Antiferroelectric-ferroelectric Phase Transition Research Articles

Design of polar boundaries enhancing negative electrocaloric performance by antiferroelectric phase-field simulations

Electrocaloric refrigeration which is environmentally benign has attracted considerable attention. In distinction to ferroelectric materials, which exhibit an extremely high positive electrocaloric effect near the Curie temperature, antiferroelectric materials represented by PbZrO3 have a specific negative electrocaloric effect, i.e., electric field decreases the temperature of the materials. However, the explanation of the microscopic mechanism of the negative electrocaloric effect is still unclear, and further research is still needed to provide a theoretical basis for the negative electrocaloric effect enhancement. Herein, the antiferroelectric phase-field model has been proposed to design polar boundaries enhancing antiferroelectric negative electrocaloric performance in PbZrO3-based materials. Based on this, we have simulated the polarization response and domain switching process of the temperature and electric field-induced antiferroelectric—ferroelectric phase transition. It is shown that the temperature range tends to increase as the density of polar boundaries increases from the antiferroelectric stripe domain, polymorphic domain to the nanodomain. Among them, the peak adiabatic temperature change of antiferroelectric nanodomains can reach −13.05 K at 84 kV/cm, and a wide temperature range of about 75 K can be realized at 42 kV/cm. We expect these discoveries to spur further interest in the potential applications of antiferroelectric materials for next-generation refrigeration devices.

Remarkable flexibility in freestanding single-crystalline antiferroelectric PbZrO3 membranes

The ultrahigh flexibility and elasticity achieved in freestanding single-crystalline ferroelectric oxide membranes have attracted much attention recently. However, for antiferroelectric oxides, the flexibility limit and fundamental mechanism in their freestanding membranes are still not explored clearly. Here, we successfully fabricate freestanding single-crystalline PbZrO3 membranes by a water-soluble sacrificial layer technique. They exhibit good antiferroelectricity and have a commensurate/incommensurate modulated microstructure. Moreover, they also have good shape recoverability when bending with a small radius of curvature (about 2.4 μm for the thickness of 120 nm), corresponding to a bending strain of 2.5%. They could tolerate a maximum bending strain as large as 3.5%, far beyond their bulk counterpart. Our atomistic simulations reveal that this remarkable flexibility originates from the antiferroelectric-ferroelectric phase transition with the aid of polarization rotation. This study not only suggests the mechanism of antiferroelectric oxides to achieve high flexibility but also paves the way for potential applications in flexible electronics.

The differences in phase transition characteristics of antiferroelectric PbZrO3 thin films via grain size engineering

PbZrO3 (PZO) possesses a unique antiferroelectric-ferroelectric (AFE-FE) phase transition under an external electric field and engages more attention in understanding and regulating the phase transition behavior. In this work, changing annealing temperature (600–750 °C) and ultralow content (5‰) ions doping are used to optimize the phase transition of PZO films via grain size engineering. As annealing temperature increases, the maximum polarization Pmax increases but forward/backward switching fields EF/EA reduce accompanied by the average grain size enhances from 622 to 686 nm. Following, 5‰ mol aliovalent ion La3+ or K+ doped PZO-650 films both enhance Pmax and EF/EA indicating the strengthened antiferroelectricity, and meanwhile the grain size enhances to ∼800 nm. A high discharge density of 31 J/cm3 is achieved for 5‰ mol La-doped PZO films at a low electric field of 1 MV/cm, which is ∼100 % higher than those of pure PZO films at different annealing temperatures. This work compares the phase transition characteristics changes in PZO films by changing annealing temperature and ultra-low content ion doping strategy, which would provide new thinking in grain size-engineered antiferroelectric materials for energy storage applications.

Energy storage performance and piezoelectric response of silver niobate antiferroelectric thin film

AgNbO3-based antiferroelectric materials have attracted extensive attention in energy storage due to their double polarization-electric field hysteresis loops, but they always suffer from low breakdown strength (Eb). Films with few defects and small thickness exhibit high breakdown strength, which helps to improve energy storage performance. In the present work, an AgNbO3 film with a small thickness of ∼200 nm is prepared via pulsed laser deposition, which has a dense microstructure and a small average grain size of ∼34.5 nm. The AgNbO3 film displays an antiferroelectric nature, as confirmed by the double polarization-electric field hysteresis loops at room temperature. The room temperature phase structure of the AgNbO3 film determined by the dielectric behaviour is the antiferroelectric M2 phase. Due to the small thickness and fine grain size, a high Eb of 1200 kV/cm is obtained, which boosts a recoverable energy storage density (Wrec) of 9.3 J/cm3 and an energy efficiency (η) of 63.7 % in the AgNbO3 film. In addition, Wrec exhibits good temperature stability at 30–120 °C. The AgNbO3 film shows an obvious piezoelectric response after the electric field-induced antiferroelectric-ferroelectric phase transition as confirmed by piezoresponse force microscopy. These results provide guidance for the development of AgNbO3 antiferroelectric films and devices with good energy storage performance.

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.

Low voltage–driven high-performance thermal switching in antiferroelectric PbZrO 3 thin films

Effective control of heat transfer is vital for energy saving and carbon emission reduction. In contrast to achievements in electrical conduction, active control of heat transfer is much more challenging. Ferroelectrics are promising candidates for thermal switching as a result of their tunable domain structures. However, switching ratios in ferroelectrics are low (<1.2). We report that high-quality antiferroelectric PbZrO 3 epitaxial thin films exhibit high-contrast (>2.2), fast-speed (<150 nanoseconds), and long-lifetime (>10 7 ) thermal switching under a small voltage (<10 V). In situ reciprocal space mapping and atomistic modelings reveal that the field-driven antiferroelectric-ferroelectric phase transition induces a substantial change of primitive cell size, which modulates phonon-phonon scattering phase space drastically and results in high switching ratio. These results advance the concept of thermal transport control in ferroic materials.

Sharp/diffuse antiferroelectric-ferroelectric phase transition regulated by atomic displacement ordering

It is the behavior of electric-field induced antiferroelectric to ferroelectric (AFE-FE) phase transition that determines the specific application scenario of antiferroelectric materials. Here, we report that the evolution of the atomic displacement ordering from full-ordered to semi-ordered modulation should be responsible for the change in the behavior of the AFE-FE transition from sharp to diffuse. The novel semi-ordered configuration is originated from the competing interaction between long-range displacement modulation and compositional inhomogeneity, which just makes the AFE-FE transition diffuse but maintains the switching field. These results provide atomic-scale understanding for AFE-FE transition and new insights for designing hysteresis-free antiferroelectric materials.

Improved energy-storage performance with superior thermal stability of [(Bi0.5Na0.5)TiO3](1-x) – [Ba(Ni0.5Nb0.5)O3]x relaxor ferroelectric ceramics

Dielectric ceramic capacitors have been extensively investigated in electronic and high-power electrical systems due to their high-power density, fast charge-discharge rates, brilliant fatigue endurance, and good high-temperature stability. In this study, the dielectric and energy-storage performance of [(Bi0.5Na0.5)TiO3](1-x) –[Ba(Ni0.5Nb0.5)O3]x (x = 0, 0.02, 0.03, 0.04, 0.05, and 0.06) relaxor ferroelectric ceramics were investigated as a function of electric field and temperature. The splitting of (200) reflections in the XRD pattern confirmed the rhombohedral phase with R3c symmetry of all samples. The scanning electron microscopy confirmed that the average grain size gradually increased with doping. The introduction of BNN reduced the temperature of the ferroelectric-antiferroelectric phase transition (Td) and antiferroelectric - paraelectric phase and enhanced the relaxor behavior of BNT ceramics. The value of the recoverable energy density (Wrec) and efficiency (η) increased from 0.049 J/cm3 to 0.627 J/cm3 and 2.13%–61.71% with an increase of x from 0 to 0.06. Further, the Wrec values also showed temperature stability with a variation of less than 8% in the range RT-383 K. Hence, the substitution of BNN in BNT positively affects the overall properties and makes it a promising candidate for energy storage application with superior thermal stability.

Multistage phase transition induced excellent capacitive energy storage performances in (Pb,La,Sr)(Zr,Sn)O3 antiferroelectric ceramics

The applications of dielectric capacitors are essential for modern pulsed-power and high-power electronic devices. Antiferroelectric ceramics have garnered much attention as promising materials for capacitive energy storage on account of their ultrahigh recoverable energy density (Wrec). However, the relatively high energy loss originating from electric field induced antiferroelectric-ferroelectric (AFE-FE) phase transition results in low energy storage efficiency (η). Herein, the La3+ ions incorporated (Pb0.98Sr0.02)(Zr0.85Sn0.15)O3 antiferroelectric ceramics were explored to obtain stable antiferroelectric phase and trigger a unique multistage AFE-FE(Ⅰ)-FE(Ⅱ) phase transition simultaneously. Consequently, this strategy led to the achievement of an ultrahigh Wrec of 13.9 J/cm3 and an enhanced η of 80.4% in the optimal composition. Notably, these ceramics have also demonstrated exceptional thermal reliability of Wrec and η in a wide temperature range, outperforming other previously reported PbZrO3-based ceramics. These results offer an efficient approach to promote the capacitive energy storage behavior in antiferroelectric ceramics.

Reversible evolution of ferroelectric-antiferroelectric phase transition in lanthanum-modified NaNbO3-based ceramics

Sodium niobate (NN) lead-free perovskites have been concentrated on due to high performance and abundant phase structure. The complex structure evolution has become a hot topic of research for this kind of materials. In this work, antiferroelectric phase is recovered by introducing La3+ dopant from modified ferroelectric states, indicating reversible composition-induced antiferroelectric-ferroelectric (AFE-FE) phase transition in NN-based ceramics. Significantly, change tendency of decreasing first and then increasing appears for phase transition temperature with increasing La3+, which is different from general phenomenon for ions dopant. Antiferroelectric orthorhombic (Pbma) is induced from ferroelectric tetragonal (P4mm) with a transient state of paraelectric cubic (Pm3m) via enhancing La3+. Further, substitution on A-site and A/B-sites are revealed with low and high content of La3+, respectively, accompanied by decreased first and then increased oxygen vacancy. Moreover, obviously deteriorated piezoelectric response is observed along with poor domain switching due to the vanishing ferroelectric domain for FE-PE-AFE phase transition. Meanwhile, weak strain, piezoelectric and dielectric properties are observed for antiferroelectric phase with antiparallel dipoles, while enhanced strain and dielectric permittivity are gained around ferroelectric-paraelectric coexistence or paraelectric region originating from electric field-induced ferroelectric state from polar nanoregions. Thus, this work demonstrated an abnormal phase transition in NN-based ceramics, promoting the understanding of antiferroelectrics.

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.

Direct photoluminescence manipulation in Er-doped AgNbO3 lead-free antiferroelectrics via reversible electric-field-induced symmetry modulations

The electric field-modulated photoluminescent (E-PL) effect has received much attention because of its potential applications in optical data storage and communication. Based on the E-induced antiferroelectric-ferroelectric (AFE-FE) phase transition, a large and reversible modulation of the PL intensity was previously realized in lanthanum-doped Pb(Zr0.9Ti0.1)O3 (PLZT) ceramics. However, such systems contain abundant leads and are thus toxic to humans and the environment. In this work, Er-doped AgNbO3 (ANO) lead-free ceramics were prepared, and their E-PL effect was investigated. From the perspective of the crystallographic symmetry, the reversibly E-induced orthorhombic Pbcm to orthorhombic Pmc21 transition results in a negative PL intensity change of 25%, which is different from the positive 30% PL modulation in the PLZT system triggered by the AFE-FE orthorhombic-rhombohedral phase transition. This symmetry-dependent negative PL modulation in ANO ceramics enriches the understanding of the E-PL effect in AFEs and provides an environmentally friendly alternative for multifunctional optoelectronics.

Engineering antiferroelectric nucleation in ferroelectric films with enhanced piezoelectricity

Tailoring ferroelectric-antiferroelectric phase transitions provides strategic advantages for potential applications in digital displacement transducers and ultrathin ferroelectric capacitors. In particular, epitaxy of artificial superlattice has been widely used and proved to be capable of creating antiferroelectric-type characteristics within intrinsic ferroelectrics. Here, we have achieved dedicatedly control of ferroelectric-antiferroelectric phase transition by introducing 2 unit-cells antiferroelectric PbZrO3 layers into the intrinsic ferroelectric BiFeO3 films, with the ultrathin PbZrO3 layers acting as the structural spacer to bridge the robust nucleation of striping phase in BiFeO3 layers. Aberration-corrected scanning transmission electron microscopy characterization revealed that the BiFeO3 layers experienced a transition to the antiferroelectric-like polymorph via interface-transferred lattice distortion of alternate cation displacement, thereby forming the periodic ferroelectric-antiferroelectric nanoscale laminas. Further piezoresponse force measurements gave the direct evidences that the modulated superlattice exhibited improved piezoelectric performance compared with typical rhombohedral BiFeO3 films. This work paves the way for engineering polarity-mismatched superlattices with enhanced piezoelectric response and enriches the fundamental of structure-functionality correlations in oxide heterosystems.

Phase Stability and Dual-Mode Photoluminescence Modulation in Er-Doped Lead Zirconate Titanate Antiferroelectrics.

The electric-field-modulation (E-modulation) of photoluminescence (PL) properties in bulk ceramics has attracted tremendous interest due to its potential application in optical data storage and communication devices. One promising approach of reversibly and largely modulating the PL intensity has been proposed in rare-earth Er3+-doped Pb0.96La0.04Zr0.9Ti0.1O3 (PLZT) antiferroelectrics (AFEs) based on the unique E-dependent antiferroelectric-ferroelectric (AFE-FE) phase transition. However, the AFE phase stability of PLZT doped with various Er contents and their E-modulated PL properties have not been systematically investigated. In this paper, the intrinsic AFE phase of PLZT-Er is found to be stabilized in the high-temperature and high-E regions with increasing Er3+ content. The enhanced AFE nature caused by increasing Er doping leads to a larger E-dependent PL tunability (∼35%). Moreover, the ceramics exhibit the characteristics of both upconversion and downconversion PL (UCPL and DCPL) effects. Based on the excellent E-dependent dual-mode PL tunability, an optoelectronic device named the optical latch is demonstrated, where an electric signal can be used to trigger a notable intensity change in both the UCPL and DCPL modes. This reversible E-dependent dual-mode capability in PLZT-Er sheds light on a feasible approach to optoelectronic applications.

Improved capacitive energy storage in sodium niobate-based relaxor antiferroelectric ceramics

Ceramic-based dielectric capacitors have become an attractive issue due to their wide applications in current pulsed-/high-power electronic devices. Antiferroelectric ceramics generally exhibit ultrahigh energy density owing to their giant polarization activated by antiferroelectric–ferroelectric phase transition under a high electric field but suffer from large hysteresis, meanwhile giving rise to low efficiency. Herein, by introducing perovskite compound Sr(Fe0.5Ta0.5)O3 into an antiferroelectric NaNbO3 matrix, a stabilized antiferroelectric phase and an improved relaxor behavior are observed. That is, relaxor antiferroelectric ceramics are constructed. Accordingly, a double polarization–electric field (P–E) loop becomes slimmer with increasing incorporation of dopants, leading to an ultrahigh recoverable energy density of 11.5 J/cm3, an energy storage efficiency of 86.2%, outstanding frequency/cycling/thermal reliability, and charge–discharge properties in 0.90NaNbO3-0.10Sr(Fe0.5Ta0.5)O3 ceramics. This work reveals that inducing the relaxor behavior in antiferroelectric materials is an effective route to improve their capacitive energy storage.

Atomic Insight into the Successive Antiferroelectric-Ferroelectric Phase Transition in Antiferroelectric Oxides.

Antiferroelectrics characterized by voltage-driven reversible transitions between antiparallel and parallel polarity are promising for cutting-edge electronic and electrical power applications. Wide-ranging explorations revealing the macroscopic performances and microstructural characteristics of typical antiferroelectric systems have been conducted. However, the underlying mechanism has not yet been fully unraveled, which depends largely on the atomistic processes. Herein, based on atomic-resolution transmission electron microscopy, the deterministic phase transition pathway along with the underlying lattice-by-lattice details in lead zirconate thin films was elucidated. Specifically, we identified a new type of ferrielectric-like dipole configuration with both angular and amplitude modulations, which plays the role of a precursor for a subsequent antiferroelectric to ferroelectric transformation. With the participation of the ferrielectric-like phase, the phase transition pathways driven by the phase boundary have been revealed. We provide new insights into the consecutive phase transformation in low-dimensional lead zirconate, which thus would promote potential antiferroelectric-based multifunctional devices.

What Determines the Critical Electric Field of AFE-to-FE in Pb(Zr,Sn,Ti)O3-Based Perovskites?

Electric-field-induced antiferroelectric-ferroelectric (AFE-FE) phase transition is a prominent feature of antiferroelectric (AFE) materials. The critical electric field of this phase transition is crucial for the device performance of AEFs in many applications, but the determining factor of the critical electric field is still unclear. Here, we have established the correlation between the underlying structure and the critical electric field by using in situ synchrotron X-ray diffraction and high-resolution neutron diffraction in Pb(Zr,Sn,Ti)O3-based antiferroelectrics. It is found that the critical electric field is determined by the angle between the average polarization vector in the incommensurate AFE state and the [111]P polarization direction in the rhombohedral FE state. A large polarization rotation angle gives rise to a large critical electric field. Further, density functional theory (DFT) calculations corroborate that the lower energy is required for driving a smaller angle polarization rotation. Our discovery will offer guidance to optimize the performance of AFE materials.

Achieving Ultrahigh Energy Storage Density of La and Ta Codoped AgNbO3 Ceramics by Optimizing the Field-Induced Phase Transitions

Energy storage capacitors are extensively used in pulsed power devices because of fast charge/discharge rates and high power density. However, the low energy storage density and efficiency of dielectric capacitors limit their further commercialization in modern energy storage applications. Lead-free AgNbO3-based antiferroelectric (AFE) ceramics are considered to be one of the most promising environmentally friendly materials for dielectric capacitors because of their characteristic double polarization-electric field hysteresis loops with small remanent polarization and large maximum polarization. An enhancement of these characteristics allows achieving a synergistic improvement of both the energy storage density and efficiency of the antiferroelectric materials. This work reports on a feasible codoping strategy enabling the preparation of AgNbO3-based ceramics with high energy storage performance. An introduction of La3+ and Ta5+ ions into the AgNbO3 perovskite lattice was found to increase the structural stability of the antiferroelectric phase at the expense of a reduction of local polar regions, resulting in the shifting of the electric field-induced antiferroelectric-ferroelectric phase transition toward higher fields. An ultrahigh recoverable energy storage density of 6.73 J/cm3 and high energy storage efficiency of 74.1% are obtained for the Ag0.94La0.02Nb0.8Ta0.2O3 ceramic subjected to a unipolar electric field of 540 kV/cm. These values represent the best energy performance in reported lead-free ceramics so far. Hence, the La3+/Ta5+ codoping has been shown to be a good route to improve the energy storage properties of AgNbO3 ceramics.

Effect of Local Structural Distortions on Antiferroelectric-Ferroelectric Phase Transition in Dilute Solid Solutions of KxNa1-xNbO3.

The fundamental principles that govern antiferroelectric (AFE)-ferroelectric (FE) transitions are not well understood for many solid solutions of perovskite compounds. For example, crystal chemical considerations based on the average Goldschmidt tolerance factor or ionic polarizability do not precisely predict the boundary between the AFE and FE phases in dilute solid solutions of alkali niobates, such as KxNa1-xNbO3 (x ≤ 0.02). Here, based on detailed structural analysis from neutron total scattering experiments, we provide insights about how the relative local distortions around the A- and B-sites of the ABO3 perovskite structure affect the AFE/FE order of the average crystallographic phases in KxNa1-xNbO3. We show that a higher (lower) ratio of B-site-centered distortions over A-site-centered distortions drives transition toward a long-range FE (AFE) phase, which is based on a competition between the long-range polarizing field of the Nb-O dipoles and the disordering effect of local distortions around the A-site. Our study provides a predictive tool for designing complex solid-solution perovskites with tunable (anti)ferroelectric polarization properties, which can be of interest for various energy-related applications such as high-density energy storage and solid-state cooling.

Improvement of Energy Storage Properties of NaNbO3-Based Ceramics through a Relaxation Strategy

NaNbO3 (NN) is a widely studied antiferroelectric ceramics in recent years. However, NN ceramics always exhibit a square P-E loop with larger P r, originating form an irreversible antiferroelectric-ferroelectric (AFE-FE) phase transition under an applied electric field and limit the further development. In this paper, a novel lead-free relaxor ferroelectric ceramic, (1−x)NaNbO3-x(0.5Bi0.5Na0.5TiO3−0.5Ba0.3Sr0.7TiO3) [(1−x)NN-xBNBST, x = 0, 0.10, 0.15, 0.20, 0.25, 0.30], was designed and prepared via a local random field relaxation strategy. Dielectric testing show that the addition of BNBST significantly improved the relaxor behavior of the NN, which is effective for enhancing the W rec and η of NN-based ceramics. When x = 0.2, the ceramic obtains a high recoverable energy storage density (W rec = 2.024 J cm−3) and energy storage efficiency (η = 63%) at a low electric field of 130 kV cm−1. Meanwhile, the polarization-electric field (P-E) hysteresis loops and charge-discharge results of the sample with x = 0.2 at different temperatures and frequencies show that it is a prospective material for pulsed energy storage capacitors.