Antiferroelectric State Research Articles

Antiferroelectricity in new silver niobate lead-free antiferroelectric ceramics (1-x)AgNbO3-xCaZrO3 (x = 0.00–0.01)

The critical need for clean energy has led to the development of lead-free electroceramics. However, lead-free antiferroelectrics seldom have been reported because of the difficulties in materials fabrication and their low electrical performance. In this work, we successfully synthesized lead-free antiferroelectric ceramics (1-x)AgNbO3-xCaZrO3 (x = 0.00–0.01) using the solid state reaction method in flowing oxygen (O2) atmosphere. Calcium zirconate (CaZrO3) dopant effectively stabilized the antiferroelectricity of silver niobate (AgNbO3) by dramatically decreasing the tolerance factor t. Additionally, we identified an orthorhombic Pbcm structure similar to that of pure AgNbO3. With the introduction of CaZrO3, phase transition temperatures M1–M2, M2–M3 and the freezing temperature Tf decreased. The shift of the M1–M2 phase transition temperature and Tf was the result of the restriction of the M1 phase due to CaZrO3 substitution. The compositions of x < 0.001 displayed a double hysteresis loop with a raised critical field EF. However, when the doping concentration exceeded 0.002, the double hysteresis loop with a higher polarization could not be obtained until the breakdown strength of EB exceeded 200 kV/cm because of the tremendously enhanced free energy barrier between the virgin antiferroelectric state and the field-induced ferroelectric state. We also evaluated the polarization hysteresis loops are also evaluated at temperatures up to 100 °C for the compositions x = 0.00–0.005. With an elevated temperature, at which the free energy barrier was reduced, the double hysteresis loop was obtained at a lower electric field when compared with that at room temperature for the compositions x = 0.004 and 0.005. These results demonstrated that by adjusting the tolerance factor t and average electronegativity difference X, the antiferroelectricity could be predicted in AgNbO3-based lead-free solid solution systems, thus providing a new strategy for designing a new class of antiferroelectric materials.

Dielectric and ferroelectric properties of lanthanum‐modified lead zirconate stannate titanate (42/40/18) ceramics

AbstractThe effect of lanthanum (La) content on the phase transformation of Pb1−3x/2Lax(Zr0.42Sn0.40Ti0.18)O3 (PLZST 100x/42/40/18, 0 ≤ x ≤ 0.06) ceramics was investigated by the dielectric and ferroelectric properties. The base composition PLZST 0/42/40/18 located in the ferroelectric (FE) rhombohedral phase region. As x increased, the compositions showed successively FE and antiferroelectric (AFE) state at room temperature, and their peak temperatures (Tmax) decreased gradually in line as Tmax = 162.21‐1507x. Evidence was presented that there were two dielectric anomalies in PLZST 2/42/40/18, which were corresponding to the FE‐AFE and AFE‐paraelectric (PE) phase transformations, respectively. With increasing the dc bias fields, the two phases merged into one. PLZST 3/42/40/18 showed AFE characteristics with the first loop outside of the second loop and there was only one dielectric inflection. The critical lanthanum content occurred at x = 0.03 from the dielectric temperature spectra and hysteresis loops. Furthermore increase in La above 0.03, these compositions showed typical antiferroelectric behaviors with double hysteresis loops. The stored energy properties of the three compositions (PLZST 4/42/40/18, 5/42/40/18 and 6/42/40/18) displayed different temperature dependencies from room temperature to 140°C (over their respective Tmax). Comparing the above results with previous investigations on PLZSTs, some questions were discussed.

An intermediate antipolar phase in NaNbO3 under compression

ABSTRACTThe crystal structure and vibration spectra of sodium niobate NaNbO3 have been studied by means of neutron diffraction, X-ray diffraction and Raman spectroscopy at high pressures. An isostructural phase transformation from the initial antiferroelectric phase to an intermediate antiferroelectric phase HP-I have been observed under 2 GPa. This transformation is caused by complex reorientations of NbO6 octahedra. Subsequent structural phase transition from the phase HP-I to an orthorhombic phase HP-III have been detected at pressures above 10 GPa. This transition leads to suppression of an antiferroelectric state of NaNbO3. The observed phase transitions are accompanied by anomalies in lattice parameters compression.

Structure, phase transition behavior, and electrical properties of Pb0.99(SnxZr0.95−xTi0.05)0.98Nb0.02O3 ceramics

Pb0.99(SnxZr0.95−xTi0.05)0.98Nb0.02O3 (PNZST(x), 0.10 ≤ x ≤ 0.18) ceramics were fabricated by conventional solid state reaction method. Effects of tin (Sn) doping and its content x on their structure, phase transition behavior, and electrical properties were investigated. Analysis of X-ray diffraction patterns and Rietveld refinement results confirmed the crystal structures of different phases and also compositional driven phase transitions. The results indicated that with the increase in the value of x, orthorhombic phase was transformed into distorted tetragonal phase through rhombohedral phase. Ceramics exhibited the orthorhombic–rhombohedral phase coexistence for 0.10 ≤ x ≤ 0.16, and orthorhombic–rhombohedral–distorted tetragonal multiphase coexistence for x = 0.18. Although the orthorhombic antiferroelectric (AFE) phase was the major phase, no double hysteresis loops were detected through electrical hysteresis loop measurements because the electric field-induced AFE to ferroelectric (FE) phase transition occurred under the applied electric field, and the induced FE phase could not reverse back to AFE state after the removal of electric field. However, the trace of AFE behavior could be observed at a lower testing electric field. Moreover, increasing Sn content led to linear increment in phase transition temperature of FERL-FERH, up to 98.7 °C for x = 0.18.

Effects of composition and temperature on energy storage properties of (Pb,La)(Zr,Sn,Ti)O3 antiferroelectric ceramics

Abstract In this work, the effects of Zr 4+ addition on the phase structure and energy storage properties of (Pb 0.97 La 0.02 )(Zr x Sn 0.945−x Ti 0.055 )O 3 (PLZST) antiferroelectric (AFE) ceramics were investigated, aiming to optimize the composition for enhanced energy storage properties. Due to the substitution of Zr 4+ with larger ion radius for Sn 4+ , the tolerance factor of PLZST AFE ceramics decreased and thus the AFE state transformed gradually from tetragonal phase to orthorhombic phase with higher ferroelectric-antiferroelectric phase switching electric field ( E A ) with increasing Zr 4+ content from x=0.65–0.85. The increase of E A led to the improvement of recoverable energy density ( U re ) from 3.18 J/cm 3 (x=0.65) to 4.38 J/cm 3 (x=0.8). However, when Zr 4+ content was more than 0.8, the U re decreased from 4.38 J/cm 3 to 4.12 J/cm 3 (x=0.85) due to the reduction of the saturation polarization. The best energy storage properties were achieved in PLZST orthorhombic AFE ceramic with Zr 4+ content of x=0.8, which exhibited a maximum U re of 4.38 J/cm 3 and very small U re variation ( 0.97 La 0.02 )(Zr 0.8 Sn 0.145 Ti 0.055 )O 3 antiferroelectric ceramic is a promising material for developing high-performance pulse power capacitors usable in wide temperature range.

Ionic Mobility and Phase Transitions in Perovskite Oxides for Energy Application

Perovskite oxides find applications or are studied in many fields related to energy production, accumulation and saving. The most obvious application is oxygen or proton conductors in fuel cells (SOFCs), but the (anti)ferroelectric compositions may find application in high energy capacitors for energy storage, efficient electrocaloric cooling, and electromechanical energy harvesting. In SOFCs, the diffusion of O vacancies and other mobile ionic species, such as H+, are at the base of the functioning of the device, while in the other cases they constitute unwanted defects that reduce the performance and life-time of the device. Similarly, the (anti)ferroelectric phase transitions are a requisite for the use of some types of devices, but the accompanying domain walls can generate extended defects detrimental to the life of the material, and structural phase transformations should be avoided in SOFCs. All these phenomena can be studied by mechanical spectroscopy, the measurement of the complex elastic compliance as a function of temperature and frequency, which is the mechanical analogue of the dielectric susceptibility, but probes the elastic response and elastic dipoles instead of the dielectric response and electric dipoles. The two techniques can be combined to provide a comprehensive picture of the material properties. Examples are shown of the study of structural transitions and hopping and tunnelling processes of O vacancies and H in the ion conductor BaCe1-xYxO3-x and in SrTiO3-x, and of the aging and fatigue effects found in PZT at compositions where the ferro- and antiferroelectric states coexist.

1PA42 ベント型分子液晶における強誘電性 : 反強誘電性の拮抗とキラリティ

1PA42 ベント型分子液晶における強誘電性 : 反強誘電性の拮抗とキラリティ

Characteristic Features of the Modulated Structure Appearing in the Multiferroic Material Bi&lt;sub&gt;1-&lt;/sub&gt;&lt;i&gt;&lt;sub&gt;x&lt;/sub&gt;&lt;/i&gt;Sm&lt;i&gt;&lt;sub&gt;x&lt;/sub&gt;&lt;/i&gt;FeO&lt;sub&gt;3&lt;/sub&gt; around &lt;i&gt;x&lt;/i&gt; = 0.15

In Bi1-xSmxFeO3 (BSFO) having the multiferroic BiFeO3 as an end material, when the Sm content increases from x = 0, it has been reported that the ferroelectric-R3c state is changed into the paraelectric-Pnma state around x = 0.14. The R3c/Pnma state boundary around x = 0.14 can be regarded as a temperature-independent morphotropic-phase boundary (MPB). The notable feature in BSFO is that, in addition to these two states, the antiferroelectric PbZrO3-type state was also found in the vicinity of the MPB. Although the PbZrO3-type state appears as a modulated structure, its detailed features have not been understood yet. We have thus examined the crystallographic features of prepared BSFO samples around x = 0.14, mainly by transmission electron microscopy. The PbZrO3-type state was confirmed to be present in samples with x = 0.15 on the basis of x-ray powder diffraction profiles measured from prepared samples at 300 K. On the other hand, the observation made by transmission electron microscopy indicated that the state for x = 0.15 is characterized by a coexistence state consisting of the ferroelectric-R3c and antiferroelectric PbZrO3-type states. In particular, the crystal structure of the PbZrO3-type state could be identified as a modulated structure with two transverse modulation waves, whose wave vectors are given by q1 = [1/2 0 0]o and q2 = [0 1/2 0]o in the orthorhombic-Pnma notation. In addition, eigenvectors of these two transverse waves were also determined to be parallel to the same [001]o direction.

Structures of Pb1−xLax[Zr0.9Mg(0.1+x)/3Nb(0.2−x)/3]O3 solid solutions, electrostriction and energy storage characteristics of a new antiferroelectric phase with disturbed translational symmetry

Solid solutions of lead zirconate magnesium niobate Pb1−xLax[Zr0.9Mg(0.1+x)/3Nb(0.2−x)/3]O3 (0⋜x⋜0.05) doped with lanthanum ions were prepared. By the analysis of temperature-driven transitions and experiments in strong electric fields, we determined the concentration and temperature intervals of the existence of antiferroelectric and ferroelectric states. X-ray diffraction proved that the antiferroelectric phase, stable with х>0.0175 at TC >Т >45°C (during the cooling process at zero field), underwent a monoclinic distortion of perovskite cell and showed a disturbed translational symmetry of the orthorhombic superstructure. The energy storage density and electrostrictive strain were measured in the process that induces the antiferroelectric⇄ferroelectric phase transitions.

Phenomenological theory in dielectric tunable materials with the tristable states

ABSTRACTBoth ferroelectrics near the critical endpoint and antiferroelectrics are konwn to take the tristable states under the electric field as a common character, showing the double hysteresis loop. This common character may become a guiding principle for searching high-tunability materials. We theoretically investigated the dielectric tunabilities in ferroelectrics and antiferroelectrics on the basis of the phenomenological theory under the assumption of the homogeneous system. It was confirmed that the large tunability is realized with no field hysteresis just above the critical temperature in ferroelectrics, while in antiferroelectric materials, it may be obtained in a limited temperature range in the antiferroelectric state.

Continuous control of local magnetic moment by applied electric field in multiferroicsBa2CoGe2O7

${\mathrm{Ba}}_{2}{\mathrm{CoGe}}_{2}{\mathrm{O}}_{7}$ exhibits a collinear-antiferromagnetic structure with the easy axis along $\ensuremath{\langle}100\ensuremath{\rangle}$ directions and an antiferroelectric order with the polarization axis along the [001] direction. By applying the electric field the magnetic moment rotates from $\ensuremath{\langle}100\ensuremath{\rangle}$ to [110] directions and, simultaneously, the antiferroelectric state changes to the ferroelectric state gradually. This magnetoelectric effect, i.e., continuous control of the local magnetic moment by the electric field, is quantitatively explained by the Hamiltonian including the dielectric energy.

Domain structures and correlated out-of-plane and in-plane polarization reorientations in Pb(Zr0.96Ti0.04)O3 single crystal via piezoresponse force microscopy

Pb(Zr1-xTix)O3 single crystal with a low titanium content (x = 4%) was studied by the piezoresponse force microscopy (PFM) and X-ray diffraction (XRD). The XRD studies showed that the crystal faces are orthogonal to the principal cubic axes and confirmed the existence of an intermediate phase between the high-temperature paraelectric (PE) phase and the low-temperature antiferroelectric (AFE) one. A significant temperature hysteresis of phase transitions was observed by the XRD: On heating, the AFE state transforms into the intermediate one at about 373 K and the PE phase appears at 508 K, whereas on cooling the intermediate phase forms at 503 K and persists down to at least 313 K. The PFM investigation was focused on the intermediate phase and involved measurements of both out-of-plane and in-plane electromechanical responses of the (001)-oriented crystal face. The PFM images revealed the presence of polarization patterns switchable by an applied electric field, which confirms the ferroelectric character of the intermediate phase. Importantly, two types of regular domain structures were found, which differ by the spatial orientation of domain walls. The reconstruction of polarization configurations in the observed domain structures showed that one of them is a purely ferroelectric 180° structure with domain walls orthogonal to the crystal surface and parallel to one of the ⟨111⟩ pseudocubic directions. Another one is a ferroelectric-ferroelastic domain structure with the 71° walls parallel to the {101} or {011} crystallographic planes. Remarkably, this domain structure shows correlated out-of-plane and in-plane polarization reorientations after the poling with the aid of the microscope tip.

Molecular Rotors Built in Porous Materials.

Molecules and materials can show dynamic structures in which the dominant mechanism is rotary motion. The single mobile elements are defined as "molecular rotors" and exhibit special properties (compared with their static counterparts), being able in perspective to greatly modulate the dielectric response and form the basis for molecular motors that are designed with the idea of making molecules perform a useful mechanical function. The construction of ordered rotary elements into a solid is a necessary feature for such design, because it enables the alignment of rotors and the fine-tuning of their steric and dipolar interactions. Crystal surfaces or bulk crystals are the most suitable to adapt rotors in 2D or 3D arrangements and engineer juxtaposition of the rotors in an ordered way. Nevertheless, it is only in recent times that materials showing porosity and remarkably low density have undergone tremendous development. The characteristics of large free volume combine well with the virtually unhindered motion of the molecular rotors built into their structure. Indeed, the molecular rotors are used as struts in porous covalent and supramolecular architectures, spanning both hybrid and fully organic materials. The modularity of the approach renders possible a variety of rotor geometrical arrangements in both robust frameworks stable up to 850 K and self-assembled molecular materials. A nanosecond (fast dynamics) motional regime can be achieved at temperatures lower than 240 K, enabling rotor arrays operating in the solid state even at low temperatures. Furthermore, in nanoporous materials, molecular rotors can interact with the diffusing chemical species, be they liquids, vapors, or gases. Through this chemical intervention, rotor speed can be modulated at will, enabling a new generation of rotor-containing materials sensitive to guests. In principle, an applied electric field can be the stimulus for chemical release from porous materials. The effort needed to obtain strong dipoles that are noncentrosymmetrically mounted onto rotors and do not hamper rotational motion is a further aspect of this research activity. Thus, materials showing dielectric properties in response to applied electric fields have been fabricated. This may lead to challenging materials that are promptly responsive to an applied electric field, altering the ferroelectric or antiferroelectric ground state by fast dipole reorientation when subjected to electric polarization.

Elastic aging from coexistence and transformations of ferroelectric and antiferroelectric states in PZT

Materials undergoing antiferroelectric/ferroelectric (AFE/FE) transitions are studied for possible applications that exploit the large volume, charge, and entropy differences between the two states, such as electrocaloric cooling, energy storage, and electromechanical actuators. Though certain compositions of PbZr1−xTixO3 codoped with La and Sn may withstand millions of electrically induced AFE/FE cycles, in other cases few thermally induced cycles and room temperature aging may cause noticeable changes in the material properties. This is particularly evident in the elastic moduli, which at room temperature can become as much as four times softer. In order to get more insight into the mechanisms involved in such elastic aging and full recovering with mild annealing at 600–800 K, the effect of La doping on PbZr0.954Ti0.046O3 is studied with anelastic measurements. Complete suppression of the time dependent phenomena is found after the transformation of the intermediate FE phase into incommensurate AFE by 2% La doping. This is discussed in terms of disappearance of the stress and electric fields at the FE/AFE interfaces, in the light of the thermally activated anelastic relaxation processes that are observed at high temperature and are due to mobile defects, presumably O vacancies.

Antiferroelectric to Ferroelectric Crossover and Energy Storage Properties of (Pb1−xLax)(Zr0.90Ti0.10)1−x/4O3 (0.02 ≤ x ≤ 0.04) Ceramics

Polarization switching behavior and energy storage performances of (Pb1−xLax)(Zr0.90Ti0.10)1−x/4O3 (PLZT x/90/10) ceramics with La compositions across the ferroelectric/antiferroelectric phase boundary, which show variable amount of antiferroelectric (AFE) orthorhombic and ferroelectric (FE) rhombohedral phases, were investigated. A low AFE to FE switching field was obtained and its value could be adjusted by La chemical modification. While the PLZT system evolves from a FE state to an AFE state as a function of La content and from an AFE state to a FE state as a function of the applied electric field, the recoverable energy (Wre) and loss energy (Wloss) range between two limits whose lower and higher values are obtained for PLZT composition in AFE state and FE state, respectively. In terms of the extent of La‐modification, the Wre has been enhanced from 0.819 J/cm3 (for PLZT 2/90/10 and electric field of ~30 kV/cm) to the highest value of 1.85 J/cm3 (for PLZT 3.5/90/10 and electric field ~65 kV/cm), followed by their subsequent reduction.

Stress Effects on Stabilizing Antiferroelectric Phase in Multilayer Ceramics

Controllable phase transformation between antiferroelectric (AFE) and ferroelectric (FE) states suggests multifunctional properties valuable for many device applications. Compared to AFE bulk ceramics with large voltage required for driving electric field‐induced phase transition, implementation of structures comprising multiple thin AFE ceramic layers can realize applications by reducing the switching operation voltage in the feasible range. Here, it is found that a compressive residual stress is developed in multilayer (Pb0.97,La0.02)(Zr0.66,Snx,Ti0.34−x)O3 (PLZST) ceramic co‐fired with multiple Pd/Ag electrode layers, and the compressive residual stress can stabilize AFE phase. AFE phase forms in the PLZST multilayer ceramic with composition corresponding to FE in the bulk materials. Thermodynamic analysis based on free energy of FE and AFE phases well explains the FE to AFE phase transformation observed in the multilayer ceramic under the compressive stress. The findings exhibit a new strategy to tune structure and functional properties of multilayer ceramics through stress engineering for achieving device applications.

Structural and electrocaloric properties of multiferroic-BiFeO3 doped 0.94Bi0.5Na0.5TiO3-0.06BaTiO3 solid solutions

Single-phase (1-x)(0.94Bi0.5Na0.5TiO3-0.06BaTiO3)-xBiFeO3 (BNT-BT-xBF, x = 0.05, 0.1 and 0.15) solid solutions are fabricated using a modified citrate method. The structural, ferroelectric and electrocaloric properties are significantly affected by the multiferroic BiFeO3 doping, which is found to favor the antiferroelectric (AFE) state of the solid solutions. The dynamic mechanical analysis suggests that the BiFeO3 induced ordering of oxygen octahedrons plays a dominant role in the formation of AFE incommensurate phases and leads to the enhanced negative electrocaloric effect (ECE). A maximum ECE temperature change of 1.65 °C under an applied field of 70 kV/cm is observed. It is suggested that the magnetoelectric coupling is effective in enhancing the negative ECE in BNT-BT-xBF.

Microstructural evolution in NaNbO3-based antiferroelectrics

Our recent study found that CaZrO3 doping can effectively enhance the antiferroelectric P phase in NaNbO3 ceramics, leading to a double polarization hysteresis loop characteristic of a reversible antiferroelectric ↔ ferroelectric phase transition [Shimizu et al., Dalton Trans. 44, 10763 (2015)]. Here, a thorough transmission electron microscope study was performed to illustrate the CaZrO3 doping-assisted antiferroelectricity stabilization. In parallel to the bright-field imaging and selected area electron diffraction from multiple zone axes, detailed dark-field imaging was utilized to determine the superlattice structural origins, from either oxygen octahedral tilting or antiparallel cation displacements. By analogy with Pb(Zr1−xTix)O3 and rare-earth doped BiFeO3 systems, the chemical substitutions are such as to an induced polar-to-antipolar transition that is consistent with a tolerance factor reduction. The resultant chemical pressure has a similar effect to the compressive hydrostatic pressure where the antiferroelectric state is favored over the ferroelectric state.

Phase transition and energy storage performance in Ba-doped PLZST antiferroelectric ceramics

(Pb0.97−xBaxLa0.02)(Zr0.7Sn0.27Ti0.03) (0 < x < 0.08) antiferroelectric (AFE) ceramics were successfully fabricated by a solid state reaction, and the effect of barium (Ba) additions and temperature on the dielectric properties and energy storage performance were investigated. The ceramics with lower Ba content undergo two phase transitions during heating from room temperature to 300 °C: orthorhombic (O)-rhombohedral (R)-cubic (C). With the increase of Ba content, dielectric constants increased and transition temperature decreased obviously. The ferroelectric phase was induced as the composition x increased from 0 to 0.08, however, which was not stable and transformed into AFE state upon heating, and then paraelectric phase, which was confirmed by DC field dependence of dielectric constant. The polarization sharply increased from 9.7 μC/cm2 at 20 °C to 24. 6μC/cm2 at 100 °C in (Pb0.89Ba0.08La0.02)(Zr0.7Sn0.27Ti0.03) ceramic. As a result, the maximum recovered energy density of 2.1 J/cm3 was obtained at 80 °C, and the corresponding energy-storage efficiency was 76.5 %, which made this material a promising potential application in capacitors for pulsed power systems.

Structural, dielectric and ferroelectric properties of lead-free Na0.5Bi0.5TiO3 ceramics prepared by spark plasma sintering technique

Lead-free Na0.5Bi0.5TiO3 (NBT) fine-grained ceramics were prepared by spark plasma sintering method. Single phase ceramics with an ABO3 perovskite structure were confirmed by X-ray diffraction method. The grain morphology was analyzed by using a scanning electron micrograph. The crystal particles arranged compactly and the typical grain size was about ≈200 nm. The depolarization temperature T d, the rhombohedral–tetragonal phase transition temperature T R−T and the temperature T m of the maximum dielectric constant corresponding to tetragonal–cubic phase transition were determined to be 453 K, approximately 623 and 793 K, respectively, from the temperature dependence of dielectric properties. The P-E hysteresis loop at different temperatures indicated the existence of antiferroelectric state at the depolarization temperature T d, which explained the antiferroelectric phase above T d. The values of P s, P r and E c reduced slightly with increasing temperature in the range 303–453 K.