Antiferroelectric Phase Research Articles

Mesomorphic, electro-optic and structural properties of binary liquid crystalline mixtures with ferroelectric and antiferroelectric liquid crystalline behaviour

ABSTRACT Two new binary liquid crystalline mixtures composed from the chiral liquid crystalline materials with partially fluorinated non-chiral chain and without lateral substitution at the molecular core have been designed and investigated by polarisation optical microscopy, differential scanning calorimetry, broad-band dielectric spectroscopy, and X-ray techniques. Both mixtures possess the paraelectric orthogonal smectic A*, the tilted ferroelectric smectic C* and the antiferroelectric smectic CA* phases over a reasonably broad temperature range. The gained results reveal a considerable improvement of (i) the broadness of the mesophases temperature range of the ferroelectric and antiferroelectric phases (up to 130 K breadth) and (ii) electro-optical properties, namely the spontaneous polarisation (up to 200 nC/cm2) and tilt angle (higher than 40o), with respect to that of the original pure compounds.

Temperature dependence and characteristics of relaxation modes in achiral polar smectic phases

ABSTRACT The paper studies relaxation modes and their corresponding amplitudes in antiferroelectric polar smectic phases made of achiral bent-core compounds. The analysis identifies two types of modes in the orthogonal phase. The nature of these modes is either pure polar or quasi tilt, but they are split into phase and amplitude modes. One of the amplitude tilt modes is a soft mode and the corresponding relaxations time becomes infinite at the transition to the tilted phase. In tilted phases, characteristic modes change the phase of equilibrium order parameters, the amplitude or both simultaneously. Of these modes, two are predominately polar, soft mode and Goldstone mode are predominately tilt modes and the rest are mixed. The nature of characteristic modes is temperature independent in all studied phases.

Energy storage properties of NaNbO3-CaZrO3 ceramics with coexistence of ferroelectric and antiferroelectric phases

Anti-ferroelectric materials with large saturated polarization, small remnant polarization, and moderate breakdown strength are receiving increasing attention for modern high-power electrical systems. Here we demonstrated that by incorporating CaZrO3 into NaNbO3 ceramics, the antiferroelectricity in NaNbO3-CaZrO3 solid solutions could be stabilized at room temperature. The effects of phase constitution and microstructure on the dielectric properties, electrical breakdown strength, and energy storage properties of the NaNbO3-CaZrO3 ceramics were investigated. Ferroelectric and antiferroelectric phase coexistence in the NaNbO3-CaZrO3 was confirmed by XRD and TEM analyses. With increasing CaZrO3 content, the grain size was reduced, and the dielectric breakdown strength was improved. Therefore, a high energy density of 0.55 J/cm3 and efficiency of 63% was obtained in the NaNbO3-0.04CaZrO3 ceramics. These lead-free NaNbO3-CaZrO3 antiferroelectrics with good electrical energy storage can be exploited for high-power storage devices.

Dielectric properties of four room temperature ferroelectric and antiferroelectric multi-component liquid crystalline mixtures

ABSTRACTDielectric properties of four recently formulated room temperature multi-component liquid crystalline mixtures with paraelectric (SmA*), ferroelectric (SmC*) and antiferroelectric (SmC*A) phases have been studied as a function of temperature and frequency. Under planer anchoring condition, dielectric spectroscopy revealed all the characteristic modes: low frequency PL and high frequency PH mode in SmC*A phase, Goldstone mode (GM) in SmC* phase and soft mode (SM) in SmA* phase. Dielectric behaviour has also been studied under the application of DC bias electric field. With bias electric field, we have been able to study the soft mode dielectric behaviour in the SmC* phase. An unknown high frequency mode (X-mode) with and without bias is also observed in SmC* phase. Dielectric results are explained in the light of generalised Landau theory. The mixtures show very high soft mode electroclinic coefficient in the SmA* phase in addition to fast switching in SmC*A and SmC* phases [30].

Incommensurately Modulated Structures in Zr-rich PZT: Periodic Nanodomains, Reciprocal Configuration, and Nucleation

Zr-rich PZT is one of the most representative materials with compositions located at the ferroelectric–antiferroelectric (FE–AFE) phase boundary. The study of its incommensurately modulated structure (IMS) is of fundamental importance in understanding the origin of its high-performance stored-energy properties and phase transformation between FE and AFE. In this study, the structural features of the IMS were investigated in detail by transmission electron microscopy. The IMS appears as submicron domains assembled by periodic arrays of two-dimensional nanodomains along a direction with the domain width of about 30 {111} spacings. The nanodomains have dual attributes of both antiphase domains and electric domains. The displacement vector across the periodic antiphase boundaries was determined to be R = [001]. The reciprocal lattice of IMS was constructed and characterized by a set of strong basic reflections of pseudocubic unit cell together with 1/2{ooe} superlattice reflections where 1/2(ooe) superl...

Determination of the temperature dependence of the helical pitch in 1.m.7(HH) liquid crystalline compounds

Homologous series 1.m.7(HH) of liquid crystalline compounds, varying in the chiral chain length m (m=4-9), were studied. These compounds are characterized by a long helical pitch in an antiferroelectric phase, which is higher than the measuring range of the available instruments. The temperature dependence of the helical pitch of these compounds was determined by the extrapolation of the results obtained for the mixtures of 1.m.7(HH) compounds with 1.4.7(HF) compound of a known helical pitch value. The helical pitch measurements were made by spectrophotometry and phase transition temperatures were measured by polarizing thermomicroscopy. Extrapolation of the results let established that the investigated liquid crystals are characterized by the helical pitch increasing and then decreasing upon heating, which is accompanied by the helical twist sense inversion from the right-handed structure to the left-handed one. Keywords: liquid crystals, antiferroelectric phase, helical pitch, miscibility study

Antiferroelectric‐ferroelectric phase transition in lead‐free AgNbO3 ceramics for energy storage applications

AbstractThe high‐energy storage density reported in lead‐free AgNbO3 ceramics makes it a fascinating material for energy storage applications. The phase transition process of AgNbO3 ceramics plays an important role in its properties and dominates the temperature and electric field dependent behavior. In this work, the phase transition behavior of AgNbO3 ceramics was investigated by polarization hysteresis and dielectric tunability measurements. It is revealed that the ferrielectric (FIE) phase at room temperature possesses both ferroelectric (FE)‐like and antiferroelectric (AFE)‐like dielectric responses prior to the critical AFE‐FE transition point. A recoverable energy storage density of 2 J/cm3 was achieved at 150 kV/cm due to the AFE‐FE transition. Based on a modified Laudau phenomenological theory, the stabilities among the AFE, FE and FIE phases are discussed, laying a foundation for further optimization of the dielectric properties of AgNbO3.

Determination of Ferro‐ and Antiferroelectricity Using the Temperature Dependence of the Pre‐Edge Features in the XANES Spectra: XANES Study of Tetragonal and Cubic ATiO3 (A = Sr, Ba, and Pb) and PbZrO3

The Ti and Zr K‐edge X‐ray absorption near edge structure (XANES) spectra of ATiO3 (A = Sr, Ba, and Pb) and PbZrO3 perovskite‐type compounds have been measured in the temperature range 20–900 K. Quantitative comparison is performed in a wide temperature range to clarify how the intensities of the pre‐edge peaks and shoulders change with temperature. In the ferro‐ and antiferroelectric tetragonal phases, the intensities of some of the peaks and shoulders decrease with increasing temperature and the peak‐top energies shift to the higher energy side. The shift can be explained by the position and decrease (increase for SrTiO3) of the D2 peak in the difference spectra. The peak‐top position of the pre‐edge peak in XANES does not always represent the true energy for independent transition to an orbital because several orbitals with similar energies overlap. The tetragonal SrTiO3 phase shows the same behavior as ferroelectric P4mm tetragonal BaTiO3 and PbTiO3 perovskite. The temperature dependence of the shoulder is also an important index. The presence of a phase with local polar tetragonal strain is important in materials and the Earth's constituent solid solutions. The existence of ferro‐ and antiferroelectricity can be determined by temperature‐dependent XANES measurements.

Origin of the intermediate phase in lead zirconate, PbZrO3

AbstractThe so‐called intermediate phase of pure PbZrO3 was investigated on a series of specimens by dielectric measurements and X‐ray diffraction. The results indicate that neither defects nor impurities are the origin of the phase. Only in specimens with a low content of pseudocubic [0 0 1]c domains does the intermediate phase appear on cooling. This preferred orientation suppresses the effect of out‐of‐phase oxygen octahedral rotations, which stabilize the antiferroelectric phase. As a result, the intermediate phase is present competitively in a narrow temperature range during cooling before the antiferroelectric phase transition.

Polar-antipolar transition and weak ferromagnetism in Mn-doped Bi0.86La0.14FeO3

Having been considered as a prime example of a room-temperature magnetoelectric multiferroic, BiFeO3 continues to attract much interest. Since functional properties of this material can be effectively influenced by chemical, electrical, magnetic, mechanical and thermal stimuli, it can serve as a model for the investigation of cross-coupling phenomena in solids. Special attention is currently paid to the study of chemical pressure-driven magneto-structural transformations. In this paper, we report on the effect of the Mn doping on the crystal structure and magnetic behavior of the Bi1−xLaxFeO3 multiferroics near their polar-antipolar (antiferromagnetic-weak ferromagnetic) phase boundary. Synchrotron x-ray and neutron powder diffraction measurements of the Bi0.86La0.14Fe1−xMnxO3 (x = 0.05, 0.1, 0.15) compounds have been performed. The diffraction data suggest that the Mn substitution results in the suppression of the ferroelectric polarization and gives rise to the appearance of the antiferroelectric (generally, PbZrO3-related) phase characteristic of the phase diagrams of the Bi1−xRExFeO3 (RE = rare-earth) systems. Depending on the Mn concentration (determining phase composition of the Bi0.86La0.14Fe1−xMnxO3 samples at room temperature), either complete or partial revival of the polar phase can be observed with increasing temperature. Magnetic measurements of the samples indicate that the Mn doping affects the stability of the cycloidal antiferromagnetic order specific to the polar phase, thus resulting in the formation of a ferroelectric and weak ferromagnetic state.

Effect of Sn substitution on the elastic anomalies and phase transition behaviors of antiferroelectric PbHfO3 single crystals studied by Brillouin scattering

The phase transition sequence of a PbHf0.7Sn0.3O3 single crystal was investigated by using Brillouin spectroscopy. The longitudinal acoustic mode showed three distinct changes at ∼370 K, ∼455 K and ∼495 K which corresponded to the antiferroelectric 1 → antiferroelectric 2 → intermediate → paraelectric phase transitions upon heating. The paraelectric phase was characterized by softening acoustic mode, increasing acoustic damping and the appearance of quasielastic central peaks which were observed upon approaching the phase transition temperature. The relaxation times derived from the acoustic mode anomalies and the central peak were consistent with each other and showed a slowing-down behavior. These precursor phenomena were attributed to the polar clusters having broken inversion symmetry. The substitution of Hf with Sn induced a very soft intermediate phase between the paraelectric and the antiferroelectric phases, where the longitudinal acoustic mode exhibited the lowest mode frequency along with substantially high acoustic damping. The transverse acoustic mode, which was observed in the two antiferroelectric phases, did not appear in the intermediate phase. These results indicated that the average symmetry of the intermediate phase may be cubic consisting of fine ferroelastic domains.

Control of the degree of compositional ordering of Pb2YbMO6 (M – Nb, Ta) perovskites by means of mechanical activation

ABSTRACTIt has been found out that compositional ordering degree of the Yb3+ and M5+ (M – Nb, Ta) ions in Pb2YbМO6 ceramics and, correspondingly, both temperature and diffusion of antiferroelectric phase transition can be varied within a wide range by means of high-energy mechanical activation. In particular, disordered modifications of Pb2YbМO6 (M – Nb, Ta) were obtained without using any additives for the first time.

Thermal strain induced large electrocaloric effect of relaxor thin film on LaNiO3/Pt composite electrode with the coexistence of nanoscale antiferroelectric and ferroelectric phases in a broad temperature range

Ferroelectric/antiferroelectric thin/thick films with large electrocaloric (EC) effect in a broad operational temperature range are very attractive in solid-state cooling devices. We demonstrated that a large positive electrocaloric (EC) effect (maximum ΔT ~ 20.7 K) in a broad temperature range (~ 110 K) was realized in Pb0.97La0.02(Zr0.65Sn0.3Ti0.05)O3 (PLZST) relaxor antiferroelectric (AFE) thin film prepared using a sol-gel method. The large positive EC effect may be ascribed to the in-plane residual thermal tensile stress during the layer-by-layer annealing process, and the high-quality film structure owing to the utilization of the LaNiO3/Pt composite bottom electrode. The broad EC temperature range may be ascribed to the great dielectric relaxor dispersion around the dielectric peak because of the coexistence of nanoscale multiple FE and AFE phases. Moreover, a large pyroelectric energy density (6.10 Jcm−3) was harvested by using an Olsen cycle, which is much larger than those (usually less than 10− Jcm−3) obtained by using direct thermal-electrical, Stirling and Carnot cycles, etc. These breakthroughs enable the PLZST thin film an attractive multifunctional material for applications in modern solid-state cooling and energy harvesting.

Electric field induced phase transition and accompanying giant poling strain in lead-free NaNbO3-BaZrO3 ceramics

A series of phase transitions in (1-x)NaNbO3-xBaZrO3 ((1-x)NN-xBZ) ceramics was observed from antiferroelectric orthorhombic phase to ferroelectric orthorhombic phase and finally into ferroelectric rhombohedral phase with increasing x. An electric field induced irreversible phase transition was found in different compositions, irrespective of their virgin phase structures. Particularly, an antiferroelectric orthorhombic phase is irreversibly transformed into a ferroelectric monoclinic phase within 0.02 ≤ x ≤ 0.05, leading to a giant poling strain of ∼0.58%. This is much larger than that observed in ferroelectric orthorhombic (0.06 ≤ x ≤ 0.07) and rhombohedral phases (0.08 ≤ x ≤ 0.11) suffering from an irreversible ferroelectric-ferroelectric (monoclinic) phase transition. The synchrotron x-ray diffraction and the measurement of longitudinal and transverse strains suggest that this irreversible phase transition should involve not only a distinct volume expansion, but also an obvious lattice elongation. The present study demonstrates a unique nature of the composition and field dependent phase stability and an underlying mechanism of giant poling strains in NN-BZ ceramics.

Stabilized antiferroelectricity in xBiScO3-(1-x)NaNbO3 lead-free ceramics with established double hysteresis loops

We previously reported various solid solution systems that demonstrated the stabilized antiferroelectric (P) phases in NaNbO3 through lowering the tolerance factor. However, all those reported modifications were achieved by adding A2+B4+O3 type solid solutions. A lead-free antiferroelectric (AFE) solid solution xBiScO3-(1-x)NaNbO3 was rationalized by adopting the tolerance factor design rule. Specifically, adding BiScO3 was found to effectively stabilize the AFE phase without changing the crystal symmetry of NaNbO3. Microstructure and electron zone axis diffraction patterns from transmission electron microscopy revealed the stabilized AFE (P) phase in this solid solution. Besides, the electric-field-induced polarization with a double-hysteresis loop was observed. The present results pointed out that the strategy could also be applied while adding A3+B3+O3 type solid solutions. In addition, it expanded the compositional design that can be applied to antiferroelectric materials.

Elemental Ferroelectricity and Antiferroelectricity in Group‐V Monolayer

AbstractFerroelectricity is usually found in compound materials composed by different elements. Here, based on first‐principles calculations, spontaneous electric polarization and ferroelectricity in 2D elemental group‐V (As, Sb, and Bi) monolayer with the puckered lattice structure similar to phosphorene is revealed. These are the first example of elemental ferroelectric materials. The polarization is due to the spontaneous lattice distortion with atomic layer buckling and has quite sizable values, comparable or even larger than that recently found in 2D monolayer compound SnTe. Interestingly, for Bi monolayer, apart from the ferroelectric phase, it is found that it can also host an antiferroelectric phase. The Curie temperatures of these elemental materials can be higher than room temperature, making them promising for realizing ultrathin ferroelectric devices of broad interest. A general model is constructed to understand and search for 2D ferroelectric and antiferroelectric materials in future studies.

Tailored dielectric tunability of alkali niobate-based antiferroelectric/relaxor-ferroelectric composites

High dielectric tunability, low loss and an appropriate level of dielectric permittivity are basic requirements of ferroelectric materials for tunable microwave devices. In this study, 0.96NaNbO3-0.04CaZrO3/0.88(K0.5Na0.5)NbO3-0.12SrZrO3, antiferroelectric/relaxor-ferroelectric composites were designed to tailor dielectric tunability. By tailoring the microstructure of the composites, a high dielectric tunability of 51.78% with a low loss of 0.015 was achieved at the composition ratio of 15/85. The nonlinear behaviours of the composites were explored by Johnson model; with increasing antiferroelectric phase, the contribution of the polarization to the free energy was increased between the antiferroelectric and relaxor-ferroelectric. Furthermore, the high resistance layer at the grain boundary region greatly inhibited the long-term migration of electrons and defective ions (mainly oxygen vacancies) in the composites. Therefore, the dielectric loss was remarkably decreased, and the excellent tunability was still preserved in the composite ceramics.

The depolarization performances of 0.97PbZrO3–0.03Ba(Mg1/3Nb2/3)O3 ceramics under hydrostatic pressure

Several 0.97PbZrO3–0.03Ba(Mg1/3Nb2/3)O3 (0.97PZ–0.03BMN) ceramics were prepared via the columbite precursor method. Their microstructures and pressure-dependent ferroelectric and depolarization performances were then studied. The X-ray diffraction patterns of ground and fresh samples indicate that a main rhombohedral symmetry crystal structure is present in the bulk and that it sits alongside a trace quantity of an orthorhombic antiferroelectric phase that results from the effect of grinding on the surface. The remanent polarization (Pr) of the 0.97PZ–0.03BMN reached 32.4 μC/cm2 at 4.5 kV/mm and ambient pressure. In an in situ pressure-induced current measurement, more than 91% of the retained Pr of the pre-poled sample was released when the pressure was increased from 194 MPa to 238 MPa. That this pressure-driven depolarization should be attributed to the pressure-induced ferroelectric–antiferroelectric phase transition is supported by the emergence of double P–E loops at high hydrostatic pressures. Moreover, the 0.97PZ-0.03BMN ceramics exhibit no temperature-induced phase transitions and little related polarization loss up to 125 °C, which suggests that Pr has excellent thermal stability. The sharp depolarization behavior at low pressures and excellent temperature stability reveal that our 0.97PZ–0.03BMN ceramics exhibit superior performances in mechanical–electrical energy conversion applications.

Effect of the lanthanum concentration on the physical properties of the (Bi0.5Na0.5)0.92Ba0.08-3x/2LaxTiO3 ceramic system

The influence of lanthanum concentration on the structural, ferroelectric and dielectric properties of BNT–BT ceramic compounds with a composition close to the morphotropic phase boundary (Bi0.5Na0.5)0.92Ba0.08-3x/2LaxTiO3 (x = 0, 1, 2 and 3 at.%) has been studied. The structural properties reveal the coexistence of both ferroelectric (P4mm) and antiferroelectric (P4bm) tetragonal phases for the lanthanum-free system. Nonetheless, for the La3+ modified samples, both antiferroelectric tetragonal (P4bm) and ferroelectric rhombohedral (R3c) phases coexist. On the other hand, slim-like hysteresis loops for the x = 1 at.% La3+ concentration have been observed, suggesting a higher stability of the antiferroelectric phase. However, for the other compositions (including the lanthanum-free sample) the P–E hysteresis loops suggested a higher stability of the ferroelectric phase. The dielectric response has shown the presence of three anomalies in the entire analyzed temperature range, which have been associated to different phase transitions with an important influence of the lanthanum content.

Piezoelectric and functional properties of materials with coexisting ferroelectric and antiferroelectric phases

A brief review of investigations of lead zirconate-titanate based solid solutions with coexisting ferroelectric and antiferroelectric types of dipole ordering is presented. Our goal is to demonstrate the importance of the inhomogeneous state of domain of these phases in formation of properties of these substances, in the search for new piezoelectric ceramic materials, as well as development of new functional materials. An analysis of physical phenomena and peculiarities of behavior of these materials caused by the presence of domains of the coexisting ferroelectric and antiferroelectric phases is presented. Several specific effects caused by this coexistence of phases which are important and significant for applications of these materials in devices are discussed.