AFE-FE Phase Transition Research Articles

Insights into enhanced antiferroelectricity in doped-niobate perovskites for high energy-storage density applications

Lead-free antiferroelectric (AFE) ceramics have attracted increasing attention in recent years for application in high-power capacitors due to their environmental friendliness and high energy density. Among these ceramics, NaNbO3 is noteworthy as one of the few lead-free perovskites displaying an AFE structure. However, despite the nature of AFE symmetry in NaNbO3 with Nb antipolar state, in most cases, it behaves like a ferroelectric (FE) material with an external electric field and exhibits a single polarization-electric field (P-E) hysteresis loop. In order to enhance the antiferroelectricity, a composition modification strategy based on the tolerance factor (t) has been used to stabilize the AFE phase effectively. Yet, in the context of NaNbO3 ceramics, the impact of doping on the evolution of antiferroelectricity has remained unexplored. Through first-principles calculations, we unveil how the chemical modification of NaNbO3 enhances antiferroelectricity by investigating local distortions that favor the AFE state over the FE state in solid solutions. This adjustment in the relative stability between the FE state and AFE state results in a significant modification in the switching barrier in NaNbO3-based antiferroelectrics, ultimately leading to well-defined double polarization loops. This work offers a rationalized atomic-scale perspective on the AFE-FE phase transition in NaNbO3-based ceramics, aiming to contribute to the development of novel lead-free antiferroelectric oxides for energy storage applications.

Evolving energy-storage performances during temperature-induced antiferroelectric P–R phase transition in NaNbO3-based lead-free ceramics

Temperature-driven antiferroelectric (AFE) P to AFE R phase transition in MnO2-doped 0.90NaNbO3-0.10CaTiO3 ceramics was investigated through polarization-field response, energy-storage and charge-discharge properties as well as ex/in-situ multiscale structure characterization. Both room-temperature AFE P and high-temperature AFE R phases show double polarization-electric field hysteresis loops, indicating a reversible field-driven AFE to ferroelectric (FE) phase transition. An abnormal variation of critical fields for the AFE-FE and FE-AFE phase transition and a faster polarization-field response contribute to the reduced polarization hysteresis for both AFE P and R phases but an obviously expanded linear polarization-field response only for AFE R phase, being responsible for a two-time significant enhancement in energy-storage properties from P phase to P–R phase boundary and then to R phase. The variation of unit cell anisotropy and domain morphology with temperature was found to play crucial roles in the modulated field-driven phase transition behavior and polarization-field response on heating.

Antiferroelectric-to-ferroelectric phase transition in hexagonal rare-earth iron oxides

The AFE–FE phase transition was demonstrated in h-DyFeO3 films with the lattice parameter c/a ratio of 1.90–1.92, which is intermediate between those of previously reported AFE and FE h-RFeO3.

Ultrahigh pyroelectric effect and energy harvesting density of Pb(Lu1/2Nb1/2)O3–PbTiO3 crystals induced by FE-AFE phase transition

Large pyroelectric and energy harvesting properties have been attracting increasing attentions due to the practical applications in infrared detectors and energy harvesting technologies. Ferroelectric-antiferroelectric (FE-AFE) phase transitions are usually accompanied by a sharp drop in polarization, which will lead to excellent pyroelectric properties and energy harvesting density. Therefore, FE-AFE phase boundary design is an effective strategy to develop new pyroelectric materials. In this paper, Pb(Lu1/2Nb1/2)O3-PbTiO3 (PLN-PT) single crystals with FE-AFE phase transitions were obtained by molten salt growth method. The temperature-induced FE-AFE phase transition was verified by temperature-dependent macrodomain structure, DSC curves and dielectric properties. Obviously, PLN-PT crystals display excellent peak pyroelectric coefficient (∼6.8 μC/(cm2·K)) with a maximum depolarization temperature of 118 °C. Meanwhile, the pyroelectric energy harvesting density is as high as 2.62 J/cm3, which is much higher than other pyroelectric materials. The results reveal that the PLN-PT crystal is a promising candidate for infrared detectors and energy harvesting devices.

Effects of compressive stress on electric-field-induced phase transition of antiferroelectric ceramics

In certain lead zirconate titanate compositions, the antiferroelectric (AFE) phase can be driven to the ferroelectric (FE) phase by electric field, and the induced FE phase can either revert to AFE or remain FE upon removal of the electric field. This results in a double or single hysteresis loop, respectively. To further explore the effects of the FE-AFE phase transition on electrical energy storage and conversion, two types of AFE ceramics were fabricated, and the effects of compressive stress on the AFE-FE phase transition were investigated. Compressive stress suppresses the volume increase associated with the AFE-FE transition, thus hindering the phase transition. Compressive stress also hinders polarization orientation in the FE phase, thus increasing the field necessary to achieve saturation polarization. For AFE compositions displaying a double hysteresis loop, the electrical energy storage performance can be enhanced by compressive stress. For the AFE compositions with a single hysteresis loop, the remanent polarization of the induced FE phase decreased and the coercive field did not change much within the range of compressive stress applied. In addition, the remanent polarization was reduced by 50% under a compressive stress of 126 MPa, indicating that this composition is a candidate for mechanical-electrical energy conversion.

Stabilization of anti-ferroelectric Pbcm phase over ferroelectric P21ma phase in intermittent ferroelectric NaNbO3 by incorporating CaTiO3

This study focuses on the structural aspect of stabilization of anti-ferroelectric (AFE) Pbcm phase over ferroelectric P21ma phase by introducing CaTiO3 in NaNbO3 perovskite. For this work, Na1−xCaxNb1−xTixO3 (x = 0.00, 0.03, 0.04, 0.05) ceramic compositions are chosen for investigation. Structural and dielectric studies are performed on these compositions to see the effect of dopants on phase transitions involved. X-ray diffraction and their respective refinement results confirmed orthorhombic structure with Pbcm space group for all the compositions. Structures are generated using refined x-ray diffraction data in order to understand the effect of doping on octahedral tilting, which plays a huge role in increasing the energy gap required for Pbcm to P21ma conversion and is responsible for establishing stable antiferroelectric phase. To get more insights into the AFE-FE phase transition and stabilization of AFE phase with respect to composition, dielectric permittivity versus temperature and polarization versus electric field studies were performed for all the above-mentioned compositions. Based on PE and structural analysis, high electric field stable AFE phase can be established for x = 0.04 composition. Reasons for high electric field stable antiferroelectric phase at x = 0.04 are presented where it is argued that the octahedral tilt distortion of perovskite structure is responsible for the increase in energy barrier required for AFE ↔ FE transformation, thus stabilizing the antiferroelectric phase.

An environmentally-benign NaNbO3 based perovskite antiferroelectric alternative to traditional lead-based counterparts

NaNbO3-based lead-free AFE R-phase ceramics with Pnma space group and nanoscale stripe domain exhibit completely reversible field induced AFE–FE phase transition, featuring a relatively low EA–F of ∼8 kV mm−1 and a large repeatable strain of ∼0.29%.

Combined effects of Bi deficiency and Mn substitution on the structural transformation and functionality of BiFeO3 films

Mn-doped BiFeO3 films with Mn contents of 5 and 10 mol. % were prepared via a chemical route. A carefully controlled amount of Bi deficiency was introduced to further tune the lattice structure and the functionality of multiferroic BiFeO3. The crystal structure of Bi1−δFe1−xMnxO3 films was investigated by X-ray diffraction and Raman spectra; a rhombohedral-to-orthorhombic phase transition was revealed. The observed double hysteresis loops and two capacitance maxima from polarization vs electric field and capacitance-voltage measurements indicate an antiferroelectric-like behavior. Additionally, the coexistence of ferroelectric (FE) and antiferroelectric (AFE) phases in Bi1−δFe1−xMnxO3 films was revealed from the domain structures obtained by piezoelectric force microscopy. The effects of Mn substitution in conjunction with Bi deficiency on the FE-AFE phase transition and electrical behavior of BiFeO3 films are discussed in detail. Meanwhile, magnetic and photoluminescence measurements on the films illustrate that Mn substitution gives rise to the net magnetic moment and the defects induced by both Bi deficiency and Mn substitution influence the electronic structure of BiFeO3 films. This study thus shows a simple and effective way to control the functionalities of BiFeO3 films.

Effect of Sn:Ti variations on electric filed induced AFE–FE phase transition in PLZST antiferroelectric ceramics

The effect of Sn:Ti variations on antiferroelectric to ferroelectric phase transition of (Pb 0.97La 0.02)(Zr 0.65Sn 0.35− x Ti x )O 3 ( x = 0.08–0.11) ceramics with compositions near antiferroelectric to ferroelectric morphotropic phase boundary was studied. X-ray diffraction showed that all samples were tetragonal phase at room temperature. With the increase of x from 0.08 to 0.1, all samples showed the typical antiferroelectric double loops. The critical value E AF of the electric-field induced antiferroelectric to ferroelectric phase transition decreased from 64 kV/cm to 38 kV/cm, and the electric field E FA of induced-ferroelectric to antiferroelectric phase transition decreased from 44 kV/cm to 10 kV/cm. A high polarization of the sample with x = 0.1 can be induced with a lower electric filed. The variations of Sn:Ti ratio had no effect on hysteresis of Δ E (= E AF − E FA), but Δ E reduced with temperature increasing. The virgin sample of which x = 0.11 was intrinsic antiferroelectric phase, but the remanent polarization of induced-ferroelectric phase remained after electric-field was removed at room temperature.

Electron emission and phase transition of Zr-rich lead zirconate titanate ferroelectrics

This letter focuses on understanding the influences of antiferroelectric–ferroelectric (AFE–FE) phase transition on the ferroelectric electron emission process. The piezoelectric constant and electron emission current of un-prepoled PZT 96.5/3.5 ceramics as a function of emission times were studied. The hysteresis loops of PZT 96.5/3.5 ceramics before and after the electron emission process were presented. The results show that emission currents obtained from PZT 96.5/3.5 ferroelectrics in different phase states were similar. It was difficult to explain the experiment results using the fast AFE–FE phase transition model. Electron emission from PZT 96.5/3.5 ferroelectrics was independent of the AFE–FE phase transition.

Electric fatigue in antiferroelectric Pb 0.97La 0.02(Zr 0.55Sn 0.33Ti 0.12)O 3 ceramics induced by bipolar cycling

Antiferroelectric lead zirconate titanate stannate (PZST) ceramics are promising materials for high-strain transducers and actuators. The degradation of the strain excited by an ac field remains largely unknown so far for this family of antiferroelectric ceramics. In this study, the bipolar electric fatigue of antiferroelectric Pb 0.97La 0.02(Zr 0.55Sn 0.33Ti 0.12)O 3 ceramics was investigated. Variations in the strain hysteresis loop and damage in the microstructure of the materials due to the electric cycling were monitored. Higher cycling field yielded a stronger fatigue effect. The material showed an increasingly asymmetric suppression of the strain hysteresis loop and diffuse AFE–FE phase transition with increasing cycle number. A damaged microstructure was observed on the polished surfaces of fatigued samples after acid etching. Electrochemical variations, the pinning of domains, randomly or preferentially orientated, due to the cycling are considered as the main fatigue mechanism of the material.

Composition Dependent Fatigue in Antiferroelectric PZST Ceramics Induced by Bipolar Electric Cycling

Bipolar electric fatigue in antiferroelectrics of the lead zirconate titanate stannate ceramics family was investigated. Variations in strain hysteresis loops and damages in microstructure of the materials due to the electric cycling were analyzed. The materials showed symmetric or asymmetric suppression of strain hysteresis loop, normal or diffuse AFE-FE phase transition and intact or damaged microstructure after 5×10-7 cycles, indicating a strong composition dependent fatigue effect and the corresponding mechanism. In general, the antiferroelectric materials exhibited much higher fatigue resistance than ferroelectric ceramics reported previously.

Bipolar electric fatigue behaviour as a function of field strength in antiferroelectric (Pb,Ba,La)(Zr,Sn,Ti)O3ceramics

The bipolar electric fatigue behaviour of antiferroelectric ceramics with the composition of Pb0.88Ba0.10La0.02(Zr0.55Sn0.35Ti0.10)O3 was investigated under various cycling fields. The material exhibits a degradation in the maximum field induced strain, a diffuse AFE-FE phase transition and an enhancement in the diffusion character of the FE-AFE phase transition due to electric cycling. Those variations increase with cycle number, indicating a logarithmic fatigue up to 108 cycles. There is no indication for the variations to be recovered, and the symmetry of the negative and positive parts of the strain hysteresis loops still remains. Higher cycling field results in a stronger deterioration of the maximum field induced strain and a larger extent of diffusion in AFE-FE and FE-AFE phase transitions. The normalized maximum strain shows nearly the same scale of degradation when the materials are cycled at various electric fields. After a heat treatment at 500°C for 1 h, the variations in the AFE-FE and FE-AFE phase transition due to cycling disappear, whereas the maximum strain resumes almost to its original value. Electrochemical variations are considered to contribute to the main fatigue mechanism for the material under investigation.

Preparation and Properties of Lead Zirconate Stannate Titanate Sintered by Spark Plasma Sintering

Lanthanum‐doped lead zirconate stannate titanate ceramics were successfully compacted to full density by spark plasma sintering (SPS). SPS samples densified at 900° or 950°C exhibit nearly full density and fine grain size (about 300 nm). Compared with samples from conventional sintering (CS), SPS samples show larger permittivity accompanied by a deterioration in dielectric loss and special strain hysteresis loops similar to those of ferroelectric relaxors, with a diffuse AFE–FE phase transition and less field‐induced longitudinal strain. The differences in the properties of SPS and CS materials are attributed to the variations of the resultant microstructures, especially the grain size, of the ceramics.

Raman Studies of the FE-AFE Phase Transition in Ceramic Li0.12Na0.88Ta0.2Nb0.8O3 Solid Solution

The ferroelectric to antiferroelectric phase transition at 350°C in ceramic Li0.12Na0.88-Ta0.2Nb0.8O3 solid solution is studied by Raman spectroscopy. As the temperature of the solid solution sample is raised, considerable broadening of translational vibration bands of cations in the octahedral and cubo-octahedral cavities and of vibration bands of the oxygen carcass is observed. Intensity of Raman band corresponding to bridge valent vibrations (BVV) of oxygens decreases to zero. The ferroelectricity of the solid solution is shown to be lost mainly because of the growing anharmonicity of vibrations of the cavity cations.

Effects of temperature on hydrostatic pressure-induced FE-AFE phase transition in PbLa(Zr, Sn, Ti)O3 ceramics

Hydrostatic pressure-induced ferroelectricantiferroelectric (FE-AFE) phase transition and the pressure dependence of dielectric properties in La-doped Pb(Zr,Sn, Ti)O3 ceramics were researched; the effects of temperature on hydrostatic pressure-induced FE-AFE phase transition and dielectric properties of the samples were studied. It was found that the temperature made the FE-AFE phase transition pressure decrease, and there existed the behavior of dielectric frequency dispersion and phase transition diffusion in the dielectric-pressure spectrum. These phenomena were very useful to enrich and develop the knowledge on the diffused phase transition behavior of polycomponent relaxor ferroelectric.

Processing and polarization behavior of Sr-containing lead zirconate titanate

Sr-containing PZT compositions were selected for identifying the ferroelectric (FE)-antiferro-electric (AFE) phase boundary within the zirconium rich region of the PbZrO3-PbTiO3-SrTiO3-SrZrO3 phase diagram and for inducing the AFE-FE phase transition upon application of an applied electric field. Processing methods, based on the powder processing and sintering, were developed for fabricating dense (98.5% of theoretical density) Sr-containing PZT samples suitable for the polarization measurements. PZT specimens, with a uniform microstructure and an average grain size of 3 μm were obtained. Polarization measurements were used to locate the FE-AFE phase boundary. Subsequently, compositions near the FE-AFE phase boundary were studied for the electric field induced AFE-FE phase transition. Field-induced AFE-FE phase switching was observed in compositions close to the AFE-FE boundary. Residual polarization upon AFE-FE transformation suggested a coexistence of both ferroelectric and antiferroelectric phases.

Raman spectroscopy investigations of nb-doped lead-zirconate-titanate ceramics with AFE-FE-PE phase sequence

Abstract Raman spectroscopy and dielectric measurements have been performed on modified PZT ceramics with Ti content between 0.03 and 0.05 and doped with 1% of Nb2O5 The temperature dependence of the Raman spectra is studied in the vicinities of the AFE-FE and the FE-PE phase transitions and discussed in correlation with the dielectric data. Coexistence of phases is observed in a wide temperature range around AFE-FE phase transition.