Showing papers on "Ferroelectric ceramics published in 2014"

Optical temperature sensor based on upconversion emission in Er-doped ferroelectric 0.5Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3 ceramic

Abstract: Optical temperature sensing properties based on upconversion emission of Er-doped 0.5Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3 ferroelectric ceramics are reported. The fluorescence intensity ratio of green upconversion emissions at 525 and 550 nm in the temperature range of 200–443 K was investigated. The maximum sensing sensitivity and temperature resolution were found to be 0.0044 K−1 and 0.4 K, respectively, suggesting that the Er-doped 0.5Ba(Zr0.2Ti0.8)O3- 0.5(Ba0.7Ca0.3)TiO3 ferroelectric ceramic possesses potential application in optical temperature sensing. Ferroelectric and piezoelectric properties were also investigated. These results reveal that the Er-doped 0.5Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3 ferroelectric ceramic is a promising multifunctional sensing material.

Enhanced electrocaloric effect in lead-free BaTi1−xSnxO3 ceramics near room temperature

Abstract: The electrocaloric effect in lead-free BaTi1−xSnxO3 (BTSn, x = 0.08, 0.105, and 0.14) ferroelectric ceramics was studied by using an indirect method. It was found that the largest electrocaloric response could be achieved in BTSn with x = xQP = 0.105 near room temperature with an adiabatic temperature change ΔT of 0.61 K and an electrocaloric strength ΔT/ΔE of 0.31 K mm kV−1, under a modest electric field ΔE of 20 kV cm−1, which is comparable with the best values reported in lead-free materials. These enhanced values are attributed to the multiphase (four phases) coexistence at x = xQP corresponding to the quasi-quadruple point composition.

Major contributor to the large piezoelectric response in (1 − x)Ba(Zr0.2Ti0.8)O3 − x(Ba0.7Ca0.3)TiO3 ceramics: Domain wall motion

Abstract: The piezoelectric activity of lead-free Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3 (BZT-xBCT) ceramics has been investigated as a function of composition by using Rayleigh analysis under subswitching-electric-field in combination with large-electric-field strain measurement. The result shows that the intrinsic piezoelectric response exhibits peak values in the vicinity of composition-induced R (rhombohedral)-MPB (morphotropic phase boundary) and MPB-T (tetragonal) phase transitions, but being much less than total d33 value. On the other hand, the extrinsic piezoelectric response, especially the one associated with reversible domain wall motion, has been greatly enhanced in the phase instability regime. Our results indicate that the extrinsic piezoelectric activity is the major contributor to the high piezoelectricity in BZT-xBCT ceramics.

Electro-caloric effect in lead-free Sn doped BaTiO3 ceramics at room temperature and low applied fields

Abstract: Structural, dielectric, ferroelectric (FE), 119Sn Mossbauer, and specific heat measurements of polycrystalline BaTi1–xSnxO3 (x = 0% to 15%) ceramics are reported. Phase purity and homogeneous phase formation with Sn doping is confirmed from x-ray diffraction and 119Sn Mossbauer measurements. With Sn doping, the microstructure is found to change significantly. Better ferroelectric properties at room temperature, i.e., increased remnant polarization (38% more) and very low field switchability (225% less) are observed for x = 5% sample as compared to other samples and the results are explained in terms of grain size effects. With Sn doping, merging of all the phase transitions into a single one is observed for x ≥ 10% and for x = 5%, the tetragonal to orthorhombic transition temperature is found close to room temperature. As a consequence better electro-caloric effects are observed for x = 5% sample and therefore is expected to satisfy the requirements for non-toxic, low energy (field) and room temperature b...

Large strain response based on relaxor-antiferroelectric coherence in Bi0.5Na0.5TiO3–SrTiO3–(K0.5Na0.5)NbO3 solid solutions

Abstract: The effect of (K0.5Na0.5)NbO3 (KNN) addition on the ferroelectric and dielectric behavior of 90Bi0.5Na0.5TiO3–10SrTiO3 (BNT–ST) lead-free piezoceramics was investigated. Polarization and strain hysteresis loops indicate that a relaxor-antiferroelectric coherence will be produced with the addition of KNN as a replacement for ST up to 5% and the destabilization of the phase coherence is accompanied by an enhancement of the bipolar strain with the increase of temperature, which is ∼0.37% (corresponding to a large signal d33* of ∼530 pm/V at 90 °C) at 5 mol. % KNN content. This strain was analyzed as derived from an electrostrictive effect at lower electric fields and a field-induced antiferroelectric-ferroelectric phase transition at higher electric fields. The large polar strain response would be of great interest for environmental friendly high-temperature actuators.

Dual-enhancement of ferro-/piezoelectric and photoluminescent performance in Pr3+ doped (K0.5Na0.5)NbO3 lead-free ceramics

Abstract: A mutual enhancement action between the ferro-/piezoelectric polarization and the photoluminescent performance of rare earth Pr3+ doped (K0.5Na0.5)NbO3 (KNN) lead-free ceramics is reported. After Pr3+ doping, the KNN ceramics exhibit the maximum enhancement of ∼1.2 times in the ferroelectric remanent polarization strength and ∼1.25 times in the piezoelectric coefficient d33, respectively. Furthermore, after undergoing a ferro-/piezoelectric polarization treatment, the maximum enhancement of ∼1.3 times in photoluminescence (PL) was observed in the poled 0.3% Pr3+ doped sample. After the trivalent Pr3+ unequivalently substituting the univalent (K0.5Na0.5)+, A-sites ionic vacancies will occur to maintain charge neutrality, which may reduce the inner stress and ease the domain wall motions, yielding to the enhancement in ferro-/piezoelectric performance. The polarization-induced enhancement in PL is attributed to the decrease of crystal symmetry abound the Pr3+ ions after polarization. The dual-enhancement of...

Electric-field–temperature phase diagram of the ferroelectric relaxor system (1 − x)Bi1/2Na1/2TiO3 − xBaTiO3 doped with manganese

Abstract: The electric-field–temperature phase diagram for the lead-free relaxor material (1 − x)(Bi1/2Na1/2)TiO3 − xBaTiO3 (x = 0.03, 0.06, and 0.09) doped with 0.5 mol% Mn (BNT-100xBT:Mn) was established. Transition lines between ergodic or nonergodic relaxor states and the field-induced ferroelectric state were determined at constant temperatures with electric-field-dependent measurements of the polarization as well as of the piezoelectric coefficient and permittivity. Near the depolarization temperature T d, the switching between two ferroelectric poling directions occurs in two steps via an intermediate relaxor state. This effect is closely related to the pinching of the ferroelectric hysteresis loop.

Enhanced ferroelectricity, piezoelectricity, and ferromagnetism in Nd-modified BiFeO3-BaTiO3 lead-free ceramics

Abstract: Lead-free multiferroic ceramics of 0.75Bi1−xNdxFeO3 − 0.25BaTiO3 + 1 mol. % MnO2 were prepared by a conventional ceramic technique and their structure, piezoelectricity, and multiferroicity were studied. The ceramics sintered at 890–990 °C possess a pure perovskite structure. A morphotropic phase boundary of rhombohedral and monoclinic phases is formed at x = 0.05. A small amount of Nd improves the ferroelectric and piezoelectric properties of the ceramics. The ferroelectric-paraelectric phase transition becomes gradually diffusive with x increasing. After the addition of Nd, the ferromagnetism of the ceramics is greatly enhanced by ∼320%. The increase in sintering temperature improves significantly the ferroelectric, piezoelectric, and ferromagnetic properties of the ceramics. The ceramics with x = 0.05 sintered at 950–990 °C possess improved ferroelectricity, piezoelectricity, magnetism and insulation with Pr of 16.5–17.5 μC/cm2, d33 of 113–121 pC/N, Mr of 0.127–0.138 emu/g, R of ∼5 × 109 Ω·cm and high ...

Mechanical confinement for improved energy storage density in BNT-BT-KNN lead-free ceramic capacitors

Abstract: With the advent of modern power electronics, embedded circuits and non-conventional energy harvesting, the need for high performance capacitors is bound to become indispensible. The current state-of-art employs ferroelectric ceramics and linear dielectrics for solid state capacitance. However, lead-free ferroelectric ceramics propose to offer significant improvement in the field of electrical energy storage owing to their high discharge efficiency and energy storage density. In this regards, the authors have investigated the effects of compressive stress as a means of improving the energy storage density of lead-free ferroelectric ceramics. The energy storage density of 0.91(Bi0.5Na0.5)TiO3-0.07BaTiO3-0.02(K0.5Na0.5)NbO3 ferroelectric bulk ceramic was analyzed as a function of varying levels of compressive stress and operational temperature .It was observed that a peak energy density of 387 mJ.cm-3 was obtained at 100 MPa applied stress (25oC). While a maximum energy density of 568 mJ.cm-3 was obtained fo...

Effects of oxygen vacancies on dielectric, electrical, and ferroelectric properties of Ba4Nd2Fe2Nb8O30 ceramics

Abstract: Effects of oxygen vacancies on the dielectric, electrical, and ferroelectric properties of Ba4Nd2Fe2Nb8O30 ceramics were investigated. A dielectric relaxation above Tc can be ascribed to the trap-controlled ac conduction around doubly ionized oxygen vacancies. The dc conductivity of the N2-annealed and O2-annealed samples is attributed to the long-range motion of the Vo⋅⋅, and that of the as-sintered sample is considered to be governed by the electronic and oxygen-vacancy ionic mixed conduction mechanism. Low concentration and random distributed oxygen vacancies are propitious to the domain switching, while high concentration and allied oxygen defects hinder the domain-wall movement.

Multiferroism and enhancement of material properties across the morphotropic phase boundary of BiFeO3-PbTiO3

Abstract: Strong phase-change magnetoelectric responses have been anticipated by a first-principles investigation of phases in the perovskite BiFeO3-BiCoO3 solid solution, specifically at the morphotropic phase boundary (MPB) between the multiferroic rhombohedral and tetragonal polymorphs. This might be a general property of multiferroic MPBs and a novel promising approach for room temperature magnetoelectricity, which requires the identification of suitable material systems. We present here a comprehensive description of the electrical and electromechanical properties across one such system; the perovskite BiFeO3-PbTiO3 solid solution. All the temperature dependence of dielectric permittivity, ferroelectric hysteresis loops, and piezoelectric coefficients have been obtained, and are discussed in relation to the previously reported perovskite structural evolution. Results show ceramic materials to be very promising for ferroelectric random access memories (remnant polarization as high as 63 μC cm−2 with a comparatively low coercive field of 4.5 kV mm−1 for MPB compositions) and high temperature electromechanical transduction (crystal piezoelectric coefficient of 87 pC N−1 with a Curie temperature above 873 K). Moreover, the occurrence of phase changes between the monoclinic and tetragonal polymorphs under high electric fields is indicated, while the canted antiferromagnetic character of the phases involved is corroborated.

Grain and the concomitant ferroelectric domain size dependent physical properties of Ba0.85Ca0.15Zr0.1Ti0.9O3 ceramics fabricated using powders derived from oxalate precursor route

Abstract: Fine powders comprising nanocrystallites of Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) were synthesized via oxalate precursor method, which facilitated to obtain homogenous and large grain sized ceramics at a lower sintering temperature. The compacted powders were sintered at various temperatures in the range of 1200 °C–1500 °C for an optimized duration of 10 h. Interestingly the one that was sintered at 1450 °C/10 h exhibited well resolved Morphotrophic Phase Boundary. The average grain size associated with this sample was 30 μm accompanied by higher domain density mostly with 90° twinning. These were believed to have significant contribution towards obtaining large strain of about 0.2% and piezoelectric coefficient as high as 563 pC/N. The maximum force that was generated by BCZT ceramic (having 30 μm grain size) was found to be 161 MPa, which is much higher than that of known actuator materials such as PZT (40 MPa) and NKN-5-LT (7 MPa).

Structure and ferroelectricity of nonstoichiometric (Na0.5Bi0.5)TiO3

Abstract: Stoichiometric (Na0.5Bi0.5)TiO3 (NBT) adopts the ABO3 perovskite structure with the A-site equally occupied by Na+ and Bi3+ ions. However, non-stoichiometric compositions can be synthesized intentionally or unintentionally. To determine the effect of A-site nonstoichiometry on the crystal structure and ferroelectricity of NBT, the composition of (Na0.5−xBi0.5+x)TiO3+x was varied using x = −0.01, −0.005, 0, 0.005, and 0.01. High resolution synchrotron x-ray diffraction and Rietveld refinement revealed that a shift in either direction from x = 0 results in a decrease in the spontaneous ferroelastic strain. Ferroelectric hysteresis and piezoelectric coefficients were found to be optimum in the stoichiometric composition.

An analysis of lead-free (Bi0.5Na0.5)0.915-(Bi0.5K0.5)0.05Ba0.02Sr0.015TiO3 ceramic for efficient refrigeration and thermal energy harvesting

Abstract: This article demonstrates the colossal energy harvesting capability of a lead-free (Bi0.5Na0.5)0.915-(Bi0.5K0.5)0.05Ba0.02Sr0.015TiO3 ceramic using the Olsen cycle. The maximum harvestable energy density estimated for this system is found to be 1523 J/L (1523 kJ/m3) where the results are presented for extreme ambient conditions of 20–160 °C and electric fields of 0.1–4 MV/m. This estimated energy density is 1.7 times higher than the maximum reported to date for the lanthanum-doped lead zirconate titanate (thin film) system. Moreover, this study introduces a generalized and effective solid state refrigeration cycle in contrast to the ferroelectric Ericson refrigeration cycle. The cycle is based on a temperature induced polarization change on application of an unipolar electric field to ferroelectric ceramics.

Enhancing electrical energy storage density in anti-ferroelectric ceramics using ferroelastic domain switching

Abstract: Capacitors form an indispensable part of many modern electrical and electronic devices. An ideal capacitor is expected to possess high power and energy density along with enhanced energy recovery characteristics. Anti-ferroelectric materials form a suitable candidate for ceramic-based capacitor applications, owing to their low loss and high energy density. However, these materials show ample room for improvement through physical means. In this regard, the present work deals with mechanical tuning of the energy storage density and recoverable efficiency in known anti-ferroelectric materials. For this study, various configurations of (Pb1?xLax)(Zr0.90Ti0.10)1?x/4O3 (PLZTx) ceramics have been investigated. Both mechanical confinement and temperature applications have been shown to improve the performance characteristics of all selected compositions. This behavior has been explained on the basis of competing ferroelectric and ferroelastic domain rotations. The application of suitable stress/temperature reduces hysteresis losses and delays anti-ferroelectric???ferroelectric phase transformation, which increases the electrical energy storage capacity of these materials. Mechanical confinement was observed to provide an increase in energy storage density and efficiency by approximately 38% and 25%, respectively, for the PLZT4 composition. The highest recoverable energy density of 698 m J cm?3 was achieved under compressive stress of a 100 MPa and 60 kV cm?1 applied electric field.

Antiferroelectricity induced by electric field in NaNbO3-based lead-free ceramics

Abstract: Electric fields are known to favor a ferroelectric phase with parallel electric dipoles over an antiferroelectric phase. We demonstrate in this Letter that electric fields can induce an antiferroelectric phase out of a ferroelectric phase in a NaNbO3-based lead-free polycrystalline ceramic. Such an unlikely ferroelectric-to-antiferroelectric phase transition occurs at fields with a reversed polarity and competes with the ferroelectric polarization reversal process.

Residual ferroelectricity in barium strontium titanate thin film tunable dielectrics

Abstract: Loss reduction is critical to develop Ba1−xSrxTiO3 thin film tunable microwave dielectric components and dielectric energy storage devices. The presence of ferroelectricity, and hence the domain wall contributions to dielectric loss, will degrade the tunable performance in the microwave region. In this work, residual ferroelectricity—a persistent ferroelectric response above the global phase transition temperature—was characterized in tunable dielectrics using Rayleigh analysis. Chemical solution deposited Ba0.7Sr0.3TiO3 films, with relative tunabilities of 86% over 250 kV/cm at 100 kHz, demonstrated residual ferroelectricity 65 °C above the ostensible paraelectric transition temperature. Frequency dispersion observed in the dielectric temperature response was consistent with the presence of nanopolar regions as one source of residual ferroelectricity. The application of AC electric field for the Rayleigh analysis of these samples led to a doubling of the dielectric loss for fields over 10 kV/cm at room temperature.

Low electric-field driven ultrahigh electrostrains in Sb-substituted (Na,K)NbO3 lead-free ferroelectric ceramics

Abstract: Lead-free (Na0.52K0.48)(Nb1−ySby)O3 (NKNSy) ferroelectric ceramics were reported to exhibit an ultrahigh electrostrain (dynamic d33* (=S/E) of 800–1100 pm/V) in a relatively low driving electric field range (1–4 kV/mm). As evidenced by in-situ synchrotron x-ray diffraction and dielectric measurements, the mechanism of generating large strains was ascribed to both the low-field induced reversible rhombohedral-monoclinic phase transition (1–2 kV/mm) and the enhanced domain switching (2–4 kV/mm) owing to the normal to relaxor phase transformation, which contribute to ∼62% and ∼38% of the total strain, respectively. The results indicate that the NKNSy compositions would have excellent potentials for applications of lead-free actuator ceramics.

Dielectric Relaxor Evolution and Frequency‐Insensitive Giant Strains in (Bi0.5Na0.5)TiO3‐Modified Bi(Mg0.5Ti0.5)O3–PbTiO3 Ferroelectric Ceramics

Abstract: The 0.45Bi(Mg0.5Ti0.5)O3–(0.55 − x)PbTiO3–x(Bi0.5Na0.5)TiO3 (BMT–PT–xBNT) ternary solid solution ceramics were prepared via a conventional solid-state reaction method; the evolution of dielectric relaxor behavior and the electrostrain features were investigated. The XRD and dielectric measurements showed that all studied compositions own a single pseudocubic perovskite structure and undergo a diffuse-to-relaxor phase transition owing to the evolution of the domain from a frozen state to a dynamic state. The formation of the above dielectric relaxor behavior was further confirmed by a couple of measurements such as polarization loops, polarization current density curves, as well as bipolar strain loops. A large strain value of ~0.41% at a driving field of 7 kV/mm (normalized strain d33* of ~590 pm/V) was obtained at room temperature for the composition with x = 0.32, which is located near the boundary between ergodic and nonergodic relaxor. Moreover, this electric field-induced large strain was found to own a frequency-insensitive characteristic.

Characterisation of ferroelectric bulk materials and thin films

Abstract: Electrical Measurement of Ferroelectric Properties.- Piezoelectric Resonance.- Direct Piezoelectric Measurement - The Berlincourt Method.- Characterisation of Pyroelectric Materials.- Interferometry for Piezoelectric Materials and Thin Films.- Temperature Dependence of Ferroelectric and Piezoelectric Properties of PZT Ceramics.- Measurement and Modelling of Self-Heating in Piezoelectric Materials and Devices.- Piezoresponse Force Microscopy.- Indentation Stiffness Analysis of Ferroelectric Thin Films.- Losses in Piezoelectrics via Complex Resonance Analysis.- Dielectric Breakdown in Dielectrics and Ferroelectric Ceramics.- Standards for Piezoelectric and Ferroelectric Ceramics.

Microstructures, dielectric, and piezoelectric properties of W/Cr co-doped Bi4Ti3O12 ceramics

Abstract: W/Cr co-doped Bi4Ti3O12 (BTWC) ceramics {Bi4Ti3−xWxO12 + x + 0.2 wt. % Cr2O3 (x = 0–0.1)} with a high piezoelectricity were prepared by a conventional ceramic process, and effects of W/Cr dopant on the microstructures, dielectric, and piezoelectric properties of ceramics were explored. It is found that W6+ modified the grain morphology and size of ceramics, promoting the forming of the regular schistose grains with a size of ∼10 μm in the ceramic at x = 0.05. BTWC ceramics showed a continuous decrease in Tc and a gradual increase in er with the increasing W doping content. While the hard-doping of Cr2O3 decreased, the TKe and tan δ of ceramics available. All the ceramics keep the nature of first-order transition and displacive ferroelectrics. The d33 and kp of BTWC ceramics were remarkably improved by the soft-doping of W6+. Excellent electrical properties (e.g., Tc = 638 °C, er = 146, tan δ = 0.56%, TKe (500 °C) = 1.30 × 10−3/ °C, τ (500 °C) = 4.08 × 10−5 s, d33 = 28 pC/N, and kp = 6.17%) have been achie...

Significant increase of Curie temperature in nano-scale BaTiO3

Abstract: The low Curie temperature (Tc = 130 °C) of bulk BaTiO3 greatly limits its applications. In this work, the phase structures of BaTiO3 nanoparticles with sizes ranging from 2.5 nm to 10 nm were studied at various temperatures by using aberration-corrected transmission electron microscopy (TEM) equipped with an in-situ heating holder. The results implied that each BaTiO3 nanoparticle was composed of different phases, and the ferroelectric ones were observed in the shells due to the complicated surface structure. The ferroelectric phases in BaTiO3 nanoparticles remained at 600 °C, suggesting a significant increase of Tc. Based on the in-situ TEM results and the data reported by others, temperature-size phase diagrams for BaTiO3 particles and ceramics were proposed, showing that the phase transition became diffused and the Tc obviously increased with decreasing size. The present work sheds light on the design and fabrication of advanced devices for high temperature applications.