Ferroelectric Aging Research Articles

Temperature-Dependent Ferroelectric Properties and Aging Behavior of Freeze-Cast Bismuth Ferrite-Barium Titanate Ceramics.

Lead-free BiFeO3-BaTiO3 (BF-BT) piezoceramics have sparked considerable interest in recent years due to their high piezoelectric performance and high Curie temperature. In this paper, we show how the addition of highly aligned porosity (between 40 and 60 vol %) improves the piezoelectric performance, sensing, and energy harvesting figures of merit in freeze-cast 0.70BiFeO3-0.30BaTiO3 piezoceramics compared to conventionally processed, nominally dense samples of the same composition. The dense and porous BF-BT ceramics had similar longitudinal piezoelectric coefficients (d33) immediately after poling, yet the dense samples were observed to age faster than those of porous ceramics. After 24 h, for example, the porous samples had significantly higher d33 values ranging from 112 to 124 pC/N, compared to 85 pC/N for the dense samples. Porous samples exhibited 3 and 5 times higher longitudinal piezoelectric voltage coefficient g33 and energy harvesting figure of merit d33g33 than dense samples due to the unexpected increase in d33 and decrease in relative permittivity with porosity. Spontaneous polarization (Ps) and remnant polarization (Pr) decrease as the porosity content increased from 37 to 59 vol %, as expected due to the lower volume of active material; however, normalized polarization values with respect to porosity level showed a slight increase in the porous materials relative to the dense BF-BT. Furthermore, the porous ceramics showed improved temperature-dependent strain-field response compared to the dense. As a result, these porous materials show excellent potential for use in high temperature sensing and harvesting applications.

Flexoelectric aging effect in ferroelectric materials

In spite of the flexoelectric effect being a universal phenomenon in the ferroelectric perovskites, the current understanding of flexoelectric aging in ferroelectrics is, actually, rather incomplete. In this paper, we have fabricated a series of Mn-doped BaTiO3 perovskite ceramics (BaTi1–xMnxO3, x = 0.1% and 1%, BTMO) to systematically investigate the corresponding flexoelectric aging behavior by controlling the concentration of Mn. We found that the variation of Mn dopant significantly effects the Curie temperature, dielectric constant, flexoelectric aging, and flexoelectric coefficient of the BTMO ceramics. Especially for the BTMO (0.1%) ceramics, obvious ferroelectric aging and flexoelectric aging phenomenon are observed at room temperature. The main reason for aging of BTMO ceramics is that the doping of Mn introduces oxygen vacancies, which tend to be stable under the action of strain gradient and electric field. Therefore, the results presented in this paper verify that the flexoelectric aging in Mn-doped BTO ceramics is closely related to ferroelectric fatigue.

Aging effect in Er3+‐doped 0.5Ba(Zr0.2Ti0.8)O3–0.5(Ba0.7Ca0.3)TiO3 ceramics

AbstractUsually, aging in poled ferroelectrics leads to degradation of certain physical properties. In this study, we found a remarkable aging effect in tetragonal Er3+‐doped 0.5Ba(Zr0.2Ti0.8)O3–0.5(Ba0.7Ca0.3)TiO3 (BZT‐BCT) ceramics after poling. It is observed that the domains can spontaneously rotate to keep their spontaneous polarization direction similar to that of the poling electric field during aging for the poled ceramics. Furthermore, compared with freshly poled ceramics, the thermally stimulated current (TSC) peak of the aged ones shifts toward a higher temperature (10°C). And the temperature of the TSC peak in the aged ceramics is exactly equal to their Curie temperature. Such features indicate that aging for the poled ceramics could stabilize the alignment of ordered ferroelectric domains. Additionally, a downward TSC peak above Curie temperature is obtained in both poled and aged ceramics, demonstrating that poling and aging can lead to ordered alignment of defect dipoles. The aging mechanism of poled Er3+‐doped BZT‐BCT ceramics has proposed and discussed in this article.

Large Electrostrain from the Ferroelectric Aging Effect around a Morphotropic Phase Boundary

A large electrostrain of ∼0.245% emerged in an intrinsic-acceptor-doped morphotropic phase boundary (MPB) system Ba(Ce0.1Ti0.9)O3–x(Ba0.7Ca0.3)TiO3 under an electric field of 30 kV/cm at 0.1 Hz. It...

Influence of non-stoichiometry on the ferroelectric aging properties of Mn-doped BaTiO3 ceramics

In the present work, the effect of the non-stoichiometry on the dielectric and ferroelectric properties especially the aging phenomenon of Bam(Ti0.995Mn0.005)O3 ceramics is studied. With the A/B site stoichiometry ratio m increased from 0.990 to 1.010, the Curie temperature is decreased from 128 to 118 °C monotonically. The non-stoichiometry shows the dramatic effect on the aging phenomenon of the Mn-doped BaTiO3 ceramics. As the aged sample with m 1 samples, it shows the normal hysteresis loop and electro-strain curve as the un-aged samples. The valence state analysis of Mn ions shows that for the m 1 samples Mn2+ and Mn4+ ions co-exist. Moreover, with m decreasing, the amount of Mn2+ ions increases. It is proposed that the non-stoichiometry affects the valence state of Mn ions, which causes the number of oxygen vacancies to change, ultimately affecting the aging effect of the Mn-doped BaTiO3 ceramics.

Ferroelectric aging effects and large recoverable electrostrain in ceria‐doped BaTiO3 ceramics

AbstractFerroelectric aging is a phenomenon that is generally observed in acceptor‐doped ferroelectrics and usually produces a large recoverable electrostrain. In this work, using an oxide ionic conducting material, a Gd‐modified ceria solution (GDC), as a dopant, we find that GDC‐doped BaTiO3 ceramics exhibit ferroelectric aging behaviors at room temperature. These ceramics show double polarization hysteresis (P‐E) loops and sprout‐shaped recoverable strain vs electric field (S‐E) curves. GDC‐doped BT ceramic (3 mol%) produces a large recoverable electrostrain of 0.12% at 3 kV/cm. The large ions of Ce3+ and Gd3+, which have small electronegativity, lead to the high mobility of oxygen vacancies and a rapid symmetry conformation for short range ordering (SC‐SRO) of points defects, which appear as fast aging effects and a large electrostrain in GDC‐doped BT ceramics at room temperature.

3D Imaging of Ferroelectric Kinetics during Electrically Driven Switching.

Čerenkov-type second-harmonic generation microscopy is used for in situ 3D imaging of the switching process of ferroelectric domains in a relaxor-type ferroelectric crystal. The lateral and longitudinal domain wall motion is optically measured and compared with the hysteresis loop to reveal the connection between the domain kinetics and the ferroelectric aging effect in strontium barium niobate.

Influence of defect structure on ferroelectric aging in donor–acceptor hybrid-doped PZT

In the present work, we report the aging effect in manganese (Mn) and niobium (Nb) hybrid-doped PZT composition. Interestingly, it is observed that the ferroelectric aging depends on the acceptor/donor ratio. In hybrid-doped PZT, at high donor dopant concentrations, aging is not observed. The underlying mechanism is correlated with the defect chemistry of the system. It is also observed that tuning the defect chemistry is an effective strategy to realize piezoceramics with enhanced dielectric and piezoelectric characteristics.

Abnormal dielectric behavior induced by defect dipoles in aged Na0.5Bi0.5(Ti,Zr)O3 thin film

Ferroelectric aging behavior was investigated in Na0.5Bi0.5(Ti0.99Zr0.01)O3 thin film on FTO/glass substrate by the dielectric constant (dissipation factor)-electric field (εr–E and tanδ–E) curves. The aged sample can be gained by keeping the fresh film for two months at room temperature. Compared with the typical single butterfly εr (tanδ)–E of the fresh sample, an abnormal loop has been exhibited in the aged one. Furthermore, with the increase of the measuring electric field or decrease of applied frequency, the aging phenomenon becomes weak and even disappeared. These present results are analyzed based on defect chemistry by the symmetry-conforming principle of defect dipoles.

External field effects on aging phenomenon of acceptor-doped BaTiO3 ceramics

Our experiments on ferroelectric aging phenomena of a series of acceptor-doped BaTiO3 ceramics demonstrate that after well-aging, all samples show a similar double hysteresis loop under smaller applied electric field, regardless of ionic radius or ionic valence of the acceptor. However, with increasing the applied electric field, the completely constricted loops gradually start to open, indicating the aging effect becomes weak under larger electric field. The unified microscopic mechanism responsible for the similar aging behavior in different acceptor-doped BaTiO3 ceramics may be that the larger field is considered to kinetically facilitate a part of oxygen vacancies short-range hopping. As a result, the defect dipole field provided by oxygen vacancies and the associated defect dipoles frozen in the original states decreases, thus contributing to the weaker aging effect.

Mechanisms of aging and fatigue in ferroelectrics

A comprehensive review of aging and fatigue phenomena in bulk polycrystalline ferroelectrics is presented. Three material classes are covered, namely the most widely used Pb[Zr1−xTix]O3 (PZT) ceramics and lead-free materials, including those based on bismuth sodium titanate Bi1/2Na1/2TiO3 (BNT) and alkali niobate [KxNa1−x]NbO3 (KNN). Aging is studied in poled and unpoled states both experimentally and theoretically. The variety of different loading regimes for fatigue includes DC electric field, unipolar, sesquipolar and bipolar cycling and all these differently combined with mechanical loading at different frequencies and temperatures. The role of device geometries and electrode materials is addressed and models describing charge migration and defect dipole re-orientation are discussed in the context of recent experimental studies.

Aging in the relaxor and ferroelectric state of Fe-doped (1-x)(Bi1/2Na1/2)TiO3-xBaTiO3 piezoelectric ceramics

Aging of piezoelectric properties was investigated in lead-free (1 − x)(Bi1/2Na1/2)TiO3-xBaTiO3 doped with 1at. % Fe. The relaxor character of the un-poled material prevents macroscopic aging effects, while in the field-induced ferroelectric phase aging phenomena are similar to those found in lead zirconate titanate or barium titanate. Most prominent aging effects are the development of an internal bias field and the decrease of switchable polarization. These effects are temperature activated, and can be explained in the framework of defect complex reorientation. This picture is further supported by electron paramagnetic resonance spectra indicating the existence of (FeTi′−VO••)• defect complexes in the Fe-doped material.

Nonmonotonic variation of aging behavior in Fe-doped BaTiO3 ceramics

The investigation of ferroelectric aging effect in Fe-doped BaTiO3 ceramics reveals that such effect is first strengthened and then suppressed with the increase content of Fe dopant. Such nonmonotonic variation of aging behavior is considered to be originated from the competition effects between increased concentration of oxygen vacancies and decreased c/a value on the formation of defect dipoles (FeTi′−Vo··)·. This study provides a feasible alternative method for modulating aging effect and will favor the applications of ferroelectrics.

Dielectric Relaxation Time Behavior of B-site Hybrid-doped BaTiO3 Ceramics

The time dependence of dielectric charge was investigated of Ba(Ti0.99-xMn0.01Tax)O3 as a function of x = 0.0, 0.5, 0.1 and 1.5 mol% through the dependency of the dielectric permittivity on the frequency. A two part signal is considered as a behavior of aging in ferroelectrics: one is the low electric field and the other is the high electric field. Aging of dielectric has been calculated under the dielectric decay function which corresponds to observed de-polarization according to aging effect driven by charged defects with high activation energy. It was found that the aging behavior change significantly with donor dopant concentration.

Recent Progress on Defect Dipoles Characteristics in Piezoelectric Materials

Defect dipoles which have pronounced effects on properties of piezoelectric materials can be introduced either by partially modifying with acceptor impurities or volatizing of cation elements in perovskite lattice during sintering. The formation mechanism of defect dipoles and responses under external fields were reviewed in the present paper.Besides,the main physic mechanisms of ferroelectric aging,hysteresis loop abnormalities and electroshapememory effects in piezoelectric materials were discussed in detail from the defect dipoles viewpoints.Based on a defect mediated reversible domain switching mechanism,large recoverable electro-strain,as well as constricted hysteresis loops were obtained in unpoled aged ferroelectric crystals and/or ceramics,which indicated that aging was not always a detrimental effect,and may be promising for future novel applications.Furthermore,the defect dipole relaxation process was briefly described and the development trends of the high reliability piezoelectric actuators were proposed.

Mechanical stress modified ferroelectric aging behavior

Mechanical stress effect on aging behavior of Bi3.25La0.75Ti3O12 (BLT) and PbZr0.53Ti0.47O3 (PZT) films was investigated. It is found that the remnant polarization decreases with time while the coercive field increases in stress-free BLT films. For unconfined PZT films, both the remnant polarization and the coercive field decrease as time elapses. The applied tensile stress weakens the aging of remnant polarization of BLT films but strengthens the aging of coercive field, while the applied tensile stress possesses opposite effect. In contrary, the applied compressive stress simultaneously improves the aging behavior of both remnant polarization and coercive field of PZT films. Mechanical-stress-induced variation of domain wall mobility in different materials was suggested as the possible origin of these observations. This work indicates that the aging behavior modification using stress could be realized, and it is helpful for promoting the reliability of ferroelectric films for industrial applications.

Defect-dipole-induced two important macroscopic effects: The dielectric relaxation and the ferroelectric aging in hybrid-doped (Ba,Ca)TiO3 ceramics

To observe the dielectric relaxor behavior and the ferroelectric aging effect, the structural and electrical properties of (Ba0.90Ca0.10)(Ti1−xCax)O3−x (BCT-C) ceramics prepared using a conventional dry route were investigated. With increased concentration of Ca on the B-site in BCT-C ceramics, the tetragonal phase is decreased while the multiphases with the cubic pervoskite structure as a major constituent is increased and remained predominant in the BCT-C ceramics with x>0.03. The increased amount of Ca on the B-site causes the high temperature phase transition to shift to the low temperature and results in an increase in the degree of diffusion and relaxation of the BCT-C ceramics. The observed dielectric relaxation behavior may be understood by a defect-dipole formed random electric field induced domain state. The aging effect controlled by the migration of mobile oxygen vacancies is rarely observed in aged BCT-C ceramics while it can be markedly observed in Bi-doped BCT ceramics. Based on the microscopic mechanism of the aging effect, the possible reasons for the aging effect are given.

Ferroelectric aging behaviors of BaTi0.995Mn0.005O3 ceramics: grain size effects

We report the ferroelectric aging effect of dense BaTi0.995Mn0.005O3 ceramics with grain size varying from 2000 nm to 150 nm. Given the identical aging process, it is revealed that the significant aging effect with clear double-hysteresis loop, observed in coarse-grain sample, is substantially suppressed with decreasing grain size. This suppression can be attributed to the reduction of tetragonal distortion and the grain boundary barrier effect in fine-grain sample. Consequently, the weak thermodynamic driving force and the limited kinetic migration are unfavorable to a reversible domain switching, resulting in a normal hysteresis loop in small grained samples.

A quantitative model for stabilization effect induced by ferroelectric aging

The stabilization effect, an increase of the reverse transition temperature TC with ferroelectric aging time, was recently found in acceptor doped ferroelectrics. Such an effect has found a microscopic explanation in the symmetry-conforming principle of point defects, which also accounts for a similar stabilization effect in ferroelastic/martensite materials. However, such a microscopic model is difficult to use to make a quantitative/semiquantitative evaluation of the aging process. In the present work, we propose a single-domain thermodynamic model that provides a semiquantitative fit to the experimentally observed stabilization kinetics. Furthermore, it predicts a new aspect of ferroelectric aging: the decrease of latent heat ΔH of the reverse transition with aging time. Such a prediction was confirmed via experimental differential scanning calorimetry results.

Control of Ferroelectric Aging by Manipulating Point Defects

In the present work, we systematically studied the aging effect of both ferroelectric single crystals and polycrystals to study how to control aging effect. We found that such hybrid-doped BaTiO3 single crystals showed obvious aging effect only when the concentration of the acceptor K+ is higher than that of the donor; when the donor F− concentration is higher than the acceptor K+, the K-F doped BaTiO3 showed almost no aging effect. Similar results were obtained in La-Mn doped BaTiO3 polycrystals. With the increase of the concentration of donor La3+ in 0.5%Mn-BaTiO3 ceramics, the aging effect gradually becomes weaker and finally disappears. Our result suggests that donor doping is an effective way of controlling the aging effect.