Polarization-electric Field Loops Research Articles

Enhanced energy storage and fast charge-discharge properties of (1-x)BaTiO3-xBi(Ni1/2Sn1/2)O3 relaxor ferroelectric ceramics

Abstract In this work, we designed novel lead-free relaxor ferroelectric ceramics of (1-x)BaTiO3-xBi(Ni1/2Sn1/2)O3 (abbreviated as (1-x)BT-xBNS, with x = 0–0.20). With an increasing concentration of BNS, (1-x)BT-xBNS solid solutions displayed a phase transition from tetragonal symmetry to pseudocubic symmetry with highly diffusive and frequency-dependent relaxor ferroelectric behavior. Modified by BNS, (1-x)BT-xBNS ceramics yielded slim polarization-electric field (P-E) loops and improved energy-storage performances. The optimal energy storage properties can be achieved at x = 0.10, and samples showed a high recoverable energy density of 2.526 J/cm3 and a remarkably high energy efficiency of 93.89% under 240 kV/cm simultaneously at ambient temperature, which represent enhancements by 925% and 286%, respectively, over pure BaTiO3. The energy storage characteristics of the 0.9BT-0.1BNS ceramic manifested good thermal stability (−55–150 °C) and frequency stability (10 Hz-1 kHz), with a variation in recoverable energy density of less than 10%. Meanwhile, the pulsed charging-discharging measurement showed that the 0.9BT-0.1BNS ceramic had a fast discharge period of 67 ns and a large power density of 19 MW/cm3. Due to the outstanding characteristics, there is potential for this new and environmentally friendly BT-based ceramic to be used in high-power pulse capacitor applications.

A-site partially ordered La0.5Y0.5FeO3 and its multiferroic characteristics

The copresence of ferroelectricity and ferromagnetism inside the same compound is a rather scarce phenomenon, and therefore, the development of room-temperature multiferroic materials is a great challenge. In the present work, La0.5Y0.5FeO3 ceramics with La and Y ions partially ordered as a rocksalt type structure have been prepared. Such ordering leads to a polar P21nm phase, which is consistent with a particular type of hybrid improper ferroelectricity that has rarely been observed. Saturated polarization-electric field loops are determined at room-temperature with a remnant polarization of 0.11 μC/cm2, together with a room-temperature predominantly antiferromagnetic order accompanied by a weak magnetization, which renders our La0.5Y0.5FeO3 ceramics an example of a room-temperature multiferroic compound.

Dielectric relaxation behavior and energy storage properties in Ba1-x(Bi0.5K0.5)xTi0.85Zr0.15O3 ceramics

The effects of (Bi0.5K0.5)2+ content on the microstructures, dielectric properties and energy storage properties of Ba1-x(Bi0.5K0.5)xTi0.85Zr0.15O3 (x = 0, 0.02, 0.04, 0.06, 0.08, 0.1; BZTO) ceramics were systematically investigated. The dielectric properties of the doped BZTO (x = 0.02–0.1) ceramics as a function of temperature exhibit a wide peak, indicating a diffuse phase transition in doped BZTO ceramics. The diffuse phase transition leads to the good dielectric stability for doped BZTO (x = 0.02–0.1) ceramics over a wide temperature range (−200 °C–120 °C). Also, the slim polarization electric field (P-E) loops were observed in the x = 0.06 and x = 0.08 samples, showing lower remnant polarization (Pr) than that of pure BZTO ceramic obviously. The x = 0.06 sample exhibits the highest energy storage density of 0.90 J/cm3 together with a high energy storage efficiency of 90.4% at 30 kV/cm.

Microwave heated lead cobalt titanate nanoparticles synthesized by sol-gel technique: Structural, morphological, dielectric, impedance and ferroelectric properties

The lead cobalt titanate nanoparticles were synthesized via the sol-gel technique followed by microwave heating at 750 °C for 45 min. The X-ray diffraction study revealed the formation of tetragonal PbCoTiO3 phases. The average crystallite size was found to be 26 nm. The surface morphology was examined using field emission scanning and transmission electron microscopes. The dielectric properties such as dielectric constant (ε′), dielectric loss (ε″), ac-conductivity (σac), real (M′) and imaginary part (M″) of dielectric modulus were investigated as a function of temperature and frequency. The impedance analysis was carried out using Cole-Cole plots to elucidate the electrical conduction mechanism. The ferroelectric behavior of PCT was described by polarization versus input electric field (P-E) loop as a function of temperature.

Recent advances in lead-free dielectric materials for energy storage

To better promote the development of lead-free dielectric capacitors with high energy-storage density and efficiency, we comprehensively review the latest research progress on the application to energy storage of several representative lead-free dielectric materials, including ceramics (ferroelectrics–relaxor ferroelectrics–antiferroelectrics), glass-ceramics, thin and thick films, and polymer-based composites. The results indicate that lead-free dielectric materials with large maximum polarization, high breakdown electric field, small remnant polarization, and slim polarization-electric field loops are more appropriate for developing dielectric capacitors with high energy density and efficiency. However, some significant drawbacks in current lead-free dielectric materials hinder the energy storage performance of these materials. Based on this, we review herein some new strategies to improve the energy-storage capacity of dielectric materials.

Formation of polar phase in Fe-doped ZrO2 epitaxial thin films

The existence of a polar phase in epitaxially grown Fe-doped ZrO2 thin films has been demonstrated. The films were prepared on yttria-stabilized zirconia substrates by ion-beam sputtering and subsequent annealing, where the composition was controlled by changing the FeO1.5-ZrO2 ratio of the sputtering target. The chemical states of elements in the 30 nm-thick xFeO1.5-(1−x)ZrO2 thin films (x = 0, 0.06, 0.10, and 0.14 nominal composition) have been measured by X-ray photoelectron spectroscopy, and the crystal structure has been examined by using X-ray diffraction and scanning transmission electron microscopy. These observations revealed that the undoped ZrO2 thin film (x = 0) is dominated by the monoclinic phase (space group: P21/c), while the films containing Fe exhibit multi-domain structures consisting of monoclinic and orthorhombic (Pbc21) phases, the latter being a polar phase, showing that the orthorhombic phase is stabilized by the addition of Fe. Concurrently, the polarization-electric field loops of the Fe-doped films exhibited hysteresis for the film with x = 0.06.

Tailoring dielectric properties and multiferroic behavior of nanocrystalline BiFeO3 via Ni doping

In order to tailor the multiferroic as well as dielectric properties, we have synthesized BiFeO3 (BFO) and Ni-doped BFO nanoparticles of composition BiFe1-xNixO3 (0 ≤ x ≤ 0.07) via the sol-gel method. The influence of Ni-doping at the Fe site of BiFeO3 on the structural, dielectric, and multiferroic properties was investigated via various characterization techniques such as Raman spectroscopy, vibrating sample magnetometer, polarization-electric field (P-E) loop tracer, and LCR meter. The Raman spectra reveal the rhombohedral distorted perovskite structure of the samples in the R3c space group. The frequency dependent dielectric measurements at room temperature show that the dielectric constant for the pristine sample is an order of magnitude lower than the 1% Ni-doped BFO sample. It is also evident that the ac conductivity increases with the increase in frequency as well as Ni content. Further, the universal dielectric response (UDR) phenomenon is responsible for the dielectric behavior of all the samples in the whole frequency range except for the BiFeO3 and BiFe0.97Ni0.03O3 samples. These samples exhibit deviation from UDR phenomenon at higher frequencies. The room temperature hysteresis (M-H) loops exhibit the saturation in magnetization at higher magnetic fields. The result demonstrates a significant influence on the saturation magnetization with the Ni doping in BFO, prompting the ferromagnetic nature of the samples. The saturation magnetization of the 7% Ni-doped sample is approximately six times higher than the pristine one. The saturated P-E hysteresis loops establish the ferroelectric nature of the synthesized samples that are enhanced significantly on Ni doping. Thus, the doping of Ni in BiFeO3 improves the multiferroic properties of the matrix.

Dielectric relaxation and phase transition behavior of (1–x)Pb(Zn1/3Nb2/3)O3-xBaTiO3 binary solid solutions

Dielectric relaxation and phase transition behaviors in (1–x)Pb(Zn1/3Nb2/3)O3-xBaTiO3 (PZN-BT) binary solid solutions have been systematically studied in this paper. All the compositions display a pure pseudo-cubic perovskite structure. As the BT contents increase from 10 mol% to 70 mol%, the phase transition peak becomes broader and broader, accompanying with decreases of ɛm (the maximum dielectric permittivity) and Tm (the temperature corresponds to the ɛm). Nevertheless, an abnormal increase of ɛm and Tm occurs when the BT contents exceeds 70 mol%, forming a “U” shaped curve of the compositional dependence of ɛm and Tm. Moreover, it is indicated from the new glass model fitting results that the characteristic parameter p, which represents the degree of relaxation, also shows a similar “U” shaped variation curve. Similarly, as shown in polarization-electric field loops, both remnant polarizations (Pr) and coercive fields (Ec) display the “U” shaped curve as the BT content changes from 10 mol% to 80 mol%. Finally, according to the similar variation of these key parameters mentioned above, a polarization mismatched model, which describes the destruction and reestablishment of the long range order arrangement in solid solutions composed of two kinds of ferroelectrics, is proposed to illustrate the underlying mechanism. In this PZN-BT system or other similar ABO3-type perovskite relaxors, the competition between the A-O and B-O coupling plays an important role to form the “U” shaped evolution of these key parameters.

Effect of donor W and acceptor Ni codoping at Ti site on the structure and electrical properties of Na0.5Bi0.5TiO3 thin film

Pure Na0.5Bi0.5TiO3 (NBT), donor W6+ doped NBT (NBTW), acceptor Ni2+ doped NBT (NBTNi), as well as donor W6+ and acceptor Ni2+ codoped NBT (NBTWNi) polycrystalline films are fabricated on indium tin oxide (ITO)/glass substrates via a chemical solution deposition method. The roles of aliovalent-ion substitution on the crystallinity, ferroelectric and dielectric properties of NBT film are mainly investigated. With the introduction of aliovalent-ion, the surface of the doped film becomes more uniform and the leakage current is reduced. Well saturated polarization-electric field (P-E) loops can be observed in W6+ and Ni2+ codoped NBT film due to its lowest leakage currents compared to those of other films. Also, the effect of voltage and frequency on the capacitance-voltage (C-V) curve and the dielectric tunability for the NBTWNi film is discussed. The ferroelectric and dielectric properties are largely improved in NBTWNi film, which can be ascribed to the synergetic effect of high-valence W6+ and low-valence Ni2+ ions. The cooperation between the acceptor and donor cations can effectively eliminate the mobile oxygen vacancies in NBT films.

Pulsed-Laser Deposited 35 Bi(Mg1/2Ti1/2) O3-65 PbTiO3 Thin Films-Part I: Influence of Processing on Composition, Microstructure, and Ferroelectric Hysteresis.

35 Bi(Mg1/2Ti1/2)O3 - 65 PbTiO3 (35 BiMT-65 PT) is a potential candidate material for a high-temperature nonvolatile ferroelectric memory. For pulsed-laser deposited 35 BiMT-65 PT films with the perovskite structure, it was found that as the chamber pressure during deposition decreased, the Mg and Pb contents in as-deposited films drop, while the concentration of Bi increases. Concurrently with the change in composition, the remanent polarization $P_{r}$ increases 64% to $\approx 21~\mu \text{C}$ /cm2 and the polarization-electric field loops rotated counterclockwise as the deposition pressure increases. Decreasing the seed layer thickness from 36 to 16 nm led to a decrease in $P_{r}$ to $\approx 14~\mu \text{C}$ /cm2. Adjusting the target composition allowed the deposition of films which had near-stoichiometric Bi and Mg concentrations, but in all cases, the grown films were lead deficient. These films had remanent polarizations of 18- $20~\mu \text{C}$ /cm2. If the lead content of the target was increased too far, the remanent polarization decreased, possibly due to the need to evolve more PbO from defective growth layers. Finally, the deposition rate showed no substantial effect on the film composition, but did have a significant impact on the ferroelectric properties. As the deposition rate decreased, the $P_{r}$ increased to $\approx 22~\mu \text{C}$ /cm2 due to enhanced crystalline quality. At laser frequencies of 5 Hz, a Mg-rich pyrochlore phase begins to form and films showed a maximum $P_{r} \approx 22~\mu \text{C}$ /cm2. The processing-composition behavior is explained via preferential adsorption of Bi on the A-site, which results in lead vacancies.

Dielectric, ferroelectric properties and photoconductivity effect of sol-gel grown SrTiO3/BaTiO3 thin film heterostructure

SrTiO3/BaTiO3 (ST/BT) thin-film heterostructure was deposited on Pt/Ti/SiO2/Si(100) substrate by spin-coating. X-ray diffraction pattern shows that the heterostructure is a perovskite structure composed of ST and BT without any impurity peaks. The dielectric constant and loss of the heterostructure at 10 kHz are 704 and 0.024, respectively. The electric-field dependence of dielectric response was investigated and the tunability of the sample under 200 kV/cm applied field is 21.5%. Compared with pure ST thin film, the polarization-electric field loops of ST/BT heterostructure display high polarization and good symmetry, which could be attributed to the introduction of BT with high dielectric constant and inhibition of the potential pitfalls movement for high barrier at ST/BT interface. Moreover, the heterostructure demonstrates photoconductivity behavior with 405 nm light illumination. The results indicate that ST/BT heterostructure is a potential material in application as multifunctional photoelectric devices.

Fabrication and Characterization of Aligned Flexible Lead-Free Piezoelectric Nanofibers for Wearable Device Applications.

Flexible lead-free piezoelectric nanofibers, based on BNT-ST (0.78Bi0.5Na0.5TiO3-0.22SrTiO3) ceramic and poly(vinylidene fluoride-trifluoroethylene) (PVDF-TrFE) copolymers, were fabricated by an electrospinning method and the effects of the degree of alignment in the nanofibers on the piezoelectric characteristics were investigated. The microstructure of the lead-free piezoelectric nanofibers was observed by field emission scanning electron microscope (FE-SEM) and the orientation was analyzed by fast Fourier transform (FFT) images. X-ray diffraction (XRD) analysis confirmed that the phase was not changed by the electrospinning process and maintained a perovskite phase. Polarization-electric field (P-E) loops and piezoresponse force microscopy (PFM) were used to investigate the piezoelectric properties of the piezoelectric nanofibers, according to the degree of alignment—the well aligned piezoelectric nanofibers had higher piezoelectric properties. Furthermore, the output voltage of the aligned lead-free piezoelectric nanofibers was measured according to the vibration frequency and the bending motion and the aligned piezoelectric nanofibers with a collector rotation speed of 1500 rpm performed the best.

Photoelectrochemical investigations in lead-free Ba (Ti0.950Sc0.025Nb0.025)O3 ferroelectric ceramics. Application to amoxicillin photodegradation

The composition Ba(Ti0.950Sc0.025Nb0.025)O3 (BTSN) belongs to the (1 − x)BaTiO3–xBaSc1/2Nb1/2O3 system (x = 0.05). The room temperature X-ray diffraction (XRD) analysis refined by the Rietveld method shows a tetragonal perovskite structure. The dielectric study, carried out on the ceramics in the ranges (77–500 K) and (102–2 × 105 Hz), exhibits a normal ferroelectric behavior. The ferroelectric-paraelectric phase transition appears at the Curie temperature (TC) of 338 K with a wide space charge region. The maximal dielectric permittivity (εr) is characterized by a broader peak than that observed in BaTiO3 at the temperature Tc. The slight deviation from the Curie-Weiss law is typical of ferroelectric materials with a diffuse phase transition. The polarization-electric field (P-E) loop of BTSN is in good agreement with the XRD analysis. The BTSN ferroelectric ceramic exhibits interesting photoelectrochemical properties with an optical gap of 2.60 eV and a flat band potential of −0.58 VSCE. We successfully tested the photocatalytic oxidation of amoxicillin, a pharmaceutical antibiotic currently released in water as pollutant on BTSN. The oxidation follows a first order kinetic with a half-life of 123 min under solar light and a conversion yield of 72%.

Dielectric and ferroelectric properties of SrTiO3-Bi0.54Na0.46TiO3-BaTiO3 lead-free ceramics for high energy storage applications

The need of lead-free ceramics with excellent dielectric behaviors and high energy storage properties have been extensively studied. In this study, (1-x)SrTiO3-x(0.94Bi0.54Na0.46TiO3-0.06BaTiO3) ((1-x)ST-xBNBT) lead-free ceramics were designed and fabricated using the conventional solid state sintering method. The results demonstrate that the dielectric constant of (1-x)ST-xBNBT ceramics increases gradually and reaches the maximum value (∼3940) with x = 0.6 at 100 Hz, which is 11.94 times as large as that of pure SrTiO3 (∼330), and the dielectric loss is lower than 0.20 at the measured frequencies for all the samples. Meanwhile, the dielectric measurements reveal an intensified diffusion and relaxor behavior. All the samples show slim polarization-electric field (P-E) loops, and the optimal recoverable energy storage density (Wrec) of 1.88 J/cm3 together with high energy storage efficiency (η) of 79% can be achieved with x = 0.5, which indicates that the (1-x)ST-xBNBT ceramics may be promising lead-free ceramics for high energy storage applications.

Enhanced electromechanical strain response in (Fe0.5Nb0.5)4+-modified Bi0.5(Na0.8K0.2)0.5TiO3 lead-free piezoelectric ceramics

By the traditional solid-state reaction method, Bi0.5(Na0.8K0.2)0.5Ti1−x(Fe0.5Nb0.5) x O3 (marked as BNKT-xFN; x = 0.00, 0.01, 0.02, 0.03 and 0.04) piezoelectric ceramics were fabricated, and the effects of FN substitution on the dielectric, ferroelectric, piezoelectric and electric field-induced strain performance were investigated. The relative dielectric permittivity and loss tangent reveal that the phase transition temperature between ferroelectric and ergodic relaxor phase is reduced from 90 °C to room temperature (RT), even below RT, with increasing FN content. Temperature dependence of polarization–electric field loops and strain-electric field curves exhibits that the ferroelectric order is disturbed gradually, and the ergodic relaxor phase forms with increasing FN content. A large unipolar strain of 0.42% and corresponding d33* (= Smax/Emax) of 642 pm/V for the sample with x = 0.04 are obtained under 6.5 kV/mm due to the phase transition from ergodic relaxor to ferroelectric. These results indicate that the (Fe0.5Nb0.5)4+ complex ion-modified BNKT-based ceramics would have great potentials for lead-free electromechanical actuator applications.

Correlation of enhanced electrical properties and domain structure of high-TC PMN-PH-PT ceramics prepared by different methods

The dielectric, ferroelectric and piezoelectric properties of the high-Curie temperature (high-TC) 0.15Pb(Mg1/3Nb2/3)O3-0.38PbHfO3-0.47PbTiO3 (0.15PMN-0.38PH-0.47PT) ceramics synthesized by three different methods were investigated. The 0.15PMN-0.38PH-0.47PT ceramics prepared by the partial oxalate route present the best electrical properties (TC = 291 °C, εm = 28,937, Pr = 32.89 μC/cm2, Ec = 9.35 kV/cm, d33 = 456.2 pC/N and Kp = 67.2%) and excellent thermal stability of the piezoactivity properties under TC. Piezoresponse force microscopy (PFM) and confocal Raman microscopy (CRM) were employed to probe the nanoscale mechanism responsible for the performance difference of the 0.15PMN-0.38PH-0.47PT ceramics prepared by three different methods, disclosing the existence of the fine stripe domains, which make up the big island domains. The interplay between the macroscopic properties and nanoscopic domain structures of the 0.15PMN-0.38PH-0.47PT ceramics has been revealed. The better ferroelectric and piezoelectric response arise from the smaller domain size, which reduces the domain wall energy; whereas the higher coercive field Ec detected by the polarization-electric field (P-E) loops results from the harder domain switching for the 0.15PMN-0.38PH-0.47PT ceramics prepared by the wet chemical synthesis techniques.

Ultraviolet-assisted cold poling of Pb(Zr0.52Ti0.48)O3 films

This paper discusses the advantages of a room-temperature poling procedure during exposure to ultraviolet light for Pb(Zr0.52Ti0.48)O3 (PZT) films. The results of these experiments include the following: for 1.7-µm-thick chemical solution-deposited PZT films, the saturation photocurrent density after a 10 min white light exposure (190–1900 nm) (no DC bias field applied) increased up to 0.066 µA/cm2 with increasing Cr thickness of top electrode in Cr/Pt bilayer electrodes. Furthermore, the d33,f piezoelectric coefficients for UV-poled samples were 40 and 20% higher than those achieved from field-only poling at either room temperature or 150 °C. Additionally, the development of an internal bias field and pinching were investigated in major and minor polarization–electric field loops. It was found that ultraviolet illumination during the poling process produced photoinduced charge carriers that became trapped by local defects and/or grain boundaries in the films.

High-energy storage performance in lead-free (0.8-x)SrTiO3-0.2Na0.5Bi0.5TiO3-xBaTiO3 relaxor ferroelectric ceramics

lead-free (0.8-x)SrTiO3-0.2Na0.5Bi0.5TiO3-xBaTiO3 ceramics (abbreviated as (0.8-x)ST-0.2NBT-xBT) were prepared by the conventional solid-state sintering method, and their crystal structure, dielectric properties, relaxor behavior and energy-storage property were investigated as a function of BT concentration. X-ray diffraction results reveal a pure perovskite structure with a pseudo-cubic phase. The dielectric measurements exhibit a relaxor behavior for all samples and the Tm gradually increases (from −49.67 °C to 67.91 °C) with increasing x. The pinched polarization-electric field (P-E) loops were observed in the samples with x ≤ 0.40 and the maximum polarization (Pm) increased from 11.37 μC/cm2 to 20.79 μC/cm2 at 8 kV/mm while x = 0.20–0.55. The maximum discharge energy-storage density (Jd) (1.78 J/cm3) is obtained in x = 0.35 ceramic with a relatively high Pm (29.19 μC/cm2) under an electric field of 17 kV/mm, which makes (0.8-x)ST-0.2NBT-xBT ceramics may be promising lead-free materials in practical high energy storage application.

Enhanced recoverable energy storage density and high efficiency of SrTiO3-based lead-free ceramics

In this study, (1−x)SrTiO3-x(Bi0.48La0.02Na0.48Li0.02Ti0.98Zr0.02O3) [(1−x)ST-xBLNLTZ] lead-free ceramics with x = 0–0.4 were designed and fabricated using the tape casting process and the subsequent conventional solid-state sintering method. The (1−x)ST-xBLNLTZ ceramics are characterized by the excellent frequency stability of the dielectric constant, large maximum polarization (Pmax), low remnant polarization (Pr), and slim polarization-electric field (P-E) loops. For the composition of x = 0.4, Pmax is increased to 30.35 μC/cm2, 3.82 times higher than that of pure SrTiO3 (7.95 μC/cm2). The breakdown strength is larger than 200 kV/cm for all the samples. The sample with x = 0.1 exhibits a high recoverable energy storage density (Wrec) of 2.59 J/cm3 and a high energy storage efficiency (η) of 85% simultaneously. The results demonstrate that the (1−x)ST-xBLNLTZ ceramics are promising lead-free materials for high energy storage applications.

Phase evolution and electrical behaviour of samarium-substituted bismuth ferrite ceramics

Bi1-xSmxFeO3 (x = 0.15–0.18) ceramics with high density were produced using spark plasma sintering. The effects of composition, synthesis conditions and temperature on the phase evolution were studied, using XRD, TEM and dielectric spectroscopy. The coexistence of the ferroelectric R3c, antiferroelectric Pnam and paraelectric Pnma phases was revealed, with relative phase fractions affected by both calcination conditions and Sm concentration. Experiments on powdered samples calcined at different temperatures up to 950 °C suggest higher calcination temperatures promote Sm diffusion, allowing samples to reach compositional homogeneity. The structural transitions from the Pnam and R3c phases to the Pnma phase were comprehensively investigated, with phase transition temperatures clearly identified. The dielectric permittivity, electrical resistivity and breakdown strength were increased upon Sm-substitution, while ferroelectric switching was suppressed. The polarization-electric field loop became increasingly narrow with increasing Sm-content, but double hysteresis loops, which may reflect a reversible antiferroelectric to ferroelectric transformation, were not observed.