Bipolar Electric Cycling Research Articles

Effects of quenching on domain switching and electric field-induced phase transformations in Na0.5Bi0.5TiO3-NaNbO3 ceramics

Quenching from high temperatures has been identified as a useful means to enhance the piezoelectric properties and thermal stability of bismuth-based perovskite ferroelectrics. In the present work, it is demonstrated that quenching leads to improvement of depolarization temperature, ferroelectric and piezoelectric properties in Na0.5Bi0.5TiO3-NaNbO3 (NBT-0.1NN) ceramics. In-situ synchrotron x-ray diffraction measurements indicated an irreversible transformation from cubic to coexisting cubic and rhombohedral phases during the application of a high electric field, for both as-sintered and quenched ceramics. These results confirm the non-ergodic relaxor ferroelectric nature of the materials. DC poling induced a transformation to single-phase rhombohedral structure in both cases, with highly textured domain configurations. These well-oriented ferroelectric domain states were relatively stable under subsequent bipolar electric field cycling. For the pre-poled NBT-0.1NN ceramics, the quenched samples were found to exhibit the highest intrinsic (lattice strain) and extrinsic (domain switching) contributions to electrostrain, due to the increased rhombohedral distortion.

Investigation of the large-signal electromechanical behavior of ferroelectric HfO2–CeO2 thin films prepared by chemical solution deposition

Investigation of the large-signal electromechanical behavior of ferroelectric HfO2–CeO2 thin films prepared by chemical solution deposition

Evolving electromechanical properties of defect engineered Pb(Zr,Ti)O3-based piezoceramics

Chemical modification is the frequently-adopted strategy to enhance the electromechanical properties of piezoelectric ceramics. However, chemically modified piezoelectric materials will inevitably produce point defects, such as dopant ions, oxygen vacancies, etc. In this study, we investigated the properties of defect-engineered Pb(Zr,Ti)O3 (denoted by PSZT–Fe) polycrystals after aging, quenching, poling, and de-aging processes. At the same time, a general mechanism on the strength of defect dipole is also put forward to explain the corresponding changes. After aging, the spontaneous polarization of PSZT-Fe can be changed instantly upon application of external electric field, but the defect dipole and its defect symmetry can’t change simultaneously. Therefore, after the external electric field is removed, the defective dipole would drive the electric domain back to its original state, resulting in restorable strain effect and macroscopic pinch polarization. Bipolar electric field cycling can effectively redistribute oxygen vacancies to a random state, so that the aged PSZT-Fe can recover the electrical properties of typical ferroelectrics, similar to quenched samples. The spontaneous polarization and defect dipole in the poled PSZT-Fe ceramics are driven by an external electric field parallel to each other, which results in the emergence of internal bias field, accounting for the asymmetric hysteresis loop.

Role of Defects in the Breakdown Phenomenon of Al1-xScxN: From Ferroelectric to Filamentary Resistive Switching.

Aluminum scandium nitride (Al1-xScxN), with its large remanent polarization, is an attractive material for high-density ferroelectric random-access memories. However, the cycling endurance of Al1-xScxN ferroelectric capacitors is far below what can be achieved in other ferroelectric materials. Understanding the nature and dynamics of the breakdown mechanism is of the utmost importance for improving memory reliability. The breakdown phenomenon in ferroelectric Al1-xScxN is proposed to be an impulse thermal filamentary-driven process along preferential defective pathways. For the first time, stable and robust bipolar filamentary resistive switching in ferroelectric Al1-xScxN is reported. A hot atom damage defect generation model illustrates how filament formation and ferroelectric switching are connected. The model reveals the tendency of the ferroelectric wurtzite-type Al1-xScxN system to reach internal symmetry with bipolar electric field cycling. Defects generated from bipolar electric field cycling influence both the energy barrier between the polarization states and that required for the filament formation.

Increased fatigue resistance in transparent lead zirconate titanate thin films with interdigitated electrodes

This work compares the fatigue behavior of fully transparent lead zirconate titanate films with a composition at the morphotropic phase boundary on fused silica glass or sapphire, respectively, fitted with coplanar interdigitated top electrodes and no bottom electrodes to that of the same systems in a traditional metal–insulator–metal parallel plate capacitor geometry. While the polarization hysteresis in the latter geometry decreases rapidly during bipolar electrical cycling, systems with coplanar electrodes show no notable fatigue up to 107 cycles. The difference is explained based on the columnar microstructure of the films: for coplanar electrode geometries, the grain boundaries of the columnar structure act as trapping sites for oxygen vacancies, preventing the build-up of agglomerates that cause fatigue by domain wall pinning.

Direct observation of electric field-induced tetragonal-orthorhombic phase transition in KNN-based piezoelectric ceramics via in-situ synchrotron diffraction

Straightly investigation of the structure-property relationship in the multiphase (K,Na)NbO3-based systems is attractive since constructing multiphase coexistence has been proved as the leading strategy to achieve high piezoelectric performance. In this study, we directly revealed a reversible electric field-induced tetragonal-orthorhombic (T-O) phase transition and the structural correlation to the high performance by in-situ synchrotron X-ray diffraction. The T and O phase coexistence is continuously observed during the whole bipolar electric cycling, among which O phase is energetically preferred in high field region and T phase is near coercive electric field. The synergistic crystal lattice variations and extensive phase fraction changes suggest that the reversible transition between the coexisted T and O phases acts as a bridge for polarization switching. Insights from this work will facilitate a deep understanding of the enhanced properties in KNN-based piezoelectrics and also shed light on the structural-related mechanism of other piezoelectric systems.

Influence of Different Solvents and High-Electric-Field Cycling on Morphology and Ferroelectric Behavior of Poly(Vinylidene Fluoride-Hexafluoropropylene) Films.

P(VdF-HFP) films are fabricated via a solution casting doctor blade method using high (HVS) and low (LVS) volatile solvents, respectively. The structural properties and the ferroelectric behavior are investigated. The surface structure and crystal phase composition are found to be strongly dependent on the type of solvent. LVS leads to a rougher copolymer surface structure with large spherulites and a lower crystallinity in contrast with HVS. The crystalline phase of copolymer films fabricated with HVS consists almost exclusively of α-phase domains, whereas films from LVS solution show a large proportion of γ-phase domains, as concluded from Raman and X-ray diffraction spectra. Virgin films show no ferroelectric (FE) switching polarization at electric field amplitudes below 180 MV/m, independent of the solvent type, observed in bipolar dielectric displacement—electric field measurements. After applying electric fields of above 180 MV/m, a FE behavior emerges, which is significantly stronger for LVS films. In a repeated measurement, FE polarization switching already occurs at lower fields. A shielding effect may be related to this observation. Additionally, Raman bands of polar γ-phase increase by high-electric-field cycling for the LVS sample. The solvent used and the resulting crystal phase composition of the virgin sample is crucial for the copolymer behavior during bipolar electrical cycling.

Evolution of electromechanical properties in Fe-doped (Pb,Sr)(Zr,Ti)O3 piezoceramics

Defects in acceptor-doped perovskite piezoelectric materials have a significant impact on their electrical properties. Herein, the defect mediated evolution of piezoelectric and ferroelectric properties of Fe-doped (Pb,Sr)(Zr,Ti)O3 (PSZT-Fe) piezoceramics with different treatments, including quenching, aging, de-aging, and poling, was investigated systematically. Oxygen vacancies with a cubic symmetry are preserved in the quenched PSZT-Fe ceramics, rendering them robust ferroelectric behaviors. In the aged PSZT-Fe polycrystals, defect dipole between Fe dopant and oxygen vacancy has the same orientation with spontaneous polarization PS, which enables the reversible domain switching and hence leads to the emergence of pinched polarization hysteresis and recoverable strain effect. And the defect dipoles can be gradually disrupted by bipolar electric field cycling, once again endowing the aged materials with representative ferroelectric properties. For the poled PSZT-Fe polycrystals, the defect dipoles are reoriented to be parallel to the applied poling field, and an internal bias field aligning along the same direction emerges simultaneously, being responsible for asymmetric hysteresis loops.

Effect of polarization fatigue on the electrocaloric effect of relaxor Pb0.92La0.08Zr0.65Ti0.35O3 thin film

The electrocaloric effect represents an adiabatic temperature change or isothermal entropy change upon the application or removal of an external electric field. However, the effect of the repetitive bipolar/unipolar electric field on the electrocaloric effect in ferroelectrics is not well understood. In this work, the electrocaloric effect after both bipolar and unipolar electrical cycling in Pb0.92La0.08Zr0.65Ti0.35O3 relaxor thin films has been indirectly evaluated using the Maxwell relationship. It was found that at room temperature, the electrocaloric temperature change ΔT under higher electric fields decreases gradually from a positive value to a negative one with the increase in the bipolar/unipolar fatigue cycle number. Intriguingly, around the Curie temperature, the positive ΔT of the film after bipolar/unipolar cycling was found to decrease under low or intermediate electric fields, while it remains almost unchanged under high electric fields. This behavior is attributed to the pinning effect of defects caused by phase decomposition during both bipolar and unipolar fatigue. Note that the increase in polarization by temperature induced domain depinning close to room temperature after the fatigue process is manifested by using the Maxwell relation indirectly. Our work further reveals the origin of both the electrocaloric effect and ferroelectric electrical fatigue and is important for the applications of practical electrocaloric refrigerators.

Enhanced endurance and stabilization in Mn-doped Pb(Lu1/2Nb1/2)O3–PbTiO3 ceramics under bipolar electric field cycling

Ferroelectric materials are widely applied in capacitors and actuators, which require both good endurance and the stabilization of electrical properties under large AC bipolar electric field cycling, however, the electric fatigue effect severely deteriorates both the endurance and stabilization. Fatigue endurance is greatly modified by point defects. This work reports the enhancement of the endurance and stabilization of Mn-doped Pb(Lu1/2Nb1/2)O3–PbTiO3 ceramics. After doping, the evolutions of remanent polarization, the coercive field and dielectric permittivity exhibited less variation than virgin samples. Defect-related abnormal self-rejuvenation was detected during the fatigue process. Under different re-annealing conditions, it was found that the screening effect of defects along the grain boundaries is responsible for the enhancement of the fatigue endurance and the stabilized fatigue behavior. This research reveals the mechanism of the abnormal self-rejuvenation effect in acceptor-doped ceramics and provides a potential method by which to control fatigue behavior via defect engineering.

Enhanced piezoelectric response of (Ba,Ca)(Ti, Zr)O3 ceramics by super large grain size and construction of phase boundary

Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) ceramics with super large grain size (>50 μm) have been successfully fabricated by sol-gel method. The effects of pH value of precursor solution on microstructure, electric properties and fatigue behavior were systematically studied. BCZT ceramics with super large grain size (35–55 μm) were prepared by BCZT powders with large particle size (136–221 nm) by controlling the pH value. The grain size and densification of BCZT ceramics decrease with the increase of pH value of precursor solution. XRD results indicate that there is the coexistence of rhombohedral and tetragonal phase in BCZT ceramics synthesized by precursor solution with a pH of 3 and are the coexistence of orthorhombic and tetragonal phase in BCZT ceramics synthesized by precursor solution with a pH of 5 and 7. BCZT ceramics shows obvious diffuse ferroelectric-paraelectric phase transition characteristic and the diffuseness behavior enhances as the pH value increases. The remnant polarization and coercive electric field of BCZT ceramics reduce with the decreased grain size caused by the increase of pH value. The excellent piezoelectric properties (d33 = 585.6 pC/N and d33∗ = 898 pm/V) of BCZT ceramics have been obtained by super large grain size and the construction of phase boundary of tetragonal phase and orthorhombic phase. Furthermore, BCZT ceramics with large grain size still has high fatigue resistance to bipolar electric cycling.

In-situ observation of evolving microstructural damage and associated effective electro-mechanical properties of PZT during bipolar electrical fatigue

We investigate the fatigue behavior of bulk polycrystalline lead zirconate titanate (PZT) during bipolar electric field cycling. We characterize the frequency- and cycle-dependent degradation in both the effective electro-mechanical properties (specifically, the electrical hysteresis and the macroscopic viscoelastic stiffness and damping measured by Broadband Electromechanical Spectroscopy, BES) and the microstructural damage evolution (quantified via scanning electron microscopy). The BES setup enables the mechanical characterization while performing electrical cycling so as to measure the evolving viscoelasticity without remounting the sample; particularly measuring the viscoelastic damping allows us to gain insight into the ferroelectric domain wall activity across the full electric hysteresis and over the full range of cycles. A clear dependence on the electric cycling frequency is observed in the rates of degradation of all measured properties including an up to 10% increase in dynamic compliance and a 70% decrease in electric displacement magnitude. We quantify the evolving micro-crack density across wide ranges of numbers of cycles and compare with changes in the effective compliance. Interestingly, the observed strong degradation in the ferroelectric hysteresis is contrasted by relatively mild changes in the effective viscoelastic moduli, while samples clearly indicate increasing levels of micro-damage.

Lead-free (Ba,Ca)(Ti,Zr)O3 ceramics within the polymorphic phase region exhibiting large, fatigue-free piezoelectric strains

Lead-free xBaZrO3-(0.85-x)BaTiO3-0.15CaTiO3; x=0.00–0.20 (xBZ) ceramics were prepared successfully using the conventional solid-state reaction method. Unipolar electric-field-induced strains of the composition x=0.125 in the polymorphic phase region (PPR) composition show an extraordinarily high normalized piezoelectric coefficient (d33⁎) of 2244pm/V with relatively low hysteresis at a low electric field of 5kV/cm, which is higher than that of most reported lead-free ceramics. The PPR composition also exhibits excellent fatigue resistance to bipolar electric cycling with negligible loss of electric-field-induced strain after 106cycles. A two-phase mixture model featuring short-range ordering, which is dispersed in the long-range ferroelectric phase, is proposed to explain the outstanding piezoelectric properties. The reversible electric-field-induced phase transition between the two states is responsible for the large normalized piezoelectric coefficient and fatigue resistance. Under repeated electric cycling, the domains become more dynamic, and the change in domain configuration becomes easier due to decreased energy requirement upon polarization reversal. Furthermore, the ceramic shows single crystal-like behavior characterized by a nearly vertical slope in the polarization hysteresis data, which correlates to the electric field induced transformation from a multi-domain state to a single-domain state. This environmentally benign lead-free ceramic, with outstanding properties, has great potential use for highly responsive and reliable actuators.

Photovoltaic Behaviors Regulated by Band-Gap and Bipolar Electrical Cycling in Holmium-Doped Bi5Ti3FeO15 Ferroelectric Films

The pure and Ho-doped Bi5Ti3FeO15 ferroelectric films with layered perovskite structure were prepared via a chemical solution deposition. One investigated the regulation of band gap and bipolar electrical cycling on photovoltaic behaviors including photovoltaic spectral response, open-circuit voltage, and short-circuit current for the films. It is shown that the photovoltaic response peak of Ho-doped Bi5Ti3FeO15 films shifts toward the visible region and the open-circuit voltage as well as short-circuit current are improved compared with the pure Bi5Ti3FeO15 films, which is attributed to the narrowed band gap after doping with Ho. And the spectral response, open-circuit voltage as well as short-circuit current of Ho-doped Bi5Ti3FeO15 films do not suffer from the fatigue like the pure Bi5Ti3FeO15 films with the action of bipolar electrical cycling. It just appears extended response peak without blue shift from the visible region. Likewise, Ho-doped Bi5Ti3FeO15 films still enjoy strong open-circuit voltage ...

Fatigue effect on polarization switching dynamics in polycrystalline bulk ferroelectrics

Statistical distribution of switching times is a key information necessary to describe the dynamic response of a polycrystalline bulk ferroelectric to an applied electric field. The Inhomogeneous Field Mechanism (IFM) model offers a useful tool which allows extraction of this information from polarization switching measurements over a large time window. In this paper, the model was further developed to account for the presence of non-switchable regions in fatigued materials. Application of the IFM-analysis to bipolar electric cycling induced fatigue process of various lead-based and lead-free ferroelectric ceramics reveals different scenarios of property degradation. Insight is gained into different underlying fatigue mechanisms inherent to the investigated systems.

Unipolar Fatigue Behavior of BCTZ Lead‐Free Piezoelectric Ceramics

(Ba,Ca)(Ti,Zr)O3 lead‐free piezoelectric ceramics have been considered to be one of the most potential lead‐free alternatives for PZT in the room‐temperature range. The stability of the piezoelectric performance during unipolar cycling is investigated in this study. It is found that the unipolar fatigue behavior is similar to soft PZT. Developments of bias field, offset polarization, asymmetry in strain, and dielectric hysteresis loops are observed during bipolar measurements. The changes are mainly contributed to the migration of charge carriers to the grain boundaries driven by the unscreened depolarization field. Redistribution of the accumulated charge carriers by bipolar electric cycling or thermal annealing can significantly recover the unipolar fatigued state. The unipolar strain response stabilized after 1000 cycles at 0.053% for an electric field of 0.6 kV/mm (d33*= 883 pm/V), which is a good characteristic for actuator applications.

Magnetoelectric fatigue of Ho-doped Bi5Ti3FeO15 films under the action of bipolar electrical cycling

Pure and Ho-doped Bi5Ti3FeO15 magnetoelectric films were prepared by a sol–gel method, and the influence of bipolar electrical cycling on the ferroelectric, leakage and magnetoelectric properties of the films were studied in detail.

Statistical electric field and switching time distributions in PZT 1Nb2Sr ceramics: Crystal- and microstructure effects

Dispersive polarization response of ferroelectric PZT ceramics is analyzed assuming the inhomogeneous field mechanism of polarization switching. In terms of this model, the local polarization switching proceeds according to the Kolmogorov-Avrami-Ishibashi scenario with the switching time determined by the local electric field. As a result, the total polarization reversal is dominated by the statistical distribution of the local field magnitudes. Microscopic parameters of this model (the high-field switching time and the activation field) as well as the statistical field and consequent switching time distributions due to disorder at a mesoscopic scale can be directly determined from a set of experiments measuring the time dependence of the total polarization switching, when applying electric fields of different magnitudes. PZT 1Nb2Sr ceramics with Zr/Ti ratios 51.5/48.5, 52.25/47.75, and 60/40 with four different grain sizes each were analyzed following this approach. Pronounced differences of field and switching time distributions were found depending on the Zr/Ti ratios. Varying grain size also affects polarization reversal parameters, but in another way. The field distributions remain almost constant with grain size whereas switching times and activation field tend to decrease with increasing grain size. The quantitative changes of the latter parameters with grain size are very different depending on composition. The origin of the effects on the field and switching time distributions are related to differences in structural and microstructural characteristics of the materials and are discussed with respect to the hysteresis loops observed under bipolar electrical cycling.

Electrical Fatigue‐Induced Cracking in Lead Zirconate Titanate Piezoelectric Ceramic and Its Influence Quantitatively Analyzed by Refatigue Method

Lead zirconate titanate (PZT) is one of the most commonly used piezoelectric ceramics. The major causes of its electrical fatigue are suggested to be domain pinning and cracking. However, their contributions to fatigue have never been quantitatively compared. This study focuses on the electrical fatigue‐induced microstructure damage in the near‐electrode regions of PZT and uses a refatigue method to determine quantitatively the contribution of the cracking mechanism to electrical fatigue. It is shown that during bipolar electrical cycling, a large number of cracks are initiated in the samples, and the cracking is particularly concentrated in the near‐electrode regions. So the loss of piezoelectric properties can be partially restored by removing such regions. For a particular fatigue stage, the cracking mechanism contributes significantly more to the electrical fatigue than the domain pinning mechanism.

Why do antiferroelectrics show higher fatigue resistance than ferroelectrics under bipolar electrical cycling?

We show that our fatigue model developed recently for ferroelectrics could explain why antiferroelectrics show higher fatigue resistance than ferroelectrics under bipolar electrical cycling. The better fatigue endurance of antiferroelectrics in comparison with their ferroelectric counterparts originates from their lower depolarization field, their lower local injected power density, and consequently their lower local phase decomposition probability at the phase nucleation sites. The model, which could explain the fact that unipolar pulses will produce no or little fatigue in ferroelectrics, predicts that evident fatigue will occur in at least one of the two hysteretic branches of antiferroelectrics under unipolar electrical cycling.