pr) and saturation polarization (Ps) of pure ceramics are 22.4 and 28.3 mC/cm2, respectively, and its coercive field (Ec) is 3.8 kV/cm. With the increase of ZnO content, the values of both Pr and Ps gradually decrease from 21.7 and 27.5 mC/cm 2 at x¼0.02 to 20.5 and 26.3 mC/cm2 at x¼0.08, respectively, h. kp d31 (pC/N) k31 Qm Tc (1C) 0.707 −367 0.422 44.6 107 0.646 −341 0.365 46.1 122 0.647 −342 0.357 46.7 136 0.635 −320 0.352 56.8 143 0.608 −289 0.336 62.7 154 nat J. Du et al. / Ceramics Inter9388 as shown in Fig. 4(b). In addition, the Ec value shows an increasing trend with increase of ZnO content, and the corresponding values are 4.3, 4.7, 5.5, and 6.0 kV/cm for PNN–PFN–PZT+xZ with x¼0.02, 0.04, 0.06 and 0.08, respectively. It is indicated that the domain switching becomes more difficult accompanied by a higher Zn2+ ion concentra- tion, which may be attributed to the increased amount of the tetragonal phase and the existence of the liquid phase in the grain boundary. 3.3. Temperature stability Fig. 5 shows the temperature dependence of εr and tan δ of the PNN–PFN–PZT+xZ ceramics measured at 1 kHz. As can be seen all samples exhibit relaxor dielectric behaviors as characterized by the diffused dielectric peaks, and εr and tan δ are strongly influenced by ZnO content. The Curie temperature (Tc) gradually increases from 107 1C to 136 1C and 154 1C as x increases from 0.0 to 0.04 and 0.08, respectively. Mean- while, the corresponding maximum dielectric constants εmax Fig. 3. The d33, kp, εr and tan δ of PNN–PFN–PZT+xZ ceramics sintered at 1200 1C as a function of ZnO content. ional 39 (2013) 9385–9390 are 23,930, 223,817, and 27,470. The Tc shifting to a higher temperature with increasing ZnO content may be attributed to the fact that Tc of PZN (∼140 1C) is higher than those of PNN (∼−120 1C) and PFN (�110 1C). It should be noted that the maxima of tan δ for all PNN–PFN–PZT+xZ ceramics are lower than 7% near their Curie temperature. In order to further demonstrate the effect of ZnO doping on the temperature stability of PNN–PFN–PZT ceramics, the temperature coefficients (Δfr/fr 30 1C and Δd31/d31 30 1C) of the resonant frequency (fr) and the piezoelectric constant (d31) were measured in temperatures ranging from 30 1C to 140 1C; the equation is as follows: temperature coefficient ΔP P1ðT1Þ ¼ P2ðT2Þ−P1ðT1Þ P1ðT1Þ � 100%; where P2(T2) and P1(T1) are the measured electrical parameters at T2 and T1. Fig. 6 shows the temperature coefficients of fr and d31 for the PNN–PFN–PZT+xZ ceramics as a function of temperature. The Δfr/fr 30 1C of pure PNN–PFN–PZT ceramics initially decreased slightly and then increased to 11.8% at 100 1C with the increase of the ambient temperature (T) as shown in Fig. 6(a). The Δfr/fr 30 1C of the ZnO-doped samples increased monotonically with increasing ambient temperature. Fig. 4. (a) Polarization–electric field (P–E) hysteresis loops and (b) the values of Ps, Pr, and Ec of PNN–PFN–PZT+xZ ceramics sintered at 1200 1C as a function of ZnO content. Fig. 6. Temperature dependence of (a) Δfr/fr 30 1C and (b) Δd31/d31 30 1C and rnat Here, the slope of Δfr/fr 30 1C versus T decreases gradually with the increased ZnO content, indicating that the temperature stability of the resonant frequency can be improved through ZnO doping. Zhang et al. [32] insisted that the temperature stability is closely related to the performance of the PZT ceramics. Fig. 6(b) shows the Δd31/d31 30 1C of the PNN–PFN–PZT+xZ ceramics as a function of temperature. The temperature coeffi- cient Δd31/d31 30 1C exhibits an inverse tendency compared with the Δfr/fr 30 1C for all samples. The Δd31/d31 30 1C for the sample at x¼0.0 initially slightly increases, and then decreases sharply by about −50% at T, ranging from 30 1C100 1C. d31 rapidly decreases, especially at around its Curie temperature (Tc¼107 1C). The slopes of Δd31/d31 30 1C versus T decrease with the increase in content of ZnO, indicating the improvement of temperature stability with the increased ZnO content. The enhanced temperature stability can be related to the domain-wall activity and the domain structure [19,21,32]. Therefore, the ZnO-modified PNN–PFN–PZT ceramics possess high piezoelectric properties and good tempera- Fig. 5. Temperature dependence of εr and tan δ for PNN–PFN–PZT+xZ ceramics with different ZnO contents sintered at 1200 1C measured at 1 kHz. J. Du et al. / Ceramics Inte ture stability. 4. Conclusions PNN–PFN–PZT+xZnO ceramics with pure perovskite struc- ture have been fabricated through the conventional ceramic sintering technique. All ceramics exhibit pure perovskite structure and the phase structure changes from rhombohedral to tetragonal on varying ZnO content. The relative dielectric constant εr achieves its maximum at x¼0.04. The piezoelectric constant d33 and the planar electromechanical coupling factor kp gradually decreased, while the mechanical quality factor Qm and the coercive field Ec gradually increased with the increase of ZnO content, which should be attributed to the presence of the MPB and the hardening effect. The Curie temperature Tc exhibited an obvious increasing trend with the increased ZnO content. The temperature coefficients of Δfr/fr 30 1C and Δd31/ d31 30 1C showed the inverse tendency and a flat temperature behavior for the ZnO-doped samples. The PNN–PFN–PZT +xZ ceramics with x¼0.04 exhibited optimal properties: d33, ional 39 (2013) 9385–9390 9389 kp, εr, tan δ, Qm, Ec, and Tc are 810 pC/N, 0.647, 6243, 2.74%, 46.7, 4.7 kV/cm and 136 1C, respectively. Finally, the addition of ZnO significantly improved the temperature stability of the electrical properties for the PNN–PFN–PZT ceramics. Acknowledgments This work was supported by the National Natural Science Foundation of China (90923029, 51161120326), the Program for Changjiang Scholars and Innovative Research Team in University (IRT0968), the Funding for Outstanding Doctoral Dissertation in NUAA (BCXJ11-02), the Program for New Century Excellent Talents in University (NCET-10-0070), the Funding of Jiangsu Innovation Program for Graduate Educa- tion (CXZZ11-0194) and the PAPD of Jiangsu Higher Educa- tion Institutions. Δk31/k31 30 1C for PNN–PFN–PZT+xZnO ceramics as a function of temperature. References modified Pb(Mg1/3Nb2/3)O3–PbZrO3–PbTiO3 ceramics, Applied Physics Letters 100 (2012) 152902. [18] J. Du, J. Qiu, K. Zhu, H. Ji, X. Pang, J. 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