High-temperature Piezoelectric Materials Research Articles

Multiscale Structural Engineering Boosts Piezoelectricity in Na0.5Bi2.5Nb2O9-Based High-Temperature Piezoceramics.

High-temperature piezoelectric materials, which enable the accurate and reliable sensing of physical parameters to guarantee the functional operation of various systems under harsh conditions, are highly demanded. To this end, both large piezoelectricity and high Curie temperature are pivotal figures of merit (FOMs) for high-temperature piezoceramics. Unfortunately, despite intensive pursuits, it remains a formidable challenge to unravel the inverse correlation between these FOMs. Herein, a conceptual material paradigm of multiscale structural engineering was proposed to address this dilemma. The synergistic effects of phase structure reminiscent of a polymorphic phase boundary and refined domain morphology simultaneously contribute to a large piezoelectric coefficient d33 of 30.3 pC/N and a high Curie temperature TC of 740 °C in (LiCeNd) codoped Na0.5Bi2.5Nb2O9 (NBN-LCN) ceramics. More encouragingly, the system has exceptional thermal stability and is nonsusceptible to mechanical loading. This study not only demonstrates that the high-performance and robust NBN-LCN high-temperature piezoceramics hold great potential for implements under harsh conditions but also opens an avenue for integrating antagonistic properties for the enhancement of the collective performance in functional materials.

The impact of co-doping Ce, W, and Mn on the microstructure and piezoelectric performance of high-temperature piezoelectric ceramics based on CaBi2Nb2O9

CaBi2Nb2O9 (CBN) is a bismuth layered ferroelectric material with extremely high Curie temperature and low dielectric loss, which has great application potential in ultra-high temperature field. However, because of its low piezoelectric coefficient, its practical application still faces great challenges. This study successfully prepared Ca1-xCexBi2Nb1.98(W2/3Mn1/3)0.02O9 (x = 0–0.05) two-layer ferroelectric ceramics using direct-reaction sintering method. A pseudo tetragonal structure was successfully constructed near x = 0.02 using the substitution method of Ce4+ at site A, and W6+ and Mn4+ at site B, which altered the crystal structure of CBN based ceramics. The properties of CBN-based piezoelectric ceramics have been significantly improved by this modification. It has a higher piezoelectric constant (d33 = 20.6 pC/N) and Curie temperature (Tc = 950 °C), while having a lower dielectric loss (tanδ = 0.031 at 500 °C). In addition, CaBi2Nb2O9 based piezoelectric ceramics also show excellent thermal stability. After annealing at 900 °C for 2 h, the d33 value remained high at 19.2 pC/N, retaining about 93.2% of its original value. Therefore, these findings indicate that Ca1-xCexBi2Nb1.98(W2/3Mn1/3)0.02O9 is a high-temperature piezoelectric material with great potential.

The optimal high-temperature piezoelectric cuts of α-BiB3O6 crystals and their fatigue behaviors at high-temperature and low-pressure

The optimal piezoelectric crystal cut of the α-BiB3O6 crystal exhibited excellent temperature stability over a wide temperature range of 20–650 °C.

Structures, dielectric properties and AC impedance characteristics of BiFeO3–BaTiO3 high-temperature lead-free piezoceramics synthesized by the hydrothermal method

Among the lead-free piezoceramics, ([Formula: see text])BiFeO[Formula: see text]BaTiO3 (BF-BT) is considered a promising candidate for high-temperature piezoelectric materials owing to its high Curie temperature ([Formula: see text]C) and good electromechanical properties. In this work, the hydrothermal synthesis method was used to prepare the precursor powders of BiFeO3 and BaTiO3, and then the mixed powder compacts with the chemical composition of 0.7BF–0.3BT were sintered under pressureless conditions. The influence of the hydrothermal reaction times (12–24[Formula: see text]h) of BiFeO3 on the structures and electric properties of the sintered ceramics was instigated. First, all the samples synthesized with the tetragonal BaTiO3 and BiFeO3 powders were identified with relatively stable dielectric properties. As the hydrothermal reaction time to synthesize BiFeO3 increased, the dielectric properties as well as the temperature stability of the 0.7BiFeO3–0.3BaTiO3 ceramics also improved. At the condition of a hydrothermal reaction time of 24[Formula: see text]h, the sample obtained possesses both the lowest temperature coefficient of dielectric constant ([Formula: see text]C between RT and [Formula: see text]C) and the highest Curie temperature ([Formula: see text]C at 100[Formula: see text]kHz). Moreover, at high temperatures, it exhibits a higher AC impedance than others. The calculating result based on the resistive constant-phase-element model (R-CPE) circuit model showed that the grain boundary of the 0.7BF–0.3BT ceramics contributes more resistance to the conductivity at high temperatures. In summary, the hydrothermal reaction proved to be a useful way that achieves the preparation of single-phase 0.7BF–0.3BT ceramics with improved electrical properties.

Ultra-high Curie temperature transparent piezoelectric Bi doped Ca2Nb2O7 single crystals

Ca2Nb2O7 is a promising material for high-temperature piezoelectric applications due to its ultra-high Curie temperature, which makes it a suitable candidate for use in harsh environments. However, their piezoelectric performance needs improvement. Here, through chemical engineering methods, we have successfully grown Bi3+ doped Ca2Nb2O7 single crystals using the optical floating zone technique. The Ca1.94Bi0.06Nb2O7 single crystals achieved better high-temperature stability, transparency and a higher piezoelectric constant of 12.8 pC/N at 298 K and 20.0 pC/N at 660 K. In addition to the dopant effects, mechanisms for enhancing the piezoelectric properties of perovskite-like layer structure (PLS) materials have been identified, highlighting the significant contribution of the NbO6 octahedron and interlayer ions. These findings offers valuable insights into improving the performance of PLS materials, which is crucial for promoting their practical applications as high-temperature lead-free piezoelectric materials.

Significantly enhanced performance and conductivity mechanism in Nb/Mn co-doped CaBi4Ti4O15 ferroelectrics

With the rapid development of high-end industries, the demand for high-temperature piezoelectric materials is significantly increasing. However, realizing the ultra-high performance to meet more applications still faces major scientific and engineering challenges of our time. Here, a new Nb/Mn co-doped CaBi4Ti4O15 (CBT) high-temperature piezoelectric material system of CaBi4Ti4-x(Nb2/3Mn1/3)xO15 was synthesized by the conventional solid-state sintering method. The results show that the addition of the dopants tends to break the long-range ferroelectric chain and soften the flexibility of polarization, resulting in more distorted crystal structure and better ferroelectric properties of CBT ceramics. The ultra-high piezoelectric constant (d33 = 26.8 pC/N) is thus attained in CBT-based ceramics with x = 0.12, which is about several times larger than that of pure CBT ceramics. Moreover, numerous nano-sized layered domain structures that lie on the lateral plane of grains are observed in ceramics, with lower domain wall energy and better dynamic features under electric fields, mainly responsible for the origin of enhanced performance. Besides, excess dopants could make the conductivity mechanism of CBT ceramics transform from p-type to n-type, and also result in a shift of conduction relaxation mechanism from defect dipole rotation polarization to electron relaxation polarization. The work not only provides a promising candidate for high-temperature piezoelectric materials, but also opens a window for optimizing performance by tailoring domain structures using chemical modification.

Simultaneously Achieving Large Piezoelectricity and Low Dielectric Loss in High-Temperature BiScO3-PbTiO3-Based Ceramics.

High-temperature piezoelectric materials are pivotal to technology applications fields including defense, aerospace, nuclear energy, and oil well logging. However, the acquisition of excellent piezoelectric properties is usually at the cost of temperature stability (reduced Curie temperature and increased high-temperature dielectric loss), which hinders the application of piezoelectric ceramics in harsh environments. In this study, we investigated the effect of Nb5+ donor and Mn2+/3+ acceptor doping on the dielectric and piezoelectric properties of BiScO3-PbTiO3 (BS-PT)-based ceramics. In contrast to the acceptor doping, it was found that the donor doping not only enhances the piezoelectric properties but also effectively suppresses the dielectric loss at a high temperature by reducing the oxygen vacancy concentration. Eventually, we simultaneously attained an excellent piezoelectric performance (d33 is 553 pC/N at room temperature and 1528 pC/N at 400 °C, respectively) and a low dielectric loss (less than 2% in the temperature range of 150-300 °C) but still with a high Curie temperature (TC ∼ 445 °C) in Nb5+-doped BS-PT ceramics. Furthermore, different in situ measurements were used to demonstrate the remarkable temperature stability up to a high depolarization temperature of ∼400 °C. This work represents significant progress in high-temperature piezoelectric materials and provides a guideline for future efforts on enhancing the piezoelectricity and suppressing the dielectric loss at high temperature.

Enhanced electrical performance in CaBi4Ti4O15 ceramics through synergistic chemical doping and texture engineering

High-temperature piezoelectric materials with excellent piezoelectricity, low dielectric loss and large resistivity are highly desired for many industrial sectors such as aerospace, aircraft and nuclear power. Here a synergistic design strategy combining microstructural texture and chemical doping is employed to optimize CaBi4Ti4O15 (CBT) ceramics with bismuth layer structure. High textured microstructure with an orientation factor of 80%–82% has been successfully achieved by the spark plasma sintering technique. Furthermore, by doping MnO2, both advantages of hard doping and sintering aids are used to obtain the excellent electrical performance of d33 = 27.3 pC/N, tanδ∼0.1%, Q31∼2,307 and electrical resistivity ρ∼6.5 × 1010 Ω·cm. Up to 600 °C, the 0.2% (in mass) Mn doped CBT ceramics still exhibit high performance of d33 = 26.4 pC/N, ρ∼1.5 × 106 Ω·cm and tanδ∼15.8%, keeping at an applicable level, thus the upper-temperature limit for practical application of the CBT ceramics is greatly increased. This work paves a new way for developing and fabricating excellent high-temperature piezoelectric materials.

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.

Dielectric Spectroscopy Studies and Modelling of Piezoelectric Properties of Multiferroic Ceramics

Compounds and solid solutions of bismuth ferrite (BiFeO3)—barium titanate (BaTiO3) system are of great scientific and engineering interest as multiferroic and potential high-temperature lead-free piezoelectric materials. In the present paper, the results of research on the synthesis and characterisation of 0.67Bi1.02FeO3–0.33BaTiO3 (67BFBT) ceramics in terms of crystal structure and dielectric and piezoelectric properties are reported. It was found that the produced 67BFBT ceramics were characterised by a tetragonal crystal structure described by the P4mm space group, an average crystallite size <D> ≈ 80 nm, and an average strain <ε> = 0.01%. Broad-band dielectric spectroscopy (BBDS) was employed to characterise the dielectric response of polycrystalline ceramics. The frequency range from ν = 10−1 Hz to ν = 105 Hz was used to characterise the influence of the electric field strength on dielectric response of the ceramic sample at room temperature. The dielectric spectra were checked for consistency with the Kramers–Kronig test, and the high quality of the measurements were confirmed. The electric equivalent circuit method was used to fit the dielectric spectra within the frequency range that corresponded to the occurrence of the resonant spectra of the radial mode for thin disk sample, i.e., from ν = 105 Hz to ν = 107 Hz and the temperature range from T = −20 °C to T = 50 °C. The electric equivalent circuit [RsCPE1([L1R1C1]C0)] was used, and good fitting quality was reached. The relevant calculations were performed, and it was found that the piezoelectric charge coefficient exhibited a value of d31 = 35 pC/N and the planar coupling factor was kp = 31% at room temperature. Analysis of impedance spectra performed in terms of circumferential magnetic field made it possible to establish an influence of magnetic field on piezoelectric parameters of 67BFBT multiferroic ceramics. Additionally, the “magnetic” tunability of the modulus of the complex dielectric permittivity makes 67BFBT a sensing material with vast potential.

Enhanced electromechanical properties and thermal stability of antimony-modified BiScO3-PbTiO3 high-temperature piezoelectric ceramics

The search for a suitable donor dopant to improve the piezoelectric response of BiScO3-PbTiO3 (BS-PT) piezoelectric ceramics without sacrificing temperature stability is crucial for developing high-temperature piezoelectric materials for the application in the elevated temperature. In this study, the effects of Sb5+ donor doping on the microstructure, dielectric, ferroelectric, piezoelectric and electromechanical properties of the BS-PT ceramics were investigated. It was found that the Sb5+ dopant acts as the grain growth inhibitor, resulting in a dense and fine-grain microstructure. An enhanced piezoelectric properties d33 of 535 pC N−1 with a high Tc of 440 °C was simultaneously achieved in 0.25 mol%Sb5+ doped BS-PT (BSPT-0.25Sb) ceramic. The results of in-situ piezoelectric constants and electromechanical coupling coefficients as a function of temperature indicate that the BSPT-0.25Sb ceramic has a high depolarization temperature Td of 400 °C, which is much higher than those of the most widely used PZT-based piezoelectric ceramics. Furthermore, BSPT-0.25Sb ceramic has much higher resistivity and lower dielectric loss than PZT-4 and PZT-8 at high temperature. The excellent piezoelectric properties and thermal stability of the BSPT-0.25Sb ceramic indicate that it is a promising piezoelectric material for high-temperature applications.

Structure, Electrical Properties, and Thermal Stability of the Mn/Nb Co-Doped Aurivillius-Type Na0.5Bi4.5Ti4O15 High Temperature Piezoelectric Ceramics

In order to meet the urgent need for high temperature piezoelectric materials with a Curie temperature over 400 °C, the Mn/Nb co-doped strategy has been proposed to improve the weak piezoelectric performance of the Aurivillius-type Na0.5Bi4.5Ti4O15 (NBT) high temperature piezoelectric ceramics. In this paper, the crystal structure, electrical properties, and thermal stability of the B-site Mn/Nb co-doped Na0.5Bi4.5Ti4-x(Mn1/3Nb2/3)xO15 (NBT-100x) ceramics were systematically investigated by the conventional solid-state reaction method. The crystal structural analysis results indicate that the NBT-100x ceramics have typical bismuth oxide layer type phase structure and high anisotropic plate-like morphology. The lattice parameters and the grain sizes increase with the B-site Mn/Nb co-doped content. The electrical properties were significantly improved by Mn/Nb co-doped modifications. The maximum of the piezoelectric coefficient d33 was found to be 29 pC/N for the NBT-2 ceramics, nearly twice that of the unmodified NBT ceramics. The highest values of the planar electromechanical coupling factor kp and thickness electromechanical coupling factor kt were also obtained for the NBT-2 ceramics, at 5.4% and 31.2%, respectively. The dielectric spectroscopy showed that the Curie temperature Tc of the Mn/Nb co-doped NBT-100x ceramics is slightly higher than that of unmodified NBT ceramics (646 °C). The DC resistivity of the NBT-2 ceramics is higher than 106 Ω∙cm at 500 °C. All the results together with the good thermal stability demonstrated the Mn/Nb co-doped ceramics as an effective method to improve the NBT based piezoelectric ceramics and the potential candidates of the Mn/Nb co-doped NBT-100x ceramics for high temperature piezoelectric applications.

Structure and thermal stability investigations of (1-x)CaBi2Nb2O9- xNa0.5Bi2.5Nb2O9 ceramics

In this paper, (1-x)CaBi2Nb2O9-xNa0.5Bi2.5Nb2O9 [(1-x)CBN-xNBN; x = 0, 0.1, 0.3, 0.5 and 0.7] ceramics were prepared by the traditional solid-state method. The structure and properties of CBN and NBN are very close to each other, and XRD shows that Na/Bi ions have entered the lattice of CBN. By adjusting the content of NBN in (1-x)CBN-xNBN ceramics, the crystal structure of the ceramics undergoes a pseudo-tetragonal distortion that can significantly improve thermal stability. Analysis of the data of XRD refinement confirms there is pseudo-tetragonal phase at x = 0.1 to 0.5. Moreover, the remnant polarization Pr is obviously improved due to the reduction of grain size and pseudo-tetragonal distortion. Although the Curie temperature of the CBN-NBN piezoelectric ceramics decreases, the tanδ at high temperatures is significantly reduced and the DC resistivity is increased. The 0.5CBN-0.5NBN ceramic shows excellent comprehensive properties: d33 of 13.8 pC/N, Tc of 873 °C, tanδ of 2.1% at 500 °C, and Pr of 8.92 μC/cm2, especially the d33 maintains 94.9% of the initial d33 after depolarization at 850 °C, which has competitiveness in the high-temperature piezoelectric materials.

Inducing ferromagnetism and magnetoelectric coupling in the ferroelectric alloy system BiFeO3–PbTiO3 via additives

There is a growing interest in BiFeO3-based alloys because of the possibility it offers for developing high-temperature high-performance piezoelectric materials and for their interesting multiferroic properties. Often such ceramics are synthesized with additives either to reduce/suppress leakage current that the system inherits from the parent compound BiFeO3 or to promote sintering via formation of the liquid phase. We demonstrate here the propensity for stabilizing ferromagnetism in the ferroelectric solid solution BiFeO3–PbTiO3 (BF–PT) when synthesized with additive MnO2. Detailed investigation revealed that the ferromagnetic property of the ceramic is extrinsic and caused by the additive enabled precipitation of trace amount of the ferrimagnetic Pb-hexaferrite phase, not easily detected in conventional x-ray diffraction measurements. We also show that the ferromagnetic property is induced in Co-modified BF–PT. However, in this case, the additive stabilizes the CoFe2O4 spinel ferrite phase. While our findings offer a strategy to develop particulate magnetoelectric multiferroic composites using additive assisted precipitation of the ferrimagnetic phase(s) in BiFeO3-based ferroelectric alloys, it also helps in better understanding of the electromechanical response in BFO-based alloys.

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.

Textured CaBi4Ti4O15 ceramics with large piezoelectricity, excellent thermal stability and high resistivity

The bismuth layer-structured ferroelectrics (BLSF) are promising high-temperature piezoelectric materials, in which large piezoelectricity, good thermal stability and high electrical resistivity are desired. Here highly textured CaBi4Ti4O15 BLSF ceramics with orientation factor of 82% have been fabricated by spark plasma sintering technique. The piezoelectric coefficient d33 is significantly enhanced by 250%, from 7.2 pC/N for the texture-less sample to 25.3 pC/N for the textured one, accompanied by a high Curie temperature TC= 788 °C. The variation of d33 is below 5% in the temperature range of 25–500 °C, showing excellent thermal stability. The textured sample exhibits high electrical resistivity ρ = 2.1 × 1011 Ω·cm, an order of magnitude larger than that of the texture-less sample. At the temperature as high as 500 °C, the textured sample still maintains excellent electrical properties of d33 = 24.2 pC/N, tanδ = 9.9% and ρ = 2.7 × 106 Ω·cm, suggesting that the textured CaBi4Ti4O15 ceramics could be a potential candidate for high-temperature piezoelectric sensor or detector applications.

Enhanced electrical properties and conduction mechanism of A-site rare-earth Nd-substituted CaBi2Nb2O9

Calcium bismuth niobate (CaBi2Nb2O9, CBN) is considered to be one of the most promising high-temperature (HT) piezoelectric materials owing to its high Curie temperature of ∼940 °C, however, its low electrical resistance and poor piezoelectric properties at elevated temperatures limit its applications at high temperatures. In this work, we report the significantly enhanced dc electrical resistivity and piezoelectric performance of CBN ceramics through rare-earth Nd-substitution. The crystal structure, microstructure, and dielectric, electrical, ferroelectric and piezoelectric properties of Nd-modified CBN with nominal compositions of Ca1−x Nd x Bi2Nb2O9 (CBN-100xNd) have been investigated in detail. The results indicate that the substitutions of Nd3+ ions for Ca2+ ions increase the piezoelectric properties, and reduce the dielectric loss tanδ at high temperatures. The dc and ac conduction mechanisms indicate that the conduction mechanism is closely related to oxygen vacancies that are reduced through the donor substitutions of Nd3+ for Ca2+, thereby resulting in a significant improvement in the dc electrical resistivity. The optimal composition of CBN-3Nd exhibits a high piezoelectric constant d 33 of 13.5 pC N−1, and a high Curie temperature T c of 948 °C. More importantly, the CBN-3Nd exhibits good thermal stability of the electrical properties (ρ= 2.6 × 107 Ω cm at 500 °C and 1.8 × 106 Ω cm at 600 °C, k p = 6.1%–6.2% at RT ∼ 500 °C), which demonstrates that the Nd-modified CBN ceramics are promising piezoelectric materials for use in HT piezoelectric sensors.

Effect of BaO-2B2O3 sintering aid on the structural and electrical properties of CaBi2Nb2O9 high-temperature piezoelectric ceramic

The effects of a BaO-2B2O3 sintering aid on the microstructural, ferroelectric, dielectric, and piezoelectric properties of CaBi2Nb2O9 were investigated in detail. TEM results confirm the presence of an amorphous phase at the grain boundary and the trace of some Ba elements occupying the Ca sites in the crystal lattice. The result of XPS spectroscopy, Raman spectroscopy, and electrical test system reveals that the addition of a sintering aid can effectively reduce the oxygen vacancies in the ceramics and improve the DC resistivity (in the low-temperature region) and ferroelectric and dielectric properties of the samples. Meanwhile, the addition of BaO-2B2O3 does not decrease the Curie temperature (TC) of the ceramics. The addition of a 1 wt. % BaO-2B2O3 sample possesses the excellent electrical properties with large remnant polarization (Pr = 12.8 μC/cm2), piezoelectric coefficient (d33=16.6 pC/N), and high TC (937 °C). This study shows that the prepared ceramics have great potential in the application of high-temperature piezoelectric materials.

Enhanced ferroelectric, piezoelectric and dielectric properties of (1-x)CaBi2Nb2O9-xBaZr0.2Ti0.8O3 high-temperature piezoelectric composite ceramics

Among Aurivillius layer-structured materials, CaBi2Nb2O9 is a best potential candidate for ultrahigh-temperature applications because of its highest Curie temperature of about 940 °C. In this paper, (1-x)CaBi2Nb2O9-xBaZr0.2Ti0.8O3 composite ceramics were prepared by conventional solid-state sintering method. The dielectric results show that the introduction of BaZr0.2Ti0.8O3 not only increases the permittivity of the material, but also reduces its dielectric loss. The optimum electrical properties were obtained in the x = 0.01 sample with piezoelectric coefficient (d33) of 15.1 pC/N and high ferroelectric remnant polarization (Pr) of 9.9 μC/cm2. Furthermore, the composite samples show good thermal depoling performance, the d33 of the x = 0.01 sample is 13.8 pC/N, which is about 91% of the initial value after depoling at 800 °C. Therefore, (1-x)CaBi2Nb2O9-xBaZr0.2Ti0.8O3 is one of the candidates for high temperature piezoelectric materials.

Anisotropic effects of oxygen vacancy defects on the electrical properties of highly oriented bismuth titanate ferroelectric ceramics

Bismuth titanate (Bi4Ti3O12, BIT) exhibits a high Curie temperature and anisotropic electrical performance owing to its layered perovskite structure, and hence, it is an important ferroelectric material for high-temperature piezoelectric applications. It is crucial to understand the effects of the anisotropy in BIT-based ferroelectrics for developing novel high-temperature piezoelectric materials. In this study, a highly textured BIT ceramic was fabricated using the tape-casting technique from highly grain-oriented BIT platelets prepared by the molten salt method. The textured BIT ceramic showed a dense microstructure and high grain orientation along the (00l) plane with a texturing degree F00l = 0.86. It exhibited significant anisotropy in the electrical properties along the directions parallel and perpendicular to the axis of the tape-casting plane. Double ferroelectric hysteresis P–E loops and normal ferroelectric P–E loops were observed in the parallel and perpendicular samples, respectively. In addition to the layered crystal structure and domains, the anisotropy in the arrangement of the oxygen vacancy defects and their transport in the structure led to a significant anisotropy in the ferroelectric properties of the textured BIT ceramics. This work demonstrates the anisotropic arrangement of the oxygen vacancy defects and its effect on the electrical properties of high-temperature bismuth layer-structured ferroelectrics.