Electric Field Limit for Piezoelectric Materials

Ferroelectrics, 319:4556, 2005Copyright Taylor & Francis Inc.ISSN: 0015-0193 print / 1563-5112 onlineDOI: 10.1080/00150190590965370

Electric Field Applicability Limits for PZT Ceramics

T. MALYSH AND J. ERHARTDepartment of Physics and International Center for Piezoelectric Research,Technical University of Liberec, Halkova 6, CZ-461 17 Liberec 1,Czech Republic

Electric field applicability limits were measured by the resonant methods for D.C. andpulse electric field depoled PZT ceramics. It is found that the limiting fields for soft PZTare in the range of 500700 V/mm for D.C. depoling and in the range of 200500 V/mmfor pulses. Hard PZT ceramics is resistant to the depoling fields up to 1000 V/mm eitherfor D.C., or pulse depoling fields. Relative changes in the magnitude of the electrome-chanical properties are 320% for the electric fields up to 1000 V/mm. Some electrome-chanical tensor components appear more pronounced sensitivity to the external fieldsthan others.

Keywords PZT ceramics; poling

PACS: 77.84.Dy; 77.22.Ej

1. IntroductionNowadays, poled PZT ceramics serve as a basis for the production of many components inelectromechanical devices. In recent years many authors were engaged in investigations ofconditions under which changes of electromechanical properties of PZT ceramics would bepossible. PZT ceramics is commercially poled by the strong D.C. voltage at elevated temper-atures, but the poling conditions are not usually provided to the customers. In applications,alignment of the dipole moments in ferroelectric ceramics is influenced by the electric fieldin the direction opposite to the poling field. If it is strong enough, such electric field couldcompletely destroy the polarization orientation and therefore also the piezoelectric proper-ties. While the poling (as well as the following application of electric field, i.e. so calleddepoling) process is basically the dynamic process, different poling (and depoling) resultsare supposed from the D.C. or pulse-poling voltage. Poling-dependent material propertieswere recently studied in soft and hard lead zirconate titanate (PZT) [1, 2], lead titanate(PbTiO3) [3] and barium titanate (BaTiO3) [4] ceramics for the electric fields exceeding thecoercive field.

Main aim of this contribution is the measurement of the electromechanical propertiesfor several types of PZT ceramics (hard as well as soft) as a function of the depoling voltage.Electric field limits for the application of PZT ceramics without the substantial change ofthe material properties will be specified.

Received September 6, 2004; In revised form February 28, 2005.Corresponding author. E-mail: [email protected]

[271]/45

46/[272] T. Malysh and J. Erhart

Table 1Material Properties of Poled PZT Ceramics Before Depoling

d33 d31 k31 kp kt T33 s E11 cE33 EPZT type [pC/N] [pC/N] (%) (%) (%) [0] [1012Pa1] [1011Pa] [1]APC 850APC 856

480609

186196

3532

6062

4847

21502870

14.814.4

1.160.99

0.320.45

APC 840APC 841APC 880

274301299

97114

92

293229

555954

464646

114012841044

11.211.011.1

1.251.311.24

0.440.400.44

Figure 1. Piezoelectric strain constant d33 after depoling: (a) by D.C. and (b) after voltage impulsesapplied for bar samples.

Electric Field Applicability Limits [273]/47

2. ExperimentSamples of PZT ceramics have been supplied by the American Piezo Ceramics InternationalLtd., Mackeyville, PA, USA. Samples include soft (APC 850 and 856) as well as hardPZT (APC 840, 841 and 880) ceramics. Due to the resonant method used for the materialproperties measurement [5], sample shapes were bar and disc for each PZT type. Dimensionsof bar-shaped samples werelength 15 mm, width 4 mm and thickness 1 mm. Discs were15 mm in diameter and 1 mm in thickness. Main faces of the discs and bars were electrodedby the fired silver paste.

Figure 2. Piezoelectric strain constant d31 after depoling: (a) by D.C. and (b) after voltage impulsesapplied for bar samples.


Virgin PZT samples were poled at elevated temperature in strong D.C. electric field.According to our previous tests, the poling temperatures have been selected high enoughto ensure the saturated material properties with moderate aging after the poling. Soft PZTceramics has been poled at 90C and hard PZT at 130C, both types by the D.C. electricfield 2 kV/mm for 5 min in silicon oil bath. Due to the aging in the material coefficients,the measurements were done one day after the poling. Then the samples were aged for onedecade (i.e. for the next ten days) and material properties were measured again. At the same

Figure 3. Electromechanical coupling factor k31 after depoling: (a) by D.C. and (b) after voltageimpulses applied for bar samples. Data missing in curves for APC850 and APC856 are due to thenon-resonant response of samples in certain depoling field range.


time, the electric field depoling of the samples was performed. PZT aging and changes in thematerial properties due to the depoling process would be separated in such way. Depolinghas been done by the electric fields of 250 V/mm, 500 V/mm, 750 V/mm and 1000 V/mmof the opposite direction as poling field at room temperature. Depoling field was appliedeither as D.C. field, or in the form of unipolar rectangular pulses (pulse shape: zero field for1 s, applied D.C. field for 1 s etc.) for the same total time as poling field (i.e. for 5 minutes,which means approximately 100 pulses and PZT samples were subjected to the non-zeroelectric field for 2.5 minutes).

Figure 4. Electromechanical coupling factor kp after depoling: (a) by D.C. and (b) after voltageimpulses applied for disc samples. Data missing in curves for APC850 and APC856 are due to thenon-resonant response of samples in certain depoling field range.


Material property measurement has been done by the resonant methods according tothe IRE Standard 1961 [5]. Length-extensional vibrations of the bar (measured resonant fr,antiresonant fa frequency and sample capacitance C0 at 1 kHz frequency) resulted in thevalues of material properties s E11, k31, d31, T33. Radial disc vibrations (measured resonantfr frequencies for fundamental and the third overtone mode, antiresonant fa frequency ofthe fundamental mode and sample capacitance C0 at 1 kHz frequency) give us the valuesof s E12, kp, T33 and Poissons ratio E . Thickness-extensional disc vibrations could be usedfor cE33, kt measurements (measured resonant frequencies of the fundamental f1 and thirdovertone mode f3). Measurements of the impedance spectra have been performed on the

Figure 5. Electromechanical coupling factor kt after depoling: (a) by D.C. and (b) after voltageimpulses applied for disc samples.


impedance analyzer HP4192A. Moreover, d33 has been directly measured on d33-meter(ZJ-3C type). Material properties of the poled PZT ceramics before depoling are listed inTable 1.

3. Results and Discussion

D.C. Voltage Depoling

Significant changes in the material coefficients occur in soft PZT ceramics for the values ofs E12,

E , k31, kp, d31, d33, T33. At certain electric field value, the piezoelectric coefficient d33

Figure 6. Elastic compliance s E11 after depoling: (a) by D.C. and (b) after voltage impulses appliedfor bar samples.


changes its sign (from + to ) for soft PZT. In such case, the sign of d33 could be directlymeasured by the d33-meter. The change in sign means that reverse poling occurred. Similarchange in the sign of d31 coefficient cannot be found by the resonant methods, but it is alsosupposed when d33 changes its sign. Depoling by the electric field of this magnitude woulddepolarize soft PZT ceramics more or less; however no virgin state will be reproduced again.

Generally, in case of homogeneous perovskite material, the antiparallel domain states(such as ) have all even-rank tensors equal in all components. Odd-rank tensors, on the

Figure 7. Poissons ratio after depoling: (a) by D.C. and (b) after voltage impulses applied for discsamples. Data missing in curves for APC850 and APC856 are due to the non-resonant response ofsamples in certain depoling field range.


contrary, should have all components of the opposite sign for the antiparallel domains. Dueto the ceramics non-homogeneity and non-uniform domain structure such relationship isnot exactly fulfilled for the macroscopic material properties.

Depoling behavior for the measured quantities is shown in Figs. 19 for the piezoelec-tric, elastic and dielectric properties. Even-rank materials tensors (e.g. the permittivity T33and elastic compliance s E11) do not change the sign by reverting the sign of polarization ori-entation, but just show the substantial property changes in the range of electric field whered33 changes sign. Odd-rank tensors (e.g. piezoelectric coefficient d33) change their signs as

Figure 8. Elastic modulus cE33 after depoling: (a) by D.C. and (b) after voltage impulses applied fordisc samples.


Table 2Electric Field Applicability Limits for PZT Ceramics

D.C. depoling Pulse depoling

APC 850 700 V/mm 500 V/mmAPC 856 200500 V/mm 200 V/mm

Figure 9. Permittivity T33 after depoling: (a) by D.C. and (b) after voltage impulses applying for discsamples.


Table 3Relative Changes (in %) of Material Coefficients for Hard PZT Ceramics

Relative changes of material coefficients (in %)D.C. depoling Pulse depoling

Bar Disc Bar Disc

PZT type d 33 d 31 k 31 s E11 d 33 k p T33 d 33 d 31 k 31 s E11 d 33 k p T33

APC 840APC 841APC 880

2.67.9

10.4

10.32.65.4

13.815.5

0.7

17.93.63.6

8.611.6

8.8

16.53.61.1

10.45.15.5

10.315.919.3

8.24.74.0

4.12.84.5

7.72.74.5

7.94.85.8

3.73.45.4

6.24.35.4

a result of the reverted polarization orientation as it was observed. Limits for the electricfields, not changing the properties substantially, are listed in Table 2. For the hard PZTceramics, there were no significant changes of the material coefficients observed up to theelectric fields of 1000 V/mm. Relative changes of the material coefficients over the entiredepoling electric field range studied are listed in Table 3. Relative changes are expressed asa ratio of the maximum change of the property vs. the same property value for not depoledsample (in absolute value).

Pulse Depoling

Similar behavior as for the D.C. voltage depoling occurs also in this case. Soft PZT ce-ramics is more sensitive to the depoling field intensity and the limit fields are even smallerthan for D.C. voltage depoling. This clearly illustrates the dynamic nature of the polingas well as depoling process. Limiting fields for soft PZT ceramics are listed in Table 2.Relative changes of the material coefficients for hard PZT (listed in Table 3.) have similarmagnitude (i.e. 320%) like for D.C. depoling (i.e. 118%). There is no big differencebetween D.C. and pulse depoling for the hard PZTs studied up to the electric fields of1000 V/mm.

4. ConclusionsD.C. and pulse electric field applicability limits were measured for the set of hard as well assoft PZT ceramics (soft APC 850 and 856, hard APC 840, 841 and 880) up to 1000 V/mmelectric field strength. Soft PZT ceramics has applicability limits 200700 V/mm for D.C.field and 200500 V/mm for pulses. Ceramics is more sensitive to the pulse electric fieldthan to D.C. signal. Changes in the material properties are realized by the domain wallmovement, which is more complex phenomenon in pulsed electric fields. Hard PZTs havetheir electric field applicability limits higher than 1000 V/mm and therefore out of thetested electric field range. Hard PZT ceramics acquired relative changes in the materialscoefficients measured in the range of 3 to 18%. Piezoelectric coefficients are the mostsensitive material properties studied with respect to the depoling field.

Our measured values agree well with the published data on soft and hard ceramics,namely with the limits of 100300 V/mm for soft PZT ([6], Philips, grades PXE5 or 52)under D.C. depoling and of 300500 V/mm for hard PZT ([6], Philips, grades PXE 41,


42 or 43). Data similar to our findings were published also for A.C. depoling for MorganMatroc PZT ceramics [7], i.e. 700 V/mm for soft PZT-5A type and >1000 V/mm for hardPZT-4D and PZT-8 types. Manufacturer of studied PZT types (i.e. APC International Ltd.)published electric field applicability limits as high as 720 V/mm for D.C. and 360 V/mmfor A.C. field for APC840, 600 V/mm for D.C. and 320 V/mm for A.C. field for APC850and 800 V/mm for D.C. and 400 V/mm for A.C. field for APC880 [8].

Some tensor components are more microstructure-dependent than others, e.g. the Pois-sons ratio E shows bigger changes than cE33, which corresponds to the polarization ori-entation for elementary dipole moments in the direction parallel and perpendicular to theapplied field. Such effects are related to the textures created by the external fields, graingeometry etc., which are not topic of this paper.

AcknowledgmentThis work has been supported by the Ministry of Education, Youth and Sport under theproject MSM 242200002 and by the Grant Agency of the Czech Republic under the projectNo. 202/03/0569.

References1. T. Ogawa, Ceramics International 26, 383390 (2000).2. T. Ogawa and K. Nakamura, Jpn. J. Appl. Phys. 38, 54655469 (1999).3. T. Ogawa, Jpn. J. Appl. Phys. 39, 55385541 (2000).4. T. Ogawa, Jpn. J. Appl. Phys. 40, 56305633 (2001).5. IRE Standard, Measurements on piezoelectric ceramics (1961).6. Data handbook, Piezoelectric ceramics, specialty ferrites, Philips Components 1997, p. 16.7. Data book for designers, Piezoelectric ceramics, Morgan Matroc Ltd., p. 12.8. Piezoelectric ceramics, Principles and Applications, APC International Ltd., 2002 (see Table 1.7,

p. 29).

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