BIT Ceramics Research Articles

Internal stress and electrical properties of the CBT-BiT ceramics with intergrowth structure

Intergrowth ceramic series (1-x) CaBi4Ti4O15 - x Bi4Ti3O12, x = 0, 0.2, 0.4, 0.6, 0.8, 1, were prepared by traditional solid-state reaction process. (1-x) CBT – x BiT ceramics were investigated systematically in the evolution of structural and electrical properties, especial focus on the role of conductivity and spontaneous polarization by the construction of intergrowth structure. On the one hand, an increase in internal stress of bismuth layers (Bi2O2)2+ in CBT-BiT intergrowth structure with a long-range disorder array, inducing a raising in spontaneous polarization. On the other hand, a decrease in the aspect ratio (length/thickness) of grains and the conductivity for CBT-BiT ceramics by intergrowth structured construction, which is beneficial for domain deflection and piezoelectricity. Moreover, the relaxation mechanism of all ceramics is dominated by the dipole conduction mechanism containing oxygen vacancies. The optimal piezoelectric performance for (1-x) CBT – x BiT ceramics was obtained with x = 0.8 (d33 ∼ 19 pC/N), exhibiting higher Curie temperature of 696 °C.

Realizing Super‐High Piezoelectricity and Excellent Fatigue Resistance in Domain‐Engineered Bismuth Titanate Ferroelectrics

AbstractBismuth titanate (BIT) is widely known as one of the most prospective lead‐free ferroelectric and piezoelectric materials in advanced high‐temperature sensing applications. Despite significant advances in developing BIT ferroelectrics, it still faces major scientific and engineering challenges in realizing super‐high performance to meet next‐generation high‐sensitivity and light‐weight applications. Here, a novel ferroelectric domain‐engineered BIT ceramic system is conceived that exhibits super‐high piezoelectric coefficient (d33 = 38.5 pC N−1) and inverse piezoelectric coefficient (d33* = 46.7 pm V−1) at low electric field as well as excellent fatigue resistance (stable up to 107 cycles). The results reveal that the introduction of high‐density layered (001)‐type 180° domain walls with flexible polarization rotation features and the formation of small‐size multi‐domain states with low energy barriers are mainly responsible for the excellent electrical performance. To the best of knowledge, it is the first time to reveal such intriguing domain structures in BIT ceramics in detail, especially from the atomic‐scale perspective by using atomic number (Z)‐contrast imaging in combination with atomic‐resolution polarization mapping. It is believed that this breakthrough conduces to comprehensively understand structural features of ferroelectric domains in BIT ceramics, and also opens a window for future developments of super‐high performance in bismuth layer‐structured ferroelectrics via domain engineering.

Oxygen vacancies and electrical properties of different valence ions (W6+, Nb5+, Zr4+, Cr3+) doped Bi4Ti3O12 ceramics

Numerous literatures have attested that donor doping in BiT ceramics will inhibit the generation of oxygen vacancies to improve electrical properties, but our study detects an originality that acceptor doped into BiT ceramics can also reduce the concentrate of oxygen vacancies and raise the values of Curie temperature and piezoelectric constant. A serious BiT-based ceramics with different valence transition metal dopants of W6+, Nb5+, Zr4+, Cr3+ were prepared via traditional solid phase method, achieving a high Curie temperature of 680–699 °C and a large piezoelectric constant of 7–17 pC/N. To improve the structural and electrical properties of BiT-based ceramics, this paper researched the concentration of oxygen vacancies with charge compensation effect of ions substitution by investigating the phase composition, microstructure, dielectricity, and conductivity systematically. The results show that all transition metal dopants enter the B-site of BiT ceramics to different extent and Cr partially replace the A-site of BiT ceramics, while the relaxation behavior and conduction mechanism of these ceramics are mainly contributed by the migration of oxygen vacancies. Due to the increase in the number of free electrons formed by donor doping W6+ and Nb5+ into BiT ceramics, the reduction in the number of trapped electrons proffered by equivalent doping Zr4+ that occupied the Ti3+ position and the consumption in the vacancies of Bi and O provided by Cr3+ that occupied the A-site after Bi volatilization, the oxygen vacancies defects of the BiT-based ceramics were decreased after ions doped.

Improvement of piezoelectric properties of Bi4Ti3O12 ceramics by Mn/Ta co-doping and direct reaction sintering

Bi4Ti3-x (Mn1/3Ta2/3)xO12 piezoelectric ceramics were prepared by conventional sintering and direct-reaction sintering in this study. The effect of B-site Mn/Ta co-substitution and sintering method on the microstructure and electrical properties of Bi4Ti3-x (Mn1/3Ta2/3)xO12 piezoelectric ceramics was systematically investigated. The experimental results show that the combination of high-valent Ta and low-valent Mn ions replacing Ti4+ ions reduce the concentration of oxide vacancy defects in BITMT ceramics. The direct-reaction sintering is a simpler preparation method and the prepared samples have more uniform grain distribution and higher density. The resistivity of the direct reaction sintered sample with x = 0.05 at 500 °C is 7.19 × 105 Ωcm, the residual polarization is 8.1 μC/cm2, and the temperature stability of the piezoelectric constant is good. Therefore, the present study suggests that the piezoelectric properties of Mn and Ta co-doping of BIT ceramics could be greatly enhanced via the direct-reaction sintering, which provides a promising alternative to the conventionally sintered for a more cost-effective preparation for BIT ceramics.

Sintering characteristics of plate-like bismuth titanate ceramics with preferred c - axis orientation for memory storage devices

Bismuth titanate (Bi4Ti3O12) (BIT) has been an attractive material due to its high Curie temperature, large remnant polarization and relatively low processing temperature, making it suitable for piezoelectric, pyroelectric and non-volatile random access memory storage devices. In this present work, polycrystalline textured bismuth titanate ceramics were synthesised by the cost-effective molten salt synthesis method. The effect of sintering conditions on the structural, morphological and dielectric properties have been carried out in detail. The X-ray diffraction studies reveal the formation of the monophasic structure of BIT ceramics with a preferential orientation along the c-axis. It is also noticed that the orientation along the c-axis increases with an increase in sintering temperature. Interestingly, the parameters like crystallite size and micro-strain calculated from the Williamson - Hall method could be tailored as a function of sintering temperature. The microstructural studies carried out using FESEM technique suggested the presence of plate-like morphology of BIT ceramics and subsequently, the elemental mapping analysis used to confirm the uniform distribution of the elements Bi, Ti and O present in the ceramic sample. The Fourier transform infrared and X-ray photoelectron spectroscopic studies have been done to identify the constituent chemical bonds and oxidation states of BIT ceramics. Interestingly, it is noted that the value of the dielectric constant increases with the increase in sintering temperature of BIT ceramics. Furthermore, the high dielectric constant value of 200 obtained at 100 kHz for 950 °C sintered sample could establish this material for the embedded capacitor in memory storage devices.

Enhanced electrical properties and thermal stability of W/Cr co‐doped BIT-based high‐temperature piezoelectric ceramics

Bi 4 Ti 3 O 12 (BIT), a typical layered-structure ferroelectric with a high Curie temperature ( T C ), is a promising material for high-temperature sensors. Herein, W/Cr co-substitution at the B-site of BIT ceramics (BITWC100 x ) is carried out to investigate the phase structure, domain structure, and electrical properties. The W/Cr addition apparently reduces the concentration of oxygen vacancies, effectively improving the ferroelectric and piezoelectric properties as well as the resistivity of the BIT ceramics. The BITWC2 ceramic exhibits a high piezoelectric coefficient ( d 33 = 31.1 pC/N), a moderate T C (651 °C), a large remnant polarization ( P r = 12.2 μC cm −1 ), and a prominent direct current resistivity (5.49 ×10 6 Ω·cm at 500 °C). Moreover, the BITWC2 ceramic possesses a large d 33 of 26.6 pC/N at an annealing temperature of 600 °C, indicating the excellent thermal stability of the piezoelectric coefficient. Overall, the BITWC100 x ceramics can be used in piezoelectric devices at temperatures up to 500 °C. • BITWC100 x ceramics with a high T C and excellent electricity properties can be used in high-temperature piezoelectric devices. • The information of domain structure is obtained by PFM. • The refinement of the domain size contributes to enhancement of piezoelectric properties of BITWC100 x 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 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.

Effect of alternative mechanochemical method on modified bismuth titanate

Bi4 – x La x Ti3O12 (BiLT, x = 0.60–1.00) ceramics have been successfully synthesized by the alternative mechanochemical method and investigated their structural, microstructure, dielectric, and ferroelectric properties. Based on thermal stability of synthesized samples, compounds were calcined at 750 °C. No secondary phase is observed in the powder X-ray diffraction patterns. Plate-like shape with enhanced density is seen in the scanning electron microscope micrographs. EDAX pattern confirmed the chemical composition of samples. Prepared ceramic sample had relatively appreciable remanent polarization value (≈14.5 µC/cm2) at room temperature. Microstructure significantly influenced the dielectric and ferroelectric properties of the modified BiT ceramics. Synthesized compounds explored desirable electronic properties for innovative ferroelectric-based device applications.

Highly orientated Bi4Ti3O12 piezoceramics prepared by pressureless sintering

Bismuth titanate (Bi4Ti3O12) has great potential for applications over 400 °C owning to its great Curie temperature (TC ∼ 675 °C). But the relatively low piezoelectric constant d33 (< 8 pC/N) has restricted the practical high-temperature application. In this work, a new combination of the molten salt method and pressureless sintering was used to prepare textured Bi4Ti3O12 piezoceramics with a high degree of grain orientation (f = 0.83), large d33 (29.7 pC/N) with a comparatively high TC (628 °C). These demonstrate that the combination is a low cost, effective and simple way to achieve highly orientated BIT ceramics with excellent performance. The mechanism and origin of the grain orientation have been deeply investigated, and the compression pressure during the molding process is proposed to be the main driving force for grain orientation, which would be very helpful for guiding the design and fabrication of novel highly orientated materials.

Ferroelastic properties and compressive stress-strain response of bismuth titanate based ferroelectrics

Ferroelectric materials have been widely studied for applications in numerous devices due to their controllable ferroelectric/ferroelastic properties under electric field or mechanical stress. Recently, a type of bismuth layer-structured ferroelectrics, W/Cr co-doped BIT ceramics, has attracted much attention due to its high Curie temperature, large spontaneous polarization, and particularly enhanced ferroelectric properties. Nevertheless, as a significant consideration for the reliability and durability of devices, the mechanical properties associated with ferroelastic behaviors of this type of ceramics are generally ignored. In this study, a type of W/Cr co-doped BIT ceramics with optimal chemical composition of Bi4Ti2·95W0·05O12.05+0.2 wt% Cr2O3 (BTWC) was synthesized via the solid-reaction technology. Ferroelastic domain structures and ferroelastic switching behaviors together with mechanical failure properties of the sintered ceramics were investigated in details. PFM observations reveal the existence of pseudo-90° and -180° ferroelastic domain structures in BTWC ceramics. The nonlinear deformation of stress-strain curve originates from ferroelastic domain switching induced by mechanical stress of sufficient magnitude. Moreover, the ferroelastic switching plays a significant role in improving the fracture toughness of BTWC ceramics. Additionally, the ceramics sintered at higher temperature are expected to exhibit a better ferroelastic switching behavior yet lower failure stress. The work can provide design consideration of loading conditions for practical applications of BTWC ceramics.

Stabilizing temperature‐capacitance dependence of (Sr, Pb, Bi)TiO3‐Bi4Ti3O12 solutions for energy storage

Abstract(1‐x)Sr0.7Pb0.15Bi0.1TiO3‐xBi4Ti3O12 ((1‐x)SPBT‐xBIT, x = 0‐0.125) bulk ceramics were developed and calcined via the solid‐state method, aimed at the application of pulsed power capacitors. The phase structures, temperature stability, hysteresis loop, and discharge properties were systematically investigated. Considering both the temperature stability and dielectric properties, 0.925SPBT‐0.075BIT bulk ceramics with a capacitance variation satisfying the X7R specification were developed for pulsed power capacitors. The energy storage density was 0.252 J/cm3, and the ceramics showed high temperature stability at 80 kV/cm. The discharge current waveforms of the 0.925SPBT‐0.075BIT ceramics were recorded. A high discharge power density of approximately 1.01 × 108 W/kg with an 8 Ω load resistor and short discharge period of 84 ns were achieved at 50 kV/cm. The good temperature stability properties and high power density show that the 0.925SPBT‐0.075BIT ceramics are well suited for pulsed power capacitors with a wide temperature range.

Enhanced pyroelectric and piezoelectric responses in W/Mn-codoped Bi4Ti3O12 Aurivillius ceramics

The pyroelectric and piezoelectric properties of 4 at% Mn-doped Bi4Ti2.9W0.1O12 (BiTW-Mn) Aurivillius ceramic were investigated and compared to Bi4Ti2.9W0.1O12 (BiTW) counterpart, which were fabricated using a conventional solid state reaction method. High resistivities of 4.9 × 1012 and 2.5 × 1011 Ω cm at 100 °C were obtained in the W-doped and W/Mn-codoped BiT ceramics, respectively. They showed similar activation energies and ionic-p-type mixed conduction mechanisms. Higher pyroelectric coefficients of 57.1 μC/m2K and piezoelectric coefficients of 21 pC/N, as well as much lower dielectric loss of 0.003 were achieved in W/Mn-codoped ceramics. These property changes were mainly induced by MnTi −Vo defect dipoles. The effect of acceptor doping was evidenced by an internal bias field, shown by a horizontal offset in the polarization-field behavior. The improved properties together with high thermal stability indicate that BiTW-Mn may be a promising candidate for pyroelectric and piezoelectric devices at elevated temperatures.

Bi4Ti3O12 multilayered ceramic tapes produced by aqueous tape casting and laminating process: Structural and dielectric properties

In this work, multilayered bismuth titanate ceramic tapes engineered by combining aqueous tape casting and laminating process were produced. The structural and dielectric properties of green and sintered multilayered materials, with 1–5 layers, were explored. Diffraction peaks related to the bismuth titanate phase of structure Bi4Ti3O12 were identified in the precursor powder and the green and the sintered tapes. In addition, a Bi2Ti2O7 structure phase was indexed to the sintered tape. Modifications of the dielectric behavior with the increase in the number of layers composing the samples and with the sintering procedure were observed. Considering the green multilayered BIT ceramics, values between 10 and 14 as a function of the distinct number of layer were found at 1.0 GHz. On the other hand, for the sintered BIT multilayered, values between 2.3 and 8.5 in a wide frequency range were observed, showing a constant behavior as a function of the employed frequency. The results provided interesting insights for tailoring the structural and dielectric properties of the multilayered bismuth titanate ceramic tapes, placing them as a promising candidate fulfilling the needs in a wide variety of technological applications.

Gamma-ray irradiation effects on electrical properties of bismuth layer-structured ferroelectric ceramics

Abstract In this study, we prepared the bismuth layer-structured ferroelectric (BLSF)-type Bi 4 Ti 3 O 12 (BiT), Bi 3.25 La 0.75 Ti 3 O 12 (BLaT), and Bi 3.1 Nd 0.9 Ti 3 O 12 (BNdT) ceramics using the solid-state reaction method. The prepared ceramics were irradiated at room temperature by using a 60 Co gamma-ray source in a dose range of 0–3000 kGy with a dose rate of 10 kGy/h to compare the structure and electrical properties of the irradiated ceramics. The X-ray diffraction analysis shows that the BLSF structure was well formed in all ceramics without a secondary phase. There was no structural change such as grain size change and secondary phase formation despite the cumulative gamma-ray dose of 3000 kGy. A comparison of the electrical properties with gamma-ray irradiation shows that the BiT ceramics exhibits a larger reduction ratio compared to the BLaT and BNdT ceramics. The rate of change of the remnant polarization (2 P r ) value with the gamma-ray irradiation doses was − 14.2%, − 8%, and − 3.4% in BiT, BLaT, and BNdT ceramics, respectively, at a cumulative gamma-ray dose of up to 3000 kGy. Furthermore, the dielectric relaxation phenomenon in BiT ceramics at low frequency was observed when gamma rays of 1000 kGy or more were irradiated. Based on these results, in this study, we investigated the structure and electrical properties of BLSF ceramics with gamma-ray irradiation.

Influence of Bi 4 Ti 3 O 12 doping on structural and piezoelectric properties of (K 0.4425 Na 0.52 Li 0.0375 )(Nb 0.87 Ta 0.06 Sb 0.07 )O 3 lead-free ceramics

Abstract Recently, (K, Na, Li)(Nb, Ta, Sb)O3 ceramics have attracted much attention of researchers, and have become one of the most popular systems of KNN-based ceramics. In this paper, Bi4Ti3O12 was added in the (K0.4425Na0.52Li0.0375)(Nb0.87Ta0.06Sb0.07)O3 ceramics (KNLNTS-x mol% BIT) to improve their piezoelectric properties. The phase formation and microstructure of KNLNTS-x mol% BIT ceramics were examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM). With the addition of BIT, the permittivity maxima of samples shifted toward higher temperature firstly and then shifted to lower temperature. All samples showed well ferroelectric behavior and the density of (1-x)KNLNTS-x mol% BIT ceramics were increased and reached a relative density of 99.4%. High piezoelectric properties of d33 = 255 pC/N, kp = 0.451, Qm = 186 were obtained for the samples containing 0.50 mol% BIT.

Dielectric properties of Bi4Ti3O12 ceramics by impedance spectroscopic method

Various lead-free ceramics have been investigated in search for new high-temperature dielectrics. In particular, Bi4Ti3O12 is a type of ferroelectric ceramics, which is supposed to replace leadcontaining ceramics for its outstanding dielectric properties in the near future. Ferroelectric ceramics of Bi4Ti3O12 made by conventional mixed oxide route have been studied by impedance spectroscopy in a wide range of temperature. X-ray diffraction patterns show that Bi4Ti3O12 ceramics are a single-phase of ferroelectric Bi-layered perovskite structure whether it is calcined at 800 °C or after sintering production. This study focused on the effect of the grain size on the electric properties of BIT ceramics. The BIT ceramics with different grain sizes were prepared at different sintering temperatures. Grain becomes coarser with the sintering temperature increasing by 50 °C, relative permittivity and dielectric loss also change a lot. When sintered at 1 100 °C, r values peak can reach 205.40 at a frequency of 100 kHz, the minimum dielectric losses of four different frequencies make no difference, all close to 0.027. The values of Ea range from 0.52 to 0.68 eV. The dielectric properties of the sample sintered at 1 100 °C are relatively better than those of the other samples by analyzing the relationship of the grain, the internal stresses, the homogeneity and the dielectric properties. SEM can better explain the results of the dielectric spectrum at different sintering temperatures. The results show that Bi4Ti3O12 ceramics are a kind of dielectrics. Thus, Bi4Ti3O12 can be used in high-temperature capacitors and microwave ceramics.

Electrical properties of CaBi4Ti4O15–Bi4Ti3O12 piezoelectric ceramics

CaBi4Ti4O15–Bi4Ti3O12 (CBT–BIT) ceramics were synthesized using a solid state reaction method. The X-ray diffraction (XRD) analysis revealed the existence of bismuth layered perovskite phase with orthorhombic crystal structure. High-resolution transmission electron microscopy (HRTEM) confirmed the alternate arrangement of CBT part and BIT part along c axis in the intergrowth structure. CBT–BIT ceramics showed excellent thermal stability of the dielectric loss (tanδ), but the relaxation of dielectric loss in the 100Hz to 1MHz frequency range had been observed. Meanwhile, an enhanced piezoelectric constant (d33) value of 15pC/N was observed without degradation even the temperature up to 650°C. The dc resistivity (ρdc) of CBT–BIT performed a high value of 5.68×1014(Ωcm) at room temperature (RT). In addition, the ρdc values of CBT–BIT within the temperature range of 100–450°C were close to those of CBT and kept almost one hundred times higher than those of BIT.

Influence of processing route on electrical properties of Bi4Ti3O12 ceramics obtained by tape-casting technology

Bismuth titanate powders (Bi4Ti3O12-BIT) were fabricated by solid state reaction (SSR) and polymeric precursor method (PPM). From these powders, Bi4Ti3O12 pellets were obtained by tape-casting using plate-like templates particles prepared by a molten salt method. The BIT phase crystallizes in an orthorhombic structure type with space group Fmmm. Agglomeration of the particles, which affects the densification of the ceramic, electrical conduction and leakage current at high electric fields, was monitored by transmission electronic microscopy (TEM) analyses. FEG-SEM indicated that different shape of grains of BIT ceramics was influenced by the processing route. Both SSR and PPM methods lead to unsaturated P–E loops of BIT ceramics originating from the highly c-axis orientation and high conductivity which was affected by charge carriers flowing normally to the grain boundary of the crystal lattice.

Crystalline structure, ferroelectric properties, and electrical conduction characteristics of W/Cr co-doped Bi4Ti3O12 ceramics

W/Cr co-doped BIT (BTWC) ceramics {Bi4Ti3−xWxO12+x+0.25wt% Cr2O3 (x=0–0.1)} with a strong ferroelectricity and a high electrical resistivity were prepared by a conventional ceramic process, and effects of W doping content on their crystalline structures, ferroelectric properties and electrical conduction characteristics were also explored. By the co-doping of W/Cr, the crystallographic evolution happened in BTWC ceramics, and then the degree of the lattice distortion of BTWC ceramics decided on their spontaneous polarization and influenced their electrical resistivity. Moreover, both the increased applied field and measurement temperature can improve the Pr. The great improvement in remanent polarization and resistivity of BTWC ceramics were mainly attributed to the decreased concentration of oxygen vacancies by doping W6+. The Bi4Ti2.95W0.05O12.05+0.25wt% Cr2O3 ceramic possessed a large Pr of 16μC/cm2 and a high ρdc (600°C) of 2.94×106Ωcm, respectively, which makes it a promising candidate for high-temperature applications.

Intergrowth Bismuth Layer-Structured Na0.5Bi2.5Nb2O9–Bi4Ti3O12 High Temperature Ferroelectrics Ceramics

Intergrowth superlattice structural Na0.5Bi2.5Nb2O9–Bi4Ti3O12 (NBN–BIT) ceramics were synthesized by solid-state reaction method. In the temperature dependence of dielectric permittivity, two anomalies appeared at 663 and 780 °C, respectively. The dielectric loss tan δ of the NBN–BIT ceramics was very low, especially from room temperature to 400 °C. The ferroelectric hysteresis loop measurement revealed P r and E c of NBN–BIT ceramics are 10.5 μC/cm2 and 18.5 kV/cm, the P r nearly as twice as that of the NBN ceramics. The results show that ferroelectric properties of NBN–BIT ceramics increase comparing with pure NBN, and NBN–BIT ceramics are promising candidate materials for high temperature applications.