Polarization Hysteresis Research Articles

Improved ferroelectric, piezoelectric, and magnetic properties in BiFeO3–(Ba0.85Ca0.15)TiO3 ceramics through Mn addition

Integrating multiple functions in a single compound is still attractive and necessary to meet the demand of device miniaturization. In this work, we systemically modulate multifunctional properties in the 0.74BiFeO3–0.26(Ba0.85Ca0.15)TiO3–x wt. % MnO2 solid solution with the addition of MnO2. A highly rectangular and saturated polarization–hysteresis (P–E) loop is obtained with a large remanent polarization Pr of 49.5 μC/cm2 as x=0.8. Furthermore, the piezoelectric coefficient d33 also obviously improved with an optimized d33=137 pC/N by the introduction of MnO2 due to the grain size effect, the improvement of insulation, and relaxation regulation. With the addition of MnO2, the remanent magnetization Mr increases monotonically because of the enhanced exchange interactions between Fe2+and Fe3+. The results may provide an effective way to explore promising multifunctional materials in BiFeO3-based ceramics.

Dielectric and ferroelectric properties of (Bi0.5Na0.5)0.94-δBa0.06Ti1−xNbxO3 lead-free ceramics

Lead-free ceramics (Bi0.5Na0.5)0.94-δBa0.06Ti1−xNbxO3 (x = 0, 0.01, 0.02, 0.03, 0.04, 0.05) were prepared via a solid-state sintering method. The ceramics exhibit pure perovskite structure as x ≤ 0.04, while the ceramic with x = 0.05 has a secondary phase. The rhombohedral (R)–tetragonal (T) morphotropic phase boundary exists in all the samples. The relative content of the T phase increases due to the Nb5+ doping. The ceramics show dense microstructures with mean grain sizes around 1–2 μm. The changes of dielectric constant and dielectric loss as a function of temperature for the unpoled and poled samples were compared. Two dielectric anomalies appear on the dielectric curves around the temperatures denoted as TRE and Tm. With the increase of Nb5+ amount, the values of TRE decrease and Tm increase. The Nb5+-doped ceramics exhibit better temperature stability of dielectric constant during a wide high-temperature window. The polarization hysteresis (P–E) loops change from typical ferroelectric loops for the sample with x = 0 to constricted P–E loops with increasing Nb5+ amount. The ceramic with x = 0.03 shows a maximum strain (Smax) of 0.55% and piezoelectric strain constant (d33*) of 675 pm/V.

Magnetodielectric effect and spin state of iron ions in iron-substituted bismuth pyrostannate

The magnetic and magnetodielectric properties of bismuth pyrostannate $$\hbox {Bi}_{{2}}(\hbox {Sn}_{1-{x}}\hbox {Fe}_{{x}})_{{2}}\hbox {O}_{{7}}$$ ( $$x = 0.1$$ and 0.2) have been examined. Using the Mossbauer spectroscopy and electron paramagnetic resonance, the high-spin state and crystallographic positions of iron ions have been established. The coexistence of triclinic symmetry domains in the $$\hbox {Bi}_{{2}}(\hbox {Sn}_{{1-{x}}}\hbox {Fe}_{{x}})_{{2}}\hbox {O}_{{7}}(x = 0.1)$$ compound with the monoclinic symmetry below 140 K has been found. For the $$\hbox {Bi}_{{2}}(\hbox {Sn}_{{1-{x}}}\hbox {Fe}_{{x}})_{{2}}\hbox {O}_{{7}}$$ composition with $$x = 0.2$$ , the nonlinear field dependence of magnetization in the paramagnetic region up to room temperatures has been observed. The electric polarization hysteresis and the magnetoelectric effect in the $$\hbox {Bi}_{{2}}(\hbox {Sn}_{{1-{x}}}\hbox {Fe}_{{x}})_{{2}}\hbox {O}_{{7}}$$ compound have been disclosed. The magnetic field-dependent anomalous behavior of magnetization has been explained by the magnetoelectric effect.

Ultrahigh energy-storage performance in lead-free BZT thin-films by tuning relaxor behavior

Relaxor ferroelectric thin films show excellent energy-storage performance for pulse-power applications. In this study, La-doped Ba1-xLax(Zr0.25Ti0.75)O3 (BLZT, x = 0–8%) thin films were grown on LaNiO3 buffered Ca2Nb3O10-nanosheet/Si substrates. BLZT thin films indicate prominently increasing relaxor behavior with increasing La-doping concentration, which is conducive to obtaining a very slim polarization hysteresis loop with a low remanent polarization and a high breakdown strength. As a result, BLZT thin films with 5 mol.% La-doping simultaneously exhibit a great 72.2 J/cm3 recoverable energy-storage density and a large 78.6% energy-storage efficiency under a high 3.8 MV/cm breakdown strength. These results present a promising environmentally friendly candidate for the next generation of advanced energy-storage capacitor applications.

Theoretical and numerical analysis of the Landau–Khalatnikov model of ferroelectric hysteresis

An initial-boundary value problem for the reaction-diffusion Landau–Khalatnikov equation applied to describe polarization switching in ferroelectrics is studied from both theoretical and computational points of view. The existence and uniqueness of a weak solution of the initial-boundary value problem are proved. An absolutely stable monotonic numerical scheme of the second-order accuracy combined with an iterative procedure is constructed. Numerical simulation of the polarization hysteresis in ferroelectrics with the first-order phase transition is performed. The results of the computations obtained on the base of different modifications of the model are compared with experimental data. An important role of the diffusion term and its scaling effect for an adequate description of the polarization switching in ferroelectrics are shown.

Built‐in bias fields for retention stabilisation in hafnia‐based ferroelectric tunnel junctions

Ferroelectric tunnel junctions have recently attracted a lot of research interest, not only for memory operation but also for e.g. neuromorphic computing. Retention characteristics of these devices are of utmost importance in many applications. The authors have recently demonstrated the feasibility of double-layered ferroelectric tunnel junctions where the ferroelectric hafnium zirconium oxide acts as the memory layer and the dielectric aluminium oxide as the tunnelling barrier. The depolarisation field from the unscreened polarisation charges that is introduced by this structure causes serious limitations on the retention behaviour due to the unintentional back-switching of ferroelectric domains. This leads to a diminishing memory window over time. By using a built-in bias field from different work function metal electrodes, in this case platinum and titanium nitride with 0.85 eV difference, one can shift the polarisation hysteresis curve and counteract the electric depolarisation field. This leads to a more stable on-current over time while only marginally increasing the off-current degradation. Extrapolation to ten years shows a much larger memory window compared to the symmetric metal electrode structure.

Probing Antiferroelectric‐Ferroelectric Phase Transitions in PbZrO3 Capacitors by Piezoresponse Force Microscopy

AbstractFunctional characterization of antiferroelectric (AFE) materials typically involves macroscopic testing of their nonlocal integrated information on their dielectric properties, such as polarization hysteresis loops, field‐dependent strain, and capacitance while the local AFE properties have been rarely addressed. Here, a new protocol is demonstrated for local probing of the antiferroelectric/ferroelectric (AFE/FE) phase transition in PbZrO3 capacitors by piezoresponse force microscopy (PFM). PFM spectroscopy of the local AFE/FE phase transition parameters is performed and their spatial variability via two‐dimensional mapping is investigated. It is shown that AFE hysteresis loops recorded by PFM in the bias‐on regime exhibit four characteristic amplitude peaks. Within the framework of Landau theory, these features are attributed to a considerable increase in the electromechanical strain response due to the dielectric constant divergence during AFE/FE phase transitions. The proposed approach can be used to differentiate between the antiferroelectric and nonpolar dielectric phases in functional devices using the electrically induced polarization.

All chemical solution deposition of epitaxial porous BiFe0.93Mn0.07O3 thin films

BiFeO3 as a type of single-phase room temperature multiferroic materials has aroused intensive investigations in recent years. Construction of porous BiFeO3 thin films is helpful for integration of other materials with desirable functionalities. Here, epitaxial BiFe0.93Mn0.07O3 (001) thin films were prepared on SrRuO3-buffered LaAlO3 (001) single crystal substrates by an all-solution chemical solution deposition, which is beneficial for large area thin film fabrication with low cost. Through addition of F-127 copolymer into the precursor solution, pores can be effectively introduced in BiFe0.93Mn0.07O3 (001) thin films while the epitaxy can be maintained. The amount of pores is gradually increased with increasing of the F-127 addition. The leakage current density is not obviously changed and the conduction mechanism can be well fitted through Ohmic behavior. Electric field dependent polarization hysteresis loops can be effectively maintained and the room temperature magnetic moment is obviously improved with the introduction of pores in epitaxial BiFe0.93Mn0.07O3 (001) thin films. The results will provide a facile route to fabricate large area epitaxial porous BiFeO3 thin films as an effective template for integration of other materials to realize desirable functionalities.

Ferroelectricity of Dion–Jacobson layered perovskites CsNdNb2O7 and RbNdNb2O7

Crystallography and dielectric properties in Dion–Jacobson layered perovskites, CsNdNb2O7 and RbNdNb2O7, have been examined in dense polycrystalline samples, and polarization hysteresis loops that substantiate ferroelectricity have been observed at room temperature. The theoretical mechanism for the spontaneous polarization, “hybrid improper ferroelectric mechanism,” induced by a combination of two types of non-polar octahedral rotations, is confirmed in these two phases. Our samples show remanent polarizations of 2–3 μC cm−2, which are much larger than those obtained in polycrystalline samples with the hybrid improper ferroelectricity reported so far. A dielectric constant in CsNdNb2O7 exhibits an anomaly at 625 K, corresponding to the ferroelectric transition, as previously revealed by X-ray and neutron diffractometry. No dielectric anomaly is observed for RbNdNb2O7 throughout the temperature range studied here (≤773 K), which is consistent with the previous diffractometry showing the persistence of polar I2cm symmetry up to 790 K.

Structural, dielectric, ferroelectric and tuning properties of Pb-free ferroelectric Ba0.9Sr0.1Ti1-xSnxO3

A series of Pb-free ferroelectric materials Ba0.9Sr0.1Ti1-xSnxO3 (BSTS-x) with 0 ≤ x ≤ 0.15 was successfully prepared via solid-state reaction method. The effect of Sn substitution on the crystal structure, microstructure, dielectric behavior, ferroelectric and tunable features of BSTS-x ceramics were systematically investigated. Room temperature (RT) x-ray diffraction (XRD) analysis using the Rietveld refinement method reveals that all the synthesized BSTS-x ceramics were well crystallized into single perovskite structure. The results show a tetragonal phase for 0.00 ≤ x ≤ 0.02, which evolves to orthorhombic and tetragonal coexisting phases for 0.05 ≤ x ≤ 0.07. The composition x = 0.10 showed a mixture of tetragonal, orthorhombic and rhombohedral phases at RT, while a single cubic phase is observed for x = 0.15. The crystal phases determined by XRD were confirmed by Raman spectroscopy. Enhanced dielectric permittivity with a maximum value of ε'~35000 is observed for x = 0.10 at RT. The ferroelectric behavior of BSTS-x ceramics was investigated through polarization hysteresis loops and tunability measurements. High tunability of 63% at RT and under the low DC-applied electric field of 1.40 kV/cm is achieved for x = 0.10.

Combine effect of BaSnO3 and BaSeO3 substitution on structural and electrical properties of Bi0·5K0·5TiO3 ceramics

In this research article, structural (crystal structure, micro structure) and electrical (dielectric, impedance and conductivity) properties of BaSnO3 (BSn) and BaSeO3 (BSe) modified (Bi0·5K0.5) TiO3 ceramic (i.e., (1–2x)((Bi0·5K0.5)TiO3)+xBaSnO3+xBaSeO3 with x = 0, 0.05, 0.10, 0.15 (BKT-BSn-BSe) have been fabricated via a high-temperature cost effective mixed oxide reaction process. The structural, micro structural and electrical characteristics of the parent compound ((Bi0·5K0.5) TiO3) have significantly been influenced by the substitution of BSn–BSe (in equal ratio) in it over a high temperature (100–500 °C) and frequency (1 kHz–1 MHz) range. Structural analysis of the compounds, carried out by the room temperature X-ray diffraction (XRD) data, confirms the formation of single phase compounds with tetragonal structure. The surface morphology of the materials, exhibits the homogeneous distribution of grains (with few voids) throughout the surface of the materials. The presence of bulk and grain boundary effect of the material is confirmed by the nature of Nyquist plot. J-E characteristics of the compounds show a negative temperature co-efficient of resistance (NTCR) behavior in them, similar to that of a semi-conductor. The ferroelectric phenomena of the prepared materials are studied by field dependence of polarization (PE) hysteresis loop study.

On the simulation of the hysteresis loop of polycrystalline PZT thin films

We investigate experimentally and numerically the polarization hysteresis loop of a PZT thin film utilized in MEMS actuators. A fully coupled electromechanical phase-field technique is employed for the numerical prediction part, starting from a simplified model of the thin film proposed on the basis of several experimental evidences. It is shown that polycrystalline nature of the film plays a fundamental role. In particular the simulations demonstrate that grains with dielectric interfaces and stochastic orientation of the crystallographic directions have a significant impact on the overall hysteresis loop.

Structural, Electrical, and Magnetic Characteristics of Chemically Synthesized Lead-Free Double Perovskite: BiMgFeCeO6

In the present paper, structural, microstructural, dielectric, electrical, and magnetic characteristics of a chemically synthesized double perovskite compound BiMgFeCeO6 have been reported. An analysis of room temperature X-ray diffraction data has shown formation of compound with orthorhombic symmetry. Study of micrographs of the pellets has shown the homogeneous distribution of grains, grain boundaries, and presence of required elements in the sample. Detailed studies of dielectric (er, tan δ) and impedance parameters of the material have provided an insight into the electrical properties and understanding of types of relaxation process occurred in the material. The semiconductor characteristic (i.e., negative temperature coefficient of resistance behavior) of the compound at high temperature has been observed in the temperature-dependent dc conductivity study. As the characteristics of the frequency dependence of ac conductivity of the material follow Jonscher’s universal power law, the validity of analysis and good quality of the sample are confirmed. The occurrence of ferroelectric polarization (hysteresis loop), magnetization loop, and magnetoelectric pattern in the material confirms the multiferroicity in it.

Room temperature charge storage ability and magnetoelectric coupling of flexible polymer nanocomposite films

Abstract We have fabricated flexible films of bismuth ferrite (BFO), terbium manganate (TMO) nanofiller incorporated polyvinyl alcohol (PVA) composite to achieve improved energy storage capacity at room temperature. A systematic observation on capacitance–bias voltage (C–V), ferroelectric and magneto-dielectric properties are done to evaluate the impact of the nanofillers in PVA matrix. BFO-PVA films show enhanced dielectric properties whereas decrement is noticed in TMO-PVA films. Mott-Schottky analysis is used here to understand the dielectric behaviour vividly. The Maxwell-Wagner-Sillars (MWS) type interfacial space charge polarisation causes the electrical polarisation hysteresis loops. The dielectric constant gradually decreases with increasing applied magnetic field. It indicates the negative magneto-dielectric effect of the films. The enhancement in the magneto-dielectric sensitivity is observed in all the composite films than that of pristine PVA.

Enhanced Dielectric and Energy Storage Properties in Fe‐Doped BCZT Ferroelectric Ceramics

x mol% Fe‐doped Ba(Zr0.2Ti0.8)O3‐50 mol%(Ba0.7Ca0.3)TiO3 (abbreviated as xFe:BCZT) ferroelectric ceramics with x = 0, 0.075, 0.375, 0.75, 1.5, and 3 are fabricated via conventional solid‐state reaction methods. Fe incorporates into the lattice, and all the xFe:BCZT ceramics show pure perovskite structure except 3Fe:BCZT ceramics in which tiny amount of iron oxide is detected via X‐ray diffraction (XRD). The average grain sizes are significantly reduced from ≈20 to ≈2 μm with increasing Fe‐doping content. The Curie temperature of xFe:BCZT ceramics decreases with increasing Fe‐doping concentration and the room temperature dielectric constant significantly increased. Polarization hysteresis loops become slim after Fe‐doping. The recoverable energy storage density Wrec of xFe:BCZT ceramics is slightly enhanced to 0.240 J cm−3 with an energy storage efficiency η% = 70.1% at x = 0.075 under E‐field of 50 kV cm−1. The η% can be enhanced to as high as 93.8% at x = 3 with Wrec = 0.153 J cm−3 due to a slim P–E loops via Fe‐doping. The results indicate a potential method to fabricate high efficiency energy storage materials via Fe‐doping.

Enhanced energy storage properties of Sr(Sc0.5Nb0.5)O3 modified (Bi0.47La0.03Na0.5)0.94Ba0.06TiO3 lead-free ceramics

Excellent energy storage performance of dielectric capacitors is highly desired in all kinds of energy storage devices. In this study, Sr(Sc0.5Nb0.5)O3 was introduced to enhance the energy storage properties of (Bi0.47La0.03Na0.5)0.94Ba0.06TiO3 (BLNBT) ceramics. All ceramic samples were sintered densely, and the phase structure, microstructure, dielectric and ferroelectric properties were then systematically investigated. Two distinct dielectric anomaly peaks, which are detected from the dielectric properties as a function of temperature, suggest not only a phase transition, but also indicate typical relaxor features. The breakdown strength is significantly improved, and the polarization versus electric field hysteresis loops become slim with the increasing content of SSN. The optimum energy storage performance is achieved in 0.85BLNBT–0.15SSN ceramic with the recoverable energy density of 1.83 J/cm3 and energy efficiency of 82.32% under a moderate electric field of 185 kV/cm. The excellent energy storage performance of 0.85BLNBT–0.15SSN ceramic makes it a promising candidate material for advanced pulsed power capacitors.

Phase evolution in (1−x)(Na0.5Bi0.5)TiO3-xSrTiO3 solid solutions: A study focusing on dielectric and ferroelectric characteristics

In the present work, the nature of phase evolution of (1−x)(Na0.5Bi0.5)TiO3-xSrTiO3 (NBT-xST) solid solutions with x of 0–0.6 is revealed by characterizing the dielectric and ferroelectric properties. Two unique dielectric anomalies associated with high-temperature nanoregions (PNRs) in the ergodic relaxor (ER) state and low-temperature PNRs in the nonergodic relaxor (NR) state are identified. Characteristic temperatures, including TB,TRT∗, Tm, Td and TT∗, are determined in fresh and poled states on the basis of the characteristics of the evolution of these two dielectric anomalies. The whole evolution of the transition from the NR state to the ER state is reflected by the temperature-dependent polarization versus electric field (P-E) hysteresis loops, i.e., from the square loops, via the double-like loops, to the slim loops. The characteristic temperatures, including TP-N, TN-R and TR-dis, are determined by the characteristics of the evolution of P-E loops. Accordingly, a phase diagram of NBT-xST was constructed according to these characteristic temperatures. Most importantly, the relationship between polarization responses and heterogeneous polar phase coexistence has been established and a schematic diagram is given. This work will help to understand the phase evolution and its impact on the macroscopic properties of NBT and the associated NBT-based solid solutions.

Hysteresis of the Electric Polarization in a Two-Layer Ferromagnetic Film with a Vortical Distribution of Magnetization

Hysteresis of the electric polarization of a two-layer exchange-coupled ferromagnetic film whose layers have the easy-plane and easy-axis anisotropy upon magnetization reversal is studied numerically. The magnetization reversal was carried out by a magnetic field perpendicular to the film plane from the saturation state along the easy magnetization axis. The dependences of the average electric polarization and the reduced magnetization of the film layers on the external magnetic field strength are constructed. The feasibility of sign reversal of the electric polarization in a magnetic field in films whose thickness is smaller than the transverse dimensions is found. No polarization sign reversal is observed in thicker films upon magnetization reversal.

Aeroacoustic investigation of an oscillating airfoil in the pre- and post-stall regime

The present study describes an experimental investigation of the aerodynamic and aeroacoustic characteristics of a sinusoidally oscillated NACA 0012 airfoil. The experiments were conducted in an aeroacoustic wind tunnel with a uniquely designed Kevlar-walled test section. Prior to experiments, these Kevlar walls were calibrated carefully and shown to provide reliable and accurate aerodynamic and aeroacoustic measurements. Two different regimes of interest, namely the pre- and post-stall angle of attack regimes, have been examined for lift curve polars, far-field noise spectra and unsteady surface pressure spectra. Interestingly, when the lift curve polar hysteresis is small at pre-stall angles of attack, the unsteady surface pressure spectra of the oscillating airfoil can be predicted with satisfactory accuracy using a position-based weighted averaging approach from its static counterparts. On the other hand, such a method becomes invalid at post-stall angles due to the presence of a significant dynamic stall hysteresis. Instead, an increase in the mean surface pressure and far-field noise spectra is observed at dynamic stall conditions. Furthermore, a short-time Fourier transform analysis reveals that the increase of the surface pressure spectra is a direct result of the periodic production and convection of dynamic stall vortices.

Temperature dependence on ferroelectric properties and strain performance of PLZT ceramics containing 9 mol% La

ABSTRACT PLZT ceramics containing 9 mol% La and 50–70 mol% Zr were prepared by two-stage sintering to enhance the densification and the microstructure. Dielectric properties were investigated and the phase transition from relaxor to normal ferroelectric as an increasing amount of Zr could be observed. Induced strain (butterfly loop) and polarization (hysteresis loop) were measured at the maximum electric field of 12.5 kV/cm and the temperature range of 25–140°C. It was found that temperature dependence played an important role to phase transition from ferroelectric to paraelectric, which governed polarization and strain of PLZT ceramics. Zr/Ti ratios could also determine ferroelectric and induced strain properties where morphotropic phase boundary (MPB) would maximize polarization and strain in terms of piezoelectric coefficient.