Thermochemical studies on Bi4Ge3O12 and Bi4Ti3O12 single crystals

The specific heat values of Bi₄Ge₃O₁₂ and Bi₄Ti₃O₁₂ single crystals have been studied using a DSC instrument in the temperature range from 323 to 1273 K. The temperature range at which the anomaly associated with transition from polarized to non-polarized phase in Bi₄Ti₃O₁₂ occurred, has been estimated using the shape of the Bi₄Ge₃O₁₂ heat capacity curve as a “normal” one. The heat effect and the entropy change of the transition were evaluated.     

Mechanism of Formation of Bi4Ti3O12

The mechanism of solid-phase reaction of Bi₄Ti₃O₁₂ formation was studied. Formation of the layered perovskite-like bismuth titanate occurs via intermediates with sequential changes in the coordination polyhedron of bismuth. A correlation is analyzed between the temperature of the onset of activation of the solid-phase reaction and the melting point of the surface (intergrain) phase based on bismuth oxide.     

Bi4Ti3O12 Thin Films from Mixed Bismuth-Titanium Alkoxides

Bi₄Ti₃O₁₂ thin films were obtained by the sol-gel method. The precursor solution was prepared by allowing the two metallic alkoxides, Bi(OC₂H₄OCH₃)₃ and Ti(OC₂H₄OCH₃)₄, to react in 2-methoxy-ethanol to form the mixed alkoxide. This stable sol was deposited by spin-coating onto platinized silicon substrates. X-Ray diffraction patterns indicate that the perovskite initial crystallization temperature is 460°C for powder samples and it ranges between 400 and 500°C, for thin films, as a function of the number of coating layers. Dense, smooth and crack free thin films with grain sizes ranging from 20 nm to 500 nm are obtained, depending on the number of coating layers and on the post-deposition temperature annealing.     

Enhanced photocatalytic removal of hexavalent chromium and organic dye from aqueous solution by hybrid bismuth titanate Bi4Ti3O12/Bi2Ti2O7

Research on Chemical Intermediates - A hybrid bismuth titanate Bi4Ti3O12/Bi2Ti2O7 obtained via a one-step annealing procedure was employed as photocatalyst to oxidize rhodamine B dyes (RhB) and...     

Transparent thin films of Bi2WO6, Bi4Ti3O12 and Sr0.75Ba0.25Nb2O6

Transparent thin films were prepared by a sol–gel method starting from precursor formation in solution, subsequent spin coating followed by a heating ramp up to a maximum of 700 °C. Starting from a Bi₂MoO₆ synthesis route, the phase formation and thin film processing of the bismuth containing materials Bi₂WO₆, Bi₃Ti₄O₁₂ and additionally of the tungsten–bronze structure Sr_0.75Ba_0.25Nb₂O₆ were studied. Spin coating was used to adjust the film thickness in a wide range from 6 to 200 nm. All films were obtained as multicrystalline pure phases according to X-ray diffraction analyses. Scanning electron micrographs revealed homogeneous coatings composed of nanoparticles with a crystallite size varying between 20 and 100 nm, furthermore the UV–VIS spectra demonstrated a high transparency of the films, 80–90% at 600 nm.     

Atomic Simulations of Aurivillius Oxides: Bi3TiNbO9, Bi4Ti3O12, BaBi4Ti4O15 and Ba2Bi4Ti5O18 Doped with Pb,Al, Ga,In, Ta

The Aurivillius oxides were originally of interest for their ferroelectric properties and have recently been explored in the field of oxide ion conductivity. Atomistic simulation methods have been carried out for Bi₃TiNbO₉, Bi₄Ti₃O₁₂, BaBi₄Ti₄O₁₅ and Ba₂Bi₄Ti₅O₁₈ doped with Pb, Al, Ga, In, Ta to determine defect energy in the materials by employing efficient energy minimization procedures. The calculations rest upon the specification of an interatomic potential model, which expresses the total energy of the system as a function of the nuclear coordinates. The Born model framework, which partitions the total energy into long‐range Coulombic interactions and a short‐range term to model the repulsions and van der Waals forces between electron charge clouds, is employed. This is embodied in the GULP simulation code. Dopant solution energy versus ion size trends are found for both isovalent and aliovalent dopant incorporation at Bi and Ta sites. Trivalent dopants (Al, Ga, In) and Pb are more favorable on the Bi site, whereas Ta dopants preferentially occupy the Ti site.     

Dielectric Response of Bi4Ti3O12/PVDF Composite Electrodes for Energy Storage

This study is reporting the role of embedded ferroelectric ceramics Bi₄Ti₃O₁₂ (BTO = 1–5 wt%) into the polyvinylidene fluoride (PVDF) composites on its structural, bonding, surface morphology, and dielectric response. Especially lead free flexible composite electrodes have lot of attention due to its high dielectric permittivity and energy storage density. X-ray diffraction spectra confirms monophasic orthorhombic structure of composites, while Fourier transform infrared (FTIR) spectra confirms the bonding behavior. Scanning electron microscopy (SEM) images surface morphology of homogeneously distributed ceramic particles with interconnected network. Dielectric constant has been found to be improved from 9.56 to 13.73 for BTO_5%PVDF_95% composites at frequency of 1 kHz attributes promoted interfacial polarization of PVDF and effectively limited the charge leakage in the composites, implying promising applications in flexible electronic devices.     

Bi3.25Nd0.75Ti3O12纳米结构: 可控合成及其可见光催化活性

用水热法制备不同形貌的掺钕钛酸铋(Bi3.25Nd0.75Ti3O12,BNdT)纳米粉体.透射电子显微镜(TEM)结果表明,通过控制OH-浓度可以得到不同形貌的纳米粉体.基于不同条件下制备的样品微结构分析,提出了这些不同形貌的形成机制.紫外-可见漫反射光谱(UV-Vis DRS)表明BNdT样品的带隙能(Eg)约为1.984 eV.利用可见光照射下甲基橙降解实验评价了BNdT样品的光催化性能.结果表明,BNdT的光催化活性比商用TiO2催化剂P25和掺氮TiO2高得多.OH-浓度为10 mol·L-1时制备的BNdT纳米线光催化效率最高,经可见光照射360min,浓度为0.01 mmol·L-1甲基橙溶液的降解率可达到93.0%,且循环使用4次后,其光催化活性并没有明显降低,表明BNdT是一种稳定有效的可见光催化剂.     

pH值对水热法制备的Bi4Ti3O12晶体光催化活性的影响

采用无助剂、非模板的水热法可控制备Bi4Ti3O12（BIT）晶体．通过调节反应物的pH值可以选择性地获得BIT纳米球、纳米带和纳米片．通过对不同pH值制备的样品的结构分析研究了这些不同形貌的形成机制．pH值为1制备的IT样品在可见光下光催化活性最高．基于不同pH值制备的BIT样品的形状、尺寸和局部结构振动分析了光催化活性不同的原因。     

The Formation of Ferroelectric Bismuth Titanate (Bi4Ti3O12) from an Aqueous Metal-Chelate Gel

Bismuth titanate (Bi₄Ti₃O₁₂) was synthesized by an aqueous solution-gel process starting from solutions of bismuth acetate and a peroxocitrato-Ti(IV) complex. To gain insight into the thermal decomposition pattern of the gel several thermal analysis techniques were employed: DTA, TGA-EGA (evolved gas analysis by on-line coupling to a FTIR or mass spectrometer) and HT-DRIFT. Transmission electron micrographs showed that the gel is chemically homogeneous down to ca. 5 nm and that this homogeneity is preserved throughout the heat treatment. High-temperature X-ray diffraction measurements were used to make an in situ study of the phase formation. It has been found that single phase Bi₄Ti₃O₁₂ is formed at 625°C.     

Combined structural refinement of Bi3.5La0.5Ti3O12 using neutron and X-ray powder diffraction data

A combined structural refinement of Bi3.5La0.5Ti3O12 against both neutron and X-ray diffraction data was performed at 298 K on the basis of the Raman study. The upshift of Raman peaks suggested that the substitution sites of La atoms in Bi3.5La0.5Ti3O12 were only the Bi sites in the perovskite units. Of the two crystal structural models (orthorhombic and monoclinic systems) considered for the crystal structural system of Bi3.5La0.5Ti3O12, the weighted R factor, Rwp, and goodness-of-fit indicator, S (=Rwp/Re), of the monoclinic system were lower than those of the orthorhombic one. The final Rwp and S values based on the monoclinic system were 7.04% (6.34 and 7.76% for the neutron data and the X-ray data, respectively) and 1.45, respectively. The lattice parameters obtained from the combined structural refinement were a = 5.4321(1) A, b = 5.4161(1) A, and c = 32.8614(3) A. The beta angle was 89.95(4) degrees . Spontaneous polarizations calculated from the refined structural parameters were 27.0 microC/cm2 for the monoclinic system and 1.8 microC/cm2 for the orthorhombic one.     

Regulating Spin Polarization through Cationic Vacancy Defects in Bi4Ti3O12 for Enhanced Molecular Oxygen Activation

Molecular oxygen (O₂) activation technology is of great significance in environmental purification due to its eco-friendly operation and cost-effective nature. However, the activation of O₂ is limited by spin-forbidden transitions, and efficient molecular oxygen activation depends on electronic behavior and surface adsorption. Herein, we prepared cationic defect-rich Bi₄Ti₃O₁₂ (BTO-MV2) catalysts containing Ti vacancies (V_Ti) for O₂ activation in water purification. The V_Ti on BTO nanosheets can induce electron spin polarization, increasing the number of spin-down photogenerated electrons and reducing the recombination of electron-hole pairs. An active surface V_Ti is also formed, serving as a center for adsorbing O₂ and extracting electrons, effectively generating ⋅OH, O₂⋅⁻ and ¹O₂. The degradation rate constant of tetracycline achieved by BTO-MV2 is 3.3 times faster than BTO, indicating a satisfactory prospect for practical application. This work provides an efficient pathway to activate molecular oxygen by constructing new active sites through cationic vacancy modification technology.     

Aurivillius Phases in the Bi4Ti3O12/BiFeO3 System: Thermal Behaviour and Crystal Structure

Four compounds of the Bi₄Ti₃O₁₂/BiFeO₃ system with the formula Bi₂Bi_n?1(Ti,Fe)_nO_3n+3, n = 3, 4, 4.5 and 6 were studied using high‐temperature X‐ray powder diffraction and differential thermoanalysis methods. The crystal structure of the n = 6 phase was refined by the Rietveld method. An unusual behaviour of thermal expansion attributed to an orthorhombic‐to‐tetragonal transformation was revealed. For all the compounds, the lattice parameter c vs temperature T dependence has three regions in the range of T = 20 –750 °C interpreted as (1) expansion of the initial orthorhombic phase, (2) a pronounced structure reconstruction to the tetragonal phase, (3) an expansion of the tetragonal phase. The crystal structure of Bi₇Ti₃Fe₃O₂₁ based on 6‐layer‐perovskite blocks is proposed from X‐ray powder diffraction data. The Rietveld refinement of the structure in the orthorhombic space group F2mm with lattice parameters a = 5.4699(3), b = 5.4924(3), c = 57.551(3) Å (R_p = 9.4, R_wp = 11.9, R_exp = 4.7, R_B = 4.4 %) shows that a distorted 6‐layer model fits the data of Bi₇Ti₃Fe₃O₂₁.     

Antiferromagnetic Stabilization in the Ti8O12 Cluster

Using the evolutionary algorithm USPEX and DFT+U calculations, we predicted a high‐symmetry geometric structure of the bare Ti₈O₁₂ cluster composed of 8 Ti atoms forming a cube, in which O atoms are at midpoints of all of its edges, in excellent agreement with experimental results. Using natural bond orbital analysis, adaptive natural density partitioning algorithm, electron localization function, and partial charge plots, we find the origin of the particular stability of bare Ti₈O₁₂ cluster: unique chemical bonding where eight electrons of Ti atoms interacting with each other in antiferromagnetic fashion to lower the total energy of the system. The bare Ti₈O₁₂ is thus an unusual molecule stabilized by d‐orbital antiferromagnetic coupling.     

Multifunctional material Bi4Ge3O12: thermodynamic properties

Thermodynamic characteristics of a single crystal of bismuth orthogermanate (Bi₄Ge₃O₁₂), which are necessary to improve device portfolio, have been studied. It has been shown that bismuth orthogermanate is thermodynamically stable against decomposition into binary oxides at 50 °C, which gives us grounds to consider this compound promising for various applications.     

The Influence of Heat Treatment Mode on the Properties of Bi4Ti3O12 Thin Films by Chemical Solution Deposition Technique

Bi₄Ti₃O₁₂ thin films were prepared by chemical solution deposition technique on n-Si(lOO). Bismuth nitrate and titanium butoxide were used as starting materials. In this paper, we used this technique to prepare Bi₄Ti₃O₁₂ thin films heat treated by both rapid annealing for 30 seconds in a rapid annealing heater and annealing in a furnace for 30 minutes, and found that the heat treat mode greatly influences the properties of the films. The crystallization temperature of the film made from rapid annealing is about 500℃, while that of the film prepared by heating in a furnace is about 550℃. X-ray diffraction pattern of the film heat treated by the former has stronger (004), (006), (008), (0010) peaks than that of the film heat treated by the latter, which suggests that the rapid annealing heat treat mode favors preferential c-oriental film. The grain size of the film obtained by rapid annealing is smaller than that of the film prepared by heating in a furnace. When the films were both annealed at 600℃,the coercive field of the film heat treated by the former is 45 kV/cm, while that of the film heat treated by the latter is 87 kV/cm.