Polarization Hysteresis Research Articles

Voltage controlled N\xe9el vector rotation in zero magnetic field

Multi-functional thin films of boron (B) doped Cr2O3 exhibit voltage-controlled and nonvolatile Néel vector reorientation in the absence of an applied magnetic field, H. Toggling of antiferromagnetic states is demonstrated in prototype device structures at CMOS compatible temperatures between 300 and 400 K. The boundary magnetization associated with the Néel vector orientation serves as state variable which is read via magnetoresistive detection in a Pt Hall bar adjacent to the B:Cr2O3 film. Switching of the Hall voltage between zero and non-zero values implies Néel vector rotation by 90 degrees. Combined magnetometry, spin resolved inverse photoemission, electric transport and scanning probe microscopy measurements reveal B-dependent TN and resistivity enhancement, spin-canting, anisotropy reduction, dynamic polarization hysteresis and gate voltage dependent orientation of boundary magnetization. The combined effect enables H = 0, voltage controlled, nonvolatile Néel vector rotation at high-temperature. Theoretical modeling estimates switching speeds of about 100 ps making B:Cr2O3 a promising multifunctional single-phase material for energy efficient nonvolatile CMOS compatible memory applications.

Structural evolution, dielectric relaxation and modulus spectroscopic studies in Dy substituted NBT-BT ferroelectric ceramics

We report the effect of partial substitution of Dy3+ rare earth ion in NBT-BT lead free ceramics on its structural, microstructural, ferroelectric and dielectric phase transitions. The Rietveld refined X-ray diffraction analysis revealed a coexistence of dual phase with major monoclinic (Cc) along with minor tetragonal (P4mm) in all Dy-NBT-BT ceramics. The T-dependent dielectric broad band spectroscopic study revealed that Dy-substituted NBT-BT ceramics exhibits two diffuse dielectric anomalies renowned as Ferro (FE) to anti Ferro (AFE) i.e., depolarization phase transition ( $$T_{d}$$ ) and Antiferro (AFE) to paraelectric (PE) i.e., curie phase transition ( $$T_{C}$$ ), below 150 °C and well above 300 °C temperature regions respectively. The complex frequency dependent dielectric and modulus spectroscopy analysis supports the Non-Debye type dielectric relaxation process was dominated for all the measured ceramics. T-dependent AC-conductivity study revealed, thermally activated charge carries and single ionized oxygen vacancies are found to contribute conduction process at different temperature regions. Room temperature polarization hysteresis (P–E) loops analysis exposed a slim asymmetric shape with Dy substitution increasing that indicates conversion of hard to soft ferroelectric character. Remnant polarisation ( $$P_{r}$$ ) and coercive field ( $$E_{c}$$ ) decreases with dopant concentration shows the tetragonality dominance with Dy substitution. Furthermore, an optimum recoverable energy density 1.477 J/cm3 was obtained in NBT-BT at Dy = 0.03 compositions that designate the materials could be useful for future high energy storage density applications.

Origin of the Large Field-Induced Strain and Enhanced Energy Storage Response of Rare-Earth-Doped Lead-Free 0.854BNT-0.12BKT-0.026BT Ceramics.

In this study, effects of rare-earth elements such as Nd, Gd, and Ce on the structural and electrical properties of lead-free bismuth sodium potassium barium titanate Bi0.487Na0.427K0.06Ba0.026TiO3 (0.854BNT-0.12BKT-0.026BT) (BNKBT) ceramics have been investigated in detail. Solid-state reaction method was used to prepare undoped, 1.0 mol% Nd, 1.0 mol% Gd, 1.0 mol%, 2.1 mol%, and 2.7 mol% Ce-doped BNKBT ceramic powder compositions. A pure single perovskite structure was observed in the X-ray diffraction (XRD) patterns for all the BNKBT ceramic systems, although doping was found to cause changes in peak splitting and peak positions due to their site preference. The Curie temperatures have not shifted significantly with doping, but the relative permittivity values were found to have increased. The nonergodic normal ferroelectric character of undoped BNKBT ceramic switched to an ergodic relaxor character at room temperature with Nd, Gd, and Ce doping with pinched polarization vs electric field hysteresis loops. Increased field-induced strain levels were observed in the doped BNKBT ceramics with 1 mole% Ce doping yielding a giant field-induced strain of 0.38% under an E -field of 65 kV/cm. Nd-doping, on the other hand, resulted in the highest releasable energy density of 0.64 J/cm3 at 65 kV/cm. Consequently, the rare-earth-doped BNKBT ceramics were found to be promising for both digital actuator and high-energy-density capacitor applications due to their favorable electrical properties.

Evolution of electromechanical properties in Fe-doped (Pb,Sr)(Zr,Ti)O3 piezoceramics

Defects in acceptor-doped perovskite piezoelectric materials have a significant impact on their electrical properties. Herein, the defect mediated evolution of piezoelectric and ferroelectric properties of Fe-doped (Pb,Sr)(Zr,Ti)O3 (PSZT-Fe) piezoceramics with different treatments, including quenching, aging, de-aging, and poling, was investigated systematically. Oxygen vacancies with a cubic symmetry are preserved in the quenched PSZT-Fe ceramics, rendering them robust ferroelectric behaviors. In the aged PSZT-Fe polycrystals, defect dipole between Fe dopant and oxygen vacancy has the same orientation with spontaneous polarization PS, which enables the reversible domain switching and hence leads to the emergence of pinched polarization hysteresis and recoverable strain effect. And the defect dipoles can be gradually disrupted by bipolar electric field cycling, once again endowing the aged materials with representative ferroelectric properties. For the poled PSZT-Fe polycrystals, the defect dipoles are reoriented to be parallel to the applied poling field, and an internal bias field aligning along the same direction emerges simultaneously, being responsible for asymmetric hysteresis loops.

Comparing the electromechanical properties of CaTiO3‐ and BaZrO3‐modified Bi0.5Na0.5TiO3–SrTiO3 ceramics

The effects of CaTiO3 (CT) and BaZrO3 (BZ) modification upon the crystal structure and electromechanical properties of lead‐free Bi0.5Na0.5TiO3–SrTiO3 piezoelectric ceramics were compared within a doping range of 0–4 mol%. The different effects of CT and BZ modification upon the phase transition are clearly observed in the polarization and strain hysteresis loops. The CT‐modified specimens maintain strong ferroelectricity without any abnormal enhancement in the electric field‐induced strain. However, the addition of as little as 1 mol% BZ induces a transition from a nonergodic relaxor phase to an ergodic relaxor phase, thus resulting in disruption of the ferroelectric order and the generation of a high field‐induced strain. The present authors believe that the substitution of large ions (such as Zr4+) into the B‐sites, rather than the A‐sites, of the Bi0.5Na0.5TiO3‐based ceramics plays a significant role in the phase transition behavior.

Fabrication of bismuth silicate Bi2SiO5 ceramics as a potential high-temperature dielectric material

Bismuth silicate Bi2SiO5 (BSO) is known as an interesting new type of ferroelectric oxide; however, bulk ceramics of BSO have never been obtained because it easily decomposes at high temperature. In this study, we fabricated BSO ceramics for the first time using a sol–gel technique and investigated their potential as a dielectric material for high-temperature capacitor applications. A precursor powder was prepared by a sol–gel synthesis route using tetraethyl orthosilicate and bismuth nitrate pentahydrate as raw materials and then sintered under a small uniaxial pressure of 5 MPa with an addition of CH3COOLi as a sintering aid. A BSO ceramic with the highest relative density of 88.5% was obtained at a very low sintering temperature of 620 °C with preventing significant thermal decomposition. A crystal structure analysis revealed that the obtained BSO ceramic belongs to the ferroelectric monoclinic phase. The dielectric permittivity of the ceramic showed a superior temperature stability (± 5%) at temperatures up to 200 °C, followed by a sharp peak attributed to the ferroelectric–paraelectric phase transition at around 390 °C. The BSO ceramic also showed slim and pinched polarization hysteresis loops due to the random grain orientation and domain wall clamping, leading to a high energy storage efficiency over 75% at temperatures up to 100 °C.

Analysis of the Nonlinear Response of Piezo-Micromirrors with the Harmonic Balance Method

In this work, we address the simulation and testing of MEMS micromirrors with hardening and softening behaviour excited with patches of piezoelectric materials. The forces exerted by the piezoelectric patches are modelled by means of the theory of ferroelectrics developed by Landau–Devonshire and are based on the experimentally measured polarisation hysteresis loops. The large rotations experienced by the mirrors also induce geometrical nonlinearities in the formulation up to cubic order. The solution of the proposed model is performed by discretising the device geometry using the Finite Element Method, and the resulting large system of coupled differential equations is solved by means of the Harmonic Balance Method. Numerical results were validated with experimental data collected on the devices.

Rietveld refinement structure, electric, dielectric and ferroelectric properties of lead-free Ba0.985Sr0.015Zr0.10Ti0.90O3 ceramics

Ba0.985Sr0.015Zr0.10Ti0.90O3 (BSZT) compound is prepared using the standard solid-state reaction technique to explore for energy storage applications. Samples prepared from this compound are sintered at various sintering temperatures (Ts) of 1200, 1250 and 1300 °C, respectively. Influences of Ts on the structural, morphological, dielectric and ferroelectric properties are studied in detail. Rietveld refinement is used on the X-ray diffraction pattern to confirm the crystal structure of the BSZT samples and each sample indicates the tetragonal phase with the P4mm space group. Interestingly, with increasing Ts, the tetragonality increases up to 1250 °C, and then decreases for further increasing Ts, suggesting a transformation to the cubic structure. Morphological analysis of the BSZT samples show that a dense microstructure is attained for higher Ts. Temperature-dependent dielectric studies show that the degree of diffuseness increases up to 1250 °C, and then decreases for further increasing Ts, suggesting a weakening of the relaxor ferroelectric behavior. A non-Debye type relaxation process in the complex impedance and the modulus spectroscopy studies confirm the significant contribution of both the grain and grain boundary to the electrical response of the studied sample. The ferroelectric behaviors of the sample are explored from the polarization versus electric field hysteresis loops. Ferroelectric properties are significantly improved with the Ts.

Electric field poling effect on the photosensitivity of samarium-doped bismuth ferrite ceramics

This work highlights improved photosensing performance in ITO/(Bi0.93Sm0.07)FeO3/Au heterostructure through a prior electric field poling. Maximal responsivity (R) of 2.0×10−2A/W and specific detectivity (D*) of 2.2×1011 Jones were obtained under 405-nm irradiation. The mechanism behind the observed photosensing performance is linked to the combined effects of the polarization-induced electric field and built-in electric fields at the interfaces (i.e., p–n junction and Schottky barrier). The net internal electric field established in the device serves as the driving force for the separation and transport of the photo-generated electron–hole pairs. The reduced direct optical bandgap (Eg) of 2.13 eV, the well-defined ferroelectric polarization hysteresis loops, and the conduction pathways formed by the electric field-stimulated interconnection of domain walls and grain boundaries play significant roles in the remarkable photosensitivity of (Bi0.93Sm0.07)FeO3 ceramics, thus providing insight into optimizing BiFeO3-based materials for near-UV photodetector.

Self-assembled three-dimensional framework of PbTiO3:ε-Fe2O3 nanostructures with room temperature multiferroism

Hybrid multiferroic systems composed of complex oxides have drawn sustained attention for decades due to their intriguing physical effects and potential technological exploitations. Designing innovative nanostructures of multiferroic nanocomposites to overcome inherent shortcomings for conventional layered (e.g. clamping effect) and vertically aligned (e.g. leaky) films are instrumental to realize genuine multiferroic behaviors. Here the self-assembled architecture with three-dimensional (3D) framework of heterostructures is fabricated, wherein well-ordered multiferroic ε-Fe2O3 (ε-FO) nanoboats are embedded in a ferroelectric perovskite PbTiO3 (PTO) matrix. The biphasic system combines strong interfacial magnetoelectric couplings of vertically aligned heterostructure and addressed leakage issue via preferential epitaxy of a high-resistance transition layer of PTO. Additionally, the two phases maintain full lattice coherence along vertical interfaces allowing for efficient interfacial strain coupling. Ferroelectricity and piezoelectric switching of the 3D nanostructured PTO:ε-FO film have been corroborated macroscopically by polarization hysteresis (Ps ~ 45 μC cm−2) and locally by piezoresponse force microscopy, and strong magnetoelectric coupling has been manifested as a sizable modification of piezoelectric switching characteristics via applying a DC magnetic field, all conducting at room temperature. The novel 3D multiferroic-ferroelectric heterostructure offers great potential for nanoengineering of multiferroic composites, thus opens an avenue towards superior microelectronics and spintronics.

Coexistence of the electric polarization and conductive current in the bismuth–neodymium ferrite garnet films

The Nd1Bi2Fe5O12/Nd2Bi1Fe4Ga1O12 polycrystalline films on the glass substrate and the Nd0.5Bi2.5Fe5O12 epitaxial films on the single-crystal gadolinium gallium garnet substrate have been investigated by impedance and dielectric spectroscopy. The inductive contribution to the impedance and two relaxation channels related to ferroelectric domains and migration polarization have been established. The magnetocapacitance and magnetoimpedance have been determined. The conductive and polarization currents and the phase difference between them for the films of two types have been determined. The critical temperatures of the polarization disappearance and hysteresis I–V have been found. A model of the polarization caused by the piezoelectric effect and flexoelectric interaction has been proposed. I–V hysteresis is explained by the presence of ferroelectric domains near the interface and is associated with the hysteresis of the electric polarization.

Structure, ferroelectric, and dielectric properties of (Na1−2xCax)NbO3 ceramics

Mimicking the scheme of incorporating La3+ to Pb(Zr1−xTix)O3, Ca2+ is used to substitute Na+ in the lead-free NaNbO3 compound, with A-site vacancy introduced to maintain charge neutrality. The anticipated relaxor behavior is expected to suppress the remanent polarization and improve the energy storage properties of NaNbO3-based ceramics. Specifically, (Na1−2xCax)NbO3 (x = 0.01, 0.02, 0.04, 0.08) ceramics were prepared with the solid-state method, and their structures and electric properties were investigated. X-ray diffraction and transmission electron microscopy reveal the existence of minor amount of CaNb2O6 second phase. Polarization vs. electric field hysteresis loop measurements verify the suppression of remanent polarization in compositions of x ≤ 0.04. The temperature-dependent dielectric tests indicate that both the relaxation and diffuseness parameters monotonically increase with Ca2+ content. The results demonstrate that the introduction of a smaller donor dopant and charge-compensating vacancies on the A-site in NaNbO3 is an effective strategy to disrupt the long-range dipole order.

Large polarization and record-high performance of energy storage induced by a phase change in organic molecular crystals.

Dielectrics that undergo electric-field-induced phase changes are promising for use as high-power electrical energy storage materials and transducers. We demonstrate the stepwise on/off switching of large polarization in a series of dielectrics by flipping their antipolar or canted electric dipoles via proton transfer and inducing simultaneous geometric changes in their π-conjugation system. Among antiferroelectric organic molecular crystals, the largest-magnitude polarization jump was obtained as 18 μC cm−2 through revisited measurements of squaric acid (SQA) crystals with improved dielectric strength. The second-best polarization jump of 15.1 μC cm−2 was achieved with a newly discovered antiferroelectric, furan-3,4-dicarboxylic acid. The field-induced dielectric phase changes show rich variations in their mechanisms. The quadruple polarization hysteresis loop observed for a 3-(4-chlorophenyl)propiolic acid crystal was caused by a two-step phase transition with moderate polarization jumps. The ferroelectric 2-phenylmalondialdehyde single crystal having canted dipoles behaved as an amphoteric dielectric, exhibiting a single or double polarization hysteresis loop depending on the direction of the external field. The magnitude of a series of observed polarizations was consistently reproduced within the simplest sublattice model by the density functional theory calculations of dipole moments flipping over a hydrogen-bonded chain or sheet (sublattice) irrespective of compounds. This finding guarantees a tool that will deepen our understanding of the microscopic phase-change mechanisms and accelerate the materials design and exploration for improving energy-storage performance. The excellent energy-storage performance of SQA was demonstrated by both a high recoverable energy-storage density Wr of 3.3 J cm−3 and a nearly ideal efficiency (90%). Because of the low crystal density, the corresponding energy density per mass (1.75 J g−1) exceeded those derived from the highest Wr values (∼8–11 J cm−3) reported for several bulk antiferroelectric ceramics , without modification to relaxor forms.

Comment on “Giant pyroelectric energy harvesting and a negative electrocaloric effect in multilayered nanostructures” by G. Vats, A. Kumar, N. Ortega, C. R. Bowen and R. S. Katiyar, Energy Environ. Sci., 2016, 9, 1335

In the ferroelectric phase, the change of polarization with temperature from partially switched polarization hysteresis loops has no relation with the electrocaloric effect (ECE) and hence cannot be used in Maxwell relation to deducing ECE.

МАТЕМАТИЧЕСКИЕ МОДЕЛИ ПОЛЯРИЗАЦИОННЫХ ХАРАКТЕРИСТИК СЕГНЕТОЭЛЕКТРИКОВ В РАМКАХ ТЕОРИИ ЛАНДАУ - ГИНЗБУРГА - ДЕВОНШИРА

The paper presents the overview and implementation of mathematical models of ferroelectric polarization characteristics within the framework of the Landau - Ginzburg theory. Mathematical models of polarization switching in ferroelectrics are formalized by means of several types of differential problems. Based on difference methods the computational schemes are constructed for various modifications of the Landau - Khalatnikov model. Numerical simulation of the polarization hysteresis in ferroelectrics with the first-order phase transition is performed. The computational results obtained in Matlab are compared with the experimental data.

Investigation of the Effects of Reduced Sintering Temperature on Dielectric, Ferroelectric and Energy Storage Properties of Microwave-Sintered PLZT 8/60/40 Ceramics

In this study, (Pb0.92La0.08) (Zr0.60Ti0.40) O3 (PLZT 8/60/40) ceramics were synthesized using a high-energy ball-milling technique followed by microwave sintering at different temperatures from 900 °C to 1200 °C. The optimal microwave sintering temperature for the PLZT 8/60/40 ceramics was found to be 1150 °C, which is relatively low compared with conventional sintering temperature. The sintered ceramics show the pure perovskite phase, uniform grain microstructure (1.2 µm) and high density (~99.5%). The polarization vs. electric field (P-E) hysteresis curves were used to investigate the ferroelectric and energy storage properties. The switching characteristic in P-E loops and occurrence of domain switching current in current vs. electric field (I-E) loops confirms their ferroelectric nature. The PLZT ceramics, which were sintered at 1150 °C, show the highest remnant polarization (Pr) of ~32.18 μC/cm2 and domain switching current (Imax) of ~0.91 mA with a low coercive field (Ec) of ~10.17 kV/cm. The bipolar and unipolar strain vs. electric field (S-E) hysteresis loops were also measured and the highest unipolar strain was found to be ~0.26% for the PLZT ceramics sintered at 1150 °C. The unipolar S-E curves were used to derive the piezoelectric coefficient (d33~495 pm/V) and a strain hysteresis loss (~5.8%).

Multiferroic and magnetoelectronic polarizations in BaFe12O19 system

Coexistence of ferroelectricity and ferromagnetism in one single phase of a solid is of great interest because of the potential application for novel electronic devices. We report on the enhanced ferroelectricity jointly co-existing with excellent magnetic performance in M-type barium hexaferrite (BaFe12O19), which demonstrating a classic electric polarization (P-E) hysteresis loop with full saturation. Two nonlinear current peaks in the I–V curve for polarization switch and giant abnormal change of dielectric constant near Curie temperatures provide sufficient experimental evidences to verify the ferroelectricity of BaFe12O19 ceramics. It holds a large remnant polarization of 55.7 μC/cm2 and a suitable coercive field at 441 kV/cm. Two peaks at 194 °C and 451 °C in the temperature-dependent dielectric spectrum of BaFe12O19 ceramics are considered to be the phase transition from ferro-to antiferro- and antiferro-to para-electric structures. A conventional strong magnetic hysteresis loop was also observed. The influence of oxygen vacancies on the band structure, electric and magnetic properties has been discussed in detail. The magnetically induced E-polarization upon the BaFe12O19 ceramics was achieved in the form of alternating spin current waves. These combined multiple functional responses of large ferroelectrics and strong ferromagnetism reveal the excellent multiferroic features of BaFe12O19, which would bring forth the great opportunity to create novel electric devices with active coupling effect between magnetic and electric orders.

Soft Perovskite-Type Antiferroelectric with Giant Electrocaloric Strength near Room Temperature.

Antiferroelectric materials, characterized by an antiparallel array of adjacent dipoles, are holding a bright future for solid-state refrigeration based on their electrocaloric (EC) effects. Despite great advances of inorganic oxides and some organic soft polymers, their EC effects are achieved under quite high electric fields that result in too low EC strengths for practical application. Currently, it is a challenge to exploit soft antiferroelectric with strong EC strengths. Here, by the mixed-cation alloying, we present a new perovskite-type soft antiferroelectric, (isopentylammonium)2CsPb2Br7 (1), which incorporates both an organic spacing cation and an inorganic perovskitizer Cs+ moiety. Remarkably, the synergic cooperativity between the reorientation of the organic spacer and atomic displacement of Cs+ cation triggers its multiple ferroelectric-antiferroelectric-paraelectric phase transitions at 321 and 350 K. Their natural polarization vs electric field hysteresis loops are characterized to confirm ferroelectric and antiferroelectric orders of 1, respectively. It is emphasized that, under a low electric field of 13 kV/cm, the antipolar dipole realignment in 1 endows a giant near-room-temperature EC strength (ΔTEC/ΔE) of 15.4 K m MV-1 at antiferroelectric phase. This merit is on par with the record-high value of BaTiO3 (∼16 K m/MV) but far beyond the state-of-the-art soft polymers. The underlying EC mechanism for 1 is ascribed to the extremely low critical field to switch dipoles, involving the reorientation of the organic spacer and the shift of the Cs+ cation. Besides, notable EC entropy change (∼4.1 J K-1 kg-1) and temperature change (∼2 K) reveal potentials of 1 for solid-state refrigeration. As far as we know, this discovery of near-room-temperature EC strengths is unprecedented in the hybrid perovskite family, which sheds light on the exploration of new soft antiferroelectrics toward high-efficiency refrigeration devices.

Synthesis and characterization of K0.5Bi0.5TiO3–BaTiO3 piezoelectric ceramics for energy storage applications

In this study, potassium bismuth titanate–barium titanate (KBT–BT)-based lead-free piezoelectric perovskite ceramic material is synthesized via conventional solid state reaction method. The structural, morphological, ferroelectric, piezoelectric and dielectric properties are analyzed using suitable characterizations and their potential for energy storage application is validated. Rietveld refinement on powder X-ray diffraction patterns revealed that the sintered KBT–BT ceramics belong to tetragonal system with P4mm space group at room temperature. The morphology of the sample was observed to be inhomogeneous with abnormal grain growth. The KBT–BT ceramics showed excellent dielectric and ferroelectric properties (ɛr = 2916; Pr = 17.40 µC/cm2, Ec = 39.97 kV/cm). Particularly polarization hysteresis (P–E) loops recorded at ambient temperature resulted in a high recoverable energy storage density (Wrec ~ 0.61 J cm3) and exhibited extremely high efficiency (η ~ 39.3%) at 1 Hz. Large accompanying normalized strains of ~ 46% corresponding to a strain d33 of 83 pm/V were observed.

ANALYSIS THE EFFECTS OF FERROELECTRIC ELECTRIC FIELD ON CURRENT-VOLTAGE CHARACTERISTICS OF THE FERROELECTRIC FIELD EFFECT TRANSISTOR USING SRBI2TA2O9 THIN FILM

This paper presents a new analytical expression for current-voltage characteristics of the Ferroelectric Field Effect Transistor (FeFET), a promising candidate for nonvolatile memories. For this research, a FeFET model using Pt/SrBi2Ta2O9/Insulators/Si thin film as an effect gate stack was proposed and assessed. Firstly, we have studied the effects of ferroelectric polarization on current-voltage characteristics of FeFET based on the analytical method of CMOS device, the polarization hysteresis properties versus electric field (P-E) of the ferroelectric material was explicitly analysed with two parameters of saturated and unsaturated polarization. Then, by mathematical analysis, the current-voltage values was calculated under different conditions such as using differences of substrate doping concentration, oxide thickness, ferroelectric thickness, working temperature, etc. Finally, the calculated results were simulated by the Matlab software that gave us an overview of the device properties.