Showing papers on "Ferroelectric ceramics published in 2016"

Lead-free relaxor ferroelectric ceramics with high optical transparency and energy storage ability

Abstract: We prepared highly transparent relaxor ferroelectric ceramics based on (K0.5Na0.5)NbO3 using a pressure-less solid-state sintering method without using hot isostatic pressing and spark plasma sintering. A high energy storage density of 2.48 J cm−3 and high transparency in the visible region (ca. 60% at 0.7 μm) were achieved for the 0.8(K0.5Na0.5)NbO3–0.2Sr(Sc0.5Nb0.5)O3 ceramics with submicron-sized grains (about 0.5 μm). The energy storage density of 2.48 J cm−3 exceeded all previous reports for lead-free bulk ceramics. These results demonstrate that the 0.8(K0.5Na0.5)NbO3–0.2Sr(Sc0.5Nb0.5)O3 ceramics are promising lead-free transparent dielectric materials for use in transparent electronic devices. This study not only opens up a new avenue for the design of lead-free transparent ferroelectric ceramics with a high energy storage density, but also expands the applications of (K0.5Na0.5)NbO3-based ceramics into new areas beyond piezoelectric applications.

Lead-free AgNbO3 anti-ferroelectric ceramics with an enhanced energy storage performance using MnO2 modification

Abstract: Dielectric ceramic materials have been actively studied for advanced pulsed power capacitor applications. Despite the good properties obtained in lead-based ceramics, lead-free counterparts are highly desired due to environmental regulations. This study revealed the potential of AgNbO3 to be a promising lead-free ceramic for energy storage applications. AgNbO3 ceramics fabricated using a conventional solid-state reaction method under an O2 atmosphere show a characteristic anti-ferroelectric (AFE) double hysteresis loop at an electric field of >130 kV cm−1, with a peak recoverable energy storage density (Wrec) of 1.6 J cm−3 at 140 kV cm−1. In addition, the incorporation of MnO2 into AgNbO3 can further increase Wrec, exceeding 2.3 J cm−3 at 150 kV cm−1 by the reduction of the remnant polarization, which is due to the enhanced AFE stability induced by the addition of MnO2. Of particular importance is that the 0.1 wt% MnO2-doped AgNbO3 ceramics were found to possess a good thermal stability with Wrec = 2.5–2.9 J cm−3 over a temperature range of 20–180 °C at 150 kV cm−1 and 1 Hz.

Diffuse Phase Transitions and Giant Electrostrictive Coefficients in Lead-Free Fe3+-Doped 0.5Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3 Ferroelectric Ceramics

Abstract: The electrostrictive effect has some advantages over the piezoelectric effect, including temperature stability and hysteresis-free character. In the present work, we report the diffuse phase transitions and electrostrictive properties in lead-free Fe3+-doped 0.5Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3 (BZT-0.5BCT) ferroelectric ceramics. The doping concentration was set from 0.25 to 2 mol %. It is found that by introducing Fe3+ ion into BZT-0.5BCT, the temperature corresponding to permittivity maximum Tm was shifted toward lower temperature monotonically by 37 °C per mol % Fe3+ ion. Simultaneously, the phase transitions gradually changed from classical ferroelectric-to-paraelectric phase transitions into diffuse phase transitions with a weak relaxor characteristic. Purely electrostrictive responses with giant electrostrictive coefficient Q33 between 0.04 and 0.05 m4/C2 are observed from 25 to 100 °C for the compositions doped with 1–2 mol % Fe3+ ion. The Q33 of Fe3+-doped BZT-0.5BCT ceramics is almost twice t...

Defect dipole induced large recoverable strain and high energy-storage density in lead-free Na0.5Bi0.5TiO3-based systems

Abstract: In this letter, we propose an effective route to obtain large recoverable strain, purely electrostrictive effects and high energy-storage density by inducing defect dipoles into Na0.5Bi0.5TiO3 (NBT)-based relaxor ferroelectrics. It has been found that pinched and double polarization hysteresis loops with high maximum polarization (Pmax) and negligible remanent polarization (Pr) can be observed due to the presence of acceptor-induced defect dipoles. A large recoverable strain of 0.24% with very little hysteresis and high electrostriction coefficient of 0.022 m4 C2 with purely electrostrictive characteristics were acquired when 11 mol. ‰ Mn-doped. Meanwhile, a high recoverable energy density of 1.06 J/cm3 with excellent temperature stability was obtained at the same composition owing to the enlarged value of Pmax-Pr (36.8 μC/cm2) and relatively high electric field (95 kV/cm). Our achievement can open up the exciting opportunities for ferroelectric materials in high-precision positioning devices and high ele...

Giant electrostrictive effects of NaNbO3-BaTiO3 lead-free relaxor ferroelectrics

Abstract: A giant electrostrictive effect was observed in (1 − x)NaNbO3-xBaTiO3 relaxor ferroelectric ceramics, which exhibit a high electrostrictive coefficient Q33 of ∼0.046 m4/C2 twice as large as those of Pb- and Bi-based perovskite relaxor ferroelectric ceramics. The theoretical analysis suggests that Q33 should be strongly correlated with chemical species of cations in a perovskite structure in which a strong ionic bond is of great benefit compared with a covalent bond. A hysteresis-free large electrostrictive strain of ∼0.148% up to at least 70 Hz was obtained in the x = 0.25 sample, demonstrating significant advantages over piezoelectric effects in high-precision ceramic actuators.

Inverse barocaloric effects in ferroelectric BaTiO3 ceramics

Abstract: We use calorimetry to identify pressure-driven isothermal entropy changes in ceramic samples of the prototypical ferroelectric BaTiO3. Near the structural phase transitions at ∼400 K (cubic-tetragonal) and ∼280 K (tetragonal-orthorhombic), the inverse barocaloric response differs in sign and magnitude from the corresponding conventional electrocaloric response. The differences in sign arise due to the decrease in unit-cell volume on heating through the transitions, whereas the differences in magnitude arise due to the large volumetric thermal expansion on either side of the transitions.

Dual strain mechanisms in a lead-free morphotropic phase boundary ferroelectric.

Abstract: Electromechanical properties such as d33 and strain are significantly enhanced at morphotropic phase boundaries (MPBs) between two or more different crystal structures. Many actuators, sensors and MEMS devices are therefore systems with MPBs, usually between polar phases in lead (Pb)-based ferroelectric ceramics. In the search for Pb-free alternatives, systems with MPBs between polar and non-polar phases have recently been theorized as having great promise. While such an MPB was identified in rare-earth (RE) modified bismuth ferrite (BFO) thin films, synthesis challenges have prevented its realization in ceramics. Overcoming these, we demonstrate a comparable electromechanical response to Pb-based materials at the polar-to-non-polar MPB in Sm modified BFO. This arises from 'dual' strain mechanisms: ferroelectric/ferroelastic switching and a previously unreported electric-field induced transition of an anti-polar intermediate phase. We show that intermediate phases play an important role in the macroscopic strain response, and may have potential to enhance electromechanical properties at polar-to-non-polar MPBs.

Enhanced energy-storage properties of BaZrO3-modified 0.80Bi0.5Na0.5TiO3–0.20Bi0.5K0.5TiO3 lead-free ferroelectric ceramics

Abstract: Large energy-storage density is observed in BaZrO3 (BZ)-modified 0.80Bi0.5Na0.5TiO3-0.20Bi0.5K0.5TiO3 (BNBK) lead-free ferroelectric (FE) ceramics synthesized by conventional solid-state reaction. The energy-storage property of (1 − x)BNBK–xBZ has been investigated. Certain content of BZ can enhance the energy-storage property of BNBK by enhancing the breakdown strength. The largest energy-storage density W 1 = 0.73 J/cm3 and efficiency of energy storage η = 0.75 at E = 70 kV/cm are achieved in the 0.96BNBK–0.04BZ, which is significantly higher than that of BNT-based and lead-containing FE materials reported. Its energy-storage density exhibits the superior thermal stability with temperature range of 30–100 °C. Those properties promise that the environmental friendly (1 − x)BNBK–xBZ ceramics are candidate for applications of energy-storage devices.

Size dependent magnetic and electrical properties of Ba-doped nanocrystalline BiFeO3

Abstract: Improvement in magnetic and electrical properties of multiferroic BiFeO3 in conjunction with their dependence on particle size is crucial due to its potential applications in multifunctional miniaturized devices. In this investigation, we report a study on particle size dependent structural, magnetic and electrical properties of sol-gel derived Bi0.9Ba0.1FeO3 nanoparticles of different sizes ranging from ∼ 12 to 49 nm. The substitution of Bi by Ba significantly suppresses oxygen vacancies, reduces leakage current density and Fe2+ state. An improvement in both magnetic and electrical properties is observed for 10 % Ba-doped BiFeO3 nanoparticles compared to its undoped counterpart. The saturation magnetization of Bi0.9Ba0.1FeO3 nanoparticles increase with reducing particle size in contrast with a decreasing trend of ferroelectric polarization. Moreover, a first order metamagnetic transition is noticed for ∼ 49 nm Bi0.9Ba0.1FeO3 nanoparticles which disappeared with decreasing particle size. The observed stro...

Formation mechanism of highly [0 0 1]c textured Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 relaxor ferroelectric ceramics with giant piezoelectricity

Abstract: We investigated the synthesis mechanism and giant piezoelectricity of highly [0 0 1] c textured Pb(In 1/2 Nb 1/2 )O 3 -Pb(Mg 1/3 Nb 2/3 )O 3 -PbTiO 3 (PIN-PMN-PT) relaxor based ferroelectric ceramics (texture fraction ∼94%) with BaTiO 3 (BT) templates. The onset of texture occurred at ∼88% relative density (RD), and rapid increase in texture fraction happened with RD > 94%. A PbO-rich grain boundary liquid of ∼6–13 nm thickness, detected at oriented crystalline interfaces, facilitated epitaxial nucleation and subsequent [0 0 1] PIN-PMN-PT ||[0 0 1] BT growth of textured grains on BT templates. Interfaces between BT templates and PIN-PMN-PT textured grains were found to be coherent and defect-free at the atomic scale, and there was almost no barium diffusion across the interfaces during the texturing process. Nanodomains were clearly visible in the oriented grains. [0 0 1] c poling ordered the domain structures of textured ceramics and resulted in a more uniform domain size of several hundred nanometers. The textured ternary PIN-PMN-PT ceramics exhibited ∼200% improvement in piezoelectric response relative to their random counterparts, as a result of their piezoelectric anisotropy and engineered domain status along with higher mobility of domain walls.

Excitation of fundamental shear horizontal wave by using face-shear (d36) piezoelectric ceramics

Abstract: The fundamental shear horizontal (SH0) wave in plate-like structures is extremely useful for non-destructive testing (NDT) and structural health monitoring (SHM) as it is non-dispersive. However, currently, the SH0 wave is usually excited by electromagnetic acoustic transducers (EMAT) whose energy conversion efficiency is fairly low. The face-shear ( d36) mode piezoelectrics is more promising for SH0 wave excitation, but this mode cannot appear in conventional piezoelectric ceramics. Recently, by modifying the symmetry of poled PbZr1−xTixO3 (PZT) ceramics via ferroelastic domain engineering, we realized the face-shear d36 mode in both soft and hard PZT ceramics. In this work, we further improved the face-shear properties of PZT-4 and PZT-5H ceramics via lateral compression under elevated temperature. It was found that when bonded on a 1 mm-thick aluminum plate, the d36 type PZT-4 exhibited better face-shear performance than PZT-5H. We then successfully excite SH0 wave in the aluminum plate using a face-sh...

Direct electrocaloric measurement of 0.9Pb(Mg1/3Nb2/3)O3-0.1PbTiO3 films using scanning thermal microscopy

Abstract: We show that scanning thermal microscopy can measure reversible electrocaloric (EC) effects in <40 μm-thick ceramic films of the relaxor ferroelectric 0.9Pb(Mg1/3Nb2/3)O3-0.1PbTiO3, with the substrate present. We recorded roughly the same non-adiabatic temperature change (±0.23 K) for a thinner film that was driven harder than a thicker film (±31 V μm−1 across 13 μm versus ±11 V μm−1 across 38 μm), because the thicker film lay relatively closer to the substantially larger adiabatic values that we predicted by thermodynamic analysis of electrical data. Film preparation was compatible with the fabrication of EC multilayer capacitors, and therefore our measurement method may be exploited for rapid characterisation of candidate films for cooling applications.

Large enhancement of the electrocaloric effect in PLZT ceramics prepared by hot-pressing

Abstract: In this contribution, we demonstrate the optimization of the microstructures of the Pb0.85La0.1(Zr0.65Ti0.35)O3 (PLZT) relaxor ferroelectric ceramics and subsequent enhancements in their polarization and electrical resistivity by using a hot-pressing process. The resulting superior breakdown strength of hot-pressed PLZT enables the application of high electric field to induce a giant electrocaloric effect, in which the adiabatic change of temperature (ΔT) and the isothermal change of entropy (ΔS) are around 2 times greater than those of the samples prepared by the conventional sintering approach using muffle furnace. Moreover, the addition of extra PbO to make up the loss of Pb in the high-temperature sintering leads to the further improvements in the phase composition and electrical properties of PLZT, due to inhibition of the pyrochlore phase formation. The relationship among the sintering conditions, the content of excess PbO, and the microstructure as well as the electrical characteristics of PLZT hav...

Morphotropic NaNbO3-BaTiO3-CaZrO3 lead-free ceramics with temperature-insensitive piezoelectric properties

Abstract: A morphotropic NaNbO3-based lead-free ceramic was reported to have temperature-insensitive piezoelectric and electromechanical properties (d33 = 231 pC/N, kp = 35%, Tc = 148 °C, and low-hysteresis strain ∼0.15%) in a relatively wide temperature range. This was fundamentally ascribed to the finding of a composition-axis vertical morphotropic phase boundary in which coexisting ferroelectric phases are only compositionally driven and thermally insensitive. Both phase coexistence and nano-scaled domain morphology deserved well enhanced electrical properties, as evidenced by means of synchrotron x-ray diffraction and transmission electron microscopy. Our study suggests that the current lead-free ceramic would be a very promising piezoelectric material for actuator and sensor applications.

Phase transformation induced by electric field and mechanical stress in Mn-doped (Bi1/2Na1/2)TiO3-(Bi1/2K1/2)TiO3 ceramics

Abstract: Electric-field- and stress-induced phase transformations were investigated in polycrystalline 0.5 mol. % Mn-doped (1−x)(Bi1/2Na1/2)TiO3-x(Bi1/2K1/2)TiO3 (x = 0.1, 0.2). To characterize the effect of electric field and stress on the stability of the ferroelectric and relaxor states, polarization- and current density-electric field curves, as well as the stress-strain response as a function of temperature were characterized. Analogous to the observed electrical behavior, the macroscopic mechanical constitutive behavior showed a closed hysteresis at elevated temperatures, indicating a reversible stress-induced relaxor-to-ferroelectric transformation. The electrical and mechanical measurements were used to construct electric field–temperature and stress-temperature phase diagrams, which show similar characteristics. These data show that a mechanical compressive stress, similarly to an electric field, can induce long-range ferroelectric order in a relaxor ferroelectric.

Room temperature dual ferroic behaviour of ball mill synthesized NdFeO3 orthoferrite

Abstract: Phase pure NdFeO3 has been achieved using high energy ball milling of oxide precursors with subsequent sintering. It is established that structural arrangement of NdFeO3 regulates the multifunctional feature of the material. Rietveld refinement of the room temperature X-ray diffraction pattern shows that the Fe-O-Fe bond angle significantly favors the super exchange interaction, which is predominantly antiferromagnetic in nature. Magnetization measurement illustrates antiferromagnetic behaviour with a weak ferromagnetic component caused by the canted nature of the Fe3+ spins at room temperature. Absorption bands in the visible ambit, apparent from the UV-Vis diffuse reflectance studies, is found due to the crystal ligand field of octahedral oxygen environment of Fe3+ ions. The direct band gap is estimated to be 2.39 eV from the diffuse reflectance spectrum. The lossy natured ferroelectric loop having a maximum polarization of 0.23 μC/cm2 at room temperature is found to be driven by the non-collinear magne...

Crystallographic dependence of internal bias in domain engineered Mn-doped relaxor-PbTiO3 single crystals

Abstract: The incorporation of acceptor dopants and the resulting internal bias in Pb(Zr,Ti)O3 (PZT) piezoelectric ceramics lead to reduced electrical and mechanical losses, but at the expense of decreased electromechanical properties. Analogous to PZTs, acceptor doped relaxor-PbTiO3 (relaxor-PT) single crystals show an improved mechanical quality factor (decreased mechanical loss), but with a minimal impact on the electromechanical properties. In this research, the internal bias and associated impacts on electromechanical properties were studied in Mn-doped Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 (Mn:PIN–PMN–PT) single crystals, showing strong crystallographic orientation dependent behaviors. By active control of defect dipoles through domain engineering, different defect dipole configurations were obtained (defect dipole engineering), leading to the unique characteristics of relaxor-PT single crystals when compared to the conventional polycrystalline ferroelectric ceramics.

Retention of intermediate polarization states in ferroelectric materials enabling memories for multi-bit data storage

Abstract: A homogeneous ferroelectric single crystal exhibits only two remanent polarization states that are stable over time, whereas intermediate, or unsaturated, polarization states are thermodynamically instable. Commonly used ferroelectric materials however, are inhomogeneous polycrystalline thin films or ceramics. To investigate the stability of intermediate polarization states, formed upon incomplete, or partial, switching, we have systematically studied their retention in capacitors comprising two classic ferroelectric materials, viz. random copolymer of vinylidene fluoride with trifluoroethylene, P(VDF-TrFE), and Pb(Zr,Ti)O3. Each experiment started from a discharged and electrically depolarized ferroelectric capacitor. Voltage pulses were applied to set the given polarization states. The retention was measured as a function of time at various temperatures. The intermediate polarization states are stable over time, up to the Curie temperature. We argue that the remarkable stability originates from the coexistence of effectively independent domains, with different values of polarization and coercive field. A domain growth model is derived quantitatively describing deterministic switching between the intermediate polarization states. We show that by using well-defined voltage pulses, the polarization can be set to any arbitrary value, allowing arithmetic programming. The feasibility of arithmetic programming along with the inherent stability of intermediate polarization states makes ferroelectric materials ideal candidates for multibit data storage.

Effects of oxygen vacancies on polarization stability of barium titanate

Abstract: Oxygen vacancy, a kind of native point defects in ferroelectric ceramics, usually causes an increase of the dielectric loss. Based on experimental observations, it is believed that all of the oxygen vacancies are an unfavorable factor for energy saving. By using molecular dynamics simulations, we show that the increase of coercive and saturated electric fields is due to the difficulty to switch local polarization near an oxygen vacancy, and so that a ferroelectric device has to sustain the rising consumption of energy. The simulation results also uncover how oxygen vacancies influence ferroelectric properties.

Effect of cooling rate on phase transitions and ferroelectric properties in 0.75BiFeO3-0.25BaTiO3 ceramics

Abstract: The effect of the cooling rate on the electrical properties was investigated in the 0.75BiFeO3-0.25BaTiO3 ceramics. The air-quenched samples had superior ferroelectric and piezoelectric properties to the slowly cooled samples. The quenching effect weakened when the quenching temperature was less than 700 °C and eventually disappeared at 500 °C and below. The X-ray diffraction and transmission electron microscopy showed that the cooling rate had a significant effect on the crystal structure and domain structure. The slowly cooled sample showed a very small rhombohedral distortion and a poorly developed domain structure, which leads to weak ferroelectric and piezoelectric properties at room temperature. The quenched and slowly cooled samples had a ferroelectric rhombohedral structure (R3c) at room temperature and a paraelectric cubic structure (Pm-3m) at temperatures above 650 °C. On the other hand, the slowly cooled sample had a centro-symmetric orthorhombic (Pbnm) structure at intermediate temperatures, w...

Phase structure–electrical property relationships in Pb(Ni1/3Nb2/3)O3–Pb(Zr,Ti)O3-based ceramics

Abstract: Generally, the phase structure change of Pb(B′ B″)O3–PZT solid solutions near a morphotropic phase boundary (MPB) can be originated from composition variations. Here our results show that the excess PbO and the sintering temperature can also result in the ferroelectric phase structure change in the Pb(Ni1/3Nb2/3)O3–Pb(Zr,Ti)O3 (PNN–PZT)-based ceramics near the MPB. The dielectric, piezoelectric, and ferroelectric properties are dependent on the tetragonal phase content (TP) which is closely associated with the excess PbO and the sintering temperature. The temperature dependence of the polarization (P)–electric field (E) hysteresis loops reveals that the tetragonal phase in the PNN–PZT-based ceramics has a lower activation energy (Ea) for domain wall movement than that of the rhombohedral phase, thus resulting in easier polarization rotation. This is responsible for the phase structure–electrical property relationships in the PNN–PZT-based ceramics, exhibiting the dependence of the tetragonal phase content (TP) on the electrical properties.

Upper limit of the electrocaloric peak in lead-free ferroelectric relaxor ceramics

Abstract: The electrocaloric effect (ECE) of two compositions (x = 0.06 and 0.07) of (1 − x)(Na0.5Bi0.5)TiO3-xKNbO3 in the vicinity of the morphotropic phase boundary is studied by direct measurements. ΔTmax = 1.5 K is measured at 125 °C under 70 kV/cm for NBT-6KN while ΔTmax = 0.8 K is measured at 75 °C under 55 kV/cm for NBT-7KN. We show that the “shoulder,” TS, in the dielectric permittivity, marks the upper limit of the ECE peak under high applied electric fields. These results imply that the range of temperature with high ECE can be quickly identified for a given composition, which will significantly speed up the process of materials selection for ECE cooling.