Paraelectric Phase Research Articles

Enhanced energy storage performance inBaZrxTi1-xO3 lead-free ferroelectrics near phase transitions.

The present study explores the energy storage properties of BaZrxTi1-xO3 through phase-field modeling, focusing on the impact of composition and temperature on energy storage performance. The obtained results reveal a variety of polarization phases and configurations based on Zr compositions and temperatures. A detailed phase diagram for temperature-composition of BaZrxTi1-xO3 is established, closely aligning with experimental measurements. Variations in Zr content and temperature have a significant impact on the polarization-electric field response, influencing the energy storage properties. Calculations of energy storage properties are derived from the polarization-electric field response. In addition, a thorough diagram is developed to illustrate the discharge energy density of BaZrxTi1-xO3 as a function of temperature and composition. Notably, high discharge energy density is achievable near the Curie temperature, corresponding to the transition from ferroelectric to paraelectric phase. Furthermore, the present study emphasizes the importance of the disparity between maximum and remanent polarization, as well as the electric field-dependent effective permittivity, in determining the discharge energy density.&#xD.

Characterization of HZO Films Fabricated by Co-Plasma Atomic Layer Deposition for Ferroelectric Memory Applications

Plasma-enhanced atomic layer deposition (ALD) is a common method for fabricating Hf0.5Zr0.5O2 (HZO) ferroelectric thin films that can be performed using direct-plasma (DP) and remote-plasma (RP) methods. This study proposed co-plasma ALD (CPALD), where DPALD and RPALD are applied simultaneously. HZO films fabricated using this method showed wake-up-free polarization properties, no anti-ferroelectricity, and high fatigue endurance when DPALD and RPALD started simultaneously. To minimize defects in the film that could negatively affect the low polarization properties and fatigue endurance, the direct plasma power was reduced to 75 W. Thus, excellent fatigue endurance for at least 109 cycles was obtained under a high total remanent polarization of 47.3 μC/cm2 and an applied voltage of 2.5 V. X-ray photoelectron spectroscopy and transmission electron microscopy were used to investigate the mechanisms responsible for these properties. The HZO films fabricated by CPALD contained few lattice defects (such as nonstoichiometric hafnium, nonlattice oxygen, and residual carbon) and no paraelectric phase (m-phase). This was attributed to the low-carbon residuals in the film, as high-energy activated radicals were supplied by the adsorbed precursors during film formation. This facilitated a smooth transition to the o-phase during heat treatment, which possessed ferroelectric properties.

Temperature dependence of the frequency shifts related to the thermodynamic quantities close to phase transitions in NaNO2

ABSTRACT This study examines a linear relationship between the frequency shifts, ( 1 / w ) ( ∂w / ∂T ) p , and the variation of the dielectric constant, ( 1 / ϵ ) ( ∂ϵ / ∂T ) p , close to phase transitions in ferroelectric crystalline systems, in particular, ferroelectric NaNO2 as studied here. Both quantities (frequency and dielectric constant) are described by the power-law formulae below the Curie temperature Tc (ferroelectric phase), Tc < T < Ti (incommensurate phase) and T > Ti (paraelectric phase). The divergence behaviour of the mode Grüneisen parameter (ɣp ) is obtained, whose temperature dependence can also be described by a power-law formula in NaNO2. It is also shown that the heat capacity Cp can be evaluated from the thermal expansion (αp ) by means of the same critical exponent since they exhibit similar critical behaviour near Tc and Ti in this crystal.

Calculation of the order parameter and dielectric susceptibility under the electric field near the incommensurate phase in NaNO2 using Landau model

ABSTRACT Temperature dependences of the order parameters (P and Ψ) and inverse susceptibilities (χp −1 and χΨ -1 ) are calculated for the ferroelectric(FE)-incommensurate (INC) – paraelectric (PE) transitions in NaNO2 at zero (E = 0) and constant electric fields E by the Landau phenomenological model. For the calculation of the polarisation P and the order parameter Ψ, the phase line equations are fitted to the observed data (E = 0) from the literature. On this basis, E-T phase diagram including the ferroelectric, incommensurate and paraelectric phases is constructed using the observed (E-T) data for NaNO2 as reported in the literature. In the presence of the polarisation P (secondary order parameter), which has a biquadratic coupling with the Ψ (primary order parameter) in the incommensurate phase, the Landau model presented here describes the observed behaviour of the FE-INC and INC-PE transitions in NaNO2. Under constant electric fields, our predictions can be compared with the experiments. This method of calculation can be applied to some other crystals exhibiting the incommensurate phase between the FE and PE phases.

A Novel Multiple Shape Memory Effect in PVDF‐Based Ferroelectric Copolymers and Terpolymers

AbstractShape memory polymers (SMPs) have been extensively investigated because of their wide range of biomedical and robot applications. In most of SMPs, only one temporary shape can be formed and recovered through the mechanism of melting or glass transition. Herein, a multiple shape memory effect (mSME), i.e., formation of at least two temporary shapes, can be realized in polyvinylidene fluoride (PVDF)‐based ferroelectric polymers by exploiting their expanded ferroelectric–paraelectric (F‐P) phase transition temperature range. Although P(VDF‐TrFE) (TrFE: trifluoroethylene) (55/45) copolymer is thought to be a normal ferroelectric, its ferroelectric phase transforms into a paraelectric phase through an intermediate relaxor ferroelectric‐like state and mSME is observed in this extended phase transition temperature range. By incorporating CTFE (chlorotrifluoroethylene) into P(VDF‐TrFE), P(VDF‐TrFE‐CTFE) becomes a relaxor ferroelectric with a further extended phase transition temperature range. The terpolymer exhibits improved mSME and at least three temporary shapes can be formed and recovered. A comparison of SME and structures of several PVDF‐based copolymer and terpolymers suggests that the amount of polar phase is a critical factor affecting the SME. This study not only demonstrates mSME in ferroelectric polymers, which expands their application potential, but also provides an in‐depth understanding of the shape memory mechanism of the polymers.

High energy density and energy efficiency in AgNbO3-based multilayer ceramic capacitors induced by coexisted antiferroelectric and paraelectric phases

AgNbO3-based lead-free antiferroelectric materials have been attracted increasing attention due to their excellent energy storage performance. But most of the AgNbO3-based ceramics still suffer from low energy efficiency. Herein, coexisted antiferroelectric phase and paraelectric phase are realized in La-doped AgNbO3-based multilayer ceramic capacitors at room temperature, which resulted in slim polarization-electric field loops with hysteresis-free and high breakdown strength over 1000 kV/cm. Both the hysteresis-free polarization-electric field loops and high breakdown strength are beneficial for the energy storage density and energy efficiency. In (Ag0.64La0.12)NbO3 multilayer ceramic capacitors, a high breakdown strength of 1060 kV/cm was attained, which contributes to a recoverable energy storage density (Wrec) of 9.1 J/cm3 and an energy efficiency (η) of 95.8%. Furthermore, the Wrec and η remains above 7.5 J/cm3 and above 83% in the temperature range of 30 °C to 130 °C under 1000 kV/cm, and remains above 4.8 J/cm3 and above 91% in the frequency range of 1 to 100 Hz under 700 kV/cm. This work provides a feasible method for preparing AgNbO3-based ceramics with high energy storage performance.

High pressure ferroelectric-like semi-metallic state in Eu-doped BaTiO3.

We have conducted a detailed high-pressure (HP) investigation on Eu-doped BaTiO3 using angle-resolved x-ray diffraction, Raman spectroscopy, and dielectric permittivity measurements. The x-ray diffraction data analysis shows a pressure-induced structural phase transition from the ambient tetragonal to the mixed cubic and tetragonal phases above 1.4GPa. The tetragonality of the sample due to the internal deformation of the TiO6 octahedra caused by the charge difference from Eu doping cannot be lifted by pressure. Softening, weakening, and disappearance of low-frequency Raman modes indicate ferroelectric tetragonal to the paraelectric cubic phase transition. However, the pressure-induced increase in the intensity of [E(LO), A1(LO)] and the octahedral breathing modes indicate that the local structural inhomogeneity remains in the crystal and is responsible for spontaneous polarization in the sample. The low-frequency electronic scattering response suggests pressure-induced carrier delocalization, leading to a semi-metallic state in the system. Our HP dielectric constant data can be explained by the presence of pressure-induced localized clusters of microscopic ferroelectric ordering. Our results suggest that the HP phase coexistence leads to a ferroelectric-like semi-metallic state in Eu-doped BaTiO3 under extreme quantum limits.

Origin of ultrahigh-performance barium titanate-based piezoelectrics: Stannum-induced intrinsic and extrinsic contributions

Despite the pivotal role of stannum doping in achieving ultrahigh piezoelectric performance in barium titanate-based ceramics, the fundamental mechanisms underlying this enhancement remain elusive. Here, we introduce a single variable nonstoichiometric stannum strategy in lead-free barium titanate-based ceramics with giant piezoelectricity, revealing that stannum doping contributes intrinsically and extrinsically to enhance piezoelectricity. Density functional theory calculations elucidate the intrinsic enhancement of polarization arising from lattice distortion and increased space for titanium-oxygen bonds induced by optimal stannum doping, which is corroborated by Rayleigh analysis. A phase transition from ferroelectric multiphase coexistence to paraelectric phase is observed, alongside a rapid miniaturized and eventually disappeared domains with increasing stannum doping. This evolution in phase structure and domain configuration induces a nearly vanishing polarization anisotropy and low domain wall energy, facilitating easy polarization rotation and domain wall motion, thereby significantly contributing to the extrinsic piezoelectric response. Consequently, the origins of ultrahigh performance can be attributed to the synergistic effect of stannum-induced intrinsic and extrinsic contributions in barium titanate-based ceramics. This study provides fundamental insights into the role of doping elements and offers guidance for the design of high-performance piezoelectrics.

Phase transitions in typical fluorite-type ferroelectrics

While ferroelectric hafnia (HfO2) has become a technically important material for microelectronics, the physical origin of its ferroelectricity remains poorly understood. The tetragonal P42/nmc phase is commonly assigned as its paraelectric mother phase but has no soft mode at the Brillouin zone center. In this work, we propose that the paraelectric—ferroelectric transition in the fluorite-type Pca21 ferroelectric family can be described by a Pcca—Pca21 transition, where the Pcca mother phase will evolve into either the Pca21 ferroelectric phase or the centrosymmetric P21/c monoclinic phase, depending on the strain conditions. The Pcca phase is directly linked to both phases in the context of continuous phase transition. Hafnia is regarded as a special case of this family in that it has accidental atomic degeneracy because all anions are oxygen. The theory is also correlated with the seven-coordination theory that explains the ferroelectricity in hafnia from a chemical perspective. In addition, the strain conditions to promote the ferroelectric phase in hafnia are discussed.

An investigation of the structure property relation of Na2MnWO6 for device application

This communication delves into the structural, microstructural, dielectric, impedance, modulus, and optical properties of the double-perovskite ceramic Na2MnWO6. Our X-ray diffraction study revealed a multiphase crystal structure in this ceramic, a result of high-temperature mixed-oxide synthesis. Morphological studies indicated a nearly uniform grain scattering and distribution with minimal spaces. The Maxwell-Wagner model, by addressing alternative polarisation mechanisms, studied the frequency-dependent dielectric properties. Our study of temperature-dependent dielectric permittivity identified a ferroelectric to paraelectric phase transition dielectric aberration. The material’s NTCR characteristic was determined using impedance analysis. Jonscher’s power law showed that the conduction mechanism follows the overlapping of large polaron tunnelling and correlated barrier hopping models, establishing the link between conductivity and frequency. Relaxation and conduction activation energies support electron hopping. UV spectroscopy revealed a band gap of 4.01 eV, and temperature-dependent resistance studies suggest a potential use in thermistors with due parameters. These findings significantly enhance our understanding of NMWO, paving the way for its potential uses in electronics and optics, owing to its unique structural, electrical, and optical features.

Growth of Single Crystals of (K1-xNax)NbO3 by the Self-Flux Method and Characterization of Their Phase Transitions.

In this study, single crystals of (K1-xNax)NbO3 are grown by the self-flux crystal growth method and their phase transitions are studied using a combination of Raman scattering and impedance spectroscopy. X-ray diffraction shows that single crystals have a perovskite structure with monoclinic symmetry. Single crystal X-ray diffraction shows that single crystals have monoclinic symmetry at room temperature with space group P1211. Electron probe microanalysis shows that single crystals are Na-rich and A-site deficient. Temperature-controlled Raman scattering shows that low temperature monoclinic-monoclinic, monoclinic-tetragonal and tetragonal-cubic phase transitions take place at -20 °C, 220 °C and 440 °C. Dielectric property measurements show that single crystals behave as a normal ferroelectric material. Relative or inverse relative permittivity peaks at ~-10 °C, ~230 °C and ~450 °C with hysteresis correspond to the low temperature monoclinic-monoclinic, monoclinic-tetragonal and tetragonal-cubic phase transitions, respectively, consistent with the Raman scattering results. A conduction mechanism with activation energies of about 0.5-0.7 eV was found in the paraelectric phase. Single crystals show polarization-electric field hysteresis loops of a lossy normal ferroelectric. The combination of Raman scattering and impedance spectroscopy is effective in determining the phase transition temperatures of (K1-xNax)NbO3.

Tadpole-Like Polar Molecule Encapsulated in a Two-in-One Supramolecular Cage: Molecular Motion, Phase Transition and Ferroelectricity.

Molecule-inclusive closed cage compounds present a unique platform for molecular motion in an isolated environment. This study showcases the incorporation of a tadpole-like polar molecule (1-propyl-1H-imidazole, PIm) into a supramolecular cage formed by duad semicage p-tert-butylcalix[4]arene. The ferroelectric phase transition as well as the cage-confined motion of encapsulated PIm was studied in detail. The unusual quadrastable state of the PIm in the paraelectric phase allows for the modulation of dipolar polarization over a broad temperature/frequency range. This compound represents the first example of a clathrate molecular ferroelectric featuring a molecule-inclusive supramolecular cage, and it also contributes to the understanding of cage-confined molecular dynamics.

Technology and Dielectric Properties of BLT4 Ceramics Modified with Special Glass

Lead-boron special glass was doped into Ba0.996La0.004Ti0.999O3 (BLT4) ceramics in order to control the sintering process and grain growth, consequently obtaining materials with a well-developed microstructure. Changes in the microstructure resulted in a significant decrease in electrical permittivity along with a substantial increase in its frequency dispersion. Glass-doped ceramics, similar to pure BLT4, are characterized by a first-order phase transition from the ferroelectric phase to the paraelectric phase. The temperature of this transition shifts slightly towards higher values with the increase in glass dopant concentration.

Study on the effects caused by defect LaK in KH2PO4 crystal

Based on first-principles calculations, we have investigated the effects of different charged states of LaK on the defect formation energies (DFE), lattice distortions, electronic structures, and optical properties of paraelectric phase (PE-KDP) and ferroelectrical phase (FE-KDP) crystals. Our calculations indicate that LaK·· is readily formed in both crystal structures, and the degree of H–O bond distortion is more pronounced in PE-KDP. This could explain the formation of small growth mounds on the surface of La-doped crystals observed in the experiments, as well as the large decrease in the hardness of La-doped crystals. Furthermore, the band gap value of La-doped crystals is smaller than that of perfect crystals. This can be attributed to the fact that the 5d orbitals of La affect the 2p orbitals of O located in the conduction band minimum (CBM), resulting in a splitting of the energy levels and the formation of a defective energy level that enters the forbidden band. The optical spectra have been obtained considering the electron-phonon coupling. Large stokes redshift and nonradiative jump will lower the crystal laser damage threshold. The La-doped PE-KDP has an absorption band at 3.03 eV (409 nm) in good agreement with the experimentally observed absorption band at 390 nm.

Two types of cubic components coexisting in the paraelectric phase of relaxor ferroelectric Pb(Mg1/3Nb2/3)O3 revealed by synchrotron radiation X-ray diffraction

The crystal structures of relaxor ferroelectric Pb(Mg1/3Nb2/3)O3 (PMN) have been investigated using synchrotron radiation X-ray powder diffraction. Two different types of cubic components coexist in the paraelectric phase at 600 K. The first is Cubic-I, in which the Pb ion is isotropically off-centered from the corner of the perovskite-type unit cell. The other, Cubic-II, has the Pb ion preferentially off-centered in the <111> directions from the corner. The volume fractions of Cubic-I and Cubic-II are approximately 83% and 17%, respectively. Previous studies have shown that only approximately 20% of PMN transitions to a rhombohedral structure at 100 K. This observation suggests a close relationship between Cubic-II and the rhombohedral structure at low temperatures. The intrinsic structural inhomogeneity observed in the paraelectric phase, such as variations in the disordering behavior of Pb ions, is potentially linked to the relaxor characteristics of PMN.

Unveiling a giant electrocaloric effect at low electric fields through continuous phase transition design

The reported electrocaloric (EC) effect in ferroelectrics is poised for application in the next generation of solid-state refrigeration technology, exhibiting substantial developmental potential. This study introduces a novel and efficient EC effect strategy in (1–x)Pb(Lu1/2Nb1/2)O3-xPbTiO3 (PLN-xPT) ceramics for low electric-field-driven devices. Phase-field simulations provide fundamental insights into thermally induced continuous phase transitions, guiding subsequent experimental investigations. A comprehensive composition/temperature-driven phase evolution diagram is constructed, elucidating the sequential transformation from ferroelectric (FE) to antiferroelectric (AFE) and finally to paraelectric (PE) phases for x=0.10−0.18 components. Direct measurements of EC performance highlight x=0.16 as an outstanding performer, exhibiting remarkable properties, including an adiabatic temperature change (ΔT) of 3.03 ​K, EC strength (ΔT/ΔE) of 0.08 ​K ​cm kV−1, and a temperature span (Tspan) of 31 ​°C. The superior EC effect performance is attributed to the temperature-induced FE to AFE transition at low electric fields and diffusion phase transition behavior contributing to the wide Tspan. This work provides valuable insights into developing high-performance EC effect across broad temperature ranges through the strategic design of continuous phase transitions, offering a simplified and economical approach for advancing ecofriendly and efficient solid-state cooling technologies.

Exploring the structural characteristics and electrical conductivity of MnTiO3 across ferroelectric and paraelectric phases

In this study, we present the ceramic's structural, dielectric, and impedance characteristics obtained through the solid-state reaction method synthesis. Initial structural analysis was conducted utilizing X-ray diffraction at room temperature. The XRD results show that MnTiO3 exhibits rhombohedral symmetry. SEM images of MnTiO3 show the presence of both cubic and large agglomerated grains. This demonstrates the effectiveness of the dielectric HN model in controlling the mechanism. The alternating current (ac) conductivity, when examined in relation to frequency, displays a remarkable adherence to the Johnscher's power law. The change in electrical modulus and the width at half maximum (FWHM) of the curve indicate that the as-prepared sample exhibits a non-Debye relaxation mechanism. Both the temperature data and the frequency dependence of the impedance were used to analyze the electrical conductivity of the sample, which showed a negative temperature coefficient resistance (NTCR).

The electronic and optical properties of Al interstitial defects in KH2PO4 crystal: First principles study

KH2PO4 (KDP) crystals are widely used as frequency multipliers in inertial confinement controlled fusion ignition devices. The electronic and optical properties of KDP crystals with Al interstitial defects based on first principles are investigated. The results show that neutral and +3 charged Al interstitial can exist stably in the crystal. The +3 charged defect produces a larger lattice distortion. Bond length varies from −18.78 % to 43.71 % in the paraelectric phase(P-KDP) and from −25.57 % to 66.09 % in the ferroelectric phase (F-KDP). At the same time, +3 charged Al interstitial may also cause HO bond to break, resulting in the generation of H interstitials, which may compensate for the H vacancies in as-grown KDP. This may make the laser damage threshold slightly increase when KDP crystal is doped with +3 charged Al ion at low concentration. The optical spectra of Al interstitial are calculated, and the results show that in the paraelectric and ferroelectric phases, the optical transition of Al ions generally produces a large lattice relaxation energy, such as the lattice relaxation energy of up to 4.00 eV in the +2 to +3 charged defect transition in the paraelectric phase. This shows that the optical transition of Al interstitial will cause serious damage to the crystal. In the paraelectric phase, the absorption peaks of optical transitions found in the ultraviolet and visible regions are consistent with experiments. The absorption peak of the +1 to +2 charged defect transition is at 260 nm, which is very close to the absorption peak at 270 nm measured by experiments. The analysis of the Huang-Rys factors and transition displacement further confirms the conclusion that the optical transition of the defect charged state will cause serious crystal damage.

Lattice match between coexisting cubic and tetragonal phases in PMN-PT at the phase transition

(1−x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-PT) perovskite-like solid solutions are recognized for their outstanding electromechanical properties, which are of technological importance. However, some significant aspects of the crystal structures and domain assemblages in this system and the role of these characteristics in defining the functional performance of PMN-PT remain uncertain. Here, we used synchrotron x-ray diffraction to investigate the phase transition linking the paraelectric (cubic) and ferroelectric (tetragonal) phases in a single crystal of 0.65PMN-0.35PT. We analyzed the evolution of reciprocal-space maps across this transition. These maps were collected using small temperature step (1 K) and a high reciprocal-space resolution to reveal changes in the splitting of Bragg peaks caused by the formation of ferroelastic domains in the low-symmetry phase. Our results uncovered a two-phase state, cubic plus tetragonal phases, which exists over a narrow temperature range of only ≈4 K and exhibits a thermal hysteresis of ≈1.8 K. Remarkably, within this state, the lattice parameter of the cubic phase, aC, matches the orientational average of the lattice parameters for the tetragonal polymorph, 23aT+13cT. We discuss the implications of this matching, highlighting the possibility of it being realized by the formation of an assemblage of tetragonal twin domains separated from the cubic phase by a strain-free {110} boundary, as in the “adaptive phase” but without domain miniaturization.

Atomic-Scale Tracking Topological Phase Transition Dynamics of Polar Vortex-Antivortex Pairs.

Non-trivial topological structures, such as vortex-antivortex (V-AV) pairs, have garnered significant attention in the field of condensed matter physics. However, the detailed topological phase transition dynamics of V-AV pairs, encompassing behaviors like self-annihilation, motion, and dissociation, have remained elusive in real space. Here, polar V-AV pairs are employed as a model system, and their transition pathways are tracked with atomic-scale resolution, facilitated by in situ (scanning) transmission electron microscopy and phase field simulations. This investigation reveals that polar vortices and antivortices can stably coexist as bound pairs at room temperature, and their polarization decreases with heating. No dissociation behavior is observed between the V-AV phase at room temperature and the paraelectric phase at high temperature. However, the application of electric fields can promote the approach of vortex and antivortex cores, ultimately leading to their annihilation near the interface. Revealing the transition process mediated by polar V-AV pairs at the atomic scale, particularly the role of polar antivortex, provides new insights into understanding the topological phases of matter and their topological phase transitions. Moreover, the detailed exploration of the dynamics of polar V-AV pairs under thermal and electrical fields lays a solid foundation for their potential applications in electronic devices.