Effects of trace of Bi2O3 addition on the morphology of strontium ferrite particles

A strontium ferrite powder added with trace of Bi₂O₃ was prepared by the conventional high-temperature solid phase reaction. The effects of Bi₂O₃ addition on the morphology of Sr-ferrite particles fired at different temperatures and times were investigated. The results show that a small quantity of Bi₂O₃ addition accelerates the reaction of SrO and Fe₂O₃ to form SrM ferrite and obviously improves the morphology and size of the strontium ferrite particles. A possible mechanism was proposed to interpret the influence of trace of Bi₂O₃ addition on the morphology of strontium ferrite particles.     

Air-brazed Al2O3 joint with a novel bismuth glass

Polycrystalline alumina ceramics were air-brazed using bismuth glass with a chemical composition of 50Bi₂O₃–40B₂O₃–10ZnO (mol.%) at a relatively low temperature. ZnAl₂O₄ particles were formed insitu in the joints and the particles grew rapidly with an increase in joining temperature and holding time increasing. In addition, penetration of the alumina substrate by the glass became increasingly serious at higher temperatures and holding durations. The mechanical properties of the joints were investigated and the maximum shear strength was determined to be 50 MPa when brazed at 650 °C for 0 min.     

Core–Shell Structure and Dielectric Properties of Ba0.991Bi0.006TiO3@Nb2O5–Co3O4 Ceramics

To meet the needs of future multilayer ceramic capacitors (MLCCs), thinner dielectric layers are necessary. To achieve this goal, the grain size and uniformity of the particles must be effectively controlled. In this study, we confirmed a core–shell particle structure by means of X‐ray diffraction, scanning electron microscopy, and energy‐dispersive spectroscopy. The dielectric properties of the ceramics were measured using an LCR meter. We found Ba_0.991Bi_0.006TiO₃ particles form a core that was coated with a homogeneous Nb₂O₅–Co₃O₄ layer (~9 nm). The relationship between core–shell structure and ε_r‐T curves of the Ba_0.991Bi_0.006TiO₃@Nb₂O₅–Co₃O₄ ceramics by different sintering temperature has been investigated. Dense, fine‐grained Ba_0.991Bi_0.006TiO@Nb₂O₅–Co₃O₄ ceramics were obtained by sintering at 1160°C. The ceramics met the X8R requirements, with a maximum dielectric constant of 2795, and a low dielectric loss at room temperature of 0.89%.     

Bi4Ti3O12 nanoparticles prepared by hydrothermal synthesis

The influence of hydrothermal conditions (including starting materials, reaction temperature and time) on the crystal structure and the morphology of Bi₄Ti₃O₁₂ particles are discussed in this paper. Bi₄Ti₃O₁₂ nanocrystalline particles were hydrothermally synthesized at temperatures in the range of 180–230 °C for 4–12 h, from Bi(NO₃)₃·5H₂O, TiCl₄ and NaOH solution. The XRD results revealed that a typical bismuth layered perovskite structure Bi₄Ti₃O₁₂ was obtained. The TEM showed that the Bi₄Ti₃O₁₂ nanoparticles are tabular, and the sizes are about 200 nm.     

Effect of bulk and nanoparticle Bi2O3 on attenuation capability of radiation shielding glass

The aim of this study is to examine the effect of Bi₂O₃ concentration and particle size on Bi₂O₃ glass. The tested glasses had the composition of SiO₂–Bi₂O₃–CaO–MgO–B₂O₃–K₂O–Na₂O–ZnO. Ordinary glass was compared with glasses with 10% Bulk Bi₂O₃, 10% Bi₂O₃ Nanoparticles (NPs), 20% Bulk Bi₂O₃, and 20% Bi₂O₃ nanoparticles. The mass attenuation coefficients (MACs) of all the investigated glasses were determined between 0.0595 MeV and 1.41 MeV. The results demonstrated that increasing the Bi₂O₃ content in the glass matrix improved their shielding capability, as well as showing that the NPs provided greater attenuation than the bulk Bi₂O₃ at the same concentration. The percent increase in the MAC between the bulk and nano Bi₂O₃ was also calculated and analyzed. From the MAC values, the LAC of the glass was determined and similar results were found compared to the MAC figure. The HVL and MFP of the glass were then analyzed and the results demonstrated that the glass with Bi₂O₃ NPs attenuated the same amount of photons at a smaller thickness, making the NP shield more effective. The heaviness of the samples illustrated that all the tested samples have a smaller weight than pure lead, making them more desirable. The attenuation factor of the glass (Att. Factor %) showed that increasing the Bi₂O₃ content in the samples and increasing the thickness of the shields both improve the shielding capability of the glass. Lastly, the d_lead of the glasses was determined, indicating that the greatest reduction in thickness occurs near the K-absorption edge of bismuth. Overall, the glass with 20% Bi₂O₃ NPs demonstrated to have the greatest potential for radiation shielding applications.     

Newly developed BGO glasses: Synthesis,optical and nuclear radiation shielding properties

In this research paper, we studied the optical and nuclear shielding efficiency of newly developed BGO glasses with the following compositions (in wt%): 32Bi₂O₃–68GeO₂, 42Bi₂O₃–58GeO₂, 47Bi₂O₃–53GeO₂, 52Bi₂O–48GeO₂, 62Bi₂O₃–38GeO₂. BGO glasses were prepared by traditional melt quenching method. To obtain the band gap values of fabricated BGO glasses, optical absorption spectra were used for evaluation of optical properties. The mass attenuation coefficients (μ/ρ) were achieved for prepared glasses at 0.015–15 MeV photon energies employing MCNPX Monte Carlo code and WinXcom program. Moreover, broad-range of nuclear shielding parameters for gamma ray, neutrons and charged particles such as mass attenuation coefficient, half value layer, effective atomic number, buildup factors, mass stopping powers, projected ranges, fast neutron removal cross sections and damage factors were calculated. The refractive index is calculated from E_opt, As Bi₂O₃ concentration is enhanced, E_opt is also increased as well as the optical electronegativity and consequently the refractive index. In addition, the results showed that BIGE5 glass sample with highest Bi₂O₃ contribution has excellent nuclear radiation shielding ability among the other fabricated glass samples.     

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.     

Optical and structural properties of ZnO NPs and ZnO–Bi2O3 nanocomposites

Pure ZnO and ZnO–Bi₂O₃ nanocomposites with 5 wt% and 10 wt% of Bi₂O₃ content were synthesized using the co-precipitation method. Optical properties such as refractive index (n), extinction coefficient (k), bandgap (E_g), and Urbach energies, as well as the band structure, were determined by modeling the experimental transmittance and reflectance UV–Vis spectra. The deduced bandgap and Urbach energies for pure ZnO (3.758 eV) increase with the increase of the doping degree of Bi₂O₃ in ZnO–Bi₂O₃ nanocomposite films. X-ray diffraction and scanning electron microscopy (SEM) was used to study the structural and morphological properties of these nanocomposite films. Pure ZnO and nanocomposites with Bi₂O₃ exhibit crystalline domains with wurtzite hexagonal structures, and as the doping degree of Bi₂O₃ increases, the crystallite size decreases. Based on SEM micrographs, the ZnO nanoparticles (NPs) structure shows the presence of aggregation. Moreover, Bi₂O₃ NPs in the nanocomposite film led to the further aggregation in the form of large rods. The elemental and chemical properties of the nanocomposites were investigated using infrared and energy-dispersive X-ray spectroscopy. The charge transfer process in the studied system is between ZnO and Bi₂O₃ conduction bands. Density-functional theory (DFT) calculations were performed for ZnO, Bi₂O₃, and ZnO-Bi₂O₃ compounds to investigate structural, optical, and electronic properties, being in agreement with the experimental results.     

Effect of Bi2O3 content on sintering and crystallization behavior of low-temperature firing Bi2O3–B2O3–SiO2 glasses

The sintering behavior of a Pb-free Bi₂O₃–B₂O₃–SiO₂ glass system was examined as a function of Bi₂O₃ content. The glass transition temperature and the crystallization temperature of the glasses decreased with different decreasing gradients as the Bi₂O₃ content increased. The change in temperature affected the sintering behaviors of the glasses. In the case of the 40 mol% Bi₂O₃ addition, large pore accompanied over-firing phenomenon was observed when the sample was sintered over the optimum sintering temperature. However, over-firing was not observed in the sample with 45 mol% of Bi₂O₃ because of the crystallized phases during sintering. When the Bi₂O₃ content was 50–55 mol%, the crystallization temperature became lower than the glass transition temperature, which resulted in the crystallization of glass and it hindered densification.     

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.     

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.     

Effect of dual liquid phase sintering aids on the densification and microstructure of low temperature sintered alumina ceramics

Alumina ceramics was prepared by pressureless sintering technology in which a CuO–TiO₂–Bi₂O₃ mixture (0–4.0 wt% Bi₂O₃ and 4.0 wt% CuO and TiO₂) was added as dual liquid phase sintering aids. The phase compositions, microstructural feature, and sintering behaviour of the alumina ceramics were analyzed. The results showed that adding 2.5 wt% Bi₂O₃ to alumina ceramics can increase the contribution rate of initial stage of sintering to the sintering process. The relative density of the sample reached 97.63% after sintering at 1200 °C for 90 min. Measurements from differential scanning calorimetry, with the addition of CuO–TiO₂–Bi₂O_3, demonstrated the formation of two liquid phase points, 827.4 and 936.8 °C. Notably, the solid solution temperature of TiO₂ and Al₂O₃ ceramics diminished thanks to the dual liquid phase sintering aids, and at the same time the activation energy required also dropped from 368.96 to 137.31 kJ/mol. Research indicates that the combined action of dual liquid phase sintering and solid-state reaction sintering has promoted the densification of alumina ceramics during the sintering process while at the same time inhibiting the growth of abnormal grains so that a homogeneous microstructure can be formed.     

Reaction pathways in the solid state synthesis of multiferroic BiFeO3

The obtaining of multiferroic BiFeO₃ as a pure single-phase product is particularly complex since the formation of secondary phases seems to be unavoidable. The process by which these secondary impurities are formed is studied by analyzing the diffusion and solid state reactivity of the Bi₂O₃-Fe₂O₃ system. Experimental evidence is reported which indicates that the progressive diffusion of Bi³⁺ ions into the Fe₂O₃ particles governs the solid state synthesis of the perovskite BiFeO₃ phase. However a competition is established between the diffusion process which tends to complete the formation of BiFeO₃, and the crystallization of stable Bi₂Fe₄O₉ mullite crystals, which tend to block that formation reaction.     

Experimental determination of the liquidus line in the high Bi2O3 region in the TiO2–Bi2O3 system

Liquidus line in the high-Bi₂O₃-containing region of the TiO₂–Bi₂O₃ system was determined experimentally. The equilibrating and quenching technique with subsequent electron probe microanalyser (SEM-EDS) microanalysis were employed. Based on the data, liquidus line was constructed between 60 and 92 mol% Bi₂O₃. The current results showed a higher solubility of Bi₂O₃ in the liquid phase in equilibrium with the Bi₄Ti₃O₁₂ compound compared with the existing phase diagram. In addition, differential scanning calorimetry (DSC) was used to estimate the transformations covering the composition range from 60 to 95 mol% Bi₂O₃. Further, the phase diagram of the TiO₂–Bi₂O₃ system was calculated using a quasichemical model for the liquid phase. The thermodynamic properties of the intermediate compounds were estimated from the data of TiO₂ and Bi₂O₃ pure solids.     

Matrix phase induced boosting photoactive performance of ZnO nanowire turf-coated Bi2O3 plate composites

A new nanocomposite consisting of ZnO nanowire turf-coated Bi₂O₃ plates was synthesized using a method combining a chemical bath and hydrothermal crystal growth through sputtering ZnO seed layer-assisted growth. Structural analysis revealed that highly crystalline, high-density, one-dimensional (1D) ZnO crystals were uniformly coated on the organized two-dimensional (2D) Bi₂O₃ plates with a single β phase or dual α/β polymorphic phases. The Bi₂O₃–ZnO composites exhibited enhanced absorption properties in the ultraviolet and visible regions compared with pristine Bi₂O₃ and ZnO. Furthermore, the Bi₂O₃–ZnO composites exhibited higher photoactive performance than that of the pristine Bi₂O₃ and ZnO because of the low recombination rate of photoinduced electron−hole pairs caused by the vectorial transfer of electrons and holes between ZnO and Bi₂O₃ and the substantially increased surface area of the unique composite morphology. The ZnO nanowire turf-coated Bi₂O₃ plates with a α/β-Bi₂O₃ matrix exhibited photoelectrochemical and photocatalytic properties superior to those of the composite with a single β-Bi₂O₃ matrix. The coexistence of α/β homojunction in the Bi₂O₃ matrix and the abundant heterojunctions between the ZnO nanowires and Bi₂O₃ plates substantially enhanced photoexcited charge separation efficiency. Growing high-density 1D ZnO on 2D Bi₂O₃ via a combination methodology and crystallographic phase control provided a promising material design route for nanocomposite systems with high photoactivity for photoexcited device applications.     

Bi5O7I/Bi2O3 composite photocatalyst with enhanced visible light photocatalytic activity

A series of Bi₅O₇I/Bi₂O₃ composite photocatalysts were first synthesized via chemical etching method. Their crystalline phase, composition, light absorption ability and photoluminescence emission performance were characterized by XRD, EDX, UV–vis and PL methods, respectively. And malachite green was used as the model pollutant to investigate the visible light photocatalytic activities of the composite photocatalysts. It is found that 80.48% Bi₅O₇I/Bi₂O₃ showed the highest activity for its relatively stronger absorption ability for visible light and best separation efficiency of electron–hole pairs. Last, the photocatalytic mechanism of the Bi₅O₇I/Bi₂O₃ composite was put forward qualitatively.     

Fabrication and characterization of La2O3–Fe2O3–Bi2O3 nanopowders: Effects of La2O3 addition on structure,optical, and radiation-absorption properties

In this study, we fabricated and characterized six new nanopowders representing variations of La₂O₃–Fe₂O₃–Bi₂O₃, i.e., 100Bi₂O₃, 30Fe₂O₃–70Bi₂O₃, 3La₂O₃–27Fe₂O₃–70Bi₂O₃, 7La₂O₃–23Fe₂O₃–70Bi₂O₃, 10La₂O₃–20Fe₂O₃–70Bi₂O₃, and 20La₂O₃–10Fe₂O₃–70Bi₂O₃ (represented by 100B, 30F70B, 3L27F70B, 10L20F70B, and 20L10F70B, respectively). These nanopowders were prepared by the microwave-assisted hydrothermal synthesis method. Saponin extract from soapnuts was used as the nanoparticle capping agent. The structural, optical, and gamma radiation characteristics were measured, calculated, and analysed, respectively. The chemical structures of the nanocomposites influenced their optical and radiation shielding characteristics. The optical bandgaps of the 100B, 30F70B, 3L27F70B, 7L23F70B, 10L20F70B, and 20L10F70B nanopowders were 3.16, 3.13, 3.43, 3.45, 3.46, and 3.58 eV, respectively. The ranges of the mass attenuation coefficients of the nanopowders were computed, using XCOM, to be 0.0412–5.1624, 0.0401–4.5406, 0.0401–4.5285, 0.0401–4.5129, 0.0401–0.5015, and 0.0400–4.4156 cm²/g, respectively, and the ranges of mass energy absorption coefficients were found to be 0.0232–1.7525, 0.0228–1.5484, 0.0228–1.5598, 0.0288–1.5746, 0.0228–1.5853, and 0.0227–1.6192 cm²/g, respectively, for photon energies in the range of 0.1–10 MeV. The order of the dose rate trend was as follows: 30F70B < L27F70B < 7L23F70B < 10L20F70B < 20L10F70B. Analysis of the photon interaction parameters showed that the synthesized nanopowders could function well as fillers in radiation-shielding matrices.     

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.     

Characterisation and microstructure of Pd and bimetallic Pd–Pt catalysts during methane oxidation

The catalytic oxidation of methane was studied over Pd/Al₂O₃ and Pd–Pt/Al₂O₃. It was found that the activity of Pd/Al₂O₃ gradually decreases with time at temperatures well below that of PdO decomposition. The opposite was observed for Pd–Pt/Al₂O₃, of which the activity decreases slightly with time. Morphological studies of the two catalysts showed major changes during operation. The palladium particles in Pd/Al₂O₃ are initially composed of smaller, randomly oriented crystals of both PdO and Pd. In oxidising atmospheres, the crystals become more oxidised and form larger crystals. The activity increase of Pd–Pt/Al₂O₃ is probably related to more PdO being formed during operation. The particles in Pd–Pt/Al₂O₃ are split into two different domains: one with PdO and the other likely consisting of an alloy between Pd and Pt. The alloy is initially rich in palladium, but the composition changes to a more equalmolar Pd–Pt structure during operation. The ejected Pd is oxidised into PdO, which is more active than its metallic phase. The amount of PdO formed depends on the oxidation time and temperature.