Antiferroelectric Phase Research Articles

Realizing simultaneously excellent energy storage and discharge properties in AgNbO3 based antiferroelectric ceramics via La3+ and Ta5+ co-substitution strategy

AgNbO3 based antiferroelectric (AFE) ceramics have large maximum polarization and low remanent polarization, and thus are important candidates for fabricating dielectric capacitors. However, their energy storage performances have been still large difference with those of lead-based AFEs because of their room-temperature ferrielectric (FIE) behavior. In this study, novel La3+ and Ta5+ co-substituted AgNbO3 ceramics are designed and developed. The introduction of La3+ and Ta5+ decreases the tolerance factor, reduces the polarizability of B-site cations and increases local structure heterogeneity of AgNbO3, which enhance AFE phase stability and refine polarization-electric field (P–E) loops. Besides, adding La3+ and Ta5+ into AgNbO3 ceramics causes the decrease of the grain sizes and the increase of the band gap, which contribute to increased Eb. As a consequence, a high recoverable energy density of 6.79 J/cm3 and large efficiency of 82.1%, which exceed those of many recently reported AgNbO3 based ceramics in terms of overall energy storage properties, are obtained in (Ag0.88La0.04)(Nb0.96Ta0.04)O3 ceramics. Furthermore, the discharge properties of the ceramic with discharge time of 16 ns and power density of 145.03 MW/cm3 outperform those of many lead-free dielectric ceramics.

Evidence for antipolar displacements in NaNbO3 thin films

An antipolar phase is confirmed for NaNbO3 thin films grown by pulsed laser deposition on SrTiO3 (100) substrates. Reciprocal space maps and transmission electron microscopy reveal the presence of characteristic 1/4 superlattice reflections, indicative of the antipolar displacement of Na and Nb-ions. Furthermore, x-ray diffraction unveils the presence of two different orientations of the same phase for thin films beyond a critical thickness of about 60 nm. This orientation change with increasing thickness can be explained as an extraordinary strain compensation mechanism, changing magnitude and sign of the strain at the same time. The polarization vs electric field behavior exposes a characteristic thickness dependence, with the antiferroelectric phase stabilized for very thin films and a field induced ferroelectric hysteresis for a film of 310 nm having a maximum polarization of 26.5 μC cm−2, which is among the highest values reported for NaNbO3 thin films grown on SrTiO3 (100).

Local probing of the non-uniform distribution of ferrielectric and antiferroelectric phases

Local probing of the non-uniform distribution of ferrielectric and antiferroelectric phases

Excellent energy‐storage property and thermal stability of PLZT‐based antiferroelectric ceramics

Abstract(Pb, La)(Zr, Ti)O3 antiferroelectric (AFE) materials are promising materials due to their energy‐storage density higher than 10 J cm−3, but their low energy‐storage efficiency and poor temperature stability limit their application. In this paper, the (1 − x)(Pb0.9175La0.055)(Zr0.975Ti0.025)O3–xPb(Yb1/2Nb1/2)O3 (PLZTYN100x) AFE ceramics were prepared via two‐step sintering method and investigated thoroughly. With the doping of Yb3+ and Nb5+, the phase structure transforms from the orthorhombic phase (AFEO) to the coexistence of the orthorhombic‐and‐tetragonal phases. This structure reduces the free energy difference between the AFE and ferroelectric phases and reduces the fluctuation of energy with temperature, improving the energy storage efficiency and temperature stability. When the x = 0.05 (PLZTYN5), the AFE ceramic exhibits excellent temperature stability and ultrahigh energy storage performance, whose recoverable energy density (Wrec) is 6.8–8.2 J cm−3 at 30 kV mm−1 in the temperature range from −55 to 75°C, and efficiency (ƞ) is 78%–86.7%. In addition, the change of Wrec is less than 15%, exceeding the performance of most AFE ceramics. The results demonstrate that the PLZTYN5 ceramic has great potential in pulse power capacitors.

Enhanced Energy Density and Efficiency in Lead‐Free Sodium Niobate‐Based Relaxor Antiferroelectric Ceramics for Electrostatic Energy Storage Application

AbstractAntiferroelectric ceramics are recently, a research hotspot for electrostatic energy storage because of their large electric‐field induced polarization. Lead‐free sodium niobate (NaNbO3)‐based ceramics are one of the emerging antiferroelectric counterparts. However, the unstable antiferroelectric phase seriously restricts the further improvement of energy density and efficiency. In this work, by introducing binary perovskite end‐member BiFeO3–BaTiO3 with lower tolerance factor and average electronegativity into NaNbO3 ceramics, the stablized antiferroelectric phase with improved relaxation characteristic is identified by slim double‐like polarization‐electric field (P–E) loops and four‐peak current–electric field (I–E) curves. Meanwhile, the antiferroelectric P to R phase transition is verified through Raman spectra, X‐ray diffraction (XRD) patterns, and dielectric performance. In particular, the enhanced electric breakdown strength Eb is achieved by synergic contributions from ultralow dielectric loss, reduced grain size, and so on. Consequently, the sample with optimized composition displays ultrahigh recoverable energy storage density (Wrec) of 14.5 J cm−3 and satisfied efficiency (η) of 83.9%, which shows the superiority in the state‐of‐the‐art dielectric ceramics. These results provide a feasible route by regulating the relationship between antiferroelectric structure and properties to explore high‐performance dielectrics for electrostatic energy storage applications.

Enhanced energy storage performances under moderate electric field in aliovalent A/B-site co-doped AgNbO3

Energy storage properties of Nd3+ and Hf4+ A/B-site co-doped AgNbO3 (Ag1-2xNdxNb1-xHfxO3, x = 0.005–0.02) ceramics were investigated. The introduction of Nd3+ and Hf4+ stabilizes the antiferroelectric phase and enhances the energy storage density. Besides, aliovalent doping of Nd3+ and Hf4+ increases the relaxor characteristic, leading to low energy storage loss in the polarization and high energy storage efficiency. Above the antipolar dipole freezing temperature (Tf), temperature-stable polarization is obtained, leading to a good temperature stability of energy storage properties. Ag0.97Nd0.015Nb0.985Hf0.015O3 exhibits excellent energy storage performances, with a recoverable energy storage density of 3.94 J/cm3 and energy storage efficiency of 64.0% under a moderate electric field of 235 kV/cm. The energy storage density increases with the temperature, and the energy storage efficiency maintains good temperature stability, with a variance of 11% in the range of 25 °C to 175 °C under an applied electric field of 200 kV/cm.

Investigation on antiferroelectricity of Pb0.97La0.02(Hf1−xTix)O3ceramics with low Ti content (0 ≤ x ≤ 0.1)

AbstractPbHfO3was found with antiferroelectricity early and identical to PbZrO3in many aspects but much less attention was received. In the present work, the PbHfO3‐based ceramics with compositions of Pb0.97La0.02(Hf1−xTix)O3(PLHT, 0 ≤ x≤ 0.1) were fabricated, and their antiferroelectricity was investigated. All the compositions have an initially antiferroelectric (AFE) phase and by introducing Ti content, the AFE phase is destabilized. Typical AFE‐like double polarization‐electric field (P–E) loop was observed in compositions with 0 ≤ x≤ 0.08. Whenx= 0.10, the composition is initially AFE but remains ferroelectric (FE) phase after the removal of the external electric field, resulting in an FE‐like singleP–Eloop. The temperature dependence of phase transition and multiple phase transition behavior in PLHT was also studied. This work revealed the antiferroelectricity in PLHT with low Ti content. In addition, the potential application of PLHT for energy storage and conversion was also discussed. A recoverable energy density of 7.1 J/cm3and efficiency of 78.5% were achieved in Pb0.97La0.02HfO3at 300 kV/cm.

Achieving Ultrahigh Energy Storage Density in Lead-Free Sodium Niobate-Based Ceramics by Modulating the Antiferroelectric Phase

Achieving Ultrahigh Energy Storage Density in Lead-Free Sodium Niobate-Based Ceramics by Modulating the Antiferroelectric Phase

Study of Structural and Electrical Properties of Li and Nb Modified BNT Thin Film and Observation of Enhanced Electrocaloric Effect near Room Temperature

A detailed investigation was done on Li and Nb modified Bi0.5Na0.5TiO3 (BNT) thin films where structural, dielectric, ferroelectric and electrocaloric properties were studied. All thin films were synthesized using pulsed laser deposition. Structural investigation revealed that addition of Li and Nb do not alter the parent rhombohedral structure and all compositions were observed to have rhombohedral structure. However Ferroelectric and dielectric analysis clearly revealed that addition of Li and Nb affect the Ferroelectric (FE) -Antiferroelectric (AFE) phase transition temperature (T d , depolarization temperature) and bring it down towards the room temperature and consequently a mixed phase of FE and AFE was observed near room temperature for composition x = 0.06. A sudden change in polarization in x = 0.06 composition with increasing temperature, subsequently leading to significantly high (∂P/∂T) E along with FE-AFE transition contributed to large electrocaloric (ΔT) = − 4.32 K in composition x = 0.06 ∼ 35 °C.

Arctic curves of the 6V model with partial DWBC and double Aztec rectangles

Previous numerical studies have shown that in the disordered and anti-ferroelectric phases the six-vertex (6V) model with partial domain wall boundary conditions (DWBC) exhibits an arctic curve whose exact shape is unknown. The model is defined on a s × n square lattice (s ⩽ n). In this paper, we derive the analytic expression of the arctic curve, for a = b = 1 and (Δ = 0), while keeping the ratio s/n ∈ [0, 1] as a free parameter. The computation relies on the tangent method. We also consider domino tilings of double Aztec rectangles and show via the tangent method that, for particular parameters, the arctic curve is identical to that of the 6V model with partial DWBC. Our results are confirmed by extensive numerical simulations.

Differences of the temperatures of ferroelectric and magnetic phase transitions of perovskites

Binary and ternary AB′0.5 B″0.5O3 oxides with a complex perovskite structure, possessing the consecutive ferroelectric or antiferroelectric phase transitions at T C and ferromagnetic, antiferromagnetic, or ferrimagnetic phase transitions at T N, are considered together with classical ferroelectrics and antiferroelectrics. The common correlations between these temperatures, their differences T С-T N and interatomic bond A-O (δ AO) or B-O (δ BO) strains are revealed. Some common correlations between their temperatures T С, T N, T С-T N differences, and δ AO or δ BO are revealed. It is established that these differences for multiferroics are in common dependences with classical ferroelectrics and antiferroelectrics.

Ferroelectric Smectic Liquid Crystals as Electrocaloric Materials

The 1980s saw the development of ferroelectric chiral smectic C (SmC*) liquid crystals (FLCs) with a clear focus on their application in fast electro-optic devices. However, as the only known fluid ferroelectric materials, they also have potential in other applications, one of which is in heat-exchange devices based on the electrocaloric effect. In particular, ferroelectric liquid crystals can be both the electrocaloric material and the heat exchanging fluid in an electrocaloric device, significantly simplifying some of the design constraints associated with solid dielectrics. In this paper, we consider the electrocaloric potential of three SmC* ferroelectric liquid crystal systems, two of which are pure materials that exhibit ferroelectric, antiferroelectric, and intermediate phases and one that was developed as a room-temperature SmC* material for electro-optic applications. We report the field-induced temperature changes of these selected materials, measured indirectly using the Maxwell method. The maximum induced temperature change determined, 0.37 K, is currently record-breaking for an FLC and is sufficiently large to make these materials interesting candidates for the development for electrocaloric applications. Using the electrocaloric temperature change normalised as a function of electric field strength, as a function of merit, the performances of FLCs are compared with ferroelectric ceramics and polymers.

Electric-induced devil’s staircase in perovskite antiferroelectric

Antiferroelectric ceramics can realize ultra-high energy storage, which benefits from transformation between an antiferroelectric phase and a ferroelectric phase. Understanding the mechanism of such phase transition is the key point for building the structure-property correlation. Here, we report the observation of electric-induced devil’s staircase in the course of antiferroelectric–ferroelectric phase transition in PbZrO3-based antiferroelectric ceramics by in situ transmission electron microscopy. The dynamic evolution as-revealed in both reciprocal- and real-space involves stepwise rather than monotonic increase in modulation periods along with simultaneous proliferation of nanodomains. Desynchrony of phase transition is observed for incommensurate domains with different initial modulation periods within a single antiferroelectric domain. Then, the synergistic effect of the devil's staircase and as small as possible the initial modulation period is believed to contribute to the superior energy-storage performance. These findings will be helpful for the development of theories for antiferroelectric–ferroelectric phase transition and the design of high-power antiferroelectric materials.

Emergence of paraelectric, improper antiferroelectric, and proper ferroelectric nematic phases in a liquid crystal composed of polar molecules.

We have elaborated a theoretical approach for the description of polar nematic phases observed by Nishikawa etal. [Adv. Mater. 29, 1702354 (2017)0935-964810.1002/adma.201702354], their structures, and transitions between them. Specific symmetry contributions to the pair molecular potentials provide the molecular mechanisms responsible for the formation of proper and improper polarity on the macroscopic level. An improper antiferroelectric nematic M2 phase can arise between paraelectric nematic M1 and proper ferroelectric nematic MP in the temperature scale. The local polarization in M2 arises mostly due to the local splay deformation. The director distribution in M2 represents the conjugation of cylindrical waves with opposite splay and polarization signs. The director and polarization are parallel to the cylindrical domain axes in the middle of each cylinder but exhibit considerable (mostly radial) deformation on the periphery of each cylinder. Polarization vectors are mostly stacked antiparallel on the borders between the domains without the director disruption. The domain size decreases with the decreasing temperature, the percentage of the antiferroelectric decouplings increases, and M2 exhibits the first-order phase transition into proper ferroelectric MP. With the increasing temperature the domain size in the M2 phase increases, the domination of particular polar orientation of molecules reduces, and finally, the domain size diverges at particular temperature corresponding to the second-order phase transition from M2 to paraelectric M1. Variations of the polar and nonpolar orientational order parameters are estimated within each phase and between the phases. Our experimental and computer simulation results (also presented in the paper) fully support our theoretical findings.

Atomic structural mechanism for ferroelectric-antiferroelectric transformation in perovskite NaNbO3

Sodium niobate (${\mathrm{NaNbO}}_{3}$ or NN) is described as ``the most complex perovskite system,'' which exhibits transitions between, as well as coexistence of, several ferroelectrics (FE) and antiferroelectric (AFE) phases at different temperatures. Recently, solid solutions of NN with stabilized AFE phases(s) have gained attention for energy-related applications, such as high-density energy storage and electrocaloric cooling. A better understanding of the atomic mechanisms responsible for AFE/FE phase transitions in ${\mathrm{NaNbO}}_{3}$ can enable a more rational design of its solid-solution systems with tunable functional properties. Here, we have investigated changes in the average and local atomic structure of NN using a combination of x-ray/neutron diffraction and neutron pair-distribution function (PDF) analyses. The Rietveld refinement of the x-ray/neutron-diffraction patterns indicates a coexistence of the FE $Q$ ($P{2}_{1}ma$) and AFE $P$ ($Pbma$) phases in the temperature range of $300\phantom{\rule{0.16em}{0ex}}\mathrm{K}\ensuremath{\le}T\ensuremath{\le}615\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, while PDF analysis indicated that the local structure $(r<8\phantom{\rule{0.16em}{0ex}}\AA{})$ is better described by a $P{2}_{1}ma$ symmetry. Above 615 K, the average structure transitions to an AFE $R$ phase ($Pmmn$ or $Pnma$), while PDF analysis shows an increased disordering of the octahedral distortions and Na displacements at the local scale. These results indicate that the average P/Q/R phase transitions in NN can be described as a result of complex ordering of distorted octahedral tilts at the nanoscale and off-centered displacements of the Na atoms.

Achieving high energy storage performance of Pb(Lu1/2Nb1/2)O3 antiferroelectric ceramics via equivalent A-site engineering

Manipulating the critical switching field between antiferroelectric (AFE) state and ferroelectric (FE) is an important concept for tuning the energy storage performance of AFEs. As one of the lead-based AFE systems, Pb(Lu1/2Nb1/2)O3 promises high potential in the miniaturization of pulsed power capacitors, but the extremely high critical switching field and low induced saturated polarization demonstrate severe drawbacks with respect to temperature stability and flexibility. Here, A-site Ba2+ doping engineering is used to effectively reduce the critical switching field and improve the saturated polarization in BaxPb1-x(Lu1/2Nb1/2)O3 (0.01 ≤ x ≤ 0.08, abbreviated as xBa-PLN) ceramics. We found the AFE-FE phase transition can be occurred at 80ºC with a high energy storage density of 4.03 J/cm3 for Ba0.06Pb0.94(Lu1/2Nb1/2)O3 ceramic. Our results show that Ba2+ additions destroy the antiparallel structure of AFE phase, and finally reduce the critical switching field, demonstrating a potential alternative to modulate the energy storage performance of AFEs.

First principle understanding of antiferroelectric ordering in La-doped silver niobate

The antiferroelectric Pbcm phase of silver niobate (AgNbO3) has received increasing attention owing to its environmental safety (as it is lead-free), compatibility, and superior energy-storage density compared with its ferroelectric counterparts. We comprehensively investigated the effects of La doping at Ag sites (i.e., Ag0.88La0.12NbO3) on the structural, electronic, and ferroelectric properties of AgNbO3 by using ab initio density functional theory calculations and the Berry phase method for polarization calculations, respectively. The polarization in the [001] direction of pristine AgNbO3 is estimated to be 1.9 μC/cm2, which is significantly enhanced (to 14.86 μC/cm2) for Ag0.88La0.12NbO3. The enhancement in the spontaneous polarization of AgNbO3 after the incorporation of La is attributed to suppressed distortion in the Nb–O–Nb antiparallel ordering and tilting of the NbO6 octahedra. Furthermore, the electron density maps of AgNbO3 and its doped counterpart were calculated to investigate the lattice-distortion and bond-change observations.

Effect of boron doping on energy storage performance of PLZST ceramics

In this paper, thick film antiferroelectric ceramics (1-x)(Pb0.97La0.02)(Zr0.46Sn0.48Ti0.06)O3-xH3BO3 ((1-x)PLZST-xH3BO3, x = 0–0.025) were prepared by solid state sintering and tape-casting method. The effects of boron-doping on the microstructure, dielectric properties and energy storage properties of (1-x)PLZST-xH3BO3 ceramics were investigated. Appropriate boron-doping can improve the stability of antiferroelectric phase, delay phase transition and increase saturation polarization strength. Compared with the undoped PLZST thick films, the maximum polarization intensity increased by 1.9 times and the residual polarization decreased by 37%. When x = 0.020, the maximum recoverable energy storage density is 2.74 J/cm3, and the energy storage efficiency is 88.12%.

Electrically Tunable Antiferroelectric to Paraelectric Switching in a Semiconductor.

The monoclinic α-Cu2Se phase is the first multipolar antiferroelectric semiconductor identified recently by electron microscopy. As a semiconductor, although there are no delocalized electrons to form a static macroscopic polarization, a spontaneous and localized antiferroelectric polarization was found along multiple directions. In conventional ferroelectrics, the polarity can be switched by an applied electric field, and a ferroelectric to paraelectric transition can be modulated by temperature. Here, we show that a reversible and robust antiferroelectric to paraelectric switching in a Cu2Se semiconductor can be tuned electrically by low-voltage and high-frequency electric pulses, and the structural transformations are imaged directly by transmission electron microscopy (TEM). The atomic mechanism of the transformation was assigned to an electrically triggered cation rearrangement with a low-energy barrier. Due to differences of the antiferroelectric and paraelectric phases regarding their electrical, mechanical, and optical properties, such an electrically tunable transformation has a great potential in various applications in microelectronics.

Antiferroelectricity of NaNbO3: Single‐crystal experimental study and first‐principles calculation

AbstractSimilar to the canonical antiferroelectric (AFE) compound PbZrO3 in Pb(Zr,Ti)O3 solid‐solutions, the presence of double hysteresis loops and that of electric field–induced phase transitions are important characteristics of NaNbO3 AFE materials; yet the phase transition behavior in the latter system is typically irreversible with the related mechanisms not fully understood. Here, we explore the phase transition mechanism of ferroelectric and AFE phases in NaNbO3 based on measurements of single crystals with different directions in conjunction with density‐functional theory (DFT) calculations. The tilting and distortion behaviors of the [NbO6] octahedra are explained by DFT, and the ion displacement in the lattice is traced. The tilting and distortion behaviors of the [NbO6] octahedra with different orientations are compared. We confirm that the tilt and distortion of the [NbO6] octahedra along the [1 1 1] direction is the main reason to improve the stability of AFE phase. This conclusion is verified by the experimental characterizations of large‐size NaNbO3 single crystals successfully obtained in this study.