Intermediate phases formation during the synthesis of Bi4Ti3O12 by solid state reaction

In this work, the formation of Bi₄Ti₃O₁₂ by solid state reaction from Bi₂O₃ and TiO₂ starting powders has been studied. The Bi₄Ti₃O₁₂ formation occurs through an intermediate Bi₁₂TiO₂₀ sillenite phase formed at temperatures sligthly over 300 °C. This sillenite phase is stable up to ∼750 °C, but in the presence of TiO₂ reacts to form Bi₄Ti₃O₁₂ at temperatures >500 °C. Raman spectroscopy has been used to evidence the amorphization of TiO₂, demonstrating that the Bi₄Ti₃O₁₂ formation occurs through the reaction of sillenite Bi₁₂TiO₂₀ and TiO₂.     

Study on thermolysis process of a new hydrated and protonated perovskite-like oxides H2K0.5Bi2.5Ti4O13·yH2O

A protonated form of the n?=?4 layered bismuth containing perovskite-like titanate K_2.5Bi_2.5Ti₄O₁₃ belonging to Ruddlesden-Popper phases was prepared via ion exchange reaction of interlayer K⁺ with protons. Its composition was investigated by TG ICP and EDX analysis was found to be H₂K_0.5Bi_2.5Ti₄O₁₃·H₂O. The thermal behavior of the obtained phase was investigated by STA coupled with mass-spectrometry, the structural changes, happening with the sample during heating, were examined by XRD. It was shown that the as-prepared hydrated phase undergoes two-stage dehydration at low temperatures (up to 160?°C). The further heating leads to the gradual decomposition and crystallization of new phases, notably Bi₂Ti₂O₇, Bi₄Ti₃O₁₂ and Bi₂Ti₄O₁₁. The morphology of the as-prepared sample and samples after heat treatment was examined using SEM.     

Bi@Bi4Ti3O12/TiO2 films on glass with photocatalytic and self-cleaning performance

A stable and translucent Bi@Bi₄Ti₃O₁₂/TiO₂ film was fabricated on conventional glass substrates for the first time. The film exhibited a good photocatalytic performance and efficient self-cleaning capability against organic dyes under full spectral irradiation and visible light irradiation. Bi₄Ti₃O₁₂/TiO₂ film was first prepared on a glass substrate with colloidal silica as a high temperature binder, followed by implantation of nanoscale Bi in it by an in-situ partially reduction of Bi₄Ti₃O₁₂ to generate Bi@Bi₄Ti₃O₁₂/TiO₂ films. The improved photocatalytic ability is probably attributed to the surface plasmon resonance of Bi atom as well as the enhanced electron transfer efficiency and synergistic effect of Bi₄Ti₃O₁₂ and TiO₂. According to trapping experiments, hydroxyl radicals (OH) were active species in the photocatalytic degradation of dyes under full spectral light irradiation and possible photocatalytic mechanism was proposed. The film prepared in this work may well have potential practical applications in many aspects, such as cleansing treatments for high building external decorative panels and also systematic characterization of the film suggests that the in-situ reduction is an effective and simple way to produce nanoscale Bi@Bi₄Ti₃O₁₂.     

The effect of Bi2O3 compensation during thermal treatment on the crystalline and electrical characteristics of bismuth titanate thin films

Bismuth titanate thin films are deposited on ITO/glass substrates by rf magnetron sputtering at room temperature using a Bi₄Ti₃O₁₂ ceramic target. The deposited Bi₄Ti₃O₁₂ films are annealed in a conventional furnace in ambient air for 10 min at temperatures ranging from 550 to 640 °C. One specimen is annealed in a crucible containing additional Bi₂O₃ compensation powder, while the other specimen is annealed in ambient air. XRD analysis shows that the crystal phases of films annealed with Bi₂O₃ powder are better than those of films annealed without Bi₂O₃ powder. Furthermore, the EDS results reveal that the bismuth weight percentage of the former is higher than that of the latter. SIMS analysis shows that the bismuth decreases near the surface of Bi₄Ti₃O₁₂ film annealed without Bi₂O₃ powder, but reveals a stable distribution throughout the film annealed with Bi₂O₃ powder. These results imply that bismuth is readily evaporated during the thermal treatment process, particularly from the region near the film surface. Finally, the dielectric and polarization properties of the thin films annealed with Bi₂O₃ powder are found to be superior to those of the films annealed in ambient air.     

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.     

Formation of the Ti4O7 phase through interaction between coated carbon and TiO2

Fine particles ofphotocatalytic anatase TiO₂ prepared through hydrolysis of titanium tetraisopropoxide were coated by carbon. A reduced phase, Ti₄O₇, was formed through interaction between TiO₂ and the coating carbon. EXAFS analysis on this Ti₄O₇ phase showed an intermediate Ti-Ti distance between those in anatase and rutile, which agreed with the structure composed of two-dimensional slabs of Ti-O octahedra separated by a shear plane. This carbon-coated Ti₄O₇ was confirmed to have photocatalytic activity, even though a little lower than anatase, examining the decomposition of methylene blue in water under LTV irradiation.     

Effect of Ce and La substitution on dielectric properties of bismuth titanate ceramics

Effect of Ce and La substitution on the microstructure and dielectric properties of bismuth titanate (BT) ceramics was investigated. Bismuth titanate ceramics (Bi_4−xA_xTi₃O₁₂) (A = Ce or La; x = 0, 0.5, 1) were processed by sintering of pressed pellets, prepared from nanopowder synthesized by the modified sol-gel method. Pure and La modified bismuth titanate ceramics have single Bi₄Ti₃O₁₂ phase of Aurivillius type, whereas a small amount of Bi₂Ti₂O₇ pyrochlore phase appears in Ce modified bismuth titanate ceramics. In the same time addition of La and Ce improved sinterability of BT ceramics. The results of the measurement of dielectric constant and loss tangent at different frequencies (100 Hz-1 MHz) as a function of temperature reveal that Ce modified ceramics has a diffuse phase transition. Temperature T_m, corresponding to the maximum value of the dielectric constant, is shifted to higher temperature and the maximum value of the dielectric constant is decreased with increasing frequency, which indicate that relaxor behavior is caused by Ce substitution.     

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.     

Synthesis of Bi2O3/TiO2 nanostructured films for photocatalytic applications

Dendritic growth of bismuth oxide nanostructured films was accomplished by reactive magnetron sputtering. The deposition of the Bi₂O₃ template layers was adapted to abide a vapour-liquid-solid mechanism in order to develop a 3D growth morphology with high surface area templates for photocatalytic applications. TiO₂ photocatalytic thin films were deposited at a later stage onto Bi₂O₃ layers. The obtained heterostructured films were characterized by scanning electron microscopy, X-ray diffraction and atomic force microscopy. Additionally, the photocatalytic efficiency was assessed by conducting an assay using methylene blue dye as testing pollutant under a UV-A illumination. The photocatalytic tests revealed that the Bi₂O₃ layers functionalized with TiO₂ thin films are more efficient at degrading the pollutant, by a factor of 6, when compared with the individual layered films.     

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.     

Bismuth oxide cocatalyst and copper oxide sensitizer in Cu2O/TiO2/Bi2O3 ternary photocatalyst for efficient hydrogen production under solar light irradiation

A novel Cu₂O/TiO₂/Bi₂O₃ ternary nanocomposite was prepared, in which copper oxide improves the visible light absorption of TiO₂ and bismuth oxide improves electron–hole separation. The ternary composite exhibited extended absorption in the visible region, as determined by UV–Vis diffuse reflectance spectroscopy. High-resolution transmission electron microscopy images showed close contact among the individual semiconductor oxides in the ternary Cu₂O/TiO₂/Bi₂O₃ nanocomposite. Improved charge carrier separation and transport were observed in the Cu₂O/TiO₂/Bi₂O₃ ternary composite using electrochemical impedance spectroscopy and photocurrent analysis. TiO₂ modified with bismuth and copper oxides showed exceptional photocatalytic activity for hydrogen production under natural solar light. With optimum bismuth and copper oxide loadings, the Cu₂O/TiO₂/Bi₂O₃ ternary nanocomposite exhibited an H₂ production (3678 μmol/h) 35 times higher than that of bare TiO₂ (105?μmol/h). The synergistic effect of improved visible absorption and minimal recombination was responsible for the enhanced performance of the as-synthesized ternary nanocomposite.     

Solid state synthesis and sintering of solid solutions of BNT–xBKT

Various compositions of the solid solution system (100 − x) Bi_0,5Na_0,5TiO₃–xBi_0,5K_0,5TiO₃ (x = 0, 10, 25, 50, 75, 90, 100) were prepared by the mixed oxide route. The formation reaction was analyzed by thermogravimetry coupled with mass spectroscopy and differential scanning calorimetry. In situ high temperature X-ray diffraction up to 770 °C indicated emerging and vanishing of phases during the calcination. Intermediate phases such as alkalipolytitanate (Na/K)₂Ti₆O₁₃ and bismuth titanate Bi₂Ti₂O₇ were identified as forming the perovskite phase. The formation reactions were proposed based on the data obtained. Furthermore the microstructure and the dielectric behavior of the sintered samples were observed by scanning electron microscopy, impedance spectrometry and polarization measurements.     

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.     

Thermal stability of CaCu3Ti4O12: Simultaneous thermal analysis and high-temperature mass spectrometric study

Thermal stability of calcium copper titanate was studied by differential scanning calorimetry, thermogravimetry and high-temperature mass spectrometry. Calcium copper titanate (CCTO) had no thermal effects and mass losses caused by thermal dissociation or any phase transitions, besides melting, in the temperature range of 298–1423?K. The melting point of calcium copper titanate is 1398?K. The endothermic effect at 1250?K was associated with the decomposition of copper (II) oxide segregated in the intergrain space of the CaCu₃Ti₄O₁₂-CuO ceramics. In this connection, we proposed a simple method for estimating the content of copper oxide in the CaCu₃Ti₄O₁₂-CuO composite. The processes of evaporation of CaCu₃Ti₄O₁₂ in the temperature range of 1500–2100?K were studied by high-temperature mass spectrometry. In the temperature range of 1500–1750?K, easily volatilized copper oxide was evaporated selectively from the calcium copper titanate. At the temperature of 2100?K, atomic calcium and titanium oxides, TiO and TiO₂, were present in the vapor.     

Structural and luminescence properties of RE (RE = Eu, Tb):(MgCa)2Bi4Ti5O20 ceramics

Rare-earth ions (Eu³⁺, Tb³⁺) activated magnesium calcium bismuth titanate [(MgCa)₂Bi₄Ti₅O₂₀] ceramics were prepared by conventional solid state reaction method for their structural and luminescence properties. By using XRD patterns, the structural properties of ceramic powders have been analyzed. Emission spectrum of Eu³⁺:(MgCa)₂Bi₄Ti₅O₂₀ ceramic powder has shown strong red emission at 615 nm (⁵D₀ → ⁷F₂) with an excitation wavelength λ_exci = 393 nm and Tb³⁺:(MgCa)₂Bi₄Ti₅O₂₀ ceramic powder has shown green emission at 542 nm (⁵D₄ → ⁷F₅) with an excitation wavelength λ_exci = 376 nm. In addition, from the measurements of scanning electron microscopy (SEM), Fourier transform-infrared (FTIR) and energy dispersive X-ray analysis (EDAX) results the morphology, structure and elemental analysis of these powder ceramics have been studied.     

Microwave synthesis of mesoporous WO3 doping with bismuth and photocatalytic oxidation of water to H2

Mesostructured tungstic acid was prepared from Na₂WO₄ with protonated cation-exchange using a surfactant cetyltrimethyl ammonium bromine (CTAB) as the structure-directing agent under microwave radiation. The surfactant was removed by high-temperature calcination, microwave radiation extraction and Soxhlet extraction, respectively. The effects of these methods for removal of the surfactant were investigated in detail. XRD, TEM, FT-IR and UV-Vis were employed to characterize the mesostructured materials. The results showed that the microwave extraction and Soxhlet extraction were favorable to the synthesis of mesostructured tungstic oxide. Mesoporous structure was destroyed as the calcining temperature rising to 823 K. The mesoporous structure of WO₃ prepared by microwave radiation extraction had an average pore diameter of 3.4 nm and specific surface area of 120.46m²·g⁻¹. And also, the mesoporous materials WO₃ doping with Bi₂O₃ displayed much higher photocatalytic activity than commercial Degussa P25 TiO₂ under visible light and UV irradiation.     

Sintering Process and Microwave Dielectric Properties of Bi8TiO14 Ceramics

The formation of a homogeneous Bi₈TiO₁₄ phase was successfully achieved in a specimen calcined at 600°C. However, a Bi₄Ti₃O₁₂ secondary phase also developed in specimens calcined at temperatures higher than 600°C, probably because of Bi₂O₃ evaporation. For specimens sintered above 800°C, a small amount of the Bi₈TiO₁₄ phase melted during sintering, with the liquid phase contributing to the densification of the specimens; however, Bi₄Ti₃O₁₂ and Bi₁₂TiO₂₀ secondary phases were still formed in these specimens. The microwave dielectric properties of the Bi₈TiO₁₄ phase were considerably affected by variations in the microstructure of the specimens. When the sintering temperature exceeded 825°C, the amount of secondary phases increased, and this decreased the density and Q×f values of the specimens. Bi₈TiO₁₄ ceramics sintered at 825°C exhibited promising microwave dielectric properties, with ε_r = 47.4, Q×f = 5370 GHz, and τ_f = ?16.01 ppm/°C.     

Effect of La substitution on the structural and electrical properties of BaBi4−xLaxTi4O15

Pure and lanthanum doped barium bismuth titanate BaBi_4−xLa_xTi₄O₁₅ (BBLT, x=0, 0.05, 0.15, 0.30) ceramics were prepared utilizing solid state method. The X-ray diffraction (XRD) data confirmed formation of single-phase Aurivillius compounds while SEM micrographs did not show evident grain size change of doped ceramics. Dielectric properties were investigated in 1.21 kHz to 1 MHz frequency range and in the temperature range of 20 to 727 °C. When Bi³⁺ is substituted with La³⁺, a significant disorder was induced and the material exhibited broadening of the phase transition. Impedance analysis confirmed the presence of two semicircular arcs in doped samples suggesting the existence of grain and grain-boundary conduction. The dc-conductivity and activation energies were evaluated for all compositions.     

Effect of reductant type on phase composition and ferroelectric behavior of combustion-synthesized BaTiO3 and Bi4Ti3O12

Finely dispersed BaTiO₃ and Bi₄Ti₃O₁₂ powders were prepared by solution-combustion synthesis using glycine, carbamide, and glycerol as reducing agents. The use of glycine as a reducing agent was found to yield single-phase BaTiO₃ and Bi₄Ti₃O₁₂ without additional heat treatment. Explored was the influence of reductant type and process parameters on the phase composition, crystal structure, and dielectric properties of combustion-synthesized barium and bismuth titanates.     

Effects of the starting materials and mechanochemical activation on the properties of solid-state reacted Li4Ti5O12 for lithium ion batteries

Li₄Ti₅O₁₂ was synthesized by a solid-state reaction between Li₂CO₃ and TiO₂ for applications in lithium ion batteries. The effects of the TiO₂ phase and mechanochemical activation on the Li₄Ti₅O₁₂ particles as well as the corresponding electrochemical properties were investigated. Rutile TiO₂ was more desirable in acquiring high purity Li₄Ti₅O₁₂ than anatase due to the anatase to rutile phase transformation, which was found to be more rigid in the solid-state reaction than the intact rutile phase. Mechanochemical activation of the starting materials was effective in decreasing the reaction temperature and particle size as well as increasing the Li₄Ti₅O₁₂ content. The specific capacity depended significantly on the Li₄Ti₅O₁₂ content, whereas the rate capability improved with decreasing particle size due to the enhanced contact area and reduced diffusion path. Overall, a 200 nm-sized Li₄Ti₅O₁₂ powder with a specific capacity of 165 mAh/g could be synthesized by optimizing the milling method and starting materials.