Preparation of Bi4Ti3O12 particles by crystallization from glass

Glass from the Bi₂O₃–TiO₂–B₂O₃ system was formed by rapid quenching of the melt. After annealing at 500 °C, the glass crystallized in the form of plate-like particles. The particles thus formed were separated through an acid treatment. Field emission scanning electron microscopy showed a layered structure for the particles. XRD observations revealed that the crystalline form was Bi₄Ti₃O₁₂, a useful material in the electronics industry.     

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.     

Effects of Bi4Ti3O12 addition on the microstructure and dielectric properties of modified BaTiO3 under a reducing atmosphere

The effects of Bi₄Ti₃O₁₂ addition on the microstructure and dielectric properties of Mn-modified BaTiO₃ were investigated to develop low temperature fired BaTiO₃-based ceramics with stable temperature characteristics. The sintering temperature of Mn-doped BaTiO₃ could be reduced to 1200 °C by adding more than 1 mol% Bi₄Ti₃O₁₂. TEM results show an apparent core–shell structure with 2 mol% Bi₄Ti₃O₁₂ addition. However, it was destroyed when the Bi₄Ti₃O₁₂ content increased from 2 to 4 mol%. The permittivity decreased and the Curie temperature shifted to higher temperature when the Bi₄Ti₃O₁₂ content increased from 0 to 3 mol%. The temperature characteristic of capacitance was very close to the EIA X8R specification when 2 mol% Bi₄Ti₃O₁₂ was added due to the presence of the core–shell grain structure and raised Curie temperature. With adequate Bi₄Ti₃O₁₂ addition, the BaTiO₃-based system shows great potential for applications in EIA X8R-type multilayer ceramic capacitors.     

Rapid microwave-assisted sol-gel synthesis and exceptional visible light photocatalytic activities of Bi12TiO20

Crystalline Bi₁₂TiO₂₀ and Bi₄Ti₃O₁₂ particles were selectively synthesized by rapid microwave-assisted sol-gel method. During the thermal decomposition process of the dried gel, microwave calcination played a key role in producing single phase Bi₁₂TiO₂₀. Our Bi₁₂TiO₂₀ demonstrated one of the highest visible-light photocatalytic activities for MO degradation among the reported bismuth titanate particles with various compositions. Single phase Bi₄Ti₃O₁₂ can also be prepared by either a conventional calcination at high temperature or a combined heat treatment of a conventional heating followed by microwave calcination. The photocatalytic reaction rate constant of the Bi₄Ti₃O₁₂ prepared by microwave calcination was three times higher than that of conventionally calcined Bi₄Ti₃O₁₂, further confirming the advantage of microwave calcination in preparation of highly photocatalytically active bismuth titanate.     

Mechanism of Bi0.5Na0.5TiO3 and Bi4.5Na0.5Ti4O15 template synthesis during topochemical microcrystal conversion and texturing of Bi0.5(Na0.8K0.2)0.5TiO3 piezoelectric ceramics

The mechanism by which Bi_0.5Na_0.5TiO₃ and Bi_4.5Na_0.5Ti₄O₁₅ templates are synthesized via a topochemical microcrystal conversion method using Bi₄Ti₃O₁₂ precursor and TiO₂ particles was investigated based on their crystal structures. The Bi_0.5Na_0.5TiO₃ template consisted of a mixture of plate-like and equiaxed particles, whereas the Bi_4.5Na_0.5Ti₄O₁₅ template consisted only of plate-like particles. The size of the plate-like and equiaxed particles was dependent on the size of the Bi₄Ti₃O₁₂ precursor and TiO₂ particles, respectively. The Lotgering factor and piezoelectric constant of textured Bi_0.5(Na_0.8K_0.2)_0.5TiO₃ ceramics prepared using the Bi_0.5Na_0.5TiO₃ template were lower than those of the textured Bi_0.5(Na_0.8K_0.2)_0.5TiO₃ ceramics prepared from the Bi_4.5Na_0.5Ti₄O₁₅ template. This can be attributed to the small amount of plate-like particles in the Bi_0.5Na_0.5TiO₃ template caused by the inevitable co-existence of equiaxed particles.     

Bi4Ti3O12/TiO2 heterostructure: Synthesis,characterization and enhanced photocatalytic activity

A multicomponent oxide, Bi₄Ti₃O₁₂/TiO₂ heterostructure was successfully synthesized via a two-step synthesis route based on an anodic oxidation procedure and a subsequent hydrothermal technique. X-ray diffraction confirmed that the composition of the as-fabricated sample was a Bi₄Ti₃O₁₂/TiO₂ composite. Scanning and transmission electron microscopy observation reveals that the as-synthesized sample consisted of TiO₂ nanotubes decorated with Bi₄Ti₃O₁₂ nanocubes. The photocatalytic property of Bi₄Ti₃O₁₂/TiO₂ heterostructure was evaluated by decomposing methyl orange as a model organic compound. Compared with the unmodified TiO₂ nanotube arrays, Bi₄Ti₃O₁₂/TiO₂ heterostructure exhibits a higher photocatalytic activity in the decomposition of methyl orange under UV light. The prominent photocatalytic activity could be ascribed to the formation of the heterostructure between Bi₄Ti₃O₁₂ and TiO₂ as well as a good dispersity of Bi₄Ti₃O₁₂ nanocubes, which could effectively separate the photogenerated carriers and reduce the electron–hole recombination.     

BiOCl nanosheet/Bi4Ti3O12 nanofiber heterostructures with enhanced photocatalytic activity

Aurivillius oxide semiconductors are important photocatalyst because of their unique electronic structure and layered crystal. In this paper, two kinds of Aurivillius oxide semiconductors heterostructures based on Bi₄Ti₃O₁₂ nanofibers frameworks and BiOCl nanosheets are successfully synthesized by combining the electrospinning technique and solvothermal method. The high-resolution transmission electron microscopy results reveal that an intimate interface between Bi₄Ti₃O₁₂ nanofibers and BiOCl nanosheets forms in the heterojunctions. Photocatalytic tests show that the BiOCl/Bi₄Ti₃O₁₂ heterostructures exhibit enhanced photocatalytic activity than bare Bi₄Ti₃O₁₂ and BiOCl, mainly owing to the photoinduced interfacial charge transfer based on the photosynergistic effect of the BiOCl/Bi₄Ti₃O₁₂ heterojunction. At the end, the photocatalytic mechanism with O₂⁻ production was studied.     

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.     

Fabrication and characterization of intergrown Bi4Ti3O12-based thin films using a metal-organic precursor solution

Ferroelectric intergrowth-structured Bi₄Ti₃O₁₂-based thin films have been fabricated by chemical solution deposition. Bi₄Ti₃O₁₂–SrBi₄Ti₄O₁₅ (BiT–SBTi) and SrBi₂Nb₂O₉–Bi₄Ti₃O₁₂ (SBN–BiT) precursor films crystallized in the desired intergrown BiT–SBTi and SBN–BiT structures on Pt/TiO_x/SiO₂/Si substrates by optimizing the processing conditions. Synthesized BiT–SBTi and SBN–BiT thin films exhibited ferroelectric P–E hysteresis loops. The BiT–SBTi thin films crystallized at 750 °C showed a 2P_r value approximately 20 μC/cm². Although a little smaller P_r value was observed for the SBN–BiT thin films, the squareness of a P–E hysteresis loop was superior to that of BiT–SBTi thin films. Also, the SBN–BiT thin films had a smoother surface morphology compared with BiT–SBTi thin films.     

Fabrication of textured bismuth titanate by templated grain growth using aqueous tape casting

Textured bismuth titanate (Bi₄Ti₃O₁₂) ceramics were fabricated by templated grain growth (TGG), using plate-like Bi₄Ti₃O₁₂ particles prepared by a molten salt method as the templates. The templates were aligned in the fine-grained matrix by aqueous tape casting with their major surface parallel to the casting plane. Effect of sintering conditions on the grain orientation in the material was investigated. It was found that the degree of grain orientation (Lotgering factor, f) increased with the increase in sintering temperature, soaking time and heating rate. High Lotgering factor (f⩾0.92) can be obtained through careful control of the sintering parameters. The textured Bi₄Ti₃O₁₂ ceramics showed a high anisotropy in its dielectric properties in the directions parallel and perpendicular to the casting plane.     

Modified Ba6−3xNd8+2xTi18O54 microwave dielectric ceramics

In order to improve the microwave dielectric properties of Ba_6−3xNd_8+2xTi₁₈O₅₄ solid solution ceramics, the effects of Bi₂O₃ and Bi₄Ti₃O₁₂ additives were determined. The results of SEM and EDS analyses suggested that the present ceramics with Bi₄Ti₃O₁₂ additives consisted of Ba_6−3xNd_8+2xTi₁₈O₅₄ solid solution matrix phase, and secondary phase of BaTi₄O₉, but this was not the situation of Bi₂O₃ added ceramics. XRD analysis also revealed that the unit cell volume of the matrix phase increased with increasing the amount of Bi₄Ti₃O₁₂ additive. With addition of Bi₄Ti₃O₁₂ into the present ceramics, the dielectric constant increased and the temperature coefficient of resonator frequency decreased, while the Qf value slightly decreased. The excellent microwave dielectric characteristics (ε=94·9, Qf=5620 GHz, τ_f=21·4 ppm/°C could be achieved in the present ceramics through the microstructure control.     

The growth of interfacial compounds between titanium dioxide and bismuth oxide

The growth of interfacial compounds between TiO₂ and Bi₂O₃ during transient liquid phase bonding at 900, 1000 and 1100 °C for various times was investigated. The microstructures and compositions of compounds in joints were analyzed by means of SEM and EPMA. It was found that the compound Bi₄Ti₃O₁₂ forms initially and replaces the Bi₂O₃ interlayer. Bi₂Ti₄O₁₁ then arises at the interface between Bi₄Ti₃O₁₂ and TiO₂ and the metastable Bi₂Ti₂O₇ phase appears last at the interface between Bi₄Ti₃O₁₂ and Bi₂Ti₄O₁₁. The modes and activation energies of the growth of Bi₄Ti₃O₁₂ and Bi₂Ti₄O₁₁ were determined respectively. Holes in the middle of the joint heated at 1100 °C for 24 h were also found.     

Synthesis of Protonated Derivatives of Layered Perovskite-Like Bismuth Titanates

The possibility of synthesizing protonated derivatives of layered perovskite-like titanates Bi₄Ti₃O₁₂, ABi₄Ti₄O₁₅, (A = Ba, Sr, Ca) and K_2.5Bi_2.5Ti₄O₁₃ is experimentally investigated. It is established that in the case of Bi₄Ti₃O₁₂ and ABi₄Ti₃O₁₅, single-phased protonated derivatives cannot be obtained by treating the compounds with acid solutions, due to the partial dissolution of initial oxides, accompanied by the formation of titanium dioxide. In the case of K_2.5Bi_2.5Ti₄O₁₃ titanate, a number of new protonated and hydrated derivatives are obtained and described.     

Colossal dielectric permittivity and relevant mechanism of Bi2/3Cu3Ti4O12 ceramics

Bi_2/3Cu₃Ti₄O₁₂ (BCTO) ceramics with pure perovskite phase were successfully prepared by traditional solid-state reaction technique. Uniformly distributed and dense grains with the grain size of 2–3 μm were observed by SEM. A giant low-frequency dielectric permittivity of ~3.3×10⁵ was obtained. The analysis of complex impedance revealed that Bi_2/3Cu₃Ti₄O₁₂ ceramics are electrically heterogeneous. There are three kinds of dielectric response detected in Bi_2/3Cu₃Ti₄O₁₂ ceramics, which existed in the low-frequency range, middle-frequency range, and high-frequency range, respectively. Through the study of dielectric spectrum at different temperatures, the relatively low activation energy of 0.30 eV for middle-frequency dielectric response was calculated, which suggested that this Middle-frequency dielectric response can be ascribed to grain boundaries response. In view of the analysis of dielectric spectrum at low temperatures, the activation energy of 0.07 eV for high frequency dielectric response was found. This value illustrated that dielectric response at high frequencies was associated with grains polarization effect. The comparison of dielectric spectra of Bi_2/3Cu₃Ti₄O₁₂ ceramics with different types of electrodes revealed that giant low-frequency dielectric constant was attributed to the electrode polarization effect.     

Effect of Fe/Ta doping on structural,dielectric, and electrical properties of Bi4Ti2.5Fe0.25Ta0.25O12 ceramics

Aurivillius single‐phase Bi₄Ti_2.5Fe_0.25Ta_0.25O₁₂ ceramics was prepared via high‐temperature solid‐state reaction method. The detailed structural analysis of the doped Bi₄Ti₃O₁₂ compound was carried out by Rietveld refinement of the full XRD Pattern. Dielectric and electrical properties were studied in a wide range of temperature and frequency by dielectric/impedance spectroscopies. The comprehensive analysis of frequency spectrum reveals the occurrence of two relaxation behaviors in the ceramics at low frequency and high frequency, respectively. A phase transition was observed at ~650°C in Bi₄Ti_2.5Fe_0.25Ta_0.25O₁₂ somewhat lower than the ferroelectric transition temperature of Bi₄Ti₃O₁₂. The possible reason for the decrease of ferroelectric transition temperature was discussed based on the structural analysis. The present results could be useful for designing and/or modifying properties of Bi₄Ti₃O₁₂‐related ceramics.     

Structure versus relaxor properties in Aurivillius type compounds

Structure refinements in M^IIBi₄Ti₄O₁₅ (M^II = Ca, Ba), Bi_4−xBa_xTi_3−xNb_xO₁₂, (Na_0.5Bi_0.5)_1−xBa_xBi₄Ti₄O₁₅ and Bi₄Ti₃O₁₂–PbTiO₃ systems are used to report structural features of relaxor Aurivillius phases. In compounds with relaxor-like behaviour, the average structure is almost undistorted, closed to the archetypal HT paraelectric phase, with a tolerance factor ≳0.996. The coordination number of Bi³⁺ in fluorite layers changes from {4 + 2} for ferroelectrics to {4} for relaxors. Transmission Electron Microscopy reveals some characteristic features of relaxors such as micro-twinning, shearing-type defects which attest from the existence of a compositional inhomogeneity and a disorder at a local scale.     

Na0.5Bi0.5TiO3 phase relations: Thermodynamics and phase equilibria in the systems Bi2O3 – TiO2, Na2O – TiO2, and Na2O – Bi2O3 – TiO2

The lead-free piezoelectric material sodium bismuth titanate (NBT, Na_0.5Bi_0.5TiO₃) has attracted considerable attention owing to its promising dielectric, piezoelectric, and electrical properties. However, the literature on the binary subsystems is contradictory and there are only limited data for the ternary system. The present work surveys all of the reports of the binary subsystems Bi₂O₃ – TiO₂ and Na₂O – TiO₂ and synthesizes these data into inclusive revised versions. The compatibilities for the ternary system Na₂O – Bi₂O₃ – TiO₂ were determined experimentally, thus enabling the construction of a complete isothermal section at 800 °C. The compatibilities associated with the problematic binary subsystem Na₂O – Bi₂O₃, which experiences extreme volatilisation, were determined through the generation of the absent standard-state thermodynamic functions for the relevant binary and ternary phases, thus providing a full suite of thermodynamic data for this system. The thermodynamic stability diagrams for Na₂O, Bi₂O₃, and TiO₂ thus were calculated. The isothermal section also addresses the contradictions in the literature concerning the formation of solid solutions of Bi₁₂TiO_20-x / Bi_12-xTi_1+xO_20+0.5x, pyrochlore (Bi₂Ti₂O₇ / Na_wBi_2-xTi_2-yO_7-z), BTO (Bi₄Ti₃O₁₂ / Na_xBi₄Ti₃O_12+0.5x), and NBT (Na_0.5Bi_0.5TiO₃ / Bi_1±xNa_xTiO_3.5±x). Further, it was observed that the congruent melting point of NBT, which was determined to be 1225 °C, was preceded by the onset of gradual structural destabilization at 940 °C. Also, the NBT rhombohedral → tetragonal phase transformation was observed at an onset temperature of ∼250 °C. The present work thus provides platform data for the fabrication and reactivities of materials in the ternary system Na₂O – Bi₂O₃· TiO₂ and its binary subsystems.     

Electrical and electrochemical properties of molten-salt-synthesized 0.05 mol Zr- and Si-doped Li4Ti5O12 microcrystals

This work emphasizes the structural, morphological, electrical, and electrochemical properties of 0.05 mol Zr- and Si-doped Li₄Ti₅O₁₂ synthesized using the molten salt method and applied to negative electrodes in Li-ion batteries. Formation of the spinel phase with face-centered cubic structure in the nominally pure and Zr- and Si-doped samples are revealed from X-ray powder diffraction technique. Lattice parameters refined by full-profile Rietveld method are in accordance with the literature data for the Li₄Ti₅O₁₂ (Li_1.333Ti_1.667O₄) spinel structure. The presence of possible functional groups is identified using Fourier transform infra red spectroscopy. The field emission scanning electron microscopic images indicate the formation of micron-sized (1.5–2 μm) randomly distributed polyhedral-shaped particles. The electrical conductivity studies demonstrate the grain-conducting behavior of the material. The maximum DC conductivity of 2 × 10^?5 S cm^?1 is observed for Zr-doped Li₄Ti₅O₁₂ at room temperature. The galvanostatic charge–discharge studies show that Zr-doped Li₄Ti₅O₁₂ exhibits a high discharge capacity of about 325 mAh g^?1 at 0.01 °C, higher than Si-doped Li₄Ti₅O₁₂ (200 mAh g^?1), and also that the cycling stability of Zr-doped Li₄Ti₅O₁₂ is enhanced.     

Equilibrium phases in the Bi2O3–TiO2–WO3 system

Phase relations in the Bi₂O₃–TiO₂–WO₃ ternary system were evaluated for different compositions calcined in air at 850 °C by means of XRD techniques. A solid solution area was observed for Bi₄Ti₃O₁₂ compositions with a small amount of WO₃. The experimental results suggest the existence of a new phase with a nominal composition close to Bi₃Ti_2.5W_0.5O₁₁. This phase allows the definition of four triangles of compatibility at 850 °C in the ternary system. The new phase was characterized by XRD, SEM and EDS.     

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.