State dependent pyroelectric and thermal expansion coefficients in a PZT wafer

A PZT wafer is subjected to a temperature increase from the reference temperature 20–111 °C under no electric field. During the temperature increase, the variations of remanent polarization in thickness direction and remanent in-plane strain are measured. From the measurements, the values of pyroelectric coefficient in thickness direction and in-plane thermal expansion coefficient are estimated. The temperature experiment is repeated starting at various different values of initial remanent polarization, and the dependency of pyroelectric and thermal expansion coefficients on initial remanent polarization is obtained. In the tested range of temperature, it is found that the pyroelectric coefficient can be given as a linear function of remanent polarization and that the in-plane thermal expansion coefficient is given as a linear function of remanent in-plane strain or as a quadratic function of remanent polarization.     

Temperature dependent ferroelectric and ferroelastic behaviour of PZT wafers

A study is carried out to understand the temperature dependent non-linear behaviour of PZT wafers under electrical and mechanical loading. Experiments are conducted on PZT wafers at room and elevated temperatures under a high cyclic electric field to examine their behaviour. Experimental characterization is also extended to pure mechanical loading (uni-axial compressive stress) condition at room and elevated temperatures. A temperature dependent micro-mechanical model is proposed based on internal energy to evaluate the ferrolectric and ferroelastic behaviour of PZT wafer. The developed model is incorporated into a 3D finite element framework and numerical simulations are performed. The simulated results for electrical loading are compared with experimental observations which show a significant decrease in dielectric response at elevated temperature and it is also observed that the operating temperature influences the electrical displacement and strain along poling direction (thickness direction) under mechanical loading. A parametric study has also been conducted to understand the performance of PZT wafer in which macro-state variables such as remnant polarization, remnant strain, maximum polarization, and maximum strain are extracted and discussed as a function of temperature.     

Effects of uniaxial prestress on the ferroelectric hysteretic response of soft PZT

This paper deals with the influence of preload stress on the ferroelectric hysteretic behavior of piezoelectric ceramics. The polarization and strain versus electric field hysteresis loops were measured for soft lead zirconate titanate (PZT) piezoceramic material under various uniaxial compressive stress preloads of up to −400 MPa. The investigation revealed that the superimposed compression load reduced the remnant polarization, decreased the coercive field, and also had a significant impact on the dielectric and piezoelectric properties. With increasing mechanical load, dielectric hysteresis and butterfly hysteresis became less and less pronounced, as the compressive stress prevented full alignment of the domains and induced mechanical depolarization. The slopes of the polarization and strain curves at zero electric field were measured to evaluate the dependence of permittivity and piezoelectric coefficients on the prestress. The experimental results were interpreted in terms of the non-180° domain switching process under combined electromechanical loading.     

Focus on the ferroelectric polarization behavior of four-layered Aurivillius multiferroic thin film

The well-saturated ferroelectric hysteresis loops with double remnant polarization up to 50?μC/cm² were obtained in four layered Aurivillius-type multiferroic Bi₅FeTi₃O₁₅ thin film. Pulsed positive-up negative-down polarization measurements demonstrate the intrinsic ferroelectric polarization, which present optimal rectangularity and polarization value. The hysteresis loops measurements with larger frequency range of 0.2–100?kHz indicate stable and ultra-fast switching speed of ferroelectric domains. Persistent retention properties were observed, and they are also independent of the applied electric field. In fatigue test an increased dielectric constant is observed along with the suppression of switchable polarization. Both of them can be restored partly to their original values via the stimulating of high electric field. The block domain switching due to the oxygen vacancies aggregated on domain walls are discussed for those characteristics. It is providing important contributions of domain wall pinning in the polarization degradation of Aurivillius-type ferroelectric films with four layers.     

Influence of domain switching process on the electrical fatigue behavior of ferroelectrics

We report an experimental approach, designed based on the recent findings that domain switching in ferroelectric ceramics can be separated into three regimes during antiparallel electric field loading, to investigate the influence of domain switching process on the electrical fatigue behavior of ferroelectrics. Uniaxial compressive stress (−2 MPã -100 MPa) and thermal loading (20 °C–150 °C) were used to tune the domain switching process. Under the same loading condition, the bipolar electrical fatigue behavior of soft lead zirconate titanate ceramics was systematically characterized. The amplitude and frequency of the applied electric field are 2 kV/mm and 10 Hz, respectively. By analyzing the evolution of the domain switching process, combined with the measured polarization and strain response, as well as the cracks observed on the surface of the specimen, it is found that the fatigue of ferroelectric ceramics was mainly related to the domain switching process near the coercive electric field: the regime 2 defined in this paper. The underlying mechanism was further discussed by considering the interplay between the domain switching process with the main factors affecting the electrical fatigue of ferroelectrics, namely defect redistribution, charge carrier injection, and crack initiation.     

Temperature-dependent compressive creep of ferroelectric ceramics and evolution of remnant state variables

A pre-poled lead titanate zirconate cube specimen is subject to constant compressive stress of six different magnitudes at four different room and high temperatures. Electric displacement in poling direction and strains in longitudinal and transverse directions are measured and plotted versus time. The effects of stress and temperature on creep behavior of the material are discussed. Then compressive stress of impulse type with gradually increasing magnitude is applied to the specimen and it is found that linear material properties depend linearly on so-called relative remnant polarization at all four temperatures. Using the linear relations, the evolution of remnant state variables during compressive creep is calculated and discussed. Longitudinal and transverse remnant strains are shown to depend linearly on relative remnant polarization, and the relations between relative remnant polarization and applied compressive stress are discussed.     

In Situ X‐ray Diffraction of Biased Ferroelastic Switching in Tetragonal Lead‐free (1−x)Ba(Zr0.2Ti0.8)O3–x(Ba0.7Ca0.3)TiO3 Piezoelectrics

The effect of electric poling on the bipolar switching for tetragonal BZT–BCT materials is studied using large signal polarization and strain, small signal permittivity, and piezoelectric coefficient, as well as electric field–dependent in situ XRD experiments. Charge carrier agglomeration at domain and grain boundaries with increasing poling fields gives rise to an internal bias field that gradually biases domain switching behavior. The biased switching after electric poling is quantified during a bipolar measurement cycle from analysis of the electric and structural data. For a fresh sample the ferroelastic domain texture induced by a positive and negative electric measurement field is of the same magnitude. After poling, the induced ferroelastic domain texture is larger under a positive measurement field and smaller under a negative measurement field. A very large domain texture is achieved during poling, corresponding to 85% of the domains becoming aligned with their 002 pole in field direction. While the domain texture is significantly improved at higher poling fields, relaxation upon removal of the electric field appears independent of the poling history. This suggests a large extrinsic contribution to the macroscopic strain. It also facilitates the biased ferroelastic switching arising from the internal bias field developed during poling.     

Determination of reversible and irreversible contributions to the polarization and strain response of soft PZT using the partial unloading method

Experimental work is aimed at systematically investigating the non-linear ferroelectric and ferroelastic behavior of a commercially available soft lead zirconate titanate (PZT) material. The fast partial unloading method is used to measure the material properties of unpoled soft PZT under pure electric field and of initially pre-poled soft PZT under compressive stress loading. In the first experiment using unpoled PZT, the evolution of piezoelectric constants and dielectric permittivity is determined as a function of electric field. It is found that the piezoelectric constants and dielectric permittivity depend on the electric field history. The results are used to separate the reversible strain and polarization from the irreversible ones caused by domain switching. In the second experiment using initially pre-poled PZT, it is found that the strain response is significantly dependent on the stress loading rate. The elastic moduli and piezoelectric coefficients are evaluated with respect to the compressive stress history. The measured longitudinal and transverse irreversible strains change significantly during both loading and unloading processes. An attempt is made to discuss the use of irreversible strain and irreversible polarization as internal variables for constitutive modeling. This investigation provides valuable information for modeling to predict the performance and for improving the reliability of piezoelectric devices.     

Strain effects on domain structures in ferroelectric thin films from phase‐field simulations

Strain and applied external electric fields are known to influence domain evolution and associated ferroelectric responses in ferroelectric thin films. Here, phase‐field simulations are used to predict equilibrium domain structures and polarization‐field (P‐E) hysteresis loops of lead zirconate titanate (PZT) thin films under a series of mismatch strains, ranging from strongly tensile to strongly compressive. In particular, the evolution of domains and the P‐E curves under different applied strains reveal the mesoscale mechanism, the appearance of in‐plane polarization during domain switching, that is responsible for a relatively small coercive field and remnant polarization. A Landau energy distribution is analyzed to better understand the domain evolution under various strain conditions. The results provide guidance for choice of mismatched strains to yield the desired P‐E hysteresis loops and the domain structures.     

Investigation of frequency effect on electrical fatigue and crack tip domain-switching behaviors in Pb(Mg1/3Nb2/3)0.65Ti0.35O3 ceramics via synchrotron X-ray diffraction

The effect of frequency on the electrical fatigue, crack growth and domain switching in Pb(Mg_1/3Nb_2/3)_0.65Ti_0.35O₃ ceramics has been investigated. The changes in microstructure, ferroelectric properties and domain-switching behavior of samples fatigued at 1, 10, 50 and 100 Hz were determined. In this experiment, we found that the thickness of the damaged layer under the electrodes and the crack length decrease with increasing frequency. The remnant polarization decreases while the coercive field increases with an increasing number of loading cycles. A domain orientation map around the crack tip was revealed using scanning high-energy X-ray diffraction from a synchrotron source. This showed the effect of fatigue frequency on the lattice strain distribution and ferroelectric domain texture around the crack tip.     

Domain switching and polarization fatigue in rhombohedral PIN-PMN-PT and Mn-doped PIN-PMN-PT single crystals

Domain switching process under alternating electric field was investigated by in situ polarized light microscopy in [001]-oriented Pb(In_1/2Nb_1/2)O₃-Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ (PIN-PMN-PT) and Mn-doped PIN-PMN-PT single crystals. Only one-step 71° switching was confirmed in pure and Mn-doped PIN-PMN-PT crystals by the formed domain walls, whose projections on the (001) plane are along 45° or 135° with respect to [010] direction. Moreover, polarization and strain loops during cyclic electric field were studied in depth as a function of switching cycles. Polarization fatigue appeared obviously above 1000 bipolar cycles in PIN-PMN-PT samples, while Mn-doped PIN-PMN-PT samples exhibited almost fatigue-free characteristics. By considering the thermodynamic theory, the improved fatigue resistance in Mn-doped PIN-PMN-PT crystals stems from the enhanced energy barrier of domain switching. Mn modification does not affect the domain switching paths, but it can enhance the energy barrier of domain switching, leading to the improved fatigue behaviors. Our results provide a useful insight into the underlying mechanisms between the domain switching process and polarization fatigue for applying high-performance relaxor-ferroelectric single crystals.     

The Effect of Electric Poling on the Performance of Lead‐Free (1−x)Ba(Zr0.2Ti0.8)O3–x(Ba0.7Ca0.3)TiO3 Piezoceramics

The effect of increasing poling fields on the properties of (1?x)BZT–xBCT compositions across the morphotropic phase boundary (MPB) is studied using large signal polarization and strain, small signal permittivity and piezoelectric coefficient, and XRD measurements. Successive poling causes charge carrier migration inducing an internal bias field, which becomes large with respect to the coercive field resulting in biased ferroelectric and ferroelastic switching. Improvements in piezoelectric coefficient of 9% are significantly smaller in the tetragonal 60BCT composition compared with the improvement of approximately 50% in the rhombohedral 40BCT and MPB 50BCT compositions. While the properties continue to change with increased poling fields, the remnant ferroelastic domain texture parallel to the field direction, as observed from XRD, stays approximately constant. The improvement in overall domain alignment leading to largely enhanced intrinsic piezoelectricity originates from the alignment of 180° domains and possibly non‐180° domains in grains with orientations inclined to the electric field. As a result, poling is most effective in BZT–BCT materials that have low coercive fields, show low distortions and possess more polarization orientations, such as compositions in the rhombohedral phase field or near the MPB.     

Multi-step domain switching and polarization fatigue in [110]-oriented 0.67Pb(Mg1/3Nb2/3)O3-0.33PbTiO3 single crystals

Domain switching in ferroelectrics is at the heart of many functionalities, and the visualization of switching pathway is the key to understand the fundamental properties and to promote the applications of high-performance ferroelectrics. Here, we directly documented the multi-step domain switching in [110]-oriented 0.67Pb(Mg_1/3Nb_2/3)O₃-0.33PbTiO₃ (PMN-0.33PT) single crystals under a cycling electric field with the help of in situ polarized light microscopy. Based on the characteristic domain configuration analysis, we demonstrated that the 180° switching process was consisted of multi-step 60° switching. Such a multi-step 60° switching pathway resulted in a large negative strain and an internal electric field, which contributes to a large polarization fatigue rate under the alternating electric field. Our works may provide a window to study the domain switching process and its effect on polarization fatigue in relaxor-ferroelectric single crystals.     

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.     

Domain switchings within BaTiO3 nanofibers under different polarizing voltages and loading forces

We reported scanned probe characterization of the domain switching in Barium titanate (BaTiO₃) nanofibers using piezoresponse force microscopy (PFM). The PFM phase images of BaTiO₃ nanofibers under different DC polarizing voltages illustrate that domain switchings are influenced by grain boundaries and internal field. Furthermore, the amplitude–voltage butterfly loop and the phase–voltage hysteresis loop were obtained to confirm the ferroelectric character of BaTiO₃ nanofibers. With the increase of the loading forces, the nanofiber becomes brighter, which indicates that the polarization has the trend of switching to horizontal direction.     

In situ study of electric-field-induced ferroelectric and antiferromagnetic domain switching in polycrystalline BiFeO3

Antiferromagnetic domain switching induced by ferroelectric polarization switching has previously been observed in situ in both multiferroic BiFeO₃ single crystals and thin films. Despite a number of reports on macroscopic magnetoelectric measurements on polycrystalline BiFeO₃, direct in situ observation of electric-field-induced antiferromagnetic domain switching in this material has not been addressed due to the lack of high-quality samples capable of electrical poling. Here, the electric field control of antiferromagnetic domain texture is identified in polycrystalline BiFeO₃ using in situ neutron diffraction, showing the resultant magnetic domain reorientation induced by an electric field. An antiferromagnetic domain reorientation to a value of 2.2-2.5 multiples of a random distribution (MRD) is found to be induced by an electric field that provides a non-180° ferroelectric-ferroelastic domain texture of 2.2-2.5 MRD along the field direction. The current results show well-controlled coupling of multiferroic domain texturing in single-phase polycrystalline BiFeO₃.     

Low-frequency ferroelectric switching studies in PVDF thin films across Cu or (Ag/Cu)/PVDF/Cu capacitor structures

Ferroelectric switching dynamics of polyvinylidene fluoride (PVDF) thin films in Cu or (Ag/Cu)/PVDF/Cu capacitors are explored by varying PVDF film thickness, applied electric field amplitude (4.35–87.5 MV/m) and frequency (100 mHz–200 Hz). Comprehending spontaneous polarization and its dependence upon interfaces, an electric field is critical for organic ferroelectric memory devices. In this article, quasi-static current–voltage, and polarization–electric field measurements are used to explain the relationship between the coercive field, signal amplitude, and frequency. The observed coercivity enhancement at lower PVDF film thicknesses and with rising frequencies of the applied signal is discussed with Kolmogorov-Avrami-Ishibashi domain nucleation and growth model. The relation between domain growth and the top electrode layer is further discussed from the exponent parameters.     

Domain Switching Under Cyclic Mechanical Loading in Lead Zirconate Titanate

The domain-switching behavior of lead zirconate titanate (PZT) during mechanical cyclic loading between 10 and 150 MPa was investigated by in situ time-of-flight neutron diffraction. The domain-switching behavior was represented by a change of the pole density distribution during cycling. With increasing number of cycles, domain switching becomes saturated, correlating with a decrease in the rate of remnant strain accumulation in the stress–strain curve. Moreover, a relationship was demonstrated between the macroscopic strain and that developed from ferroelastic domain switching. The contribution of ferroelastic strain to the macroscopic strain was calculated from an orientation average of the domain switching distributions and the c / a ratio. The results show that nearly 80% of macroscopic strain arises from ferroelastic domain switching during mechanical cyclic loading.     

Domain Structure Evolution and Polarization Degradation of [101]‐Oriented 0.74Pb(Mg1/3Nb2/3)O3‐0.26PbTiO3 Single Crystal underCyclic Electric Loadings

The polarization degradation of ferroelectrics, reflected in the hysteresis loop as a decrease of remnant polarization, is a serious concern in applications. In situ observation of the polarization and domain structure evolution are carried out for [101]‐Oriented 0.74Pb(Mg_1/3Nb_2/3)O₃‐0.26PbTiO₃ (PMN‐26PT) single crystal under cyclic electric field. Measurements of the polarization hysteresis loops are conducted under a polarized light microscope (PLM), which is effective in detecting the domain structure of the single crystal. Prior to the polarization measurements, the crystal was poled. Upon cyclic electric field, reversal of monoclinic (M_B) takes place, and the phase transition from M_B to orthorhombic (O) phase occurs under positive field, but not under negative field of an electric cycle at a field magnitude up to 840 V/mm. The polarization loop is asymmetrical with the positive coercive field (+E_c) much less than the negative one (?E_c). As the field cycles, micro‐cracking occurs preferably in [101] direction, and a sudden drop appears in the curves of polarization versus number of cycles. Upon electric cycling at a field magnitude of 840 V/mm, the negative polarization increases slightly with the cycle number, indicating the rotation of a M_B phase toward the applied field direction.     

Domain switching characteristics of lead zirconate titanate piezoelectric ceramics on a nanoscopic scale

Domain switching characteristics of lead zirconate titanate ceramics with and without poling under compressive loading are investigated using electron backscatter diffraction. For loading in the poling direction, the switching strain is stronger than that for loading perpendicular to the poling direction. There is strong domain switching when the domain (c-axis of the tetragonal structure) is orientated close to the loading direction. A large number of domains are switched between 85.4° and 90.0°, with many crossing the loading axis. Each grain consists of domains with three different patterns; i.e., with c-axis orientated in three directions in each grain. The patterns remain unchanged even with domain switching and strong deformation. However, the ratios among the patterns depend on compressive stress. Under stress, one or two specific domain modes are switched to about 90°, although others are not switched as much. These domain switching characteristics are related to the poling and loading directions. 90° domain switching model is proposed on the basis of twin deformation model. Due to the aspect ratio of c/a = 1.014 (tetragonal structure), the angle of the switching is less than 90° (89.2°). This angle is corresponding to the switching angle obtained by an electron backscatter diffraction analysis (Ave. 88.9°).