A Comparative Study of the Structure and Properties of Sn-Modified Lead Zirconate Titanate Ferroelectric and Antiferroelectric Ceramics

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1 Materials Science and Engineering Publications Materials Science and Engineering A Comparative Study of the Structure and Properties of Sn-Modified Lead Zirconate Titanate Ferroelectric and Antiferroelectric Ceramics Hui He Iowa State University Xiaoli Tan Iowa State University, xtan@iastate.edu Follow this and additional works at: Part of the Ceramic Materials Commons, Metallurgy Commons, and the Other Mechanical Engineering Commons The complete bibliographic information for this item can be found at mse_pubs/194. For information on how to cite this item, please visit howtocite.html. This Article is brought to you for free and open access by the Materials Science and Engineering at Iowa State University Digital Repository. It has been accepted for inclusion in Materials Science and Engineering Publications by an authorized administrator of Iowa State University Digital Repository. For more information, please contact digirep@iastate.edu.

2 A Comparative Study of the Structure and Properties of Sn-Modified Lead Zirconate Titanate Ferroelectric and Antiferroelectric Ceramics Abstract Comparative studies of the structure and property of a ferroelectric Pb 0.99 Nb 0.02 [(Zr 0.57 Sn 0.43 ) 0.88 Ti 0.12 ] 0.98 O 3 and an antiferroelectric Pb 0.99 Nb 0.02 [(Zr 0.57 Sn 0.43 ) 0.94 Ti 0.06 ] 0.98 O 3 ceramic were conducted. In addition to their different crystal structures, domain morphologies, Raman modes, and dielectric/ferroelectric properties, distinct fracture behaviors under Vickers indentation are also clearly seen. We propose that the antiferroelectric-to-ferroelectric phase transformation may have been triggered during the fracture process. Supporting evidence for localized phase transformation was provided by an in situ Raman spectroscopic experiment. Disciplines Ceramic Materials Metallurgy Other Mechanical Engineering Comments This is the peer reviewed version of the following article:journal of the American Ceramic Society 90, (2007), which has been published in final form at j x/full. Rights This article may be used for non-commercial purposes in accordance With Wiley Terms and Conditions for self-archiving. This article is available at Iowa State University Digital Repository:

3 This is the peer reviewed version of the following article:journal of the American Ceramic Society 90, (2007), which has been published in final form at This article may be used for non-commercial purposes in accordance With Wiley Terms and Conditions for self-archiving. A Comparative Study of the Structure and Properties of Sn-Modified Lead Zirconate Titanate Ferroelectric and Antiferroelectric Ceramics Hui He, and Xiaoli Tan, Department of Materials Science and Engineering, Iowa State University, Ames, Iowa Comparative studies of the structure and property of a ferroelectric Pb0.99Nb0.02[(Zr0.57Sn0.43)0.88Ti0.12]0.98O3 and an antiferroelectric Pb0.99Nb0.02[(Zr0.57Sn0.43)0.94Ti0.06]0.98O3 ceramic were conducted. In addition to their different crystal structures, domain morphologies, Raman modes, and dielectric/ferroelectric properties, distinct fracture behaviors under Vickers indentation are also clearly seen. We propose that the antiferroelectric ferroelectric phase transformation may have been triggered during the fracture process. Supporting evidence for localized phase transformation was provided by an in situ Raman spectroscopic experiment. This work was supported by the Petroleum Research Fund through contract PRF# G5. Member, American Ceramic Society. Author to whom correspondence should be addressed. 1

4 I. Introduction The PbZrO3-based antiferroelectric ceramics are of technological importance due to their wide applications in microelectromechanical systems and energy storage devices. 1-3 The electric field-induced antiferroelectric-to-ferroelectric phase transformation forms the physics basis for these applications. The most intensively studied antiferroelectric ceramics are chemically modified from PbZrO3 by adding Sn, Ti, and Nb or La to adjust the critical field for the phase transformation and optimize the properties for processing and applications. 1-7 It has been widely observed that optimized properties in these ceramics are resulted from their hierarchical microstructures: the subgrain level antiferroelectric 90 domains (the checkerboard pattern) and the nanoscale incommensurate modulations within the domains. 6-9 Increase in Ti content eventually destroys these microstructures and leads to a normal ferroelectric behavior. Both antiferroelectric and ferroelectric ceramics were developed based primarily on considerations of their electrical responses, and consequently, many of them display rather poor mechanical properties, such as low fracture toughness and high susceptibility to slow crack growth Their mechanical behavior is always of major concern because their electric and mechanical responses are intimately coupled. When driven hard repeatedly under cyclic electric loading over long periods, these ceramics may accumulate enough mechanical damage to cause subcritical crack growth or catastrophic failure On the other hand, development of cracklike flaws under mechanical loading may generate severe local field concentrations which may result in serious degradation of their electric performance. 19 The fracture process of ferroelectric ceramics is complex and sometimes inconsistent experimental data are found in literature. Based on a set of experiments comparing the fracture toughness of the ferroelectric phase (below Curie temperature) and the paraelectric phase (above 2

5 Curie temperature), a concept called ferroelectric toughening has been arguably proposed. 12,20-22 The ferroelectric domains in the ferroelectric phase are ferroelastic domains at the same time and they respond to both electrical and mechanical loadings. As a consequence of domain switching, the measured fracture toughness at ferroelectric state was almost doubled as that at paraelectric state. 21 However, to the authors best knowledge, the fracture behavior of antiferroelectric ceramics has not yet been investigated in detail. It has been noticed previously that the electric field-induced antiferroelectric-to-ferroelectric phase transformation accompanies a volume expansion on the order of 1%. 23,24 Inspired by the phase transformation toughening mechanism in ZrO2-based engineering ceramics, 25,26 we suggest that antiferroelectric ceramics may display fracture resistance superior to ferroelectric ceramics due to contributions from both the volume expansion at the phase transformation and the ferroelastic domain switching in the induced ferroelectric phase. In this paper, we present some preliminary data which appear to confirm the phase transformation toughening effect in antiferroelectric ceramics. II. Experimental Procedure The materials used in this study were an antiferroelectric Pb0.99Nb0.02[(Zr0.57Sn0.43)0.94Ti0.06]0.98O3 (abbreviated as PNZST 43/6/2) ceramic and a ferroelectric Pb0.99Nb0.02[(Zr0.57Sn0.43)0.88Ti0.12]0.98O3 (abbreviated as PNZST 43/12/2) ceramic. Uniaxial hot pressing after calcination was employed to prepare high density ceramics. Raw powders with purity better than 99.9% of PbO, Nb2O5, ZrO2, SnO2, and TiO2 were batched according to the chemical formula with 5% excess PbO powder to compensate for the lead evaporation loss in the subsequent thermal process. Isopropyl alcohol was added to the mixed powders and the slurry was then milled in a plastic bottle with zirconia media on a vibratory mill 3

6 for 6 hours. After drying the slurry in an oven at 150 C for 24 hours, the powders were calcined at 850 C for 4 hours in a covered alumina crucible. The calcined powder were then again milled for 6 hours, dried for 24 hours and calcined at 850 C for 4 hours to ensure the formation of pure perovskite phase. The perovskite phase powder was then mixed with polyvinyl alcohol binder and cylindrical compacts were formed by uniaxial cold pressing. The preformed pellets were then hot-pressed in Al2O3 dies at 1150 C for 2 hours in air. Thin slices from the hot pressed pieces were annealed at 1300 C for 3 hours with PbZrO3 as protective powder. After removal of surface layers by mechanical grinding, these ceramics were checked by X-ray diffraction for phase purity and scanning electron microscopy (SEM) for grain morphology. The antiferroelectric and ferroelectric domain structure in these ceramics was analyzed by transmission electron microscopy (TEM). Raman scattering spectra were collected at room temperature with a Renishaw invia spectrometer using the 488 nm line of the Ar + laser at 50mW of power. The laser beam was focused with a 50 lens, producing a beam size of 3~5 m on the polished specimen surface. Dielectric characterization was performed with an LCR meter (HP-4284A, Hewlett-Packard) at frequency of 1 khz in conjunction with an environmental chamber. A heating/cooling rate of 3 C/minute was used during measurement. Electric fieldinduced polarization was recorded with a standardized ferroelectric test system (RT-66A, Radiant technologies). The fracture behavior in the PNZST 43/6/2 and the PNZST 43/12/2 ceramics was compared under pure mechanical loadings by pressing a Vickers indenter against polished surfaces of thin slices (~250 m thick). The indentation load was selected as 1 kgf and the dwell time was set to be 30 seconds. III. Results 4

7 (1). Structure and electrical properties X-ray diffraction was used to check the phase purity and determine the average crystal structure of the ceramics. The results are shown in Fig. 1. It is evident that both ceramics are phase pure with a perovskite structure. The PNZST 43/6/2 ceramic takes a pseudo-tetragonal structure with lattice parameters of a=b=4.108å and c=4.086å while the PNZST 43/12/2 takes a rhombohedral structure with a=b=c=8.202å and =89.86 o. SEM examination indicates a high relative density of both ceramics, as shown in Fig. 2. The average grain size was estimated from SEM micrographs using a linear intercept method. It is 3.1 m for PNZST 43/6/2 and 4.2 m for PNZST 43/12/2, respectively. TEM analysis revealed the subgrain domain structure in both ceramics. The PNZST 43/6/2 ceramic displays a domain structure with a checkerboard-like pattern (Fig. 3(a)), which is typical for antiferroelectric ceramics. 6-9 The patches in the pattern are antiferroelectric 90 domains. Higher magnifications reveal a modulated fine structure with regular fringes at a periodicity around 2nm within the antiferroelectric domains. In contrast, regular ferroelectric domain stripes were found in the PNZST 43/12/2 ceramic (Fig. 3(b)). Raman spectra for both ceramics collected at room temperature are presented in Fig. 4. Consistent with the results of x-ray diffraction and TEM results, the ferroelectric PNZST 43/12/2 ceramic display different active Raman modes from the antiferroelectric PNZST 43/6/2 ceramic. As Ti content increases from 6 at.% to 12 at.%, the most prominent feature in the Raman spectra is the softening of the mode around 90cm -1 and the emergence of the modes around 60cm -1 and 125cm -1. Therefore, the mode around 90cm -1 (denoted as mode A hereafter) is the signature of the antiferroelectric phase and the modes around 60cm -1 (denoted as mode F1 hereafter) and 125cm -1 (denoted as F2 hereafter) are characteristic of the ferroelectric order. 27 5

8 The temperature dependence of the dielectric permittivity for PNZST 43/6/2 and PNZST 43/12/2 is shown in Fig. 5. The PNZST 43/6/2 ceramic shows a much weaker dielectric response in the test temperature range than PNZST 43/12/2. One distinct feature in the dielectric response of PNZST 43/6/2 is the presence of a plateau region between 142 C and 182 C. The dielectric constant peaks with a value of 1350 at the temperature of 182 C. According to previous studies, 4-9 PNZST 43/6/2 is paraelectric at temperatures above 182 C. Below 142 C, down to the lower limit of the test temperature range, PNZST 43/6/2 exists in the antiferroelectric state. In contrast, PNZST 43/12/2 shows a typical ferroelectric behavior with a single sharp peak. At 127 C, the dielectric constant reaches its peak value of Below 127 C, PNZST 43/12/2 displays a ferroelectric behavior. The polarization vs. electric field hysteresis measurement at room temperature confirmed the antiferroelectric order in PNZST 43/6/2 and the ferroelectric order in PNZST 43/12/2. As shown in Fig. 6, characteristic double hysteresis loops were observed in PNZST 43/6/2 while a single hysteresis loop was recorded in PNZST 43/12/2. The antiferroelectric phase in PNZST 43/6/2 at room temperature transforms to a ferroelectric phase at a critical electric field about 39 kv/cm (referred to as EF in literature), and the reverse transformation occurs when the field is lowered down to 18 kv/cm (referred to as EA in literature). Both transformations are abrupt and take place within a narrow range of field strength. For PNZST 43/12/2, a remanent polarization of 30 C/cm 2 and a coercive field of 6kV/cm were measured from the hysteresis loop. (2). Indentation fracture behavior In addition to the microstructure, Raman mode and dielectric/ferroelectric property, the mechanical fracture behavior under indentation loading was also compared in the PNZST 43/6/2 6

9 and the PNZST 43/12/2 ceramics. Again, distinct fracture behavior was observed in these two ceramics under identical mechanical conditions. The antiferroelectric PNZST 43/6/2 ceramic shows very straight cracks emitting only from corners of the indentation impression, as shown in Fig. 7(a). In contrast, the ferroelectric PNZST 43/12/2 ceramic shows excessive damage surrounding the entire indentation in addition to cracks eminating from the corners, as shown in Fig. 7(b). The microcracks in PNZST 43/6/2 have a smaller scatter in lengths than those in the ferroelectric PNZST 43/12/2. However, the total length of the long cracks (including the indentation impression diagonal) averaged over a number of indentations (>5) was ~170 m for both ceramics. Close examination of Fig. 7 also reveals that the indent for the ferroelectric PNZST 43/12/2 ceramic is larger than the indent for the antiferroelectric PNZST 43/6/2. It suggests that the strength of PNZST 43/6/2 is higher than that of PNZST 43/12/2, which is consistent with the fact that the antiferroelectric phase has a more compact molar volume. 23,24 IV. Discussion The sharp contrast in the structure and electrical properties of these two ceramics is expected and is consistent with previous studies. 4-9,27 However, the distinct indentation fracture behavior has not been reported before. We propose that the antiferroelectric ferroelectric phase switching may have occurred in the indentation fracture process and this phase change is the primary cause for the distinct fracture behavior. Indentation-induced ferroelectric-to-antiferroelectric phase transformation has been recently observed in a ferroelectric lead zirconate titanate ceramic with a composition close the ferroelectric/antiferroelectric phase boundary. 28 Since the ferroelectric phase in these oxides displays a larger molar volume than the antiferroelectric phase, 23,24,29 this transformation 7

10 corresponds to a volume contraction and hence undermines the fracture resistance. In the current PNZST 43/12/2 ceramic specimen, the ferroelectric-to-antiferroelectric transformation may not occur since the composition is quite away from the phase boundary (According to Ref. 27, the phase boundary at room temperature roughly corresponds to PNZST 43/8/2.). Therefore, only the ferroelectric toughening mechanism due to ferroelastic domain switching is operating in the case of PNZST 43/12/2. As a consequence, many microcracks form at the rim of and even within the indentation impression (Fig. 7(b)). For the antiferroelectric PNZST 43/6/2 ceramic, the compressive stresses from the indenter will not lead to any phase change. The microcracks shown in Fig. 7(a) are a result of the tangential tensile stresses near the corners, which reach a maximum at the boundary of the plastic zone. 30 The tensile tangential stress may have triggered the antiferroelectric-toferroelectric phase transformation in the PNZST 43/6/2 ceramic. As a result, the maximum tangential stress is released and a large number of microcracks surrounding the indentation impression are eliminated. Therefore, the phase transformation toughening in the antiferroelectric ceramic manifests itself as fewer indentation cracks. The excessive cracking observed in the ferroelectric PNZST 43/12/2 suggests a weaker resistance to fracture caused by the tensile tangential stress. As demonstrated in Fig. 6, the antiferroelectric-to-ferroelectric phase transformation in PNZST 43/6/2 can also be triggered by electric fields. Therefore, the antiferroelectric PNZST 43/6/2 ceramic may also show high resistance to the electric field-induced fracture. To demonstrate this, we prepared an electroded specimen with a thickness around 300 m. A Knoop indentation was made at the center of the gap between the two electrodes. The indentation has its longer axis parallel to the electrode edges so that the nominal electric field direction was 8

11 perpendicular to the indentation crack plane. The initial crack length, including the indentation impression length, was measured to be ~230 m. The indented specimen was then immersed into a 3M Fluorinert electronic liquid bath and subjected to bipolar electric fields (±20kV/cm) with a sinusoidal waveform at a frequency of 30Hz. Absolutely no crack growth was detected even after electrical cycles. We attribute the lack of crack growth to the phase transformation toughening due to the localized electric field-induced antiferroelectric-to-ferroelectric transition. The electric field applied ( 20kV/cm) is about 0.5EF for the PNZST 43/6/2 ceramic. Due to the disturbance of the indentation crack, 19 the actual electric field at the crack tip regions is significantly intensified and exceeds the critical field EF of 39kV/cm. As a consequence, the antiferroelectric-to-ferroelectric phase transformation is expected to take place in the close vicinity of the crack tip. Attempts were then made to verify the existence of local phase transformation at crack tips in PNZST 43/6/2 with micro Raman spectroscopy. Unfortunately all attempts failed in PNZST 43/6/2 because arcing discharge invariably occurred before the electric field-induced phase transformation. Therefore, a ceramic with a composition of Pb0.99Nb0.02[(Zr0.57Sn0.43)0.93Ti0.07]0.98O3 (abbreviated as PNZST 43/7/2, with 1at.% higher Ti content than PNZST 43/6/2) was prepared and tested. The as-sintered PNZST 43/7/2 ceramic displays an antiferroelectric order with a much lower EF (14kV/cm from polarization hysteresis loop measurement). The in situ Raman experiment with applied electric field was successful with the PNZST 43/7/2 specimen and the results are shown in Fig. 8. Using the Raman spectra in Fig. 4 as the reference, the antiferroelectric mode A (86cm -1 ) is strong in the as sintered PNZST 43/7/2 ceramic. At a nominal applied electric field of 15kV/cm, this mode was weakened and the ferroelectric mode F2 (122cm -1 ) started to emerge for most areas between the 9

12 two electrodes. However, at a spot in the close vicinity of a crack tip, the antiferroelectric mode A almost completely disappeared and the ferroelectric mode F2 became evident. The results, therefore, demonstrated the occurrence of the electric field-induced antiferroelectric-toferroelectric phase transformation at a local scale close to the crack tip. We also performed in situ synchrotron x-ray diffraction experiment on a PNZST 43/6/2 sample under static electric fields. 29 Lattice structure Rietveld refinement indicates that the PNZST 43/6/2 ceramic at zero field actually takes an orthorhombic structure with the space group Bmm2 and the induced ferroelectric phase takes a rhombohedral structure with the space group R3c. A volume expansion of 0.4% was measured at this electric field-induced phase transformation. 29 When the indented PNZST 43/6/2 specimen subjected to the cyclic field at an amplitude of 20kV/cm, the induced ferroelectric phase at the crack tip is surrounded by untransformed antiferroelectric phase. The volume expansion in the ferroelectric phase then leads to the generation of local compressive stresses, closing the crack wake and arresting the crack growth. Furthermore, the domain switching in the induced ferroelectric phase still contributes to ferroelectric toughening. Although supporting evidences are found for the phase transformation toughening effect in the antiferroelectric PNZST 43/6/2 ceramic under both mechanical and electrical loadings, it should be pointed out that the observed toughening effect appears not strong. This may be attributed to the low volume strain (0.4%) at the phase transformation of the PNZST43/6/2 ceramic. 29 The volume strain for toughening in ZrO2-based ceramics is about one order of magnitude higher. 26 Further studies for the antiferroelectric-to-ferroelectric transformation 10

13 toughening will be carried out in ceramics with a lower Ti content in this composition series (for a higher volume strain) under more mechanical/electrical loading configurations in the future. V. Conclusions The structure, electrical properties and indentation fracture behavior of the antiferroelectric PNZST 43/6/2 and the ferroelectric PNZST 43/12/2 ceramics are compared. As manifested by the formation of far fewer microcracks, PNZST 43/6/2 displays a higher resistance to indentation fracture. The high fracture resistance in the antiferroelectric ceramic is also demonstrated in the electric field-induced fracture process. With supporting evidences from the current set of experimental data, the antiferroelectric-to-ferroelectric phase transformation is suggested to account for the high fracture resistance in PNZST 43/6/2. 11

14 References 1 D. Berlincourt, H.H.A. Krueger, and B. Jaffe, Stability of phases in modified lead zirconate with variation in pressure, electric field, temperature and composition, J. Phys. Chem. Solids, 25, (1964). 2 W.Y. Pan, C.Q. Dam, Q.M. Zhang, and L.E. Cross, Large displacement transducers based on electric field forced phase transtions in the tetragonal (Pb0.97La0.02)(Ti,Zr,Sn)O3 family of ceramics, J. Appl. Phys., 66, (1989). 3 B. Xu, L.E. Cross and J.J. Bernstein, Ferroelectric and antiferroelectric films for microelectromechanical systems applications, Thin Solid Films, 377, (2000). 4 P. Yang, and D.A. Payne, Thermal stability of field-forced and field-assisted antiferroelectric - ferroelectric phase transformation in Pb(Zr,Sn,Ti)O3, J. Appl. Phys., 71, (1992). 5 K. Markowski, S.E. Park, S. Yoshikawa, and L.E. Cross, Effect of compositional variations in the lead lanthanum zirconate stannate titanate system on electrical properties, J. Am. Ceram. Soc., 79, (1996). 6 D. Viehland, D. Forst, Z. Xu, and J.F. Li, Incommensurately modulated polar structures in antiferroelectric Sn-modified lead zirconate titanate: The modulated structure and its influences on electrically induced polarizations and strains, J. Am. Ceram. Soc., 78, (1995). 7 D. Viehland, X.H. Dai, J.F. Li, and Z.Xu, Effects of quenched disorder on La-modified lead zirconate titanate: Long- and short-range ordered structurally incommensurate phases, and glassy polar clusters, J. Appl. Phys., 84, (1998). 8 H. He, and X. Tan, Electric field-induced transformation of incommensurate modulations in antiferroelectric Pb0.99Nb0.02[(Zr1-xSnx)1-yTiy]0.98O3, Phys. Rev. B, 72, (2005). 12

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16 19 R.M. McMeeking, Electrostrictive stresses near crack-like flaw, J. Appl. Math. Phys. (ZAMP) 40, (1989). 20 G.G. Pisarenko, V.M. Chushko, and S.P. Kovalev, Anisotropy of fracture toughness of piezoelectric ceramics, J. Am. Ceram. Soc., 68, (1985). 21 K. Mehta, and A.V. Virkar, Fracture mechanisms in ferroelectric-ferroelastic lead zirconate titanate (Zr:Ti=0.54:0.46) ceramics, J. Am. Ceram. Soc., 73, (1990). 22 G.S. White, A.S. Raynes, M.D. Vaudin, and S.W. Freiman, Fracture behavior of cyclically loaded PZT, J. Am. Ceram. Soc., 77, (1994). 23 W. Pan, Q. Zhang, A. Bhalla and L.E. Cross, Field-forced antiferroelectric-to-ferroelectric switching in modified lead zirconate titanate stannate ceramics, J. Am. Ceram. Soc., 72, (1989). 24 L. Shebanov, M. Kusnetsov, and A. Sternberg, Electric field-induced antiferroelectric-toelectric phase transition in lead zirconate titanate stannate ceramics modified with lanthanum, J. Appl. Phys., 76, (1994). 25 R.C. Garvie, R.H. Hannink, and R.T. Pascoe, Ceramic steel, Nature, 258, (1975). 26 R.H.J, Hannink, P.M. Kelly, and B.C. Muddle, Transformation toughening in zirconiacontaining ceramics, J. Am. Ceram. Soc., 83, (2000). 27 H. He, and X.Tan, In situ Raman spectroscopic study of the phase transitions in Pb0.99Nb0.02[(Zr0.57Sn0.43)1-yTiy]0.98O3 ceramics, J. Phys.: Conden. Matter, in press. 28 T.F. Juliano, Y.G. Gogotsi, T.E. Buchheit, C.S. Watson, S.V. Kalinin, J. Shin, and A.P. Baddorf, Detection of indentation induced FE-to-AFE phase transformation in lead zirconate titanate, J. Am. Ceram. Soc., 89, (2006). 14

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18 Fig. 1. X-ray diffraction patterns for the PNZST 43/6/2 and the PNZST 43/12/2 ceramics. The peaks are indexed on the basis of the parent pseudo-cubic pervoskite structure. Fig. 2. SEM micrographs of the grain morphology. (a) the PNZST 43/6/2 ceramic, and (b) the PNZST 43/12/2 ceramic. Fig. 3. TEM micrographs of the subgrain domain structure. (a) the checkerboard pattern of the antiferroelectric 90 domains in the PNZST 43/6/2 ceramic, and (b) the regular ferroelectric domains in the PNZST 43/12/2 ceramic. Fig. 4. Raman spectra collected at room temperature from the PNZST 43/6/2 and the PNZST 43/12/2 ceramics. Fig. 5. Dielectric constant vs. temperature measured at 1kHz during cooling for the PNZST 43/6/2 and the PNZST 43/12/2 ceramics. Fig. 6. Polarization vs. electric field loops measured at 4Hz at room temperature for the PNZST 43/6/2 and the PNZST 43/12/2 ceramics. Fig. 7. SEM micrographs of Vickers indentations made at 1 kgf for 30 seconds. (a) the PNZST 43/6/2 ceramic, and (b) the PNZST 43/12/2 ceramic. Fig. 8. In situ Raman spectroscopy with electric fields in PNZST 43/7/2 to verify the localized antiferroelectric-to-ferroelectric phase transformation. 16

19 (110) Intensity (arb. unit) (100) (111) (200) (210) (211) (220) (221) (003) PNZST43/6/2 PNZST43/12/ θ (deg.) Figure 1 16

20 Figure 2 17

21 Figure 3 18

22 Intensity (arb. unit) F 1 F 2 PNZST 43/12/2 A PNZST 43/6/ Raman shift (cm -1 ) Figure 4 19

23 9000 Dielectric constant PNZST 43/12/2 PNZST 43/6/ Temperature ( o C) Figure 5 20

24 30 20 Polarization (μc/cm 2 ) PNZST 43/6/2 PNZST 43/12/ Electric field (kv/cm) Figure 6 21

25 Figure 7 22

26 PNZST 43/7/2 Intensity (arb. unit) A F 2 15 kv/cm crack tip 15 kv/cm 0 kv/cm Raman shift (cm -1 ) Figure 8 23