Ferroelectric Phase Transition Research Articles

The H/F substitution strategy can achieve large spontaneous polarization in 1D hybrid perovskite ferroelectrics.

Hybrid organic-inorganic perovskite (HOIP) ferroelectrics exhibit polarization reversibility and have a wide range of applications in the fields of smart switches, memorizers, sensors, etc. However, the inherent limitations of small spontaneous polarization (P s) and large coercive field (E c) in ferroelectrics have impeded their broader utilization in electronics and data storage. Molecular ferroelectrics, as a powerful supplement to inorganic ferroelectrics, have shown great potential in the new generation of flexible wearable electronic devices. The important research responsibility is to greatly improve progressiveness and overcome the above limitations. Here, a novel one-dimensional (1D) HOIP ferroelectric, (3-F-BTAB)PbBr3 (3-F-BTAB = 3-fluorobenzyltrimethylammonium), was successfully synthesized by employing the H/F substitution strategy to modify parent compound (BTAB)PbBr3 (BTAB = benzyltrimethylammonium), which undergoes a ferroelectric phase transition with Aizu notation 2/mF2 at 420 K. Notably, (3-F-BTAB)PbBr3 demonstrates exceptional ferroelectric properties with a large P s of 7.18 μC cm-2 and a low E c of 1.78 kV cm-1. As far as we know, (3-F-BTAB)PbBr3 features the largest P s among those reported for 1D lead-based HOIP ferroelectrics. This work enriches the 1D lead-based ferroelectric family and provides guidance for applying ferroelectrics in low-voltage polar memories.

Enhanced energy-storage density in (Pb0.98La0.02)(Zr0.45-xSn0.55Hfx)0.995O3 antiferroelectric ceramics

Antiferroelectric ceramics with unique characteristics of electric-field-induced antiferroelectric to ferroelectric phase transitions and ultra-fast charging-discharging rate, which are demanded in high pulse power devices. In this work, (Pb0.98La0.02)(Zr0.45-xSn0.55Hfx)0.995O3 (PLZSH) antiferroelectric ceramics with x = 0∼0.20 were prepared via a conventional solid-state reaction approach. Incommensurate modulation structure with a 1/n<110> superlattice was observed in AFE at room temperature, which was associated with the unique domain boundaries, contributing the obvious declined AFE-FE phase transition electric field as well as the enhanced energy storage density. It was also observed that the maximum recoverable energy storage density (Wrec) increases from 2.93 J/cm3 (x = 0) to 5.72 J/cm3 (x = 0.15), and the corresponding energy-storage efficiency uprises from 82.4 % to 87.8 % with the increasing x at 280 kV/cm. The superior energy density and efficiency indicate that the obtained PLZSH antiferroelectric ceramics are promising for practical applications in pulse power devices.

The mechanism of ferroelectric phase transformation in Gd2O3 modified BCZT ceramics: Experimental studies and first-principles calculations

Lead-free (Ba0.85Ca0.15)(Ti0.90Zr0.10)O3 (BCZT)-based piezoelectric ceramics have attracted considerable interest due to their excellent piezoelectric properties and abundant phase structures. However, there is a serious lack in the theoretical calculations for the ferroelectric phase transition behavior. Here, the experimental and first-principles calculations were utilized to analyze the ferroelectric phase transition process of (Ba0.85Ca0.15)(Ti0.90Zr0.10)O3-xGd2O3(BCZT-xGd, x = 0, 0.02, 0.04, and 0.05) ceramics. The incorporation of Gd2O3 has induced a transformation from tetragonal to rhombohedral phase due to the decrease in the dislocation energy with A-site cations and the attenuation of the bonding energy between B-site cations and the planar O atoms. Moreover, the hybridization between the d orbitals of B-site atoms and the O 2p orbitals, coupled with the reduction of the polarization vector along the [001] axis, leads to enhanced weak coupling relaxation. This work provides a theoretical basis for the ferroelectric phase transition behavior of other piezoelectric systems.

A Novel Ferroelectric Rashba Semiconductor.

Fast, reversible, and low-power manipulation of the spin texture is crucial for next generation spintronic devices like non-volatile bipolar memories, switchable spin current injectors or spin field effect transistors. Ferroelectric Rashba semiconductors (FERSC) are the ideal class of materials for the realization of such devices. Their ferroelectric character enables an electronic control of the Rashba-type spin texture by means of the reversible and switchable polarization. Yet, only very few materials are established to belong to this class of multifunctional materials. Here, Pb1- xGexTe is unraveled as a novel FERSC system down to nanoscale. The ferroelectric phase transition and concomitant lattice distortion are demonstrated by temperature dependent X-ray diffraction, and their effect on electronic properties are measured by angle-resolved photoemission spectroscopy. In few nanometer-thick epitaxial heterostructures, a large Rashba spin-splitting is exhibiting a wide tuning range as a function of temperature and Ge content. This work defines Pb1- xGexTe as a high-potential FERSC system for spintronic applications.

Temperature/electric field induced photoluminescence-modulation effect in dysprosium-doped barium titanate ferroelectric ceramics

Lanthanide (Ln3+) based ferroelectric phosphors, with an integration of PL emission and ferroelectric effect, are unveiling an exciting realm of possibilities for multifunctional ferroelectric-optic materials. However, how the ferroelectric host enables the tuning on the PL emissions through modulating the local structure (e.g., lattice site, symmetry, strains etc.) of the Ln3+ activator is not established yet. In this work, a luminescent-ferroelectric material, i.e. Dy3+ doped BaTiO3 ceramic (Ba1–xDyxTiO3 (x = 0–0.07), abbr: BTO:Dy3+), was explored to address the aforementioned issues. The BTO:Dy3+ ceramics were synthesized by a solid-state reaction method. The crystal structure, photoluminescence (PL) and electric properties (dielectric constant, ferroelectric hysteresis and piezoelectric hysteresis loop) were systematically investigated. The BTO:Dy3+ ceramics show two predominant emission peaks, corresponding to the blue magnetic dipole transition (477 nm, 4F7/2 → 6H15/2) and yellow electric dipole transition (573 nm, 4F7/2 → 6H13/2), the intensity ration of which can be modulated by the ferroelectric polarization that causes the slight lattice deformation. Such a polarization-emission modulation combining with the Dy3+ doping could accelerate the color change, from yellow to blue, which is characterized to detect the phase transition, with a method and mechanism were proposed, that is, the phase change is reflected by the PL characteristic peak intensity ratio. Therefore, the current results offer a convenient photoluminescence method for detecting the ferroelectric phase transition and a feasible approach to study the interaction between the photoluminescence and polarization in ferroelectric materials, for providing new insights for the development of multifunctional materials.

Electrically Detectable Photoinduced Polarization Switching in a Molecular Prussian Blue Analogue.

Light, a nondestructive and remotely controllable external stimulus, effectively triggers a variety of electron-transfer phenomena in metal complexes. One prime example includes using light in molecular cyanide-bridged [FeCo] bimetallic Prussian blue analogues, where it switches the system between the electron-transferred metastable state and the system's ground state. If this process is coupled to a ferroelectric-type phase transition, the generation and disappearance of macroscopic polarization, entirely under light control, become possible. In this research, we successfully executed a nonpolar-to-polar phase transition in a trinuclear cyanide-bridged [Fe2Co] complex crystal via directional electron transfer. Intriguingly, by exposing the crystal to the wavelength of light─785 nm─without any electric field─we can drive this ferroelectric phase transition to completely depolarize the crystal, during which a measurable electric current response can be detected. These discoveries signify an important step toward the realization of fully light-controlled ferroelectric memory devices.

Surface Core-Level Shifts as a Toolbox to Evidence the BaTiO3 Ferroelectric Phase Transition

Surface Core-Level Shifts as a Toolbox to Evidence the BaTiO₃ Ferroelectric Phase Transition

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.

Supramolecular Organic Ferroelectric Materials from Donor-Acceptor Systems.

Organic ferroelectric (FE) materials, though known for more than a century, are yet to reach close to the benchmark of inorganic or hybrid materials in terms of the magnitude of polarization. Amongst the different classes of organic systems, donor (D)-acceptor (A) charge-transfer (CT) complexes are recognized as promising for ferroelectricity owing to their neutral-to-ionic phase transition at low temperature. This review presents an overview of different supramolecular D-A systems that have been explored for FE phase transitions. The discussion begins with a general introduction of ferroelectricity and its different associated parameters. Then it moves on to show early examples of CT cocrystals that have shown FE properties at sub-ambient temperature. Subsequently, recent developments in the field of room temperature (RT) ferroelectricity, exhibited by H-bond-stabilized lock-arm supramolecular-ordering (LASO) in D-A co-crystals or other FE CT-crystals devoid of neutral-ionic phase transition are discussed. Then the discussion moves on to emerging reports on other D-A soft materials such as gel and foldable polymers; finally it shows very recent developments in ferroelectricity in supramolecular assemblies of single-component dipolar or ambipolar π-systems, exhibiting intra-molecular charge transfer. The effects of structural nuances such as H-bonding, balanced charge transfer and chirality on the observed ferroelectricity is described with the available examples. Finally, piezoelectricity in recently reported ambipolar ADA-type systems are discussed to highlight the future potential of these soft materials in micropower energy harvesting.

Structural heterogeneity induced enhancement of physical properties in Sm‐modified K0.5Na0.5NbO3

AbstractDoping of suitable metal ions in ferroelectric oxides modifies the physical properties and can induce additional functionalities. Here, we present a detailed study on the effects of Sm concentration on the structural, dielectric, ferroelectric, and piezoelectric properties of ((K0.5Na0.5)1−3xSmx)NbO3 (KNSN) (0.00 ≤ x ≤ 0.02) ceramics. X‐ray diffraction and Raman spectroscopic analysis indicate that KNSN ceramics exhibit the single‐phase orthorhombic (Amm2) structure for x = 0.00 and the coexistence of orthorhombic and tetragonal (Amm2 + P4mm) structure for the composition range 0.005 ≤ x ≤ 0.02. The tetragonal phase fraction increases with an increase in Sm concentration. We observed dielectric relaxation behavior in KNSN at orthorhombic to tetragonal (TO–T) phase transition temperature, and its origin can be attributed to the structural heterogeneity at the inter‐ferroelectric phase boundary. Increasing Sm concentration leads to the broadening of the ferroelectric phase transition peaks. Further, the structural heterogeneity of the ceramics was seen from the slope of the dielectric constant versus log frequency and central peak behavior of Raman spectra at room temperature (RT). The study reveals that x = 0.005 shows maximum dielectric constant (Ɛr = 583), remanent polarization (2Pr = 57.02 μC/cm2), and piezoelectric coefficient (d33 = 94 pC/N) at RT and is associated with increased local structural heterogeneity due to Sm doping.

Emergent phenomena in quantum phase transition

Emergent phenomena near the quantum critical point at sufficiently low temperature attracts accumulating attentions with respect to both theories and applications. On the contrary to materials with itinerant electrons, ferroelectric materials are relatively less studied but promising in studying novel quantum orders. In this report, we focus on one clean model system, strontium titanite oxide, to explore the quantum criticality. The stabilization of a quantum paraelectric phase has been verified by the previous experimental observation of the dielectric permittivity saturating at a rather high value to the order of 104 under 4 Kelvin. To understand the underlying mechanism, we apply the quantum generalization of Ginzburg-Landau theory as well as lattice dynamics, i.e., the stiffness of soft phonon mode to rationalize the deviation from the classical paraelectric to ferroelectric phase transitions. Besides, under the effective upper critical dimension, a logarithmic correction of the relationship between relative permittivity and temperature could explain the upturn found in diagram.

Optimized Electrocaloric Refrigeration in Lead-Free NaNbO3-Based Ceramics via AFE ↔ FE Phase Transition Modulation.

An outstanding challenge for eco-friendly ferroelectric (FE) refrigeration is to achieve a large adiabatic temperature change within a broad temperature range originating from the electrocaloric (EC) effect, which is expected to be realized in antiferroelectric (AFE) materials owing to the large entropy change during electric field and thermally induced phase transition. In this work, a large EC response over a wide response temperature range can be achieved slightly above room temperature via designing the phase transition of NaNbO3. An irreversible to reversible AFE-FE phase transition on heating induced by the introduction of CaZrO3 into NaNbO3 plays a key role in the optimized electrocaloric refrigeration. Accordingly, accompanying the local structure transformation corresponding to the B-site ions, the transition temperature between the square polarization-electric field (P-E) hysteresis loop (the irreversible AFE-FE phase transition induced by the electric field) and the repeatable double P-E hysteresis loop (the electric field induced reversible AFE-FE phase transition) was tailored to around room temperature, in favor of extending large entropy change to the wide temperature range. This work provides an efficient approach to designing lead-free EC materials with excellent EC performance, promoting the advancement of environmentally friendly solid-state cooling technology.

Phase stability and energy storage properties of polycrystalline antiferroelectric BaTiO3-substituted NaNbO3 thin films

Lead-free sodium niobate (NN) thin films with varying barium titanate (BT) content and 1 mol% manganese were deposited on platinized silicon substrates by chemical solution deposition. Microstructural analysis reveals a change in nucleation mechanism, and X-ray diffraction and Raman spectroscopy confirmed a composition-driven antiferroelectric (AFE) to ferroelectric (FE) phase transition at 0.01 < x < 0.03, providing a stability interval for the AFE phase despite increasing the tolerance factor. The thin films show well-shaped ferroelectric response under applied electric field, indicating an irreversible field-induced phase transition. The composition with 7 mol% BaTiO3 showed the most promising energy storage properties (Wrec ∼5.7 J/cm3 and 68% efficiency (η)), along with excellent thermal stability up to 120 °C and largely improved cyclic stability up to 5 * 106 bipolar cycles. These findings highlight the potential of NN-based thin films as lead-free candidates for energy storage, emphasizing the importance of stabilizing the AFE phase under electric fields for practical applications.

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.

A Metal-Free Molecular Ferroelectric [4-Me-cyclohexylamine]ClO4 Introduced by Boat and Chair Conformations of Cyclohexylamine.

Organic ferroelectrics have received a great deal of interest due to their exclusive properties. However, organic ferroelectrics have not been fully explored, which hinders their practical application. Here, we presented a novel metal-free organic molecular ferroelectric [4-MCHA][ClO4 ] (1) (4-MCHA=trans-4-methylcyclohexylamine), which exhibits an above-room-temperature of 328 K. Strikingly, the single crystal structure analysis of 1 shows that the driving force of phase transition is related to the interesting chair-boat conformation change of 4-MCHA cation, in addition to the order-disorder transition of ClO4 - anion. Using piezoelectric response force microscopy (PFM), the presence of domains and the implemented polarization switching were clearly observed, which explicitly determined the presence of room-temperature ferroelectricity of 1. As far as we know, the ferroelectric phase transition mechanism attributed to the conformational change in a trans isomeric cation is very rare. This research enriched the path of designing ferroelectric materials and smart materials.

Local structural mechanism for enhanced energy storage properties in heterovalent doped NaNbO3 ceramics

In recent years, there is a growing interest for new lead-free oxides with reversible antiferroelectric (AFE)-ferroelectric (FE) phase transition for high-power energy-storage applications. NaNbO3-based ceramics are particularly attractive due to their easy synthesis and cost-effectiveness. In order to stabilize reversible AFE-FE phase transition, NaNbO3 is doped with a combination of heterovalent substitutions, although the underlying structural mechanism for the same is poorly understood. Here, we investigated local and average structures of Ca/Zr doped NaNbO3 using neutron total scattering. We show that Ca/Zr doping increases the average AFE phase (Pbma) fraction, however, the material remains as a composite of both FE (P21ma) and AFE regions. Analysis of local structure suggests that increase in the long-range AFE phase results from more extensive twinning of local FE regions, due to introduced charge disorder. We propose that enhanced energy-storage properties of Ca/Zr-doped NaNbO3 arises from localized twin boundary motion between the defect-induced pinning centers.

Strain-aided room-temperature second-order ferroelectric phase transition in monolayer PbTe: Deep potential molecular dynamics simulations

Strain-aided room-temperature second-order ferroelectric phase transition in monolayer PbTe: Deep potential molecular dynamics simulations

Quantum-Accurate Modeling of Ferroelectric Phase Transition in Perovskites from Message-Passing Neural Networks

Quantum-Accurate Modeling of Ferroelectric Phase Transition in Perovskites from Message-Passing Neural Networks

Ferroelectric phase transitions of nanoislands based on transverse ising model

Based on the transverse field Ising model, the phase transition properties of nanoislands with a spin-1/2 are studied by using the usual decoupling approximation of Fermi-type Green’s function. The phase diagram indicates that the phase transition curve (J S /J = t c , Ω S /J ∼ t c ) is highly sensitive to the interlayer exchange interaction (J R /J) and the ratio of surface to center transverse fields (Ω S /Ω). The polarization diagram reveals that the polarization curve exhibits steps attributed to spin inversion, and the temperature of the step point corresponds to the temperature at which spin configuration changes.

Thermal expansion of SrxBa1−xNb2O6 across and above the ferroelectric phase transition

Lead-free SrxBa1−xNb2O6(SBN) is of interest due to flexible chemistry, ferroelectric behavior, and electro-optic properties. The thermal expansion coefficient for SBN is reported only for compositions x = 0.35–0.59 and temperature range 20–50 °C, and for x = 0.5 composition up to 500 °C. Here, X-ray diffraction of Sr0.4Ba0.6Nb2O6 (SBN40), Sr0.5Ba0.5Nb2O6 (SBN50) and Sr0.6Ba0.4Nb2O6 (SBN60) is reported in the temperature range up to 930 °C. The thermal expansion is anisotropic, differing significantly for the a and c lattice parameters, and a larger variation in the thermal expansion of the c lattice parameters was observed as a function of composition. Above the Curie temperature, the thermal expansion coefficient is decreasing with increasing temperature and decreasing Sr content. Linear thermal expansion coefficients range from 11.45(5) to 7.90(3)·10−6 K−1 for the a lattice parameter and 9.10(1) to 4.40(1)·10−6 K−1 for the c lattice parameter depending on composition and temperature range.