BiFeO3 BaTiO3 Research Articles

Enhanced resistivity and strain stability of BiFeO3–BaTiO3 ceramics by hot‐press sintering in oxygen atmosphere

AbstractEven though BiFeO3–BaTiO3 (BF–BT) with high Curie temperature and excellent piezoelectric properties is very suitable for high‐temperature applications, its rapid reduction in resistivity with temperature limits its further application. So far, there is no effective method to improve the resistivity of BF–BT at a high‐temperature state. In this work, hot‐press sintering combined with an oxygen atmosphere was used to prepare (1 − x)BF–xBT (x = 0.2–0.33) ceramics for the first time, which reduced the sintering temperature from 1000 to 920°C. The controllable grain size can be achieved by adjusting the sintering temperature and the applied pressure. The X‐ray photoelectron spectroscopy results confirmed that using hot‐press sintering effectively avoided the generation of heterovalent Fe ions, and the resistivity of BF–BT ceramics at the high‐temperature stage was improved by two orders of magnitude. It was found that hot‐press sintering can cause the oriented growth of the sample along the (1 1 0) direction, and further refined X‐ray diffraction was used to accurately analyze the changes in the lattice structure. The hot‐press sintered samples obtained larger polarization strength, especially the electro‐induced strain showed excellent temperature stability in the wide temperature range of 30–170°C. Hot‐pressing sintering combined with an oxygen atmosphere is more suitable for preparing high insulation and electrical breakdown resistance ceramics.

High-efficiency energy storage in Nd-doped (1-x)BiFeO3–xBaTiO3 relaxor ferroelectric ceramics

Dielectric capacitors as energy storage electronics have drawn much attention due to ultrahigh power densities with quick charging and discharging rates. In this report, A-site Nd-doped (1-x)BiFeO3-xBaTiO3 (x = 0.2–0.45) relaxor ferroelectric ceramics with superior storage efficiencies were prepared with 0.1 wt% MnO2 additive. Energy-storage efficiency (η) increases from 63.7% to 89% at 190 kV/cm as BaTiO3 increases accompanied by recoverable energy densities (Wrec) in the range of 2.5–2.7 J/cm3. The energy-storage performance persists thermally stable up to 125 °C. The superior storage efficiency is associated with growth of the cubic Pm-3m symmetry and the core-shell structure with increasing BaTiO3 content. The formation of nanocluster/nanomosaic structure also plays an essential role as a barrier in suppressing the long-range polarization order. This work provides a design of binary rare-earth doped BiFeO3–BaTiO3 dielectric ceramics for thermally stable and high-efficiency electrical energy storage.

Excellent piezoelectric performance of BiFeO3–BaTiO3– La(Mg2/3Nb1/3)O3 lead-free ceramics via relaxation regulation near the morphotropic phase boundary

Although BiFeO3–BaTiO3-based lead-free ceramics have attracted much attention in recent years as a high temperature piezoelectrics, their d33 value is still difficult to exceed 200 pC/N through conventional methods. In this work, a novel (0.7-x)BiFeO3-0.3BaTiO3-xLa(Mg2/3Nb1/3)O3 (x = 0–0.005) ternary system was reported to own excellent room-temperature piezoelectric constant (d33) ∼216 pC/N and high Curie temperature (480 °C) at x = 0.003 simultaneously. It reveals that the compositions undergo an obvious phase transition from ferroelectric (FE) rhombohedral (R) phase to relaxor pseudo-cubic (PC) phase via an R–PC morphotropic phase boundary (MPB). More importantly, piezoelectric nonlinear Rayleigh analysis and S-E/P-E curves suggest that the significantly enhanced domain dynamics due to the coexistence of macrodomain and nanodomain can be observed in the x = 0.003 sample. The synergy of these two effects induce the improved d33 value observed in the x = 0.003 sample. In addition, the compositions exhibit the inhibition of defect dipoles and the improvement of the high temperature resistivity, leading to the excellent thermal stability with sensitivity coefficients ƞ less than ± 5% in the annealing temperature range of 25–400 °C. The present work provides a guideline for the subsequent design of high-temperature lead-free ceramics.

Effects of attrition milling on the microstructure and piezoelectric properties of BiFeO3–BaTiO3 ceramics

Effects of attrition milling on the microstructure and piezoelectric properties of BiFeO3–BaTiO3 ceramics

Improved chemical defects, domain structure and electrical properties of BiFeO3–BaTiO3 lead-free ceramics by simultaneous Na/Bi codoping and quenching process

Lead-free piezoelectric 0.7BiFeO3-0.3Ba1-x(Bi0.5Na0.5)xTiO3 (BF–B(BN)xT, 0.00 ≤ x ≤ 0.02) ceramics were synthesized with a solid-state reaction method utilizing modified air quenching. The impacts of Na/Bi codoping and air quenching on the structure, defects, and electrical properties of BF–B(BN)xT were investigated. Each sample exhibited a pure perovskite structure with rhombohedral (R) and pseudocubic (pC) phase coexistence. The insulation and piezoelectric properties were improved by appropriate Na/Bi codoping. Due to the enhanced lattice distortion and long parallel strip domains induced by the quenching treatment, excellent piezoelectric performance d33 = 196 pC/N and a high Curie temperature Tc = 498 °C were obtained for the quenched BF–B(BN)0.015T ceramic. In addition, in situ measurements of the electromechanical coupling factor (kp) and thermal depolarization studies demonstrated that quenching treatment improved the stability of high-temperature piezoelectric properties, and the d33 of the quenched BF–B(BN)0.015T ceramic remained at 183 pC/N at 400 °C, indicating good potential in high-temperature applications.

Synthesis and investigation of electromechanical property of lead-free BiFeO3–BaTiO3 quenched ceramics

Synthesis and investigation of electromechanical property of lead-free BiFeO3–BaTiO3 quenched ceramics

Optimized electric-energy storage in BiFeO3–BaTiO3 ceramics via tailoring microstructure and nanocluster

This study demonstrates the high energy-storage performance using 0.1 wt% MnO2–added 0.7(Bi1−xSmxFeO3)− 0.3(BaTiO3) (x = 0–0.3) ceramics through tailoring microstructures and polar order. Sequential structure transitions were identified from a co-occurrence of nonpolar pseudo-cubic Pm-3m and ferroelectric rhombohedral R3c symmetries to antipolar orthorhombic Pbam and nonpolar orthorhombic Pnma symmetries as Sm substitution increases. Recoverable energy densities (Wrec) of 4.5 J/cm3 and 4.1 J/cm3 with efficiencies (η) of 62.1% and 78.1% were achieved respectively for x = 0.15 and 0.2 at a field of 220 kV/cm. The improved energy storage is associated with microstructure modification and complex grain matrix, consisting of grain boundaries, nanocluster/nanomosaic structures, core-shell structures, and polar nanoregions. The nanocluster/nanomosaic structures may act as barriers to suppress polar order and enhance dielectric breakdown strength. This work provides an efficient route to utilize binary BiFeO3-BaTiO3 ceramics for electrical energy storage.

Compositionally tunable high temperature Mn-doped BiFeO3–BaTiO3 lead-free piezoceramics

Compositionally tunable high temperature Mn-doped BiFeO3–BaTiO3 lead-free piezoceramics

Re-entrant relaxor ferroelectric behaviour in Nb-doped BiFeO3–BaTiO3 ceramics

Re-entrant relaxor ferroelectric behaviour is identified in BiFeO3–BaTiO3 ceramics, yielding anomalous thermal variations in structural distortion and functional properties.

Microchemical homogeneity and quenching-induced property enhancement in BiFeO3–BaTiO3 ceramics

BiFeO3–BaTiO3 (BF-BT) solid solutions are promising as the basis for high temperature dielectric and piezoelectric materials, but their microstructural aspects have received relatively little attention. This study evaluates the influence of different processing procedures on the micro-chemical heterogeneity and functional properties of 0.67BF-0.33BT ceramics prepared by solid state reaction. It is shown that the use of high energy planetary ball milling after calcination is an effective method to improve chemical homogeneity and circumvent the core-shell type features found in conventional vibration-milled materials. BF-BT ceramics prepared by high energy milling exhibit enhanced remnant polarization, piezoelectric charge coefficient and coupling factor values of 0.34C m−2, 105 pC/N and 0.24, in comparison with those of vibration milled materials (0.30 C m−2, 73 pC/N and 0.19 respectively). Further improvements in functional properties were achieved by application of an air quenching process, which also led to an increase of 50 °C in both the Curie point and depolarization temperature; these modifications were correlated with increased structural distortion and volume fraction of the rhombohedral phase. Quenched BF-BT ceramics also exhibited mixed inter- and trans-granular fracture modes, whereas that of the as-sintered materials was predominantly inter-granular.

High temperature piezoelectric accelerometer fabricated by 0.75BiFeO3–0.25BaTiO3 ceramics with operating temperature over 450 °C

Owing to the high Curie temperature and good piezoelectric thermal stability, BiFeO3–BaTiO3 ceramics show great potentials for high-temperature piezoelectric sensor applications. In this paper, a compression-mode piezoelectric sensor was fabricated by the lead-free and high-temperature 0.75BiFeO3–0.25BaTiO3–MnO2 (BFBT25–Mn) ceramic and its sensitivity was characterized from room temperature to 550 °C over a frequency range of 200–1000 Hz. The output charge of the BFBT25–Mn piezoelectric sensor is independent of the measuring frequency at different temperatures. The maximum working temperature of the BFBT25–Mn piezoelectric sensor is 450 °C, about 250, 150, and 100 °C higher than those of these piezoelectric sensors fabricated by PZT-5A, BSPT64–Mn, and BSPT66–Mn ceramics, respectively. The temperature sensitivity coefficient from room temperature to 350 °C of the BFBT25–Mn piezoelectric sensor is 30% of that for the BSPT66–Mn sensor. Furthermore, the sensitivity of the BFBT25–Mn piezoelectric sensor is stable with the dwelling time at 400 °C. These results indicate that the BFBT25–Mn ceramic is a strong competitor for high temperature sensing applications.

Obtaining high energy storage performance and thermal stability simultaneously in BiFeO3–BaTiO3–Bi2LaTiNbO9 lead-free relaxor ferroelectric ceramics

In this work, bismuth layer-structured Bi2LaTiNbO9 (BLTN) was introduced into BiFeO3–BaTiO3 system. A large Wrec of 3.26 J/cm3 with a high η of 80.8% were realized in the BF-BT-0.08BLTN ceramic. The addition of BLTN facilitates to enhance the relaxor behavior and band gap of BF-BT ceramics and also suppresses the grain growth. More impressively, the x = 0.08 ceramic shows an excellent thermal stability (Δ Wrec/ Wrec < 2.2%, 25–100 °C) due to the temperature-insensitive permittivity of BLTN, which is superior to other BiFeO3-based ceramics. This work indicated that the BLTN is an effective additive for dielectric materials used in the variable temperature environment.

Optimization of calcination temperature of lead-free BiFeO3–BaTiO3 high-temperature piezoceramics

0.7BiFeO3-0.3BaTiO3+1mol% MnO2(0.7BFO-0.3BTO) ceramics were synthesized by conventional solid-state powder method under different calcination temperatures (Tcal) between 770 and 830 °C. The phase structure, microstructure, and ferroelectric and piezoelectric properties changed greatly depending on the applied Tcal. Benefitting from the formation of low defect levels and large grain size and an appropriate morphotropic phase boundary (MPB) with the rhombohedral-to-pseudocubic phase ratio = 49.1 : 50.9, BFO-BTO ceramics calcined at 785 °C showed the best ferroelectric, piezoelectric, and insulating properties (Pr = 23.1 μC/cm2, EC = 25.8 kV/cm, d33 = 167.8 pC/N, kp = 0.342%). Above Tcal = 800 °C, however, the ferroelectric and piezoelectric properties deteriorated because volatilization of Bi and reduction of Fe caused a poor insulating property and high degree of chemical inhomogeneity. Moreover, the ceramics calcined at 785 °C showed a high Curie temperature (TC) of 509.2 °C and excellent thermal aging resistance of d33 up to 450 °C, demonstrating great potential for use in high-temperature applications.

Enhanced piezoelectric properties in BF-BT based lead-free ferroelectric ceramics for high-temperature devices

Due to the high Curie temperature (TC), BiFeO3–BaTiO3 (BF-BT) ceramics have been broadly investigated in high-temperature piezoelectric devices. The piezoelectric constant is one of the most significant factors in determining the sensitivity and reliability of piezoelectric functional components. However, the poor piezoelectric constant (d33) of BF-BT ceramic has prevented the practical application of the material. In this work, we innovatively introduce the 0.93Bi0.5Na0.5TiO3-0.07BaTiO3 (0.93NBT-0.07BT) component to 0.7BF-0.3BT ceramic, to build a morphotropic phase boundary (MPB) for enhancing d33. The XRD analysis shows that the (0.7BF-0.3BT)-x(0.93NBT-0.07BT) ceramics are still in the MPB region with R–PC phases coexistence, and exhibits a homogeneous solid solution. Moreover, the introduction of 0.93NBT-0.07BT ceramic suppresses the generation of defects and facilitates grain growth, thus enhancing piezoelectric property. In consequence, an optimum piezoelectricity d33 = 213 pC/N along with Tc∼450 °C was obtained in (0.7BF-0.3BT)-0.01(0.93NBT-0.07BT). This research provides a new idea for the application of BF-BT ceramics in high-temperature piezoelectric devices.

Effects of Li/M (M = Al, Ga, In, and Er) co-doping on the electrical properties of BiFeO3–BaTiO3 ceramics

Effects of Li/M (M = Al, Ga, In, and Er) co-doping on the electrical properties of BiFeO3–BaTiO3 ceramics

Bipolar cycling effects in BiFeO3–BaTiO3 piezoelectric ceramics

BiFeO3–BaTiO3 (BF-BT) lead-free piezoelectric system has been paid much attention due to good piezoelectric properties and high Curie temperature. Poling is a process to align ferroelectric domains and increase the piezoelectric coefficients. During the poling process, unipolar direct current (dc) electric fields were applied conventionally, but recently bipolar alternating current (ac) cycling was reported to improve piezoelectric properties in rhombohedral structure piezoelectric materials. We investigated the effects of dc-poling and ac-cycling in BF-BT ceramics. The d33 increased from 210 pC/N with dc-poling to 240 pC/N with ac-cycling in the morphotropic phase boundary region of BF-BT with domain engineering. This improvement of piezoelectric properties with ac-cycling was consistent with the structural evolution related to ferroelectric domains.

Enhanced Energy Density and Efficiency in Lead‐Free Sodium Niobate‐Based Relaxor Antiferroelectric Ceramics for Electrostatic Energy Storage Application

AbstractAntiferroelectric ceramics are recently, a research hotspot for electrostatic energy storage because of their large electric‐field induced polarization. Lead‐free sodium niobate (NaNbO3)‐based ceramics are one of the emerging antiferroelectric counterparts. However, the unstable antiferroelectric phase seriously restricts the further improvement of energy density and efficiency. In this work, by introducing binary perovskite end‐member BiFeO3–BaTiO3 with lower tolerance factor and average electronegativity into NaNbO3 ceramics, the stablized antiferroelectric phase with improved relaxation characteristic is identified by slim double‐like polarization‐electric field (P–E) loops and four‐peak current–electric field (I–E) curves. Meanwhile, the antiferroelectric P to R phase transition is verified through Raman spectra, X‐ray diffraction (XRD) patterns, and dielectric performance. In particular, the enhanced electric breakdown strength Eb is achieved by synergic contributions from ultralow dielectric loss, reduced grain size, and so on. Consequently, the sample with optimized composition displays ultrahigh recoverable energy storage density (Wrec) of 14.5 J cm−3 and satisfied efficiency (η) of 83.9%, which shows the superiority in the state‐of‐the‐art dielectric ceramics. These results provide a feasible route by regulating the relationship between antiferroelectric structure and properties to explore high‐performance dielectrics for electrostatic energy storage applications.

Defect chemistry for Mn-doped and Nb-doped BiFeO3-based ceramics

BiFeO3 and BiFeO3-based ceramics commonly have high conductivity. Regarding the conduction is n-type, Mn as an acceptor is extensively used to reduce the conductivity. However, p-type conduction has been evidenced recently and Nb as a donor can reduce conductivity. To solve the controversy about the conduction mechanism, Mn-doped and Nb-doped BiFeO3–BaTiO3–SrTiO3 ceramics were studied and the corresponding defect chemistry was discussed. The work reveals some general features related to defects in BiFeO3 and BiFeO3-based ceramics.

A new method for improving the stability of high temperature piezoelectric properties in BiFeO3–BaTiO3 ceramics by regulating the relaxor transition

The piezoelectric responses were fluctuated with rising temperature for most of piezoceramics, which could affect the precision of service equipment directly. However, very few reports about improving stability of high temperature piezoelectric properties could be found out. In this work, the stability of high temperature piezoelectric properties for 0.7BFO-0.3BT ceramics was improved, which could be realized by suppressing relaxor phase transition. The ferroelectric-relaxor transition around 200 °C in 0.7BFO-0.3BT ceramics has an accelerating effect to depolarization process, which was inhibited by doping CuO, Li2CO3 and ZnO. The frequency dependency of permittivity was decreased in the temperature range of 150–350 °C after doping, and the degradation of piezoelectric properties was suppressed. Contrary to above mentioned doping ceramics, fluctuant high temperature piezoelectric properties because of the aggravated relaxor phase transition expressed after doping MnO2. As a result, the doped 0.7BFO-0.3BT ceramics with excellent electrical properties and improved stability of high temperature piezoelectric properties from room temperature to Curie temperature were obtained. The method for improving stability of high temperature piezoelectric properties opened a new window for extending the application range of high temperature piezoceramics.

Ferroelectric polarization of tetragonal BiFeO3—an approach from DFT calculations for BiFeO3–BaTiO3 superlattices—

Density functional theory calculations are conducted for tetragonal BiFeO3–BaTiO3 superlattices to investigate the influence of electronic structures on ferroelectric spontaneous polarization (P s). When the number of the perovskite unit cells in one layer (N) is decreased below 10, the P s starts to decrease from the volume-averaged one (50.9 μC cm−2) and eventually becomes half at N = 1. In the BiFeO3 cell (N = ∞) with a large P s (73.3 μC cm−2), a covalent bond arising from a Bi_6p-O_2p orbital interaction is extended through a Bi–O network and stereo-chemical lone-pair electrons of Bi are accommodated in the opposite direction of the polar c axis. In the superlattice with N = 1, the Bi–O network cannot be developed by the presence of Ba, and then the Bi–O bond becomes ionic. We show that the large P s of the BiFeO3 cell originates from the Bi_6p-O_2p mixing superimposed on the stereo-chemical nature of the lone-pair electrons of Bi.