Thickness Dependence of Dielectric,Leakage, and Ferroelectric Properties of Bi6Fe2Ti3O18 Thin Films Derived by Chemical Solution Deposition

We prepared Bi₆Fe₂Ti₃O₁₈ thin films on Pt/Ti/SiO₂/Si substrates with thickness ranging from ～300 to ～900 nm by using a chemical solution deposition route and investigated the thickness effects on the microstructure, dielectric, leakage, and ferroelectric properties of Bi₆Fe₂Ti₃O₁₈ thin films. Increasing thickness improves the surface morphology, dielectric, and leakage properties of Bi₆Fe₂Ti₃O₁₈ thin films and a well‐defined ferroelectric hysteresis loops can form for the thin films with the thickness above 400 nm. Moreover, the thickness dependence of saturation polarization is insignificant, whereas the remnant polarization decreases slightly with increasing thickness and it possesses a maximal value of ～20 μC/cm² for the 500 nm‐thick thin films. The mechanisms of the thickness dependence of microstructure, dielectric, and ferroelectric properties are discussed in detail. The results will provide a guidance to optimize the ferroelectric properties in Bi₆Fe₂Ti₃O₁₈ thin films by chemical solution deposition, which is important to further explore single‐phase multiferroics in the n = 5 Aurivillius thin films.     

Large enhancement of piezoelectric properties and resistivity in Cu/Ta co-doped Bi4Ti3O12 high-temperature piezoceramics

In this study, the electrical properties of Bi₄Ti₃O₁₂-based Aurivillius-type ceramics were tailored by a B-site co-doping strategy combining high valence Ta⁵⁺ and low valence Cu²⁺. A series of Bi₄Ti_3−x(Cu_1/3Ta_2/3)_xO₁₂ (BTCT) (x = 0, 0.005, 0.01, 0.015, 0.02, 0.025, and 0.03) ceramics were prepared by the conventional solid-state reaction method. The effect of Cu/Ta co-doping on the crystal structure, microstructure, dielectric properties, piezoelectric properties, ferroelectric properties, and electrical conductivity of these ceramics was systematically investigated. Co-doping significantly enhanced the piezoelectric properties and DC electrical resistivity of the resulting composites. The optimized comprehensive performances were obtained at x = 0.015 with a large piezoelectric coefficient (34 pC/N) and a relatively high resistivity of 9.02 × 10⁶ Ω cm at 500°C. Furthermore, the ceramic also exhibited stable thermal annealing behaviors and excellent fatigue resistance. The results of this study demonstrated great potential of the Cu/Ta co-doped Bi₄Ti₃O₁₂ ceramics for high-temperature piezoelectric device applications.     

Impedance spectroscopy of Na0.5Bi4.50+xTi4Oy (x = -0.02, 0, 0.02) ceramics with excellent dielectric properties

The electric and dielectric properties of Na_0.5Bi_4.50+xTi₄O_y (x = −0.02, 0, 0.02) prepared by conventional mixed oxide route have been investigated by impedance spectroscopy (IS) over a wide temperature range. Single-phase bismuth layer-structured perovskite patterns were observed through X-ray diffraction of the three samples Na_0.5Bi_4.5Ti₄O₁₅, Na_0.5Bi_4.48Ti₄O_y, and Na_0.5Bi_4.52Ti₄O_y. The results show that the relative permittivity (εr) increases with the increase in temperature and reaches its maximum at about 675℃. With the continuous increase in temperature, the permittivity decreases gradually. Both relative permittivity and dielectric loss show great stability at the low-temperature zone. The ceramic of x = 0.02 with Ea of 1.09 eV has the maximum oxygen ionic transport number between 600 and 800℃ for all samples. And at this time, it has the maximum electrical conductivity. All the results indicated that Na_0.5Bi_4.50+xTi₄O_y (x = −0.02, 0, 0.02) ceramics were promising base materials for high-temperature capacitor because of their high dielectric properties.     

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.     

Enhanced optical transmittance and energy-storage performance in NaNbO3-modified Bi0.5Na0.5TiO3 ceramics

Dielectric ceramics with both excellent energy storage and optical transmittance have attracted much attention in recent years. However, the transparent Pb-free energy-storage ceramics were rare reported. In this work, we prepared transparent relaxor ferroelectric ceramics (1 − x)Bi_0.5Na_0.5TiO₃–xNaNbO₃ (BNT–xNN) by conventional solid-state reaction method. We find the NN-doping can enhance the polarization and breakdown strength of BNT by suppressing the grain growth and restrained the reduction of Ti⁴⁺ to Ti³⁺. As a result, a high recoverable energy-storage density of 5.14 J/cm³ and its energy efficiency of 79.65% are achieved in BNT–0.5NN ceramic at 286 kV/cm. Furthermore, NN-doping can promote the densification to improve the optical transmittance of BNT, rising from ∼26% (x = 0.2) to ∼32% (x = 0.5) in the visible light region. These characteristics demonstrate the potential application of BNT–xNN as transparent energy-storage dielectric ceramics.     

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 F_00l = 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.     

Effects of cerium on structures and electrical properties of (Nb,Ta) modified Bi4Ti3O12 piezoelectric ceramics

Bi₄Ti₃O₁₂ high-temperature piezoelectric ceramics composed of 0.03 mol (Nb, Ta)⁵⁺ substituting B site and x mol CeO₂ (x = 0–0.05, abbreviated as BCTNT100x) substituting A site were synthesized by the conventional solid-state reaction method. The effects of Ce additive on the structures and electrical properties of resulting Bi₄Ti₃O₁₂-based ceramics were systematically investigated. In-situ temperature-dependent X-ray diffraction (XRD) confirmed that the phase structure of BCTNT100x ceramics change from orthorhombic structure to tetragonal structure as temperature increased. The ceramics at Ce content x = 0.03 illustrated optimal performances with superior piezoelectric constant (d₃₃ = 36.5 pC/N), high Curie temperature (T_C = 649 °C), and large remanent polarization (2P_r = 21.6 μC/cm²). BCTNT3 ceramics also possessed high d₃₃ of 32.5 pC/N at an annealing temperature of 600°C, with electrical resistivity preserved at 10⁶ Ω cm at 500 °C. These results demonstrate that BCTNT100x ceramics can be used as high-temperature piezoelectric devices.     

Enhanced energy storage performance in bismuth layer-structured BaBi2Me2O9 (Me = Nb and Ta) relaxor ferroelectric ceramics

Bismuth layer-structured BaBi₂Nb₂O₉ (BBN) and BaBi₂Ta₂O₉ (BBT) relaxor ferroelectric ceramics were explored as potential energy storage materials. Remarkable energy storage performances were obtained in both BBN and BBT ceramics, featured by large recoverable energy storage density (~0.84 J/cm³ and ~0.68 J/cm³) and high energy storage efficiency (~90% and ~94%), respectively. Furthermore, both the two ceramics exhibit good thermal and frequency stabilities. Delightedly, both the BBN and BBT ceramics can complete the discharge process within 0.15 μs, resulting in ultrahigh current density of 195 A/cm² and 234 A/cm² and excellent power density of 10.74 MW/cm³ and 12.89 MW/cm³, respectively. The obtained results suggest that BaBi₂Nb₂O₉ and BaBi₂Ta₂O₉ ceramics could have a promising future in energy storage applications. This study also demonstrates that the bismuth layer-structured relaxor ferroelectric ceramic can be considered as a novel potential lead-free energy storage materials, in addition to the widely studied pervoskite-structured relaxor ferroelectric ceramics.     

Enhancement of multiferroic properties of Aurivillius Bi5Ti3FeO15 ceramics by Co doping

Multiferroic Bi₅Ti₃Fe_1−xCo_xO₁₅ (BFCT-x, where x = 0, 0.1, 0.3, 0.5, 0.7) ceramics were synthesized via a conventional solid-state reaction process and their microstructural, ferroelectric, magnetic and magnetoelectric coupling properties were investigated in detail. All samples show layered perovskite Aurivillius phase with an orthorhombic structure. The highest remanent polarization (2P_r) (35 μC/cm²) has been observed in BFCT-0 ceramic while the BFCT-0.3 ceramic shows the highest remanent magnetization (M_r) (0.13 emu/g) and magnetoelectric coefficient (11.47 mV cm⁻¹ Oe⁻¹). The enhancement of magnetic properties and the magnetoelectric coupling of these ceramics are attributed to the structural distortion caused by Co substitution which subsequently led to ferromagnetic interactions via the Dzyaloshinskii-Moriya interaction.     

Effect of Li2CO3–Bi2O3 doping on the low-temperature sintering,structure, and dielectric and mechanical properties of MgO–TiO2(w) ceramics

Dense MgO–12% TiO₂(w) ceramics containing 12 wt% TiO₂, which were doped with Li₂CO₃–Bi₂O₃ composite sintering aids, were prepared at a low sintering temperature of 950 °C in this study. The effects of sintering additives on the sintering characteristics, phase composition, microstructure, and dielectric and mechanical properties of the ceramic samples were systematically investigated, and the influences of their phase composition and microstructure on the dielectric and mechanical properties were examined. The introduction of sintering aids produced a new Bi₄Ti₃O₁₂ phase in the sample structure, while the residual Bi₂O₃ mixed with the newly formed Mg₂TiO₄ and Bi₄Ti₃O₁₂ phases distributed at MgO grain boundaries formed a structure surrounding MgO grains. This structure filled the pores in the ceramic sample, which increased its density and enhanced the mechanical properties. At a Li₂CO₃–Bi₂O₃ content of 15 wt%, the density, flexural strength, and Vickers hardness of the ceramic samples reached their maximum values of 3.4 g/cm³, 218.9 MPa, and 778.7 HV, respectively. However, the further increase in the Li₂CO₃–Bi₂O₃ content deteriorated their dielectric properties although the dielectric constant and dielectric loss remained below 13.4 and 2.1 × 10⁻³, respectively. The findings of this work indicate that Li₂CO₃–Bi₂O₃ sintering aids can significantly lower the sintering temperature of MgO–12% TiO₂(w) ceramics and control their dielectric and mechanical properties through microstructural changes.     

Strong photoluminescence and good electrical properties in Eu-modified SrBi2Nb2O9 multifunctional ceramics

Bismuth layer-structured ferroelectric (BLSFs) ceramics of Sr_1−xEu_x Bi₂Nb₂O₉ (SBT-xEu, x=0.000, 0.002, 0.004, 0.006) were prepared by a conventional solid-state reaction method. All the samples have a bismuth oxide layered structure with a dense microstructure. The ferroelectric, piezoelectric, dielectric and optical properties of the ceramics were investigated. After Eu³⁺ doping, samples show a bright red photoluminescence upon blue light excitation of the 400–500 nm. Upon the excitation of 465 nm light, the materials have two intense emission bands peaking around 593 nm (yellow) and 616 nm (red). Meanwhile, good electrical properties with large piezoelectric constant d₃₃ of 14 pC/N and large remnant polarization 2P_r of 11.97 μC/cm² are obtained at x=0.006. Moreover, this material has a high Curie temperature (T_c=429 °C) and high resistivity, which makes the material resistant to thermal depolarization up to its Curie temperature. This feature indicates that the SBN-xEu ceramics have a latent use in high temperature applications.     

A realization of excellent piezoelectricity and good thermal stability in CaBi2Nb2O9: Pseudo phase boundary

Phase boundaries (PBs) are known to contribute to the outstanding performances of lead-based and lead-free materials. However, a lack of PBs restricts the promotion of piezoelectric performance in bismuth layer-structured ferroelectrics (BLSFs). In this work, a pseudo PB, ie, pseudotetragonal distortion (regulated by Ce), is proposed to promote the piezoelectric properties of CaBi₂Nb₂O₉-based ceramics, and an excellent piezoelectric constant (d₃₃) of 20.2 pC/N with a high Curie temperature of 923°C is obtained. Verified Ce incorporation into the (Bi₂O₂)²⁺ layer alters the environment of the (Bi₂O₂)²⁺ layer, thereby influencing the atomic displacement in the Nb-O octahedron and modulating the theoretical spontaneous polarization (P_s). Strengthening of the pseudotetragonal distortion is favorable to the polarization switching, and maintains the theoretical P_s of ceramics at a high level, thus realizing the promotion of d₃₃. Furthermore, pseudotetragonal distortion guarantees good thermal depoling performance of the ceramic, which remains at 89.6% (18.1 pC/N) of its initial d₃₃ after depoling at 875°C. This work provides clear guidance on obtaining high d₃₃ and good thermal stability in BLSFs.     

Doping level effects in Nb self-doped Bi3TiNbO9 high-temperature piezoceramics with improved electrical properties

Nb self-doped Bi₃Ti_1-xNb_1+xO₉ (x = 0, 0.02, 0.04, 0.06, 0.08, and 0.1) high-temperature piezoelectric ceramics were fabricated through the conventional solid-state sintering method. The effects of different Nb self-doping levels on the microstructure, piezoelectric activities, and electrical conduction behaviors of these Nb self-doped Bi₃Ti_1-xNb_1+xO₉ ceramics were studied in detail. Large doping level effects on piezoelectric activity and resistivity were confirmed, which might be ascribed to the evolution of the crystal structure and the variations of the oxygen vacancy concentration and the grain anisotropy induced by Nb doping. An optimized piezoelectric coefficient (d₃₃) of 11.6 pC/N was achieved at x = 0.04 with a Curie temperature of 906°C. Additionally, an improved DC resistivity of 6.18 × 10⁵ Ω·cm at 600°C was acquired in this ceramic. Furthermore, the ceramic exhibited excellent thermal stability with the d₃₃ value maintaining 95% of its initial value after being annealed at 850°C for 2 hours. These results showed that Nb self-doped Bi₃Ti_1-xNb_1+xO₉ ceramics might have great potentials for high-temperature piezoelectric applications.     

Low temperature synthesis of plate-like Na0.5Bi0.5TiO3 via molten salt method

In this study, plate-like Na_0.5Bi_0.5TiO₃ (BNT) templates with perovskite structure were obtained by two-step molten salt synthesis (MSS) method at a low temperature. Firstly, Bi₄Ti₃O₁₂ precursors were synthesized at 1030 °C in NaCl–KCl molten salt. Secondly, plate-like Na_0.5Bi_0.5TiO₃ particles with perovskite structure were obtained from plate-like layer-structured ferroelectric ceramic of Bi₄Ti₃O₁₂ by topochemical microcrystal conversion method. Result showed that excessive Na₂CO₃ was beneficial to facilitate the low temperature synthesis. In the case of an excess of 30 mol% Na₂CO₃, plate-like BNT particles could be obtained by synthesis at temperatures ranging from 760 °C to 800 °C, which indicated a flexible processing route. Also, it has been observed that plate-like BNT particles show a high aspect ratio with 1 μm in thickness and 10–20 μm in length. These Na_0.5Bi_0.5TiO₃ plate-like particles can be good candidates for the preparation of lead-free BNT-based piezoelectric ceramics with oriented grain microstructure.     

Enhanced piezoelectric performance in Na0.5Bi4.5Ti4O15-based bismuth-layered ceramics by Nb/Mn doping modification

In this work, Na_0.5Bi_4.5Ti_3.94–xMn_0.06Nb_xO_15+y bismuth-layered ferroelectric ceramics were prepared by a solid-state reaction method. The effect of Nb⁵⁺ content on crystal morphology, electrical properties, and piezoelectric performance were systematically investigated. The results show that the introduction of Nb⁵⁺ into Na_0.5Bi_4.5Ti_3.94–xMn_0.06Nb_xO_15+y ceramics to replace Ti⁴⁺ increases the ratio of b/a lattice parameter, leading to the TiO₆ octahedral distortion and the structural transformation tendency from the orthorhombic to tetragonal phase, which facilitates dipole movements of Na_0.5Bi_4.5Ti_3.94–xMn_0.06Nb_xO_15+y ceramics. Therefore, the ferroelectric properties of Na_0.5Bi_4.5Ti_3.94–xMn_0.06Nb_xO_15+y ceramics are improved, and an enhanced piezoelectric coefficient of 30 pC/N combining great temperature stability with d₃₃ value higher than 25 pC/N in the temperature range of 25°C–450°C has been realized in Na_0.5Bi_4.5Ti_3.94–xMn_0.06Nb_xO_15+y ceramics with x = 0.08 mol. Our work provides a good model for designing lead-free ultrahigh Curie temperature piezoelectric devices that can be practically applied in extremely harsh environments.     

Tailoring the Piezoelectric and Relaxor Properties of (Bi1/2Na1/2)TiO3–BaTiO3 via Zirconium Doping

This article details the influence of zirconium doping on the piezoelectric properties and relaxor characteristics of 94(Bi_1/2Na_1/2)TiO₃–6Ba(Zr_xTi_1?x)O₃ (BNT–6BZT) bulk ceramics. Neutron diffraction measurements of BNT–6BZT doped with 0%–15% Zr revealed an electric‐field‐induced transition of the average crystal structure from pseudo‐cubic to rhombohedral/tetragonal symmetries across the entire compositional range. The addition of Zr up to 10% stabilizes this transition, resulting in saturated polarization hysteresis loops with a maximum polarization of 40 μC/cm² at 5.5 kV/mm, while corresponding strain hysteresis measurements yield a maximum strain of 0.3%. With further Zr addition, the ferroelectric order is progressively destabilized and typical relaxor characteristics such as double peaks in the current density loops are observed. In the strain hysteresis, this destabilization leads to an increase of the maximum strain by 0.05%. These changes to the physical behavior caused by Zr addition are consistent with a reduction of the transition temperature T_F‐R, above which the field‐induced transformation from the relaxor to ferroelectric state becomes reversible.     

Critical role of CuO doping on energy storage performance and electromechanical properties of Ba0.8Sr0.1Ca0.1Ti0.9Zr0.1O3 ceramics

CuO doped Ba_0.8Sr_0.1Ca_0.1Ti_0.95Zr_0.05O₃ (BSCTZ) ceramics were prepared by a modified mechano-chemical activation technique with the aim of improving energy storage properties for ceramic capacitor applications. CuO can effectively improve the microstructural characteristics along with a transformation of BSCTZ from classical ferroelectric to relaxor, which is the prime requirement for obtaining high discharge energy density and energy efficiency. The effect of CuO doping on the microstructural, ferroelectric, dielectric, and piezoelectric properties have been systematically studied. The study reveals that an appropriate amount of CuO doping can significantly enhance the morphological properties along with improvement in material density, which is very beneficial in a material for attaining improved energy storage performance. The BSCTZ sample with 3 mol% CuO doping has shown a highly dense microstructure, high saturation polarization (33.01 μC/cm²), low remnant polarization (6.74 μC/cm²), ultrahigh discharge energy density (1.81 J/cm³) and high energy efficiency (81.9%). The CuO doping in BSCTZ has also led to a slight improvement in breakdown strength and electromechanical properties compared to pure BSCTZ ceramics, which is mainly attributed to excellent density and optimum grain size of the material.     

Triple Hysteresis Loops of PLZST Ceramics Related to Coexistence of Ferroelectricity and Antiferroelectricity

The hysteresis behaviors and phase characteristics of Pb_0.97La_0.02(Zr_0.90Sn_0.025Ti_0.075)O₃ (PLZST) ceramics were investigated in this work. A single mini hysteresis loop at 3 kV/mm with the maximum polarization (P_max) of 8.3 μC/cm² and triple hysteresis loops at 6.6 kV/mm were observed, which indicates the coexistence of rhombohedral ferroelectric phase and tetragonal antiferroelectric phase. The X‐ray Diffraction patterns and dielectric temperature spectra both demonstrate this coexistence. Moreover, the hysteresis loops with increasing temperature indicated that a ferroelectric–antiferroelectric phase transition occurred at about 60°C. These phenomena would be useful for understanding the domain evolution during ferroelectric and antiferroelectric phase transition.     

Ferroelectric and photocatalytic properties of Aurivillius phase Ca2Bi4Ti5O18

Aurivillius phase Ca₂Bi₄Ti₅O₁₈ powders with micrometer size were produced by solid-state reaction. X-ray diffraction revealed that the powders had polar orthorhombic structure with space group of B2cb. Ca₂Bi₄Ti₅O₁₈ ceramic exhibited frequency independent dielectric anomaly at 774°C. The piezoelectric coefficient d₃₃ value of poled Ca₂Bi₄Ti₅O₁₈ pellets was 0.7 ± 0.2 pC/N. Both frequency independent dielectric anomaly and detectable d₃₃ value clearly indicated that Ca₂Bi₄Ti₅O₁₈ is a ferroelectric material with Curie point of 774 ℃. UV–vis absorption spectra revealed that Ca₂Bi₄Ti₅O₁₈ had a direct band gap of 3.2 eV. Photocatalytic activity of the Ca₂Bi₄Ti₅O₁₈ powders was examined by degradation of rhodamine B (RhB) under simulated solar light. 16% of RhB solution was degraded by Ca₂Bi₄Ti₅O₁₈ powders after 4 hours UV-vis irradiation. With Ag nanoparticles deposited on the Ca₂Bi₄Ti₅O₁₈ powders surface, 50% of RhB was degraded under the same irradiation condition. The fitted degradation rate constant of Ag decorated Ca₂Bi₄Ti₅O₁₈ was 4 times higher than that of bare Ca₂Bi₄Ti₅O₁₈. This work suggested that the Aurivillius ferroelectric Ca₂Bi₄Ti₅O₁₈ is a promising candidate for photocatalytic applications.     

Ferroelectric properties of Pb(Zr0.52Ti0.48)O3–Bi3.25La0.75Ti3O12 ceramics

The ceramic samples of compound (1 ? x)Pb(Zr_0.52Ti_0.48)O₃–xBi_3.25La_0.75Ti₃O₁₂ (when x = 0, 0.03, 0.05, 0.07, 0.10, 0.15 and 0.20) were prepared by a solid-state mixed oxide method. X-ray diffraction analysis showed that complete solid solutions occurred for all compositions. Perovskite phase with tetragonal crystal structure and corresponding lattice distortion was observed. Scanning electron micrographs of sample surfaces showed equiaxed grains for all compositions. Ferroelectric measurements revealed that the addition of small amount of BLT (x = 0.03) showed high remanent polarization (～33.5 μC cm^?2) and low coercive field (～2.74 kV mm^?1). Further increasing BLT content could maintain ferroelectric properties of PZT–BLT ceramics. Based on this study, ferroelectric properties of this PZT–BLT ceramic system can be improved for being further used in ferroelectric memory applications.