Hard PZT Ceramics Research Articles

Study of domain depinning during repeated polarization reversal in hard PZT ceramics using acoustic emission

Acoustic emission (AE) has been studied during repeated polarization reversals (at 50 Hz) in hard PZT-8 ceramics. The AE and hysteresis loop were monitored at regular intervals of electric field (±20 kV cm−1 peak) application till 108 cycles. The sample did not fatigue and an increase in saturation polarization (Ps) was observed. AE was observed with zero threshold till 105 cycles when the field was increasing in both half cycles of the applied field. The initial increase in AE activity with increasing number of field cycles till 105 was explained on the basis of defect dipoles encouraging the 90° domain switches, i.e. domain depinning. The decrease in AE activity, an increase in threshold field for the observed AE and a further increase in Ps after 105 cycles were explained based on the changes in the orientation of defect dipoles with respect to Ps due to the applied field cycles. This was found to encourage the 180° domain switches but pin the 90° domains. An increase in AE at 108 cycles after applying a higher field of ±25 kV cm−1 was found to be mainly due to microcracking.

Electric Field Applicability Limits for PZT Ceramics

Electric field applicability limits were measured by the resonant methods for D.C. and pulse electric field depoled PZT ceramics. It is found that the limiting fields for soft PZT are in the range of 500–700 V/mm for D.C. depoling and in the range of 200–500 V/mm for pulses. Hard PZT ceramics is resistant to the depoling fields up to 1000 V/mm either for D.C., or pulse depoling fields. Relative changes in the magnitude of the electromechanical properties are 3–20% for the electric fields up to 1000 V/mm. Some electromechanical tensor components appear more pronounced sensitivity to the external fields than others.

Determination by Indentation Method of Sputtered PZT Films Mechanical Parameters for Si-MEMs Applications

ABSTRACTThis paper presents our investigation in characterization of mechanical parameters of PZT thin films. In the present study, we aim at measuring the transverse biaxial elastic modulus and the hardness of these piezoelectric ceramic films using nanoindentation technique. First were these measurements necessary for checking the mechanical quality of our films. But we could demonstrate the possibility of this technique to measure the true biaxial elastic modulus. This was shown to be close to hard bulk PZT ceramics for the case of our sputtered films. Moreover, this comparatively simple technique gives insight in the mechanical properties of ferroelectric films having various grain size.

Nonlinear elastic behaviour of piezoelectric ceramics

Three experimental methods of nonlinear characterization of elastic behaviour are compared, based upon constant voltage, constant current and constant frequency respectively. Equivalence between them is shown, and implementation of the last one is described in detail. The best way to describe nonlinear behaviour is to look at the alteration of the electrical impedance as a function of the current level, around the resonance frequency. By taking this description, we are able to compute the onset of hysteresis phenomena. Between the nonlinear increment of the reactance X and the resistance R appears a fairly linear relationship, while the quantities of X and R depend on the motional current through a fractional power function. In order to avoid the overheating inherent to high signal measurement, an excitation by bursts is proposed, and electrical response and velocity, obtained during the steady state, has been treated afterwards. This method has been applied to hard and soft PZT ceramics. Elastic electrical and piezoelectric behaviours have been compared, leading to some relations that can be explained by the predominance of the extrinsic processes over the intrinsic onaes.

Polarization Switching Relaxation in Pb(Zr, Ti)O3 Ceramics*

The polarization switching process was investigated in soft and hard PZT ceramics. The frequency dependence of the polarization revealed a relaxation process, which was related to 90°domain walls. The results revealed that the domain reorientation is strongly dependent of the kind of defects and their distribution into the lattice. An evidence of an upper frequency limit for the coercive field was observed.∗Paper originally presented at 10th European Meeting on Ferroelectricity, Cambridge, U.K., August 3–8, 2003.

Polarization Switching Relaxation in Pb(Zr,Ti)O3 Ceramics

The polarization switching process was investigated in soft and hard PZT ceramics. The frequency dependence of the polarization revealed a relaxation process, which was related to 90° domain walls. The results reveled that the domain reorientation is strongly dependent of the kind of defects and their distribution into the lattice. An evidence of an upper frequency limit for the coercive field was observed.

Ferroelectric domains in coarse-grained lead zirconate titanate ceramics characterized by scanning force microscopy

Ferroelectric domain configurations in silver- and lanthanum-doped lead zirconate titanate (PZT) ceramics were characterized by scanning force microscopy using contact as well as piezoelectric response force [i.e., piezoelectric force microscopy (PFM)] modes. Coarse crystallites of hard and soft PZT ceramics (12 μm in Ag-PZT and 30 μm in La-PZT average grain size, respectively) with surface oriented in the {001} planes were chosen to characterize the domain configuration. Results show the conventional right-angled domain structures, which correspond to the {110} twin-related 90° and 180° domains of homogeneous width from 50 to 150 nm. The ability of PFM to image the orientation of pure in-plane arrays of domains (containing 90°-aa- and 180°-aa-types of domain boundaries) is highlighted, and a more detailed notation for in-plane domains is proposed. In addition to such periodical domain arrays, other ordered domains were found, having a misfit of 26° with respect to the{110} domain walls and the {100} surface. This array of domain walls could not be predicted with a geometrical analysis of the intersection of domain walls at the surface according to the conventional spatial array of {110} crystallographic planes. It could be explained only with {210} planes being the domain walls. The reason for this unconventional domain configuration is explained with the clamped conditions of the investigated crystallites in the polycrystalline material.

Piezoelectric strain in lead zirconate titante ceramics as a function of electric field, frequency, and dc bias

We have investigated the electromechanical response of piezoelectric ceramics as a function of the amplitude and frequency of large electric fields and studied the effects of dc bias fields. In order to characterize the materials under these conditions, a ZMI 2000 laser interferometer system from Zygo Corp. has been installed and modified to directly measure the strains of ferroelectric ceramics. This system uses a heterodyne detection technique and has the advantages of phase detection, wide bandwidth, high stability, and easy optical alignment. Our experiment has been used to determine the strain of lead zirconate titanate (PZT) ceramics as a function of electric fields and as a function of frequency in the low frequency range. From these measurements the piezoelectric coefficients d33, d31, and d15 have been determined as a function of applied field and frequency. In addition the dependence of the piezoelectric coefficients under an applied dc bias field has been studied under quasistatic and under resonance conditions. Some of our measurements have provided evidence of the time dependence of the piezoelectric response. Results on a range of soft and hard PZT ceramics manufactured by EDO Corp. are presented. These results are discussed within the context of extrinsic contributions to the piezoelectric response.

Atomic force microscope observations of domains in fine-grained bulk leadzirconate titanate ceramics

This study describes sample preparation techniques that allow atomic forcemicroscope observation of domains on the scale of tens of nanometers infine-grained bulk lead zirconate titanate (PZT) ceramics. It is shown thatcarefully conducted light polishing and etching results in no significantdisturbance to domain morphologies in hard PZT ceramics.

Poling Field Dependence of Ferroelectric Properties in Piezoelectric Ceramics and Single Crystal

Domain structures of ferroelectric materials were investigated by measuring the poling field dependence of dielectric and piezoelectric properties. Ferroelectric materials evaluated consist of as follows: soft and hard lead zirconate titanate (PZT) ceramics with tetragonal and rhombohedral phases, lead titanate (PT) ceramics, barium titanate (BT) ceramics and a relaxor based single crystal of Pb(Zn 1/3 Nb 2/3 ) 0.91 Ti 0.09 O 3 (PZNT). Changing the poling field (E) from 0 M +E M 0 M m E M 0 to +E, the electromechanical coupling factor (k p , k 33 ), dielectric constant ( l r ) and frequency constant (fc) were measured. The minimum k p , k 33 and l r were obtained at the same E because of the 180° domain clamping. Furthermore, the E due to the domain clamping corresponded to the coercive field (Ec) determined by the poling field dependences. At the Ec, maximum fc was confirmed in the cases of soft PZT (tetragonal and rhombohedral) and hard PZT (tetragonal) ceramics, BT ceramics and PZNT single crystal. It was thought that the materials became mechanically hard by the electrical attracting through the domain clamping ( N O ). In hard PZT (rhombohedral), PT and BT ceramics, the peak of l r and/or minimum fc were observed at an E, which corresponds to the threshold of 90°, 71° or 109° domain rotations.

Bipolar pulse poling and space charge field in lead zirconate titanate ceramics

We studied the effect of repeated bipolar pulses applied to soft and hard lead zirconate titanate (PZT) ceramics on ferroelectric properties. Almost symmetrical P-E hysteresis loops were observed in the case of soft PZT ceramics. On the other hand, the loops in the case of hard PZT ceramics were asymmetrical and shifted to the positive electric field. It was found that a space charge field was generated while applying pulse and the direction of the field was fixed independently of the pulse cycles. The possibility of bipolar pulse poling was investigated. Furthermore, we discuss the effect of pulses on planar coupling factor when the pulses were applied to poled soft and hard PZT ceramics.

Domain switching and rotation in lead zirconate titanate ceramics by poling fields

Domain switching and rotation in soft lead zirconate titanate (PZT) ceramics were investigated in comparison with those in hard PZT ceramics by measuring the poling field dependence of the dielectric and piezoelectric properties. The minimum dielectric constant (fcp) and maximum frequency constant (fcp) were observed at the coercive fields, which correspond to the poling fields required to obtain the minimum planar coupling factor. These phenomena were due to the 180° domain clamping at these fields. The fields of 90° (71° or 109°) domain rotation were estimated using the relationships between the maximum fcp and minimum fcp. While minimum ϵt and maximum fcp due to domain clamping were observed in the compositions of tetragonal and rhombohedral soft PZT ceramics, domain rotations which caused maximum ϵt and minimum fcp were mainly observed in rhombohedral hard PZT ceramics. It was thought that the reason why domain rotations which caused maximum ϵt and minimum fcp were not obtained in soft PZT was the mechanical softness of the ceramics.

Electromechanical properties of lead zirconate titanate piezoceramics under the influence of mechanical stresses

In lead zirconate titanate piezoceramics, external stresses can cause substantial changes in the piezoelectric coefficients, dielectric constant, and elastic compliance due to nonlinear effects and stress depoling effects. In both soft and hard PZT piezoceramics, the aging can produce a memory effect that will facilitate the recovery of the poled state in the ceramics from momentary electric or stress depoling. In hard PZT ceramics, the local defect fields built up during the aging process can stabilize the ceramic against external stress depoling that results in a marked increase in the piezoelectric coefficient and electromechanical coupling factor in the ceramic under the stress. Although soft PZT ceramics can be easily stress depoled (losing piezoelectricity), a DC bias electric field, parallel to the original poling direction, can be employed to maintain the ceramic poling state so that the ceramic can be used at high stresses without depoling.

Effect of Domain Switching and Rotation on Dielectric and Piezoelectric Properties in Lead Zirconate Titanate Ceramics

Domain switching and rotation in soft lead zirconate titanate (PZT) ceramics were investigated in comparison with those in hard PZT ceramics by measuring the poling field dependence of the dielectric and piezoelectric properties. The minimum dielectric constant (εr) and maximum frequency constant (fcp) were observed at the coercive fields, which correspond to the poling fields required to obtain the minimum planar coupling factor. These phenomena were due to the 180° domain clamping at these fields. The fields of 90° (71° or 109°) domain rotation were estimated using the relationships between the maximum εr and minimum fcp. While minimum εr and maximum fcp due to domain clamping were observed in the compositions of tetragonal and rhombohedral soft PZT ceramics, domain rotations which caused maximum εr and minimum fcp were mainly observed in rhombohedral hard PZT ceramics. It was thought that the reason why domain rotations which caused maximum εr and minimum fcp were not obtained in soft PZT was the mechanical softness of the ceramics.

The effect of grain size on the high field dielectric properties of hard PZT ceramics

Hard (Mn-doped) PZT ceramics having grain sizes in the range 4 to 9 μm were subjected to an AC electric field with an amplitude E 0 of 0.1 to 3.5 kV mm-1. The dielectric characteristics were determined by analysis of the measured P-E (polarisation-electric field) hysteresis data. It was found that the saturation polarisation Ps, measured at a field amplitude of 3.5 kV mm-1, reduced from 29 to 21 μC cm-2 as the grain size reduced from 7.1 to 4.1 μun, indicating an increased resistance to ferroelectric domain switching in the fine-grained material. In contrast, the dielectric permittivity and loss (εr |, εr ∥), measured in the field range below the coercive field E c, both increased with a reduction in grain size; this was attributed to an increase in the domain wall density in fine-grained ceramics. Near-linear εr | - E 0 plots were obtained for 0.3 kV mm-1 < E01.7 kV mm-1, giving a good fit to the Rayleigh Law. Rayleigh coefficients of 0.81 × 10-3, 0.64 × 10-3 and 0.53 × 10-3 m V-1 were obtained for hard PZT ceramics having grain sizes of 4.1, 7.1 and 8.9 μm respectively

Field-induced destabilisation of hard PZT ceramics

Abstract The effective internal bias field Ei within both poled and unpoled hard PZT ceramics was determined as a function of field amplitude, temperature, and frequency by high field AC cycling. It was shown that the apparent value of Ei increased with the amplitude of the applied field, reaching a maximum at a field level of around 2 kV/mm. A slight reduction in Ei was evident at higher field strengths, which was attributed to an increasingly pronounced transient de-ageing effect caused by the measuring field. Field-driven de-ageing studies revealed a gradual reduction in Ei with time, which appeared to follow a logarithmic time law for poled materials. The form of the de-ageing behaviour for unpoled materials followed more closely the exponential relationship reported by previous authors.

Ferroelastic Properties of Lead Zirconate Titanate Ceramics

To increase the reliability of multilayer actuators, calculation of the mechanical stress inside the device during operation is important. This paper shows that the small‐signal value of the elastic constant s is not sufficient to describe the complicated behavior of lead zirconate titanate (PZT) ceramics. Therefore, compressive strain and depolarization have been measured as a function of large‐signal stress applied parallel to the poling direction. The nonlinear dependence of the strain and depolarization can clearly be explained by domain processes. Soft and hard PZT ceramics have been investigated. In hard PZT, domain switching appears at higher stresses than in soft PZT. Moreover, in hard PZT, the domains partly switch back during unloading. The critical stress (coercive stress) necessary for a domain‐switching process shows a dependence on the Zr:Ti ratio that is quite similar to the dependence of the electric coercive field. The influence of an electric field applied parallel to the poling direction and superimposed on the compression experiment also has been examined. The coercive stress depends linearly on the electric field. The linear coefficient of this relation is given by the ratio of depolarization to compressive strain caused by domain switching.

Grain size and domain size relations in bulk ceramic ferroelectric materials

A study of the ferroelastic domain size variations with grain sizes in Pb(Zr,Ti)O 3[PZT] ferroelectric ceramic has been conducted. Experimental results determined by a transmission electron microscopy (TEM) study on hard and soft PZT ceramics indicate that it is possible to observe a bulk metastable domain configuration in a thinned foil. The transmission electron microscopy observations demonstrate that the domain structures formed at the paraelectric-ferroelectric phase transition are strongly dependent on the elastic boundary conditions and crystallite sizes. Statistical analysis of the domain size distributions in PZT reveals that the traditional parabolic relation between grain size and domain size is only good for a limited sizerangeof 1–10 μm. For grains size > 10 μm, the exponent tends to be smaller than 1 2 , while for grain size < 1 μm the exponent is larger than 1 2 . We also report the analysis on poled ceramics which reveals for the first time direct evidence for transgranular domain switching mechanisms.