BiFeO3 BaTiO3 Research Articles

Defect Engineering with Rational Dopants Modulation for High-Temperature Energy Harvesting in Lead-Free Piezoceramics

HighlightsThe solution limit of manganese ion in BiFeO3–BaTiO3 (BF–BT) was determined by combining multiple advanced characterization methods.The defect engineering associated with fine doping can realize the co-modulation of polarization configuration, iron oxidation state and domain orientation.The BF–BT–0.2Mn piezoelectric energy harvester shows excellent power generation capacity at 250 °C, which is an important breakthrough for lead-free piezoelectric devices.

Realization of excellent piezoelectricity and high Curie temperature in BF–BT ceramics via structural regulation and domain engineering

BiFeO3–BaTiO3 (BF–BT) is one of the lead-free piezoceramic materials with high Curie temperature (TC) and high polarization. Herein, the (Bi0.5Li0.5Ti)6+ group elements are introduced into the 0.75BiFeO3−0.25BaTiO3 (0.75BF–0.25BT) system to optimize comprehensive performances via optimizing the intrinsic piezoelectric contribution and the extrinsic piezoelectric contribution. For intrinsic piezoelectric contribution, the tetragonal phase ratio of the ceramics is increased. For extrinsic piezoelectric contribution, the grain structures and the domain structures of the ceramics are improved with a relaxor state in which small-sized domains and large-sized domains coexist. The best overall performances are obtained at x = 0.010 with piezoelectric constant d33 ∼ 130 pC/N at room temperature, d33 ∼ 231 pC/N at 313 °C, resistance ρ ∼ 1.49 × 106 Ω cm at 300 °C, and Curie temperature TC ∼ 632 °C that improved significantly. Moreover, when x = 0.010, the piezoelectric thermal stability is also significantly improved, with Δd33 being less than 15% before 200 °C and maintaining 60% of d33 at 400 °C. The present experiments provide a new strategy to investigate the origin of the enhanced piezoelectric response of BF–BT ceramics as well as their applications in the field of high-temperature lead-free piezoelectricity.

High-piezoelectric lead-free BiFeO3–BaTiO3 ceramics with enhanced temperature stability and mechanical properties

BiFeO3–BaTiO3 (BF–BT) ceramics exhibit higher piezoelectric coefficients (d33), Curie temperatures (TC), and temperature stability than other high-temperature lead-free piezoelectric materials. However, despite their crucial role in piezoelectric devices, the mechanical properties of BF–BT ceramics have been underexplored. A thorough evaluation of the mechanical properties of BF–BT is crucial for developing cost-effective and durable lead-free piezoelectric ceramics. Moreover, the specific causes of the high piezoelectric response and excellent temperature stability of BF–BT ceramics remain unclear owing to the instrumental detection threshold, which limits experimental studies to temperatures above 140 °C and below the degradation temperature of d33. To investigate the intrinsic origins of the high piezoelectricity and temperature stability of BF–xBT ceramics and to enhance their mechanical properties, a two-step sintering process is used to fabricate these ceramics (0.25 ≤ x ≤ 0.40). Owing to improvements in grain refinement and reduced Bi3+ volatilization, the BF–0.33BT ceramic exhibits enhanced overall performance, with a modified small punch strength of 155 MPa, Vickers hardness of 5.2 GPa, a d33 of 220 pC/N at room temperature, TC of 466 °C, and d33 values exceeding 400 pC/N at 260 °C. Phase-field simulations, which address the limitations of device detection thresholds, reveal that with increasing temperature, the domain structure relaxes, and polarization intensity decreases. This indicates that changes in the high-temperature piezoelectric properties can be attributed to domain structure relaxation and the increase in dielectric constant. Overall, BF–BT ceramics exhibit superior piezoelectric performance, mechanical properties, and temperature stability, making them highly suitable for use in high-temperature and demanding environments.

Publisher’s Note: “High piezoelectric performance and resistivity through a laminated structure design for BiFeO3–BaTiO3 ceramic” [J. Appl. Phys. 135, 084103 (2024)]

Publisher’s Note: “High piezoelectric performance and resistivity through a laminated structure design for BiFeO3–BaTiO3 ceramic” [J. Appl. Phys. 135, 084103 (2024)]

Mn-doped 0.67BiFeO3-0.33BaTiO3 ceramic sensor for high-temperature structural health monitoring

Real-time monitoring of structural health status is very important for supersonic aircraft, since the long-term operation in harsh service environments, such as high temperatures, can cause potential damage. Structural health monitoring (SHM) based on lamb wave has been approved to be a critical technique for the reliable operation of supersonic aircraft, but is limited by the operating temperature of conventional piezoelectric sensors, which makes it difficult to meet the high-temperature monitoring requirements. The BiFeO3–BaTiO3 ceramics exhibit excellent piezoelectric properties and high Curie temperature (Tc), making them promising for high-temperature SHM of supersonic aircraft. Here, we fabricated a piezoelectric sensor using 0.67BiFeO3-0.33BaTiO3-0.25%molMnO2 (BF33BTMN-025) ceramic, which exhibits a piezoelectric charge constant (d33) of 135 pC/N at room temperature and a Tc of 448 °C. The BF33BTMN-025 ceramic sensor operates effectively at temperatures up to 200 °C and maintains stable damage monitoring sensitivity as well. Compared with Pb(Zr, Ti)O3 (PZT), BaTiO3 (BTO) and other piezoelectric sensors commonly used in SHM field, the BF33BTMN-025 ceramic sensor has a higher operating temperature and a comparable sensitivity. Our work demonstrates that the BF33BTMN-025 ceramic sensor can be employed as piezoelectric sensor for high-temperature SHM, which has a wide application potential in the field of real-time monitoring of supersonic aircraft.

Low temperature sintering and enhanced piezoelectric properties of BiFeO3–BaTiO3 ceramics by homogeneous calcination

The effect of calcination process on a phase evolution, a microstructure development and the piezoelectric properties were investigated in 0.75BiFeO3-0.25BaTiO3 (0.75BF-0.25BT) ceramics. At the relatively low calcination temperatures of 600 °C–650 °C, a Bi25FeO40 impurity phase was formed in addition to some unreacted raw materials and a perovskite phase. As the calcination temperature increased to the range of 700–900 °C, other intermediate phase BaBi4Ti4O15 was formed concurrently with small amounts of unreacted BaCO3 and perovskite matrix phase. At 950 °C a pure single perovskite phase of 0.75BF-0.25BT solid solution was observed. The sintered samples produced by using the raw powder calcined at a relatively low temperature of 600–900 °C showed a large fraction of pseudo-cubic relaxor phase (0.54–0.71 mass fraction) with the rest of a rhombohedral ferroelectric phase. They showed poor piezoelectric properties at sintering temperature below 1000 °C due to the nonuniform compositional distribution of the calcined powder. The homogeneous calcination at 950 °C for 2 h reduced greatly the optimum sintering temperature and significantly enhanced piezoelectric properties in the BF-BT ceramics. High Curie temperature as well as high piezoelectric properties were obtained at the sintering temperature as low as 920 °C: kp = 0.361, d33 = 123 pC/N and TC = 653 °C in the 0.75BF-0.25BT ceramics and kp = 0.337, d33 = 183 pC/N and TC = 525 °C in the 0.7BF-0.3BT ceramics. This low temperature sintering of the BF-BT ceramics by a homogeneous calcination could be applied to the fabrication of the lead-free multi-layer piezoelectric devices with inexpensive internal electrodes.

LiNbO3-induced phase structure evolution and improved piezoelectric properties in BiFeO3–BaTiO3 ceramics

Eco-friendly (0.73-x)Bi1.05FeO3-xLiNbO3-0.27BaTiO3 ternary ceramics were designed and prepared via a solid-state sintering route. Based on the X-ray diffraction results and Rietveld refinement, it was found that the structure of the ceramics transformed from rhombohedral to tetragonal symmetry with the addition of LiNbO3, and at x = 0.003, there existed a morphotropic phase boundary separating the two phases. Near the phase boundary, the largest values were achieved for the piezoelectric constant d33 and planar electromechanical coupling coefficient kp, being 180 pC/N and 0.27, respectively. Due to the addition of LiNbO3, the grain size tended to become smaller. Additionally, the ceramics were transitioned from normal to relaxor ferroelectrics with increasing x. Despite the fact that the LiNbO3 addition would result in a gradual decrease of Curie temperature, a relatively high Curie temperature (535 °C) was still maintained at x = 0.003, the phase boundary composition, which also showed good temperature stability of piezoelectric properties. These experimental results can provide a reference for the practical applications of high-temperature lead-free ceramics.

Local structure and defect analysis of KVO3 doped BiFeO3–BaTiO3 ceramics facing conductivity, permittivity, and magnetic properties

This study discovers the effects of KVO3 doping on BiFeO3–BaTiO3 regarding phase transitions, defect formation, and changes in electronic and magnetic behavior. The synthesized material (1-x-y)BiFeO3-xBaTiO3-yKVO3 with (x = 0.33, 0.38 and y = 0, 0.01) have pseudo-cubic structure, where the FeO6 octahedron was elongated in the z-axis, and Fe has an oxidation state of 3+ and 4+. The electrons in the 3d subshell initially showed a high spin state, transitioning to a low state after KVO3 doping. Further investigation identified phase transition Rhombohedral + Pseudo Cubic to Rhombohedral for FT33 at T∼100°C and Pseudo Cubic phase to Cubic phase for FT38 at T∼200°C. Conductivity at low temperatures ascribed to unbinding electrons, while the presence of defect-creating dipole strengthened the dipole polarization. The magnetization hysteresis of KVO3-doped samples significantly decreased due to the high spin state transformed to the low spin state of the 3d subshell of Fe in the octahedron FeO6.

Tuning the electrical conductivity and Maxwell-Wagner relaxation in BiFeO3–BaTiO3 piezoceramics

Recent research has emphasized the investigation of BiFeO3–BaTiO3 (BFO–BT) piezoelectric ceramics due to their elevated Curie temperature. Nevertheless, the substantial electrical conductivity of these ceramics poses practical challenges. This study evaluates the influence of post-annealing and manganese (Mn) doping on the conductivity, dielectric behavior, and ferroelectric properties of (1-x)BFO–xBT ceramics with a morphotropic phase boundary composition (x = 0.33). The results demonstrate that the conductivity of the ceramics in the as-sintered state is affected by Maxwell-Wagner effects arising from variations in conductivity at grain boundaries. Annealing under specific atmospheres indicates that the electrical conductivity is of the p-type, potentially associated with Fe4+ defects. Furthermore, annealing in a carefully controlled atmosphere or the introduction of Mn doping significantly alleviate these effects, leading to an enhancement in domain switching characteristics. The insights garnered from this investigation regarding annealing and doping have the potential to advance lead-free BFO–BT piezoelectric ceramics.

High piezoelectric performance and resistivity through a laminated structure design for BiFeO3–BaTiO3 ceramic

BiFeO3–BaTiO3 (BF–BT) ceramics with high Curie temperature and excellent piezoelectric coefficient are expected to be applied in high-temperature piezoelectric sensors and actuators. However, its resistivity decreases rapidly with temperature and impedes its further applications. Moreover, normal methods such as doping modification cannot address this issue. In the present work, bismuth layered Bi4Ti2.93(Zn1/3Nb2/3)0.07O12 (BIT) and perovskite 0.36BiScO3-0.64PbTiO3 (BSPT) ceramics were selected as insulating layers and were, respectively, sintered with 0.7BF–0.3BT ceramics to form laminated ceramics. The heterojunction structures effectively prevent carrier migration, and both resistivities of BIT and BSPT laminated ceramics were increased from 106 to 108−9 Ω cm at 300 °C. In addition, piezoelectric properties of the BSPT-type laminated ceramics are much higher than that of BF–BT ceramics, in which the bipolar strain was increased from 0.04% to 0.1% (4 kV/mm), and d33 was increased from 140 to 237 pC/N. Therefore, designing the insulating layer may be an effective method to realize the high-temperature application for BF–BT ceramics.

Moderate electric field driven ultrahigh energy density in BiFeO3–BaTiO3–based ceramics with improved relaxor behavior and breakdown strength

Dielectric ceramic–based capacitors have triggered growing concerns because of their potential applications in next–generation pulsed power electronic devices. However, the low energy density seriously hampers their further development, and the high energy density (>6 J/cm3) is generally realized under a giant external electric field (>500 kV/cm). Herein, an ultrahigh recoverable energy density of 8.5 J/cm3 and a high efficiency of 87 % under a moderate electric field of 470 kV/cm is obtained in the Sr(Sc1/2Nb1/2)O3 modified BiFeO3–BaTiO3 ceramics via the improved dielectric relaxation and electric breakdown strength (Eb). And the promoted band gap and reduced grain size play a key role in enhancing Eb. Moreover, the sample with the optimal composition also exhibits superb thermal reliability at a wide temperature range, and outstanding frequency and cycling stability under 350 kV/cm. This work not only provides a hopeful alternative for advanced energy storage capacitors, but also demonstrates an effective way to explore high–performance dielectric materials.

Boosting the optical, dielectric, and ferromagnetic properties of BiFeO3–BaTiO3 ceramics by Eu substitution

This study investigates the impact of incorporating Eu into 0.8BiFeO3-0.2BaTiO3 ceramics (0.8 (Bi(1-x)EuxFeO3) - 0.2BaTiO3 for x = 0 and 0.05) through cost-effective solid-state sintering. Analyzing structural, microstructural, optical, ferromagnetic, and dielectric properties, it confirms pure perovskite structures exclusively crystallizing in the rhombohedral phase. Eu3+ integration yields homogeneous distribution, reduced grain size (1.57 μm–1.40 μm), and a decreased optical band gap (2.06 ± 0.02 eV to 1.65 ± 0.02 eV). Ferromagnetic properties improve, with remnant magnetization rising from Mr = 0.4406 emu/g to Mr = 0.5096 emu/g. Dielectric analysis identifies grain contributions, and Jonsher low analysis indicates the dominance of the Model of Correlated Barrier Hopping in conduction. The study emphasizes the potential technological applications of Eu-modified 0.8BiFeO3-0.2BaTiO3 ceramics, offering valuable insights into their physical properties.

Significant impact of TiO2 purity on the phase structure and electrical properties of BiFeO3–BaTiO3 lead‐free piezoelectric ceramics

AbstractIn many studies, the properties of BiFeO3–BaTiO3 (BF–BT) ceramics vary greatly using different raw reagents, which makes it challenging to obtain reliable and repeatable properties of BF–BT‐based devices. In this work, 0.7BiFeO3–0.3BaTiO3 (0.7BF–0.3BT) ceramics were fabricated by a conventional solid‐phase synthesis using TiO2 reagents with varied purities of 98%, 99%, 99.9%, and 99.99%, respectively. The phase structure, microstructure, ferroelectric, and piezoelectric properties were comprehensively studied. All compositions of the ceramics exhibit a pseudo‐cubic phase perovskite structure, and the fraction of the rhombohedral phase increases with increasing the TiO2 purity. Additionally, backscattered electron images and energy‐dispersive spectroscopy revealed an obvious core–shell structure within grains. In particular, the 0.7BF–0.3BT ceramics prepared with 98% purity TiO2 exhibited superior ferroelectric and piezoelectric properties, d33 ∼ 220 pC/N and ∼ 230 pm/V. The ceramics prepared with higher purity TiO2 suffered from severe leakage conduction, which can be well addressed by adding excess TiO2. Our work reveals the importance of different grades of purity TiO2 on the electrical properties of BF–BT ceramics.

The improvement of piezoelectric properties in BiFeO3–BaTiO3 lead-free ceramics prepared with heat-treated rutile TiO2

The improvement of piezoelectric properties in BiFeO3–BaTiO3 lead-free ceramics prepared with heat-treated rutile TiO2

Quenching-driven advancements in functional properties of high-temperature lead-free Sc, Ga modified 0.67BiFeO3-0.33BaTiO3 relaxor ceramics

The processing method is one of the most important deciding factors in the fabrication of BiFeO3–BaTiO3 (BF-BT) based piezoceramics because of the Bi2O3 volatization. It significantly influences the functional properties, including the piezoelectric coefficients, dielectric properties, and microstructure. This study presents a significant advancement in the realm of high-temperature lead-free piezoelectric ceramics in terms of understanding effects of processing method on functional properties. In this light, a novel ceramic solid-solution, 0.67{Bi(Fe0.97Ga0.03)1-xScxO3}-0.33(BaTiO3) with x ≤ 0.07, incorporating Scandium (Sc) and Gallium (Ga) modifications, was meticulously designed and synthesized. Impact of two distinct sintering methods, namely air quenching (AQ) and closed sintering (CS) on the structure and properties of the developed materials are investigated. X-ray diffraction (XRD) and Fourier-transform infrared (FTIR) analysis verified the formation of pure perovskite phases with successful incorporation of Sc and Ga into the 0.67BF-0.33BT lattice. The FTIR analysis revealed a sharp absorptive band in the 590-604 cm−1 range, corresponding to the signature of stretching and bending vibrations of (Ti/Fe)O6 octahedra. Rietveld structure refinement confirmed the coexistence of pseudocubic (Pm-3m) and rhombohedral (R3c) phases in AQ samples, with predominantly pseudocubic phase, while CS samples closely approximated the pseudocubic phase. The microstructure of the samples exhibits small average grain size distribution (<2 μm). Temperature-dependent dielectric measurements show strong frequency dispersion in the dielectric permittivity with broadened transition peaks. The ferroelectric studies reveal low Pr and Ec values. These observations suggest a ferroelectric relaxor-like behavior of the developed materials. Moreover, the permittivity peaks maxima (Tm) temperature corresponding to CS samples for 0.04<x < 0.07 is less than 390 °C at 10 Hz while it is above 400 °C for AQ samples. The results of our study reveal that AQ samples exhibit superior electrical and ferroelectric properties as compared to the CS samples. The AQ samples demonstrate improvements in Tm (>400 °C), d33(∼35 pC/N), Pr (∼4–11 μC/cm2), PS (∼8–21 μC/cm2), Ec (∼13–25 kV/cm) with reduced dielectric loss, and a better dielectric constant over a wide temperature range.

Phase structure, domain structure, thermal stability, and high-temperature piezoelectric response of BiFeO3–BaTiO3 lead-free piezoelectric ceramics

High-temperature lead-free piezoceramics with a large piezoelectric constant d33 and a high depolarization temperature Td have long been a target of ferroelectric researchers. In this work, (1-x)BiFeO3-xBaTiO3 ceramics with MnO2 and Li2CO3 additives (BF-xBT) were fabricated with traditional ceramic preparation technology. The best piezoelectric ferroelectric properties and thermal stability d33 = 185 pC/N, Pr = 33.152 μC/cm2, Tc = 470 °C, and Td = 460 °C were obtained for x = 0.32. The tetragonal (T) phase content of BF-xBT ceramics increases gradually with an increase of BT content, and the temperature stability improves. In particular, an in-situ d33 test indicates that BF-xBT ceramics have large piezoceramics coefficients with d33 = 450.5 pC/N at a temperature of T = 334 °C. Piezo force microscopy and transmission electron microscopy tests show that nanodomains and polar nanoregions play a key role in the improvement of piezoelectric response. BF-xBT ceramics appear to be the most promising candidates to replace PZT ceramics in high-temperature applications.

BiAlO3-modified BiFeO3–BaTiO3 high Curie temperature lead-free piezoelectric ceramics with enhanced performance

BiAlO3-modified BiFeO3–BaTiO3 high Curie temperature lead-free piezoelectric ceramics with enhanced performance

Hard piezoelectric properties of lead‐free BiFeO3–BaTiO3 ceramics

AbstractHard piezoelectric properties are investigated in lead‐free BiFeO3–BaTiO3 (BF–BT) ceramics. Rhombohedral (R) phase ceramics of (1 – x)BF–xBT (x = 0.20–0.30) were prepared using a conventional solid‐state reaction and water‐quenching process. The R structure is observed in x = 0.20–0.275, and the R and tetragonal phases coexist at x = 0.30. The piezoelectric charge sensor coefficient (d33) and electromechanical planar coupling factor (kp) increase with increasing BT content, whereas the mechanical quality factor (Qm) decreases. The x = 0.20 ceramic shows the best hard piezoelectric properties: the highest Qm = 403 and the highest TC = 607°C. In contrast, x = 0.30 ceramic shows soft piezoelectric properties: d33 = 301 pC/N and kp = 0.33 with TC = 510°C. These results show that the BF–BT system in R‐phase‐rich region has good hard piezoelectric properties for transducer applications.

Phase structure and electrical properties of BiFeO3–BaTiO3 ceramics near the morphotropic phase boundary

As a promising lead-free high-temperature piezoelectric material, BiFeO3–BaTiO3 (BF-BT) is still under debate on its crystal structure, especially for the compositions in the morphotropic phase boundary (MPB). Herein, the crystal structure of (1-x)BF-xBT ceramics near the MPB with x = 0.20–0.33 was analyzed by X-ray diffraction and Raman spectroscopy. With the addition of BT, the phase transition from distorted rhombohedral to pseudo-cubic structure was determined by Rietveld refinement. Raman analysis showed the weakening interactions between the A-site cations and BO6 octahedron, as well as the degenerated distortions of BO6 octahedron. Intriguingly, the results of X-ray photoelectron spectroscopy suggested the inhibition of Fe3+ reduction and decrease in oxygen vacancy concentration by the incorporation of BT. In terms of the electrical properties, the significant decline in Curie temperature, improvement in permittivity, and reduction in high-temperature dielectric loss can be observed with the increase of BT content. The increased remnant polarization, enhanced dielectric response and decreased coercive field were helpful for the piezoelectric performance. The maximum room-temperature piezoelectric coefficient of ∼160 pC/N and high-temperature piezoelectric coefficient of ∼324 pC/N were acquired in the x = 0.30 ceramics. This work provides a clear scope for further research on the structural transformation and high-temperature piezoelectric applications of BF-BT system.

High-Temperature Piezoelectric Response and Thermal Stability of BiGaO3 Modified BiFeO3–BaTiO3 Lead-Free Piezoelectric Ceramics

BiGaO3 doped BiFeO3–BaTiO3 ceramics were prepared by the traditional solid-phase synthesis process. The phase analysis, microstructure, piezoelectric, ferroelectric, dielectric properties, and thermal stability of 0.7BiFeO3-(0.3 − x)BaTiO3-xBiGaO3 (Abbreviated as BF–BT-xBG) were investigated. The results show that the ceramics have rhombohedral (R) and tetragonal (T) structures. Particle dimensions gradually get bigger with the increase of BiGaO3 concentration, and dense ceramic grains were observed through SEM. Electrical properties of BF–BT-xBG are improved after adding a small amount of BiGaO3: piezoelectric constants d33 = 141 pC/N, electromechanical coupling coefficient kp = 0.314, mechanical Quality Factor Qm = 56.813, dielectric loss tanδ = 0.048, residual polarization intensity Pr = 18.3 µC/cm2, Curie temperature Tc = 485.2 °C, depolarization temperature Td = 465 °C for x = 0.003. The “temperature-piezoelectric performance” curve under in situ d33 indicates that piezoelectric properties d33 increase rapidly with increasing temperature. Remarkably, the piezoelectric response d33 reaches a maximum of 466 pC/N at a temperature T = 340 °C, and afterward, reduces gradually to zero with increasing temperature until 450 °C.