Relaxor Ferroelectric Behavior Research Articles

Charge glass in an extended dimer Hubbard model

The charge degrees of freedom in several different organic charge transfer salts display slow or glassy dynamics. In order to gain insight into this behaviour, we obtain the low energy theory for an extended dimer Hubbard model, taking into account the occupations of sites on neighbouring dimers. We take a classical limit of the resulting effective model of coupled spins and dimers and study it using classical Monte Carlo simulations. We find that frustration induced by intra- and inter-dimer interactions leads to glassiness in the charge degress of freedom in the absence of ordering of the spin degrees of freedom. Our results may have relevance to experimental observations of relaxor ferroelectric behaviour in the dynamics of organic charge transfer salts.

High dielectric constant, relaxor behavior and phase transitions in Na0.5Bi0.5TiO3 nanorods

We report on relaxor-ferroelectric behavior, ferroelectric to anti-ferroelectric transition and superior dielectric properties of Na0.5Bi0.5TiO3 nanorods synthesized through hydrothermal technique. Na0.5Bi0.5TiO3 nanorods are seen to crystallize in rhombohedral crystal structure. Ferroelectric to anti-ferroelectric transition is observed at 450 K, where the dielectric loss attains its maximum value. Maxwell-Wagner interfacial polarization causes the dielectric constant to be high at room temperature (9 × 105). Dielectric loss at low frequencies is observed to be minimum. Non-Debye relaxation process in Na0.5Bi0.5TiO3 nanorods are clearly seen from the frequency and temperature dependent dielectric studies. Jonscher's relation is employed to analyze the frequency dependent conductivity at various temperatures and the activation energy (Ea) value is observed to be 0.48 ± 0.02 eV. Structural-oxygen vacancy defect-dielectric property correlation is established through a detailed dielectric property analysis in Na0.5Bi0.5TiO3 nanorods.

Compositional-induced structural transformation and relaxor ferroelectric behavior in Sr/Nb-modified Bi4Ti3O12 Aurivillius ceramics

This study reports the synthesis of Sr/Nb-modified Bi4Ti3O12 Aurivillius phase, SrxBi4-xTi3-xNbxO12 (x = 0, 0.5, 1, 1.5, and 2) for lead-free relaxor ferroelectric materials using the molten-salt method. The effects of cation substitution (x content) on the structure, morphology, electrical and optical properties was investigated. X-ray diffraction and dielectric measurements revealed that the phase structures of the parent compound Bi4Ti3O12 (x = 0) experienced a gradual transformation from the orthorhombic B2cb phase to the tetragonal I4/mmm phase, for x = 1.5 and 2. Upon increasing the x content, the Curie-Weiss temperature (Tc) and dielectric constant decreased, which are explained in terms of reducing the structural distortion of orthorhombic structure. The cation substitution induced the A- and B-site cation disorder and intensified diffusion and relaxor-ferroelectric behavior. These findings will provide significant impetus for further research on relaxor ferroelectric Aurivillius phases.

Enhanced energy storage performance of BaTi0.97Ca0.03O2.97-based ceramics by doping high-entropy perovskite oxide

To improve the comprehensive energy storage performance of the BaTi0.97Ca0.03O2.97-based ceramics for pulse power capacitors, a typical bismuth-based high entropy compound, Bi(Li0.2Y0.2Mg0.2Ti0.2Ta0.2)O3 (BLYMTT) was introduced into 0.9Ba(Ti0.97Ca0.03)O3-0.1Bi0.55Na0.45TiO3 (0.9BTC-0.1BNT) matrix. The results indicate that the phase structure transforms from tetragonal phase to pseudo-cubic phase with increasing BLYMTT, and the relaxor ferroelectric behavior are also enhanced. The 0.91(0.9BTC-0.1BNT)-0.09BLYMTT ceramic simultaneously achieves a high energy storage density of 4.89 J/cm3 and efficiency of 91.2% at electric field of 240 kV/cm. Moreover, the 0.91(0.9BTC-0.1BNT)-0.09BLYMTT ceramic also exhibits superior temperature (30–100 ℃) and frequency (1–100 Hz) stability, as well as the ultrahigh power density of PD~66.01 MW/cm3 and rapid discharge rate of t0.9~97 ns at 140 kV/cm, which is of great potential for energy storage application.

Lead-Free Aurivillius Phase Bi2LaNb1.5Mn0.5O9: Structure, Ferroelectric, Magnetic, and Magnetodielectric Effects.

Aurivillius phase Bi2LaNb1.5Mn0.5O9, derived from ferroelectric PbBi2Nb2O9 by simultaneous substitution of the A-site and B-site cations, was synthesized using a molten-salt method. Here, we discuss the structure-property relationships in detail. X-ray and neutron diffraction show that Bi2LaNb1.5Mn0.5O9 adopts an A21am orthorhombic crystal structure. Rietveld refinement analysis, supported by Raman spectroscopy, indicates that the Bi3+ ions occupy the bismuth oxide blocks, La3+ ions occupy the perovskite A-site, and Nb5+/Mn3+ ions occupy the perovskite B-site. Ferroelectric ordering takes place at 535 K, which coexists with local ferromagnetic order below 65 K. The cation disorder on the B-site results in relaxor-ferroelectric behavior, and the short-range ferromagnetic order can be attributed to Mn3+/Mn4+ double-exchange. Magnetodielectric coupling measured at 5 K and 100 kHz in a field of 5 T suggests the existence of intrinsic spin-lattice coupling with a magnetodielectric coefficient of 0.20%. These findings will provide significant impetus for further research into potential devices based on the magnetodielectric effect in Aurivillius materials.

The Evolution of Phase, Microstructure and Electrical Properties of BZT–BCT–BLT Ceramic

(1 – x)[0.50Ba(Zr0.20Ti0.80)O3–0.50(Ba0.70Ca0.30)TiO3] – xBi0.50Li0.50TiO3 with x = 0, 0.02, 0.04, 0.06, 0.08 and 0.10 wt.% were prepared by a solid-state reaction method. The phase structure, microstructure, dielectric, ferroelectric and energy density properties of BZT–BCT–xBLT ceramics were investigated. The phase structure of the samples showed coexist phases between orthorhombic and tetragonal morphotropic phase boundary (MPB). The grain size morphology decreased with increased of x(BLT) contents. The diffuseness coefficient (γ) of ceramics are between 1.40 and 1.68, which showed the relaxor ferroelectric behavior in all the samples. The dielectric constant (εr ∼ 12,697) at 1 kHz can be improve with increased of x(BLT) = 0.02 wt.%. The highest recoverable energy-storage density (W rec= 0.069 J/cm3) with an excellent energy storage efficiency (η = 95.8%) under lower electric field of 20 kV/cm were found in the composition of x = 0.08 wt.%).

The Relationship of Phase Structure, Microstructure and Electrical Properties of BNT-BT-BST Ceramic

(0.935-x)Bi0.5Na0.5TiO3-0.065BaTiO3-xBa(Sn0.1Ti0.9O3) ceramics with x(BST) = 0, 0.01, 0.03, 0.05, 0.07, 0.10, and 0.15 wt.% were prepared by a solid-state reaction method. The phase structure, microstructure, dielectric, ferroelectric and energy storage properties analysis of BNT-BT-x(BST) ceramics were also studied. The phase structures of BNT-BT-x(BST) ceramics with difference of x(BST) contents were characterized by X-ray diffraction method (XRD). It was found that the samples showed coexistent phases between rhombohedral and tetragonal morphotropic phase boundary (MPB). The grain growth is inhibited with increase of x(BST) contents, which showed the average gain size decreased from 0.94 to 0.63 µm. The phase transition with the first anomaly temperature at the lower temperature (T FA) gradually decreased from 160 to 74 °C, and then tend to increase from 74 to 151 °C. Meanwhile, the second broad dielectric constant peak at higher temperature (T SA) tended to increase first, and then decrease from 307 to 281 °C. Both T FA and T SA exhibit an obvious dependence on the frequency, which showed the relaxor ferroelectric behavior. The highest density (ρ = 5.79 ± 0.15 g/cm3), recoverable energy storage density (W rec= 0.28 J/cm3) and energy storage efficiency (η = 53.85%) and the piezoelectric coefficient (d 33*= 450 pm/V.) was found in the composition of x(BST) = 0.05 wt.%.

Ferroelectric and photoelectrochemical studies of lead-free Ba0.925Bi0.05 □0.025(Ti0.65Zr0.30Sn0.05)O3 ceramic and its application to Rhodamine B oxidation under solar light

New materials with general formula Ba 0.925 Bi 0.05 □ 0.025 (Ti 0.65 Zr 0.30 Sn 0.05 )O 3 (symbolized BBiTZS) were prepared by high-temperature solid-state reaction. The room X-ray diffraction pattern suggests a cubic perovskite structure. The thermal variation of the permittivity at different frequencies showed a relaxor ferroelectric behavior. The Raman spectroscopy was in accordance of the dielectric measurements. The diffuse phase transition parameters were determined from the modified Curie–Weiss law, while the relaxor behavior was highlighted by a good fit to the Vogel–Filcher relationship. The capacitance-potential ( C sc −2 − E ) graph at pH ∼ 7 is characteristic of n -type behavior with a flat band potential ( E fb ) of −0.52 V SCE and an electron density ( N A ) of 2.7 × 10 18 cm −3 . The Electrochemical Impedance Spectroscopy, measured in the region (1 mHz - 10 5 Hz), showed a semicircle, assigned with the bulk property (27 kΩ cm 2 ); a constant phase element (CPE) is responsible for the depletion angle (−9°). With an optical of 2.00 eV, the ferroelectric BBiTZS possesses appealing photocatalytic capability and was successfully experimented for the oxidation of Rhodamine B (Rh B) exposed to solar light. According to the band diagram, electrons from the conduction band of BBiTZS are injected into dissolved oxygen, resulting in O 2 radicals, which are employed in the Rh B oxidation. UV–Visible spectrophotometry was used to follow the Rh B discoloration. On a solar irradiation of 97 mW cm −2 , a conversion of 50% is achieved in Rh B solution (10 mg L −1 ) within 100 min., and the degradation follows a first order kinetic model with a half photocatalytic-life of 90 min.

Structure and relaxor ferroelectric behavior of the novel tungsten bronze type ceramic Sr5BiTi3Nb7O30

This paper reports a novel lead-free tungsten bronze type ceramic, Sr5BiTi3Nb7O30, prepared by a conventional high-temperature solid-state reaction route. The crystal structure identified using synchrotron x-ray diffraction data and Raman spectroscopy for Sr5BiTi3Nb7O30 could be described as an average structure with the centrosymmetric space group P4/mbm and a local non-centrosymmetric structure at room temperature. In the second-harmonic generation measurement, the Sr5BiTi3Nb7O30 compound exhibits second-order nonlinear optical behavior, which suggests the material is ferroelectric. Temperature dependence of the dielectric permittivity indicates that the dielectric anomaly in Sr5BiTi3Nb7O30, associated with the disorder on the A and B sites, results in strong frequency dispersion with a low phase-transition temperature. A macroscopic and phenomenological statistical model was employed to describe the temperature dependence of the dielectric responses of Sr5BiTi3Nb7O30 and Sr6Ti2Nb8O30. The calculated sizes of polar nanoregions for both compounds imply structural disorder induced by A and B sites, giving rise to a more diffuse ferroelectric transition for Sr5BiTi3Nb7O30. The smaller polar nanoregions with smaller electrical dipole moments can be activated at lower temperatures, leading to Sr5BiTi3Nb7O30 having a lower Tm (∼260 K) than other tungsten bronze type ferroelectrics. This work charts a promising feasible route to the development of improved relaxor ferroelectrics in tungsten bronze type oxides.

Relaxor ferroelectric and dielectric properties of (1–x)Ba(Zr0.1Ti0.9)O3–xBa(Mg1/3Ta2/3)O3 ceramics

The environmentally-friendly (1–x)Ba(Zr0.1Ti0.9)O3–xBa(Mg1/3Ta2/3)O3 (x=0, 0.02, 0.04, 0.06, 0.08) relaxor ferroelectric ceramics were prepared by the conventional solid-state method and sintered in air at 1400 °C for 2 h. SEM and XRD analyses were utilized to study the surface morphologies and the crystalline structures, respectively. The effects of Ba(Mg1/3Ta2/3)O3 on the phase transformation, dielectric and ferroelectric properties of Ba(Zr0.1Ti0.9)O3 ceramics were also investigated. It is found that the average grain size of (1–x)Ba(Zr0.1Ti0.9)O3–xBa(Mg1/3Ta2/3)O3 (BZT–BMT) perovskite single-phase ceramics decreases as the content of Ba(Mg1/3Ta2/3)O3 (BMT) increases. The relaxor ferroelectric behavior with diffuse phase transition and well-defined frequency dispersion of dielectric maximum temperature is found for the ceramic with increasing x values. 0.98BZT–0.02BMT ceramic shows very good dielectric properties with the relative permittivity and the dielectric loss, measured at 100 kHz as 6034 and 0.01399 respectively at room temperature. Both remnant polarization and coercive field decreased with increasing BMT content, indicating a transition from the ferroelectric phase to the paraelectric phase at room temperature.

Phase transformations in an Aurivillius layer structured ferroelectric designed using the high entropy concept

A single phase four-layer Aurivillius structured ferroelectric ceramic, (Ca0.2Sr0.2Ba0.2Pb0.2Nd0.1Na0.1)Bi4Ti4O15 (6ABTO) was obtained using a high entropy design concept. The material, which has orthorhombic symmetry in space group A21am at room temperature, has Ca2+, Sr2+, Ba2+, Pb2+, Nd3+ and Na+ distributed not only on the A sites of the perovskite layer but also in the bismuthate layer. 6ABTO shows complex ferroelectric behavior, with a Curie point of 557 °C. Four current peaks are observed in the current - electric field curve. These peaks are attributed to a combination of a field induced phase transition and domain wall switching, which is the first reported occurrence of such current - electric field behavior for an Aurivillius structured ferroelectric material. Despite the level of disorder between the A site cations in the perovskite layer and the Bi positions in the bismuthate layer, 6ABTO does not show the relaxor ferroelectric behavior, that is commonly observed in cases of such disorder. This suggests that relaxor behavior in ferroelectrics, may be more associated with the thermal stability of dipoles, rather than the presence of polar nano-regions formed as a result of chemical disorder. The nature of the high entropy effect in 6ABTO is discussed through comparison of results from isostructural compositions containing 5, 4 and 3 of the component cations

Exploring the energy storage density in 60Bi2O3–10SrO-30Fe2O3 lead-free relaxor glass for designing energy storage devices

Strontium doped glass was synthesized by the conventional melt-quenching technique. Systematically measured dielectric properties revealed relaxor ferroelectric-like behavior in a broad range of frequency and temperature. The glassy nature of the present sample was investigated by X-ray diffraction (XRD) measurements. glass transition temperature, crystallization temperatures and melting temperature are determined by differential thermal analysis (DTA). The low frequency Raman spectra displays a Boson peak at 72 cm−1, which confirms polar clusters (PCs) formation. The present sample depicts a wide as well as diffuse peak of dielectric permittivity ε'(ω) and tangent loss tan δ. wide as well as diffuse peak shifted to the higher temperatures (from 538 K to 553 K), a typical relaxor behavior is indicated by this type of diffuse transition. The presence of polar clusters (PCs) imbedded in the glass matrix indicates the presence of relaxor ferroelectric (RFE) behavior in this glass. The measured energy storage density of the strontium doped glass was 4 mJ.cm−3 with efficiency of 70% under an applied electric field of 17 kV.cm−1 at room temperature. Magnetic properties via vibrating-sample magnetometer (VSM) show a typical anti-ferromagnetic behavior. These results depict that the present glass can be regarded a promising candidate for designing energy storage devices.

Random-field critical scaling in a model of dipolar glass and relaxor ferroelectric behavior.

Heat-bath Monte Carlo simulations have been used to study a 12-state discretized Heisenberg model with a type of random field on simple cubic lattices of size 128×128×128. The 12 states correspond to the [110] directions of a cube. The model has the standard nonrandom two-spin exchange term with coupling energy J and a random field which consists of adding an energy h_{R} to two of the 12 spin states, chosen randomly and independently at each site. We report on the case h_{R}/J=3, which has a sharp phase transition at about T_{c}/J=1.40625. Below T_{c}, the model has long-range ferroelectric order oriented along one of the eight [111] directions. At T_{c}, the behavior of the peak in the structure factor, S(k), at small |k| is a straight line on a log-log plot, which gives the result η[over ¯]=1.214±0.014. The onset of orientational order below T_{c} is very rapid for this value of h_{R}. There are peaks in the specific heat and longitudinal susceptibility at T_{c}. Below T_{c} there is a strong correction to ordinary scaling, which is probably caused by the cubic anisotropy, which is a dangerous irrelevant variable.

Dielectric and ferroelectric properties of modified-BaTiO3 lead-free ceramics prepared by solid solution method

Barium titanate (BaTiO3) has been recognized as an important perovskite ceramic since its discovery due to its excellent dielectric, ferroelectric and piezoelectric properties. Its modifications have been studied in many perspectives depending on applications. In this review, the basic principles of BaTiO3 were described, then followed by the explanation on the recent modifications of BaTiO3 to improve the dielectric properties. Relaxor ferroelectric behavior of BaTiO3 was revealed by combining BaTiO3 with other Bi-based perovskites. These modified- BaTiO3 opened the opportunities for emerging energy storage applications. Next, the modifications for ferroelectric and ferromagnetic aspects were further discussed. BaTiO3 can also be doped by other ions to enhance such properties. Solid solution between Bi-based perovskites such as BiFeO3, (Bi0.5K0.5)TiO3, or Bi(Zn0.5Ti0.5)O3 and BaTiO3 can also improve ferroelectric and ferromagnetic properties. Therefore, these details of recent BaTiO3 modifications may provide guidance for the next BaTiO3 investigations in order to gain the maximum benefits from BaTiO3.

Сегнетоэлектрические полимеры с улучшенными характеристиками

This article offers a short overview of the unique properties of PVDF-based electroactive polymers and their applications. Ferroelectric materials are widely used in modern electronics. Relaxor-ferroelectric terpolymers are multifunctional materials with high electrostrictive strain which, in turn, leads to large actuation capability. The terpolymer with clorofluoroethylene shows relaxor-ferroelectric behavior with vanishing hysteresis effect but considerably higher polarization. Therefore, such material is a potential candidate for energy-storage devices (supercapacitors).

Tailoring dielectric performance of P(VDF-CTFE) via incorporating thiophenol as a side chain

Poly(vinylidene fluoride) (PVDF) based fluoropolymers are typical ferroelectric polymers, and the large energy loss seriously hinders their applications for electric energy storage. To reduce the high dielectric loss induced by the polarization of ferroelectric phase, in this work, a series of P(VDF-DB)-graft-thiophenol copolymers (DB refers to CFCH double bond) are successfully synthesized under mild conditions using nucleophilic substitution reaction. The merits including the excellent miscibility of thiophenol with P(VDF-DB), and the promising insulating property of thiophenol segments are combined in the resulting copolymers. The results show that the relaxor ferroelectric behavior of P(VDF-DB) copolymer is effectively converted into linear-like dielectric by introducing a relatively low content of thiophenol. Meanwhile, the dielectric loss is significantly reduced, showing better dielectric energy storage performance than that of the pristine copolymer. This work provides a facile strategy for chemical modification and regulating the dielectric behavior of PVDF-based ferroelectric fluoropolymers.

Tetramethylbenzidine–TetrafluoroTCNQ (TMB–TCNQF4): A Narrow-Gap Semiconducting Salt with Room-Temperature Relaxor Ferroelectric Behavior

We present an extension and revision of the spectroscopic and structural data of the mixed stack charge transfer (CT) crystal 3,3$^\prime$,5,5$^\prime$-tetramethylbenzidine--tetrafluoro-tetracyanoquinodimethane (TMB-TCNQF4), associated with new electric and dielectric measurements. Refinement of syncrotron structural data at low temperature has led to revise the previously reported [Phys. Rev. Mat. 2, 024602 (2018)] $C2/m$ structure. The revised structure is $P2_1/m$, with two dimerized stacks per unit cell, and is consistent with the vibrational data. However, polarized Raman data in the low-frequency region also indicate that by increasing temperature above 200 K the structure presents an increasing degree of disorder mainly along the stack axis. X-ray diffraction data at room temperature have confirmed that the correct structure is $P2_1/m$ -- no phase transitions -- but did not allow to definitely substantiate the presence of disorder. On the other hand, dielectric measurement have evidenced a typical relaxor ferroelectric behavior already at room temperature, with a peak in real part of dielectric constant $\epsilon'(T,\nu)$ around 200 K and 0.1 Hz. The relaxor behavior is explained in terms of the presence of spin solitons separating domains of opposite polarity that yield to ferroelectric nanodomains. TMB-TCNQF4 is confirmed to be a narrow gap band semiconductor ($E_a \sim 0.3$ eV) with room temperature conductivity of $\sim 10^{-4}~ \Omega^{-1}$ cm$^{-1}$.

Structure, microstructure, dielectric and piezoelectric properties of (1−x–y)BiFeO3–xPbFe0.5Nb0.5O3–yPbTiO3 ceramics

Ceramics of quasi-binary concentration section ([Formula: see text] = 0.50, 0.1 [Formula: see text] 0.2, [Formula: see text] = 0.025) of the ternary solid solution system (1[Formula: see text]BiFeO3–[Formula: see text][Formula: see text][Formula: see text]O3–[Formula: see text]PbTiO3 were prepared by the conventional solid-phase reaction method. By using X-ray diffraction technique, the phase diagram of the system was constructed, which was shown to contain the regions of cubic and tetragonal symmetry and the morphotropic phase boundary between them. Grain morphology, dielectric and piezoelectric properties of the selected solid solutions were investigated. The highest piezoelectric coefficient [Formula: see text]= 260 pC/N was obtained. Dielectric characteristics of ceramics revealed ferroelectric relaxor behavior, a region of diffuse phase transition from the paraelectric to ferroelectric phase in the temperature range of 350–500 K.

Frequency and temperature dependent electric polarization, relaxation, and transport properties of Mo and W doped BaTiO3

In this article, we report the structural, dielectric, electronic, and transport properties of Mo and W doped BaTiO3 ceramic. The BaTiO3 (BTO), BaTi0.85Mo0.15O3 (BTMO), and BaTi0.85W0.15O3 (BTWO) samples were prepared by double sintering ceramic technique. The X-ray diffraction patterns confirmed the tetragonal phase of the perovskite structure with the P4mm space group including some extra phases in BTMO and BTWO. A relaxation peak in the real part of electric modulus M'' is observed for BTO and BTMO at 3kHz. The dielectric constants, (εr' , εr'') and loss tangent (tanδ) for all samples were measured from 300 K to 450 K under the application of 100kHz electric field and temperature dependent dielectric anomalies ensure a ferroelectric (tetragonal) to paraelectric (cubic) phase transition in all samples. BTO and BTMO crystals display between normal ferroelectric and ideal relaxor behavior while BTWO crystal approaches to ideal relaxor ferroelectric behavior identified as canonical relaxor. Moreover, solid–liquid state anisotropy during the phase transition in all samples has been illustrated in terms of Fröhlich entropy. Apart from this, in BTO and BTWO samples, the conduction mechanism is highly dominated by the frequency of applied field compared to BTMO sample. Moreover, all studied samples exhibit semiconducting behavior with positive temperature coefficient of resistance (PTCR) effect in between 300 K and 450 K. The BTMO sample with maximum PTCR peak (2.9%/K at 415K) may find suitability for temperature controlled device application.

Synthesis, structural characterization and functional properties of Sr0.5Ba0.5Nb2−xFexO6 ceramic powders

Sr0.5Ba0.5Nb2-xFexO6 (SBNF) ceramic powders for x=0.00, x=0.02 and x=0.03 were synthesized using coprecipitation method. The structure of the SBNF single phase with x=0.02 was identified by X-ray diffraction and Rietveld refinement; the morphology and size of the particles were observed by TEM and SEM-EDS microscopy. Electrical characterization showed that Fe doping did not cancel the typical ferroelectric relaxor behavior and magnetic characterization showed a weak ferromagnetic response, which suggest that the samples obtained can be considered as multiferroic.