Bismuth Layer-structured Ferroelectrics Research Articles

Electrical Properties of Textured Bismuth Layer-Structured Ferroelectric Ceramics with Large Number of Layers (m = 5)

Bismuth layer-structured ferroelectrics (BLSF) ceramics are attractive materials for high temperature sensor applications, because of their high Curie temperature Tc (300–900 °C), and the large anisotropy of their electromechanical coupling factor kt/kp or k33/k31. In this study, BLSF ceramics with a large number of layers, namely, (K0.5Bi0.5)2Bi4Ti5O18 + MnCO3 0.3 wt%+ Bi2O3 0.025 wt% (KBT5) and Sr0.75Ca0.25Na0.5Bi4.5Ti5O18 + CeO2 1 wt% [(SC)NBT5] ceramics, were prepared by ordinary firing (OF) and hot forging (HF) methods, and their electrical and piezoelectric properties were examined. Both KBT5 and (SC) NBT5 ceramics showed high Tc values of 545 and 424 °C, respectively. The OF-KBT5 ceramic had an electromechanical coupling factor k33 of 0.14 and a piezoelectric constant d33 of 20 pC/N, whereas the HF-KBT5 ceramic had k33 of 0.17 and d33 of 31 pC/N. On the other hand, the OF-(SC) NBT5 ceramic had k33 of 0.13 and d33 of 17 pC/N, whereas the HF-(SC) NBT5 ceramic had k33 that increased to 0.32 and d33 to 41 pC/N. The k33 and d33 of the HF ceramics were improved compared with those of the OF ceramics. Thus, the KBT5 and (SC) NBT5 ceramics with oriented grains were shown to have good piezoelectric properties with high Tc.

Rare-earth praseodymium-substituted Bi5Ti3FeO15 exhibiting enhanced piezoelectric properties for high-temperature application

Owing to their exceptional piezoelectric effects, piezoelectric materials play a crucial role in high-end technologies and contribute significantly to the national economy. Bismuth layer-structured ferroelectrics (BLSFs) possess high Curie temperatures, making them a focal point of research in high-temperature piezoelectric sensor devices. However, their poor piezoelectric performance and low direct-current (DC) electrical resistivity hinder their effective deployment in high-temperature applications. To overcome these shortcomings, we employed composition optimization by partially substituting bismuth ions with rare-earth praseodymium ions. This approach enhances the piezoelectric performance and improves the DC electrical resistivity by preventing the loss of volatile bismuth ions and stabilizing the bismuth oxide layer (Bi2O2)2+, thereby reducing the concentration of oxygen vacancies. Consequently, we achieved a large piezoelectric constant d33 of 23.5 pC/N in praseodymium-substituted Bi5Ti3FeO15, which is three times higher than that of pure Bi5Ti3FeO15 (7.1 pC/N), along with a high Curie temperature TC of 778 °C. Additionally, the optimal composition of 4 mol% praseodymium-substituted Bi5Ti3FeO15 exhibits good thermal stability of electromechanical coupling characteristics up to 300 °C. This study holds promise for a wide array of high-temperature piezoelectric applications and has the potential to accelerate the development of high-temperature piezoelectric sensor technologies.

Temperature-dependent dielectric and electromechanical properties of co-modified calcium bismuth titanate (CaBi4Ti4O15) ceramics

Bismuth layer-structured ferroelectrics (BLSFs), Aurivillius-type ceramics, are of great interest primarily due to their exceptionally high Curie temperature (Tc), rendering them invaluable in various applications such as sensors, actuators, transducers, and micro-electro-mechanical systems designed for elevated temperature operations, including ferroelectric Random-Access Memory applications. This study delves into the dielectric and electromechanical properties of Cobalt-modified Calcium Bismuth Titanate (CaBi4Ti4O15, CBT) (CBT-xCo, with x = 2, 4, and 6 mol%) prepared using a conventional solid-state route followed by sintering. By incorporation of Co, insignificant structural changes were observed, disclosed by X-ray Diffraction analysis. Scanning Electron Microscope micrographs unveiled highly anisotropic grains. The sintered density measured by Archimedes method was maximum for x = 6 mol% with value of 99.1 %. A temperature-dependent dielectric study disclosed that the Curie temperature of the CBT ceramics improved with the increase in Co concentration. Notably, CBT-4Co exhibited the lowest dielectric loss of 0.0967 at 1 MHz and the highest resistivity value of 0.1975 × 105 (Ω cm) at a temperature of 775 °C. Moreover, the electromechanical coupling (kp) and mechanical quality factor (Qm) measured at elevated temperatures unveiled distinctive properties, asserting the potential of the ceramics for high-temperature piezoelectric applications up to 450 °C. CBT-4Co demonstrated the highest kp, with a negligible variation at high temperature, although Qm declined. Results confirmed that CBT-4Co stands distinguished showcasing high Tc, minimal dielectric loss, and consistent electromechanical properties making it the prime candidate for electromechanical applications spanning the gamut from room temperature to elevated temperatures.

Ferroelectric domain structure in Bi4Ti3O12 ceramics: Insights from Confocal Raman Microscopy

Bismuth Layer-Structured Ferroelectric (BLSF) materials with Bi4Ti3O12 composition exhibit high ferroelectricity, potential for high-temperature piezoelectricity, and the puzzle of low polarizability, explored via textured ceramics and domain configurations. Here, we show that a distinctive stripe configuration of 90° domains emerges for large platelet-like grains, while the smallest grains, possessing a more equiaxial morphology, exhibit a needle-like domain structure that significantly impacts the ferroelectric properties of the ceramics. The observed hysteresis loops suggest that polarization is effectively clamped, owing to reduced mobility along the needle-like domain walls, thereby leading to a reduction in remnant polarization as grain size diminishes. It is elucidated that the domain structure is intricately linked to both internal stress within the grains and the presence of defects, notably oxygen vacancies, at the domain walls. Consequently, these multifaceted factors are identified as key determinants of the ferroelectric activity within ceramics bearing such a distinctive crystalline structure.

High‐performance bismuth titanate‐ferrite (Bi5Ti3FeO15) for high‐temperature piezoelectric applications

AbstractAdvancing the development of high‐temperature piezoelectric sensors requires high‐performance piezoelectric materials with high Curie temperatures, wherein the charge signals can be efficiently collected at elevated temperatures. The bismuth layer‐structured ferroelectric (BLSF) bismuth titanate‐ferrite (Bi5Ti3FeO15, BTF) has recently attracted considerable attention because of its high Curie temperature (TC) of ∼761°C. However, the piezoelectric properties of BTF‐based compounds have not been extensively investigated because of their extremely poor piezoelectric performances and low electrical resistivities at elevated temperatures. Herein, tungsten‐substituted BTF (BTF‐100xW) ceramics were synthesized using a solid‐state reaction method. X‐ray diffraction refinement results confirmed the lattice distortion of the BO6 octahedron, while piezoelectric force microscopy images verified an increase in the domain wall density with tungsten modification, both of which contribute to significant enhancement of the piezoelectric properties of BTF‐100xW as intrinsic and extrinsic contributions, respectively. Remarkably, BTF‐3W exhibits a high TC of 793°C and a large piezoelectric constant (d33) of 24.3 pC/N, which is over three times that of BTF (7.1 pC/N). Importantly, the substitution of tungsten decreases the concentration of oxygen vacancies, increases the direct current electrical resistivity, and improves the electrical homogeneity at high temperatures, resulting in extremely stable piezoelectric and electromechanical properties at high temperatures, with a high in‐situ relative d33 of >90% at 400°C and a small variation in the electromechanical coupling factor (kp) of <8% at temperatures up to 450°C. These results suggest that the tungsten‐substituted BTF is a potential candidate for high‐temperature piezoelectric ceramics, and is a promising material for applications in high‐temperature piezoelectric sensors.

Voigt Profile is Suitable for Impedance Spectroscopic Analysis of BLSF Ceramics

Abstract: In our earlier studies, samarium-modified bismuth layer-structured ferroelectrics (BLSF), namely SmxBi3-x TiNbO9 (SBTN); (x=0, 0.2, 0.4, 0.6. 0.8, and 1.0), prepared by solid-state reaction method, have shown broad dielectric relaxations. Among all the compositions, Bi2.6Sm0.4TiNbO9 (BST-0.4) has shown a lower tolerance factor, high remnant polarization (Pr) value, and low stretching factor. In addition, the compound has shown interesting broad dielectric relaxation and non-Debye nature. The specific reasons for the broad relaxation remain unclear. To gain more insights, we synthesized multi rare earth ion substituted compounds, namely, Bi2.6La0.2Sm0.2TiNbO9 (sample A) and Bi2.6La0.2Gd0.2TiNbO9 (sample B), using the conventional solid-state reaction method. A single impedance spectroscopic approach alone may not be sufficient to explain the asymmetric or non-Debye behavior, therefore Lorentzian, Gaussian, and Voigt fitting were adopted in the present investigation. From the analysis, the Voigt profile (Vf and Vʹf) is found to be a valuable alternative tool to understand the broad impedance non-Debye relaxations. Finally, results were corroborated by dc-conductivity data. Keywords: BLSF, Modulus spectroscopy, Relaxation, Defect-mechanism, Gaussian, Lorentz and Voigt fitting, Dc conductivity.

Room temperature ferroelectricity and ferromagnetism in Ni-substituted Bi5Ti3FeO15

Aurivillius-type bismuth layer-structured ferroelectric (BLSF) Bi5Ti3FeO15 (BTF) has recently attracted considerable attention as a typical multiferroic material because ferroelectric and magnetic orders coexist, but bulk BTF exhibits antiferromagnetic (AFM) orders and negligible intrinsic magnetoelectric (ME) coupling effects. In this study, nickel-substituted Bi5Ti3FeO15 (Bi5Ti3Fe0.5Ni0.5O15, abbreviated as BTF-Ni) was synthesized using a solid-state reaction method to explore and enhance both the magnetic and ferroelectric properties of BTF. Polarization-electric field P-E loops indicate that the BTF-Ni exhibits considerable maximum polarization P m of 11.9 μC/cm2 and remnant polarization P r of 5.8 μC/cm2, but still keeps a very high ferroelectric Curie temperature (FE T c) of 1029 K, which are much superior to those of pure BTF. Moreover, magnetization-magnetic field M-H loops indicate that BTF-Ni exhibits significant ferromagnetic properties with a large saturation magnetization M s of 60 memu/g, low coercive field H c of 31 Oe at room temperature, and a high ferromagnetic Curie temperature (FM T c) of 698 K, whereas pure BTF has an antiferromagnetic Néel temperature (T N) of 80 K. Our work suggests that nickel-substituted BTF is a potential room-temperature magnetoelectric multiferroic material.

Optimized electromechanical performance in Aurivillius compounds via hot-pressing

Bismuth layer-structured ferroelectrics (BLSFs) are widely demanded in high-temperature piezoelectric sensors, while their low piezoelectricity-induced low sensitivity of piezoelectric sensors is not appropriate for practical operation conditions. Texturing is an effective way to engineer the performance of piezoelectric ceramics by aligning the polar vectors and increasing poling efficiency. Herein, chemical substitution together with the hot-pressing technique is utilized to improve the piezoelectricity of BTN-based ceramics. Characterizations demonstrate that the grains with (100) orientation as shown in the {001} pole figure and the improved domain switching are the main causes of excellent ferroelectricity (Pr∼17.7 μC/cm2) and large piezoelectric coefficient (d33∼27 pC/N) in the textured BCTNTW-Per ceramic. The BCTNTW-Per ceramic also exhibits high TC (890 °C), low dielectric loss, high electrical resistivity (1.6 ×105 Ω•cm at 600 °C), and excellent thermal stability, demonstrating that the combination of the hot-pressing technique and traditional doping strategy is an effective way to prepare high-performance of BLSFs.

Achieving significantly enhanced piezoelectricity in aurivillius ceramics by improving initial polarization and dielectric breakdown strength

In this work, the neglected role of the dielectric breakdown strength (BDS) in piezoelectricity of bismuth layer-structured ferroelectrics (BLSFs) is revealed, enhanced initial polarization and BDS work together to improve the piezoelectricity of CaBi4Ti4O15 (CBT) ceramics via Li/Bi co-substitution. The experimental work, first-principles calculations and finite element simulation are carried out to investigate the effect of Li/Bi co-substitution in depth. The stronger spontaneous polarization (Ps) from the lattice distortion and the more favorable domain switching from the improved grain growth both contribute to an enhanced initial polarization. Besides, the changed grain-scale microstructure improves the hardness and inhibits the local discharge, the higher resistivity related to strong defect dipoles suppresses the heat generation during the poling process, all resulting in an increase of BDS by about 100%, and allowing more domains to align. This work demonstrates an effective strategy to develop BLSFs with enhanced piezoelectricity for high temperature piezoelectric applications.

Bismuth layer-structured Bi4Ti3O12-CaBi4Ti4O15 intergrowth ferroelectric films for high-performance dielectric energy storage on Si substrate

Bismuth layer-structured ferroelectrics (BLSFs) have shown a great design capability for electrical energy storage, due to a highly anisotropic lattice and dielectric property. In this work, we add another notch to their qualifications as high energy density dielectrics, by demonstrating an ultrahigh recyclable energy density (Wrec ∼ 151.1 J/cm3 @ 4 MV/cm) and a good energy efficiency (η ∼ 72.0%) in Bi4Ti3O12-CaBi4Ti4O15 intergrowth ferroelectric films integrated on Si. This performance was achieved by the combination of a high spontaneous polarization (Ps) of the intergrown superlattice, and a polycrystalline nanograin microstructure. The high Ps is obtained through design of a special lattice, which determines the up limit of the energy density. On the other hand, the nanograin structure corresponds to a reduce remnant polarization, an intermediate dielectric constant and a delayed polarization saturation, all are ideal features for achieving a high recyclable energy density and energy efficiency. Such a structure is the consequence of a limited grain growth under the effect of a buffer layer. Lastly, a remarkable fatigue-resistance and an excellent charge-retaining ability were exhibited by these lead-free BLSF films. We expect this work will pave the way for designing high performance bismuth layer-structured ferroelectric films targeted for dielectric energy storage applications.

Influences of intergrowth structure construction on the structural and electrical properties of the BBT-BiT ceramics.

Bismuth Layer Structured Ferroelectrics (BLSFs) have always been an important research direction of high Curie temperature piezoelectrical ceramics, and the construction of intergrowth structure has been considered as an effective method to improve the electric properties of BLSFs. There are many literatures about intergrowth structure improving electrical performance, but few reports analyze the influence of the construction of intergrowth structure on the internal defects and electrical properties in BLSFs. In this study, (1-x) BaBi4Ti4O15 - x Bi4Ti3O12 ceramic samples with intergrowth bismuth layer structure were fabricated by a conventional solid-state reaction method, and the mechanism of the influence of intergrowth structure construction on the structure and electrical properties of BLSFs has been discussed. The crystal structure, phase composition, microstructure, dielectric and piezoelectric performance, relaxation behavior and AC conductivity of ceramic samples were systematically investigated. It has been found that the construction of intergrowth structure can significantly inhibit the generation of oxygen vacancies. The concentration of the oxygen vacancies plays an important role, and its reduction will lead to the inhibition of grain growth and the increase of the relaxation activation energy of ceramics. In addition, the intergrowth structure construction also affects the symmetry of ceramics in the c-axis direction, thus affecting the electrical properties of ceramics.

The electric and optical properties of Bi4Ti3O12–Na0.5Bi2.5Nb2O9:Sm composite ceramics

Bismuth layer-structured ferroelectrics with a high Curie temperature (Tc) have great potential applications in optoelectronic fields. Sm doped (10-x)Bi4Ti3O12-xNa0.5Bi2.5Nb2O9 ((10-x)BIT-xNBN:Sm) composite ceramics have been prepared. The effect of NBN content on the microstructure, electrical properties, photoluminescence (PL) and photochromic (PC) properties of the ceramics have been investigated. It is found that the composite ceramics exist with BIT and NBN phases and 1BIT-9NBN:Sm ceramics have the best comprehensive electrical properties (saturated polarization, d33 = 10 pC/N). Furthermore, the PC and fluorescence modulation performances are dependent on the oxygen vacancy content of composite ceramics. Reversible PC reaction and fast response time as short as 1s have been achieved. Moreover, the influence of natural light on PC reaction has been properly eliminated. The research results indicate that regulating the compositions of (10-x)BIT-xNBN:Sm can not only optimize the electrical properties but also the PC performances. A vivid display via the quick PC reaction has been demonstrated.

Giant electromechanical response in layered ferroelectrics enabled by asymmetric ferroelastic switching

Bismuth layer-structured ferroelectrics (BLSFs) are highly desired for high-temperature piezoelectric systems owing to their high Curie temperature and large spontaneous polarization. However, the inferior electromechanical response, which results from their unique layered crystal structure and inherently low piezoelectric activities, has restricted the practical application. Here, we report discovery of a large electric-field-induced strain in a simplest BLSF Bi2WO6, which is comparable to perovskite ferroelectrics and exhibits an intriguing asymmetric loop-like feature. Through comprehensive analysis on the displacement test configuration and polarization switching process, it is demonstrated that the exotic loop-like strain curve originates from the reversible bending deformation induced by asymmetric 90° ferroelastic switching in the upper and lower surfaces. Specifically, the textured Bi2WO6 ceramic exhibits a giant nominal strain value of ∼0.75% with excellent cycling stability. This discovery raises the possibility of utilizing the bending effect and ferroelastic switching to design piezoelectric actuators and may accelerate the development of high-performance lead-free ceramics.

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.

Role of BO6 octahedral distortion on high temperature piezoelectric properties in Bi3-x(Li0.5Sm0.5)xTiNbO9

A series of bismuth layer structured ferroelectrics (BLSFs) Bi3-x(Li0.5Sm0.5)xTiNbO9 (abbreviated as BTNO-100xLS, x = 0, 0.01, 0.02, and 0.03) high temperature piezoelectric ceramics were prepared by solid state reaction sintering. The microstructure, piezoelectric properties, and electrical conductivity of the sintered ceramics were studied systematically. The introduction of (Li0.5Sm0.5)2+ ions does not change the bismuth layered structure obviously, but it will overmelt and affect its comprehensive properties with the increase of doping content. At last, the piezoelectric coefficient (d33) of ∼9.6 pC/N and the Curie temperature (Tc) is 921.3 °C, which shows good temperature stability and cycle stability, and the mechanical quality factor (Qm) reaches 2694.3 for x = 0.01 composition. These results show that BTNO-1LS is an excellent candidate for high temperature piezoelectric ceramics.

Textured Bi4Ti3O12 Ceramics: One‐Step Spark Plasma Sintering and Their Single‐Crystal‐Like Polar Anisotropy

Texturing is the most effective way to engineer the performance of bismuth layer–structured ferroelectric (BLSF) ceramics by utilizing the strong anisotropy of grains, but the existing processing approaches are still complex. Herein, a one‐step spark plasma sintering (SPS) approach is demonstrated to prepare textured Bi4Ti3O12 (BiT) ceramics with high performance. The degree of orientation can be controlled from 57% to 95% by only adjusting the sintering temperature from 840 to 1000 °C. The largest spontaneous polarization (Ps) of ≈32.2 μC cm−2 is obtained in 95% <001> textured ceramics along the direction perpendicular to the SPS pressure, accompanied with the maximum electro‐strain of ≈0.14% and piezoelectric coefficient of 14.3 pC N−1. Moreover, under the same conditions of poling and illumination, the textured ceramics exhibit unique anisotropic photoresponse in which the photocurrent polarity is dependent on the testing orientations. In particular, a short‐circuit photocurrent density of 8.76 nA cm−2 is achieved along the direction of SPS pressure after positive poling, while the value goes to −79.4 nA cm−2 along direction perpendicular to the SPS pressure. These results are expected to provide a paradigm to achieve highly textured BLSF ceramics for electric and photoelectric applications.

Understanding the piezoelectric origin of bismuth layer-structured ferroelectric polycrystal using first-principle method

Polycrystalline ferroelectric piezoelectric materials are widely used in various functional electronic devices. We present a systematic orientational average method to estimate the piezoelectric properties of ferroelectric polycrystals via first-principle calculations. This method can construct a bridge to connect the monocrystalline and polycrystalline ferroelectric piezoelectric materials, which opens a door to estimate the piezoelectric properties of polycrystals via first-principle calculations, helping the further study of piezoelectric polycrystals. The piezoelectric properties of bismuth layer-structured ferroelectrics (BLSFs) polycrystals are investigated via the method, which presents a good agreement in other theoretical and experimental results. It is found that the longitudinal polarization stretching and in-plane polarization rotation contribute the most of piezoelectricity for poled polycrystals. Unexpected polarization stretching of Bi2O2 layer and slipping between Bi2O2 layer and perovskite block are revealed, being considered to play an important role for the piezoelectricity of BLSFs.

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.

High Curie temperature bismuth layer-structured ferroelectric calcium bismuth niobate (CaBi<sub>2</sub>Nb<sub>2</sub>O<sub>9</sub>) piezoelectric ceramics

Piezoelectric materials play a key role in various kinds of modern electronic devices. High Curie temperature piezoelectric materials are required for piezoelectric sensors under critical conditions for nuclear power plants, automotive, aeronautic, and aerospace applications. These piezoelectric sensors usually withstand high temperature of 500°C or higher. To meet the requirements of these applications, piezoelectric materials must possess high piezoelectric performance and high electrical resistivity as well as high Curie temperature. The Aurivillius-type bismuth layer-structured ferroelectrics (BLSFs) are the most promising high-temperature piezoelectric materials because of their very high Curie temperature ( T c). Structurally, the BLSF compounds are composed of fluorite-like (Bi2O2)2+ layers and perovskite-like (A m −1B m O3 m +1)2− blocks, which arrange along the c axis alternately and regularly. The general formula is (Bi2O2)2+(A m −1B m O3 m +1)2−, where A is a mono-, di-, or trivalent metallic ion (or their combination) suited to dodecahedral coordination; B is a transition metallic ion suited to octahedral coordination, and m is the number of BO6 octahedral in the perovskite-like blocks and varies from 1 to 4. In this paper, the crystal structure, piezoelectric properties (herein piezoelectric constant d 33 value), and Curie temperature ( T c) of prototype BLSF ceramics have been summarized, and the summarized results indicate that the piezoelectric properties of high T c BLSF compounds are very low. The prototype BLSF ceramics with T c of >700°C exhibit low piezoelectric d 33 value of no more than 10 pC/N, and the prototype BLSF ceramics with T c of >900°C exhibit low piezoelectric d 33 value of no more than 5 pC/N. Calcium bismuth niobate, CaBi2Nb2O9 (CBN), was firstly found and synthesized by Sweden scientist Aurivillius B, in 1949. But until 2005, the investigations on the piezoelectric properties of CBN were firstly reported by Yan H X and Reece M J. After that, the piezoelectric properties of CBN have attracted much attention. The compound CBN has a very high Curie temperature T c of ~940°C, and it is considered to be potential material as piezoelectric sensors and other electronic components for high-temperature applications. However, its particular bismuth layer-structured crystal structure restricts the rotation of the spontaneous polarization ( P s) in the two-dimensional orientation ( a - b plane), and large coercive field ( E c) makes the material difficult to be poled sufficiently. The prototype CBN ceramic exhibits very low piezoelectric performance, with low piezoelectric d 33 value of 5 pC/N. In this paper, the piezoelectric properties of bismuth layer-structure ferroelectric calcium bismuth niobate (CaBi2Nb2O9) piezoelectric ceramics have been summarized. The results indicate that A-site ions substitution is more effective than B-site ions substitution to enhance the piezoelectric properties of CaBi2Nb2O9 ceramics, and A-site and B-site ions co-substitution is more desirable to optimize the piezoelectric performance. The piezoelectric d 33 can be promoted to >16 pC/N by compositions adjusting, while the Curie temperature remains higher than 900°C. Texture technologies, such as templated grain growth (TGG) and spark plasma sintering, have been introduced, and they are good methods to further enhance the piezoelectric performance of CaBi2Nb2O9 ceramics. The piezoelectric d 33 can be promoted to higher than 20 pC/N by texture technologies. Overall, the CaBi2Nb2O9 ceramics are promising materials for high-temperature piezoelectric sensor applications. Finally, perspectives on how to further enhance the piezoelectric performance of CaBi2Nb2O9 ceramics are presented.

Investigation of the role of Sm, Na in ferroelectric, piezoelectric and conduction behaviour of Strontium Bismuth Titanate ceramics

The manuscript presents a systematic study of ferroelectric, piezoelectric and conduction behaviour of Sm, Na substituted Strontium Bismuth Titanate ceramics, prepared by solid-state reaction method. The structural analysis of Bismuth layer structured ferroelectrics (BLSF) of Sr1-2xSmxNaxBi4Ti4O15 (SSNBTi) ceramics was done by X-ray Diffraction technique and it showed single-phase formation and peak shifting towards the higher angles. Scanning Electron Microscopy confirmed orthorhombic sheet-like grain structure with random orientation of grains. P-E study and Piezoelectric studies were done at room temperature (RT); improved remnant polarization (Pr = 1.95 μC/cm2), Piezoelectric charge coefficient (d33 = 21.1 pC/N) and electromechanical coupling factor (kp = 0.71) were achieved by substitution of Sm, Na (x = 0.4) in Sr of SBTi ceramics. The AC conductivity was studied from RT to 600 °C in the frequency range of 1 kHz–100 kHz. The trends shown by Activation energies obtained from Arrhenius plots suggests that the mechanism of conduction is through short-range oxygen vacancies hopping. The combination of improved ferroelectric properties and high piezoelectric constant (kp = 0.71) make the SSNBTi ceramics suitable for a wide range of sensor, actuator, and transducer applications.