Double Polarization Hysteresis Research Articles

Revealing the role of B-site cations in the antiferroelectricity of NaNbO3-based perovskites

The promising prospects of antiferroelectric perovskite oxides in the realm of energy storage applications hinge on the unique field-induced phase transitions. Once the transition is triggered by the application of an electric field, characteristic double polarization loops appear. However, NaNbO3-based materials that exhibit a reversible phase transition are still rare, which hinders the practical applications of lead-free antiferroelectrics. Here, the impact of materials chemistry on the competition between antiferroelectric and ferroelectric states is demonstrated in a series of NaNbO3-based solid solutions with varying perovskite B-site cations, while the A-site is fixed as strontium. The crystal structure is analyzed on the basis of Rietveld refinement of high-energy X-ray diffraction data. The phase transition behavior as well as the antiferroelectric and ferroelectric properties are probed by a series of electrical measurements. The antiferroelectric phase is universally observed for all investigated materials in the virgin state. The SrTiO3-substituted system shows an irreversible phase transition similar to that of pure NaNbO3. In contrast, double polarization hysteresis loops are observed in the SrHfO3-, SrZrO3-, and SrSnO3-substituted systems. It is confirmed that compounds that can reduce the tolerance factor of the system contribute to the stabilization of the antiferroelectric order, while those that can reduce the electronegativity difference lead to more pronounced double loops. The competition between antiferroelectricity and ferroelectricity is linked to the competition between covalent and ionic bonding in perovskites.

Unveiling the role of chemical pressure on antiferroelectricity in NaNbO3-based antiferroelectric ceramics

Chemical pressure is widely applied to antiferroelectrics (AFEs) as a criterion to enhance their antiferroelectricity. However, NaNbO3 (NN)-based ceramic with well-defined double polarization hysteresis (P–E) loops was rarely reported based on this strategy, and the effect of chemical pressure on antiferroelectricity remains to be understood. In this work, the Me cations (Me is Ti, Sn, Zr) with different ionic radii were introduced into the component system 0.76NaNbO3–0.20AgNbO3–0.04CaMeO3 to tune the negative chemical pressure and investigate its effect on antiferroelectricity. The enhancement of negative chemical pressure can effectively stabilize the AFE phase and reduce hysteresis, as revealed by the P–E loops and dielectric properties, which is further confirmed by the change in crystal lattice parameters and in situ Raman spectra. Rietveld refinement of x-ray powder diffraction reveals that the enhanced negative chemical pressure mainly reduces the cation off-centering displacement and [BO6] octahedral tilting angles. As a result, the 0.76NaNbO3–0.20AgNbO3–0.04CaZrO3 exhibits good reversibility of the electric field-induced antiferroelectric–ferroelectric phase transition and well-defined double P–E loops. This work reveals the underlying mechanism of chemical pressure and provides an effective way of discovering new NN-based AFEs.

MnO2 doping stabilized antiferroelectric P phase and underlying physical mechanism in NaNbO3-SrTiO3 lead-free ceramics

The incorporation of a few amount of MnO2 into 0.88NaNbO3-0.12SrTiO3 lead-free ceramics was found to effectively stabilize the antiferroelectric orthorhombic P phase before its transition into antiferroelectric orthorhombic R phase, consequently featuring completely reversible electric field-induced antiferroelectric-ferroelectric phase transition. Not only reproducible double polarization hysteresis loops but also repeated sprout-like strain-field curves ensure great application potentials in large-displacement lead-free actuators owing to both large repeatedly-utilized strains of ∼0.33% and low driving field of ∼11 kV/mm. Combined results of XPS, Raman spectroscopy and dielectric properties indicate that the stabilized antiferroelectric P phase was closely related to the reduced B-site cation polarizability and oxygen vacancy concentration, while a slight change in antiferrodistortive degree would discourage the P-R phase transition. These results indicate that ionic doping is an alternative method to alter the antiferroelectric P phase stability of NaNbO3-based lead-free ceramics by synergistically considering the influencing factors of phase and crystal structure stability.

Full Antiferroelectric Performance and GMR Effect in Multiferroic La0.75Ba0.25Fe12O19 Ceramic

The potential application of multiferroic materials in new electronic devices attracts more and more attention from people either in an academic field or industry. This paper reports that M-type lanthanum-doped barium ferrite (La0.75Ba0.25Fe12O19) demonstrates full antiferroelectric (AFE) and excellent magnetoelectric coupling effects at room temperature, while its AFE phase displays a zero macroscopic net polarization. The dramatic change in the dielectric constant near the Curie temperature far below room temperature represents the transition from ferroelectrics (FE) to antiferroelectrics. The fully separated double electric polarization hysteresis (P–E) loops confirmed its AFE performance. Its EF and EA are located at 1100 kV/cm and 850 kV/cm, respectively. The large M–H loop showed a strong magnetic property simultaneously. The UV-Vis-NIR optical spectrum revealed that La0.75Ba0.25Fe12O19 is also a semiconductor, whose direct bandgap energy (Eg) was determined to be 1.753 eV. Meanwhile, La0.75Ba0.25Fe12O19 showed strong ME coupling and a GMR effect. A 1.1 T magnetic field reduced its resistance by 110% at 30 kHz. The multiple functions combined in one phase would create new options for high energy storage capacitors, microactuators, pyroelectric safety sensors, cooling devices, and pulsed power generators and so on, as well as great opportunities for generating new electronic devices with active magnetoelectric coupling effects.

Achieving a high energy storage density in Ag(Nb,Ta)O 3 antiferroelectric films via nanograin engineering

Due to its lead-free composition and a unique double polarization hysteresis loop with a large maximum polarization (<i>P</i>_max) and a small remnant polarization (<i>P</i>_r), AgNbO₃-based antiferroelectrics (AFEs) have attracted extensive research interest for electric energy storage applications. However, a low dielectric breakdown field (<i>E</i>_b) limits an energy density and its further development. In this work, a highly efficient method was proposed to fabricate high-energy-density Ag(Nb,Ta)O₃ capacitor films on Si substrates, using a two-step process combining radio frequency (RF)-magnetron sputtering at 450 ℃ and post-deposition rapid thermal annealing (RTA). The RTA process at 700 ℃ led to sufficient crystallization of nanograins in the film, hindering their lateral growth by employing short annealing time of 5 min. The obtained Ag(Nb,Ta)O₃ films showed an average grain size (<i>D</i>) of ~14 nm (obtained by Debye–Scherrer formula) and a slender room temperature (RT) polarization–electric field (<i>P–E</i>) loop (<i>P</i>_r ≈ 3.8 μC·cm⁻² and <i>P</i>_max ≈ 38 μC·cm⁻² under an electric field of ~3.3 MV·cm⁻¹), the <i>P–E</i> loop corresponding to a high recoverable energy density (<i>W</i>_rec) of ~46.4 J·cm⁻³ and an energy efficiency (<i>η</i>) of ~80.3%. Additionally, by analyzing temperature-dependent dielectric property of the film, a significant downshift of the diffused phase transition temperature (<i>T</i>_M2–M3) was revealed, which indicated the existence of a stable relaxor-like AFE phase near the RT. The downshift of the <i>T</i>_M2–M3 could be attributed to a nanograin size and residual tensile strain of the film, and it led to excellent temperature stability (20–240 ℃) of the energy storage performance of the film. Our results indicate that the Ag(Nb,Ta)O₃ film is a promising candidate for electrical energy storage applications.

Antiferroelectric-like double hysteresis loops in Ag-doped K0.5 Na0.5NbO3 ceramics

In this work, we report the effect of Ag+ doping on the microstructure, dielectric, ferroelectric, piezoelectric, and energy storage properties of the K0.5Na0.5NbO3 (KNN) ceramics for which (K0.5Na0.5)(1-x)AgxNbO3 (KNN-xAg) ceramics with x = 0, 0.01, 0.02 and 0.03 were prepared by the conventional solid-state method. The substitution of Ag+ changes the microstructure of KNN from inhomogeneous bimodal grain distribution to homogeneous densely packed grains with an average grain size of 0.5–2.25 μm. The phase transition (TC) of KNN shifts towards the lower temperature side with Ag+ doping. Antiferroelectric-type double PE loops were observed in Ag-doped KNN ceramics at room temperature, which has improved the energy storage and piezoelectric properties of KNN. For ceramics poled at 2 kV/mm for 30 min, a d33 value of ∼149 pC/N and kp ∼0.41 were obtained. These enhanced properties in Ag-doped KNN are due to the occurrence of double polarization hysteresis loops.

Li+ and Sm3+ co-doped AgNbO3-based antiferroelectric ceramics for high-power energy storage

Ag1-x-3yLixSmyNbO3 (x≤0.05, y≤0.05) (ALSN) antiferroelectric ceramics were successfully prepared via conventional solid-state reaction and sinter routes in oxygen atmosphere for improving the energy storage characteristic of pure AgNbO3. The results indicate that all of the studied compositions display a pure orthorhombic antiferroelectric (AFE) perovskite structure, while their key parameters of electric-field-induced antiferroelectric-ferroelectric transition can be affected by Li+ or/and Sm3+ doping contents. The Sm3+ doping can enhance the stability of antiferroelectric state, giving rise to higher antiferroelectric-ferroelectric transition electric-field (EF and EB), while Li+ doping can reduce EF and EB for Sm3+ doped AgNbO3 with low Sm3+ content (y≤0.03). When co-doping the same amounts of Li+ and Sm3+ at x=y≤0.03, both EF and EB almost remain unchanged. At x=y=0.05, the diffuse phase transition (DPT) behavior of antiferroelectric-paraelectric (AFE-PE) phase transition occurred, resulting in a “slim-like” double-polarization hysteresis with significantly enhanced EF. Due to these features, both Wrec and η are improved compared with pure AgNbO3. The Wrec and η with composition at x=y=0.05 is 2.33 J/cm3 and 58% under applying electric field of 240 kV/cm, respectively. The results suggest that building DPT behavior of AFE-PE phase transition could be an alternative strategy to improve the energy storage characteristic of AgNbO3.

NaNbO3-based antiferroelectric multilayer ceramic capacitors for energy storage applications

Antiferroelectric materials feature electric-field-induced phase transitions followed by a large polarization change characterized by double polarization hysteresis loops. Therefore, antiferroelectrics are engaging for high-energy density and high-power density applications, especially in the form of multilayer ceramic capacitors (MLCCs). However, the development of lead-free antiferroelectrics with stable double hysteresis loops is still challenging, especially for compositions based on NaNbO3. To this end, we have prepared MLCCs with the newly developed antiferroelectric composition 0.90NaNbO3-0.06SrSnO3-0.04(Na0.5Bi0.5)TiO3. The double hysteresis loops were determined at 24 kV/mm in the temperature range of 25–150 °C, with resulting recoverable energy storage ranging from 1.16 to 1.42 J/cm3, respectively. Moreover, the energy efficiency is rather constant at 0.4 in the same temperature range. Finally, the MLCCs exhibit resistance to electric field cycling and could withstand up to 1000 cycles. These results verify that NaNbO3-based antiferroelectrics in the form of MLCCs are promising for use in applications.

Domain morphology of newly designed lead‐free antiferroelectric NaNbO3‐SrSnO3 ceramics

AbstractReversible antiferroelectric‐ferroelectric phase transitions were recently observed in a series of SrSnO3‐modified NaNbO3 lead‐free antiferroelectric materials, exhibiting well‐defined double polarization hysteresis loops at ambient conditions. Here, transmission electron microscopy was employed to investigate the crystallography and domain configuration of this newly designed system via electron diffraction and centered dark‐field imaging. It was confirmed that antiferroelectricity is maintained in all compositions, manifested by the characteristic ¼ superlattice reflections in the electron‐diffraction patterns. By investigating the antiferroelectric domains and domain boundaries in NaNbO3, we demonstrate that antiphase boundaries are present and their irregular periodicity is responsible for the streaking features along the ¼ superlattice reflections in the electron‐diffraction patterns. The signature domain blocks observed in pure NaNbO3 are maintained in the SrSnO3‐modified ceramics, but disappear when the amount of SrSnO3 reaches 7 mol.%. In particular, a well‐defined and distinct domain configuration is observed in the NaNbO3 sample modified with 5 mol.% SrSnO3, which presents a parallelogram domain morphology.

Large polarization and record-high performance of energy storage induced by a phase change in organic molecular crystals.

Dielectrics that undergo electric-field-induced phase changes are promising for use as high-power electrical energy storage materials and transducers. We demonstrate the stepwise on/off switching of large polarization in a series of dielectrics by flipping their antipolar or canted electric dipoles via proton transfer and inducing simultaneous geometric changes in their π-conjugation system. Among antiferroelectric organic molecular crystals, the largest-magnitude polarization jump was obtained as 18 μC cm−2 through revisited measurements of squaric acid (SQA) crystals with improved dielectric strength. The second-best polarization jump of 15.1 μC cm−2 was achieved with a newly discovered antiferroelectric, furan-3,4-dicarboxylic acid. The field-induced dielectric phase changes show rich variations in their mechanisms. The quadruple polarization hysteresis loop observed for a 3-(4-chlorophenyl)propiolic acid crystal was caused by a two-step phase transition with moderate polarization jumps. The ferroelectric 2-phenylmalondialdehyde single crystal having canted dipoles behaved as an amphoteric dielectric, exhibiting a single or double polarization hysteresis loop depending on the direction of the external field. The magnitude of a series of observed polarizations was consistently reproduced within the simplest sublattice model by the density functional theory calculations of dipole moments flipping over a hydrogen-bonded chain or sheet (sublattice) irrespective of compounds. This finding guarantees a tool that will deepen our understanding of the microscopic phase-change mechanisms and accelerate the materials design and exploration for improving energy-storage performance. The excellent energy-storage performance of SQA was demonstrated by both a high recoverable energy-storage density Wr of 3.3 J cm−3 and a nearly ideal efficiency (90%). Because of the low crystal density, the corresponding energy density per mass (1.75 J g−1) exceeded those derived from the highest Wr values (∼8–11 J cm−3) reported for several bulk antiferroelectric ceramics , without modification to relaxor forms.

Polarization reversal via a transient relaxor state in nonergodic relaxors near freezing temperature

Among the unresolved issues in the study of relaxor ferroelectrics is the role of freezing temperature, across which the dynamics of polarization reversal in relaxor ferroelectrics changes. The presence of this freezing temperature is best manifested by the appearance of a double polarization hysteresis loop just above the freezing temperature. Given that the polarization pinching evolving into a double hysteresis starts well below the freezing temperature, there exists a transient temperature regime between the nonergodic and the ergodic relaxor states. To clarify the role of the freezing temperature on the pinching, the polarization reversal near the freezing temperature of relaxor (Pb1-xLax)(Zr1-yTy)1-x/4O3 (PLZT) was monitored using three in situ electric field methods: electrocaloric effect, neutron diffraction, and transmission electron microscopy. We demonstrate that the pinching results from a two-step process, 1) domain detexturization in the ferroelectric state and 2) miniaturization of domains. This observation explains the recently reported gap between the depolarization temperature Td and the ferroelectric-to-relaxor transition temperature TF-R in lead-free relaxors. We further show that Td and TF-R, which have long been considered identical in lead-based relaxors, are not the same. The current study suggests that the mismatch between Td and TF-R is an inherent feature in both lead-based and lead-free relaxor ferroelectrics.

Double polarization hysteresis and dramatic influence of small compositional variations on the electrical properties in Bi4Ti3O12 ceramics

This work reports the existence of double polarization hysteresis (P–E) loop in Aurivillius-phase ferroelectric Bi4Ti3O12 (BiT) and reveals dramatic influence of small compositional variations on the electrical properties of it. The double polarization hysteresis is a characteristic of the interaction of defects with domain walls. This characteristic becomes more pronounced in Bi-deficient and Mg-doped BiT due to an increase in oxygen vacancy concentration at the lattices. Normal and saturated P–E loop is recalled by Nb donor doping, and associated composition Bi4Ti2.97Nb0.03O12.015 (BiT-0.03Nb) shows high remnant polarization (Pr = 12.5 μC/cm2) and large field-induced strain (S33 = 5.6 × 10−4). In addition, this doping results in bulk conductivity (σb) of BiT decreasing dramatically and associated activity energy (Ea) increasing significantly. In contrast, high oxide ion conductivity is induced with Mg2+ acceptor doping, and at 600 °C the optimum composition has ionic conductivity of ˜0.65 × 10−2 S cm−1 in the bulk.

Discovery of an Above-Room-Temperature Antiferroelectric in Two-Dimensional Hybrid Perovskite.

Antiferroelectric materials have been regarded as a promising candidate for electronic energy storage devices, due to their natural double polarization versus electric field ( P- E) hysteresis loops. Currently, two-dimensional organic-inorganic hybrid perovskites with structural diversity and tunability, have received blooming interests, whereas above-room-temperature antiferroelectrics are still unreported in this perovskite system. Herein, for the first time, we successfully acquire a two-dimensional Ruddlesden-Popper hybrid perovskite antiferroelectric, ((CH3)2CHCH2NH3)2CsPb2Br7 (1), which shows an above-room-temperature Curie temperature at 353 K, trigging by the synergistic dynamic motion of inorganic Cs atoms and organic isobutylammonium cations. Intriguingly, the antiferroelectricity of 1 existing over a wide temperature range of 298-353 K are revealed by the distinct double P- E hysteresis loops. Besides, 1 possesses remarkable energy storage efficiency up to 69%, comparable to those of some reported inorganic antiferroelectric ceramics, promoting 1 potential application in energy storage devices. This work provides an avenue to construct novel antiferroelectric materials for high-performance electronic device applications.

Structure and phase stability of lead-free antiferroelectric (Na0.96−xCa0.04Lix)(Nb0.96Zr0.04)O3 ceramics

(Na0.96−xCa0.04Lix)(Nb0.96Zr0.04)O3 (CZNNL) ceramics with high density were successfully prepared by the solid-state reaction method. The effect of Li dopants on the structure, electrical properties and stability of antiferroelectricity has been investigated. Enhanced antiferroelectric superlattice peaks was observed for CZNNL (x ≤ 0.01) using X-ray diffraction. Li substitution can effectively destabilize the antiferroelectric phase and correspondingly the ferroelectric phase can be enhanced. The field-induced polarization increase and the average grain size decrease with increasing Li concentration. The CZNNL (x = 0.01) ceramics can preserve the double polarization hysteresis loops at room temperature and at 120 °C.

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.

Stable antiferroelectricity with incompletely reversible phase transition and low volume-strain contribution in BaZrO3 and CaZrO3 substituted NaNbO3 ceramics

In this work a reproducible double polarization versus electric field (P-E) hysteresis loop clearly reveals a room-temperature stable antiferroelectricity (AFE) in virgin NaNbO3 (NN) samples doped with 6 mol% BaZrO3 and 3 mol% CaZrO3. Inconsistent but sprout-like strain versus field (S-E) curves without any negative strains between the first and non-first cycles yet display an incompletely reversible field induced AFE-ferroelectric (FE) phase transition. In/ex-situ synchrotron x-ray diffraction results suggest irrecoverable AFE states with orthorhombic and monoclinic structures before and after electric cycling, respectively, which generate an irreversible strain contribution including both irreversible volume (22%) and lattice (78%) strains. Frequency-dependent measurements of P/S-E curves demonstrate the rest of remanent strains from the time effect of back-switching from field induced FE to AFE equivalently existing in strain loops of any cycles at a fixed frequency. Compared with virgin samples, post-cycled samples exhibit a completely reversible monoclinic AFE-monoclinic FE phase transition but a relatively small poling strain. It is of particular note that the contribution of the volume strain to the poling strain is only 20% in AFE NN-based ceramics, in which a positive longitudinal strain and a negative transverse strain are concurrently observed, challenging a common knowledge that both strains in two directions should be positive for traditional Pb-based AFE ceramics. The experimental results provide new insights into the AFE phase stability of NN and an exciting possibility to take advantage of NN-based antiferroelectric ceramics for large-displacement actuators in future.

Polarization Reversal Via a Transient Relaxor State in Nonergodic Relaxors Near Freezing Temperature

Among the unresolved issues in the study of relaxor ferroelectrics is the role of freezing temperature, across which the dynamics of polarization reversal in relaxor ferroelectrics changes. The presence of this freezing temperature is best manifested by the appearance of a double polarization hysteresis loop just above the freezing temperature. Given that the pinching evolving into the double hysteresis starts well below the freezing temperature, there exists a transient temperature regime between the nonergodic and ergodic relaxor states. To clarify the role of the freezing temperature in developing the constriction, the polarization reversal near the freezing temperature of relaxor (Pb1-xLax)(Zr1-yTy)1-x/4O3 (PLZT) was monitored using three in situ electric field methods: electrocaloric effect, neutron diffraction, and transmission electron microscopy. We demonstrate that the appearance of constriction results from a two-step process, 1) reduction in domain texture in the ferroelectric state and 2) transformation to a relaxor state with nanodomains. This observation explains the recently reported gap between the depolarization temperature Td and the ferroelectric-to-relaxor transition temperature TF-R in lead-free relaxors. We further show that Td and TF-R, which have long been considered identical in lead-based relaxors, are not the same. The current study suggests that the mismatch between Td and TF-R is an inherent feature in both lead-based and lead-free relaxor ferroelectrics.

Effect of Li2O on the defect polarization in CuO‐added (K0.9Na0.1)NbO3 piezoelectric ceramics

AbstractCuO‐added (LixK0.9−xNa0.1)NbO3 [C(LxK0.9−xN0.1)N] ceramics with 0.0≤x≤0.05 were well‐sintered at 960°C for 6 hours. The lattice parameters of the specimens decreased with the addition of Li2O. Defect polarization (PD) formed between Cu2+ions and oxygen vacancies. Double polarization vs electric field (P‐E) hysteresis and sprout‐shaped strain vs electric field (S‐E) curves were observed in these specimens with a large strain of 0.16% at 7.0 kV/mm, possibly owing to the presence of PD. When the P‐E curve was measured at temperatures higher than 75°C, the C(K0.9N0.1)N ceramic exhibited a normal P‐E hysteresis curve, whereas the C(L0.04K0.86N0.1)N ceramic maintained the double P‐E hysteresis curve up to 125°C, indicating that Li2O increased the thermal stability of PD. The latter specimen also showed the sprout shaped S‐E curve with a strain of 0.15% at 7.0 kV/mm after 104 cycles of a high electric field of 7.0 kV/mm.

Unprecedented Ferroelectric-Antiferroelectric-Paraelectric Phase Transitions Discovered in an Organic-Inorganic Hybrid Perovskite.

As a promising candidate for energy storage capacitors, antiferroelectric (AFE) materials have attracted great concern due to their congenital advantages of large energy storage ability from double polarization versus electric field (P-E) hysteresis characteristics in contrast to ferroelectrics and linear dielectrics. However, antiferroelectricity has only been discovered in inorganic oxides and some hydrogen-bonded molecular systems. In view of the structural diversity and unique physical properties of organic-inorganic hybrid system, it remains a great opportunity to introduce antiferroelectricity into organic-inorganic hybrid perovskites. Here, we report that polarizable antiparallel dipole arrays can be realized in an organic-inorganic hybrid perovskite, (3-pyrrolinium)CdBr3, which not only exhibits an excellent ferroelectric property (with a high spontaneous polarization of 7.0 μC/cm2), but also presents a striking AFE characteristic revealed by clear double P-E hysteresis loops. To the best of our knowledge, it is the first time that such successive ferroelectric-antiferroelectric-paraelectric phase transitions have been discovered in organic-inorganic perovskites. Besides, a giant dielectric constant of 1600 even at high frequency of 1000 kHz and a bulk electrocaloric effect with entropy change of 1.18 J K-1 kg-1 under 7.41 kV/cm are also observed during the phase transition. Apparently, the combined striking AFE characteristic and giant dielectric constant make (3-pyrrolinium)CdBr3 a promising candidate for next generation high-energy-storage capacitors.

Large Electrostrain in K(Nb1−xMnx)O3 Lead‐Free Piezoelectric Ceramics

K(Nb1−xMnx)O3 (KN1−xMx) ceramics with 0.005 ≤ x ≤ 0.015 were sintered at 1020°C through a normal sintering process without the formation of a liquid phase. They exhibited double polarization versus electric field (P–E) hysteresis and sprout‐shaped strain versus electric field (S–E) curves owing to the presence of a defect dipole (PD), which was formed between the acceptor Mn3+ ion and the oxygen vacancy. Moreover, the aging process was not required to develop the PD. The KN1−xMx ceramics exhibited a large strain of ~0.2% at 6.0 kV/mm. For the KN0.985M0.015 ceramic, this large strain was maintained after 104 cycles of an electric field of 6.0 kV/mm. This ceramic also maintained a double hysteresis curve at 200°C. Therefore, the KN0.985M0.015 ceramic has a large electric field‐induced strain, along with good thermal and fatigue properties for multilayer piezoelectric actuators.